Integrated neuroendocrine activation is necessary to successfully overcome stressful events. Neuroendocrine activation, part of the well-known biologic phase of stress adaptative responses, is not aspecifically generated by the organism, however, due to the effects of numerous factors, in part also genetically determined. Growing evidence shows the relevance of subjective cognitive and emotional modulation elaborated in cortical and subcortical structures of the brain in determining different individual strategies of stress response. The nervous system, where all stressful stimuli exert their initial effects, is well documented to play a crucial role in the generation of adequate stress responses by correctly integrating endocrine and immune system functions to maintain homeostasis of the organism. The specific individual pattern of stress response is also determined by modulation of emotional influences, as previously hypothesized by Mason. Emo- tional structures are located mainly in the modular neuronal network represented by the limbic system. The hypothalamus, in particular, with its connections to both central and peripheral nervous structures, and neuroendocrine integrated systems represents the limbic module more properly concerned with the organization of motivated behavioral and endocrine responses. Other limbic modules related to the emotional network are the amygdala, the area where emotional or affective quality are attributed to motivationally relevant stimuli, and the septum, one of the structures involved in the inhibition or selection of behavioral responses. In humans, neocortex cognitive influences, however, operate a superimposed control of cognitive influences on emotional structures, with various reciprocal interrelationships. Both endocrine and immune systems, in turn, feed back to the brain by closely affecting nervous system plasticity, its development, and its functions during adult life and aging. The presence of hormones and hormonal receptors in brain areas other than those typically involved in the control of endocrine function, such as the hypothalamus, supports the hypothesis that brain represents a direct target of hormonal effects. These bidirectional neuroendocrine interactions, classified as experiential hormonal effects, contribute to modulate neuroendocrine responses after different kinds of stressors, including psychological stress. As hormonal experiential effects are part of the individual experience, subsequent stress adaptative responses are so extremely variable as to be hardly predictable, accounting also for the emergence of variable degrees of pathologic states related to chronic stress exposure. Neuroendo- crine axis activation may vary in different species, taking into account the varying relevance of intermediate lobe metabolism of the proopiomelanocortin molecule, whereas in the same species it may closely depend on the specific stressors employed or the duration of stress exposure until the generation of dissociated neuroendocrine activation in particular pathologic states. The neuroendocrine cascade following the application of emotional stress is generally similar to that determined by other physical stressors, and several models of socially hierarchically organized animals provide suitable examples for evaluating such mechanisms. In humans, mental stress is known to induce pronounced and reproducible activation of the sympathoadrenal system, with elevation of plasma epinephrine and norepinephrine concentrations and subsequent hemodynamic changes (i.e., heart rate increase) and metabolic consequences, such as an increase in adipose tissue lipolytic activity and a reduction in adipocyte glucose uptake activity. Nevertheless, behavioral stress can also be a consequence of particular physical stressors, deeply affecting stress adaptative responses through modulation of cortical and subcortical cognitive and emotional neuronal circuits. In particular, stressors inducing a high degree of emotionality stimulate the sympathoadrenomedullary reflex, which, in turn, is responsible for complex modulation of the hypothalamus-pituitary- adrenal axis. Higher endocrine changes have been reported in athletes after an international race compared to a national one with similar duration and intensity of muscular work, likely due to the psychological stress of the greater agonistic effort associated with the international race. Examination or medical interview represents examples of acute psychological stress, with short duration of the particular emotional state and of subsequent endocrine changes. Conversely, inadequate coping with life's vicissitudes or adverse life situations, such as insufficient social network supports, retirement from work, and actual and impending losses and separations, represent examples of variable degrees of chronic psychological stress. Other examples of behavioral stress in humans are provided by studies of patients undergoing different kinds of medical treatment, such as surgery or chronic hemodialysis, or suffering variable acute or chronic traumatic lesions; in healthy volunteers the effects of psychological challenges, such as math and speech tests, or isolation during confine- ment have been evaluated. After brain perception of a specific stressor, the crucial event in neuroendocrine activation of stress responses is the triggering of CRH release from the paraventricular nucleus of the hypothalamus. Activation of the HPA axis with secretion of glucocorti- coids (GC), mainly cortisol, 18-hydroxycorticosterone, aldosterone, and dehydroepi- androsterone, is the end-point of the neuroendocrine cascade of events generated by hypothalamic CRH release. Glucocorticoids, in turn, may deeply affect brain cells by inducing neuronal and glial synthesis of proteins useful in generating adaptative responses. As previously noted, stress-induced HPA axis activation is further enhanced by the morphologic and functional linkage between CRH and the sympathoadrenal system either at central levels through brain alpha- and beta-adrenoceptors or at the peripheral level, through ascending adrenergic fibers of the brain stem. Glucocorti- coids affect the sympathoadrenal system, stimulating enzymatic conversion of norepi- neprine to epinephrine in the adrenal medulla. Besides its main role in controlling ACTH and GC secretion, CRH may be considered the central regulator of a series of other stress-induced body functions, including activation of the sympathoadrenomedullary axis, behavioral inhibition, appetite suppression, and reproductive In fact, apart from the paraven- tricular nucleus, CRH is also present in central nervous systems involved in behavior control, such as limbic areas, median raphe nuclei, locus coeruleus, and cortical interneuron circuits with known anxiogenic effects in animal models. Its content in the locus coeruleus is particularly increased by stressors, likely influencing its norepinephrine neurotransmitter function. Arginine vasopressin (AVP) is cosecreted with CRH from the paraventricular nucleus and interacts with CRH at the anterior pituitary levels to promote ACTH secretion, with similar negative and positive regulation exerted by GC and stressors, respectively. The relevance of CRH and AVP in the regulation of stress-induced ACTH secretion varies in the different species as well as with the type of tressor. In particular, in addition to the aforementioned species differences between rats and humans in neuroendocrine axis activation after acute cold exposure, chronic intermittent psychosocial stress in male rats has been reported to enhance AVP but not CRH synthesis in CRH-producing neurons and its storage in nerve terminals of the external zone of the median eminence with subsequent enhanced pituitary POMC mRNA expression and ACTH storage, thus shifting the hypothalamic CRH/AVP signal in favor of AVP. Autoradiographic mapping studies of hormone receptors reveal specific receptors of AVP and oxytocin in certain areas of the brain, such as the limbic lobe (gyrus fornicatus), likely responsible for the behavioral actions of neuropeptides; moreover, some vasopressinergic fibers have been described to project towards the locus coeruleus and, through the fornix and stria terminalis, towards the hippocampus and septum, thereby influencing social behavior, cognitive function, and memory. Opioid peptides, widely identified immunohistochemically in cerebral areas that specifically influence cognitive, affective, and behavioral processes, are consensually secreted with ACTH in response to CRH release at pituitary levels, playing a specific role in mediating the organism's response to mental stress in humans. The role of opioids in the modulation of neuroendocrine stress responses is complex because of the presence of multiple types of both opioid peptides and opioid receptors. However, opioids are known to inhibit HPA axis functional activity and are actually considered the counterregulatory system in controlling the organism's neuroendocrine responses to stress. In particular, delta receptors have been suggested to play a modulating role in neuroendocrine responses to stress, and beta-endorphins are supposed to modulate sensitivity to painful stimuli to avoid emotional interference in behavioral strategies of response to stressors. Although stress responses are relevant to successful adaptation of an organism by increasing readily available energy substrates to sustain brain and heart activity, chronic and prolonged exposure of individuals to stress may induce excessive exposure to the central and peripheral effects of GC, causing detrimental effects to the organism itself, so-called hormonal detrimental effects. This causes alterations in the complex neuroendocrine network underlying the stress adaptative response as well as damage to neural tissue. Similarly, age and age-related degenerative brain diseases also deeply affect the efficiency of stress-induced neuroendocrine secretive mechanisms. Degenerative alterations of the aging brain may be a useful example of disruption of the balance in the individual neuroendocrine responses to adequately counteract the perturbative event represented by the stressful stimulus, with impaired ability to cope with stress. In particular, an increased risk of developing premature atheroscle- rosis is associated with stress through the specific metabolic effects of GC in promoting the secretion of very low density lipoproteins and other metabolic changes related to insulin resistance with stress-induced increases in blood glucose levels that cannot be properly metabolized. Stress adaptative responses, however, involve activation of neuroendocrine axes other than the HPA, such as those controlling GH and prolactin release or those regulating thyroid and gonadal function. Elevated GH and prolactin plasma levels have been reported after various stressors, such as physical exercise, surgery, stressful interviews involving the effects of activa- tion of numerous monoaminergic pathways and the modulating effects of the opioid peptide system, the latter particularly concerning inhibition of dopaminergic control of prolactin secretion; however, common stressors, such as academic stress, are not always able to elicit the GH and prolactin response. Moreover, GH secretion is reduced after severe emotional stress. In particular, GC appear to play two opposite roles in GH control, facilitatory at pituitary levels with enhancement of GH gene transcription and an increase in GHRH receptor synthesis, and inhibitory due to enhancement of hypothalamic somatostatin release related to beta-adrenoceptor activity. This effect, however, requires more prolonged exposure, and accounts for the known development of psychosocial dwarfism. Circulating thyroid hormone levels are important regulators of cellular metabolism and energy expenditure; in this context, the hypothalamus-pituitary-thyroid (HPT) axis is strongly involved in the stress-adaptative response, with reduction in thyroid hormone levels after prolonged exposure to stress, likely due to the increased periph- eral thyroid hormone turnover. The HPT axis alteration is particularly evident in the presence of other neuroendocrine aberrations such as functional amenorrhea in athletic women. In such cases, despite the reduced negative feedback of thyroid hormones, no increase in 24-hour mean thyroid-stimulating hormone (TSH) plasma levels or any alteration in the circadian rhythm of TSH secretion was present as expression of the derangement in feedback regulation andor metabolism of thyroid hormones, the effects of prolonged GC exposure likely accounting for the reduced TSH response to thyroid-releasing hormone stimulation. Secondary hypothalamic amenorrhea is often associated with emotional stress, weight loss, excessive physical exercise, and eating disorders such as anorexia nervosa and bulimia. In primates as well as in rodents, GnRH pulsatility is negatively regulated by intrahypothalamic CRH-41. Evidence now exists that CRH-41 mediates its inhibitory action on GnRH neurons by activation of the hypothalamic opioids, with beta-endorphins being the most likely candidate. Furthermore, opioid peptides have also been hypothesized to mediate the known estrogen negative effects on luteinizing hormone (LH) release. We therefore evaluated gonadotropin qualitative and quantitative abnormalities in women affected by stress-induced amenorrhea and anorexia nervosa. Previous data in stress-induced amenorrhea and in patients with anorexia nervosa demonstrated LH pulses similar to those in the pre- and peripubertal period, with sleep-related nocturnal peaks and low and delayed luteinizing-hormone releasing-hormone (LHRH) LH responses, whereas follicle-stimulating hormone (FSH) response to LHRH appeared to be quantitatively normal, although delayed. Primary dysfunction of hypothalamic release of GnRH has been hypothesized to occur in patients with anorexia nervosa in terms of abnormalities of GnRH pulsatile rhythm with lower frequency and reduced amplitude45 and is related to stress-induced activation of the HPA axis, accounting for altered production of gonadotropin isoforms and for subsequent impaired ovarian stimulation, with amenorrhea and low 17 beta-estradiol plasma levels in the presence of apparently normal gonadotropin plasma levels evalu- ated by radioimmunoassay. Moreover, secretion of different gonadotropin isoforms with variability in the posttranslational conformational structure determines differences in gonadotropin evaluation using two different analytic methods, such as radioimmunoassay and immunoradiometric assay (IRMA), and suggests altered gonadotropin biologic activ- ity related to this alteration. Glycosylation of pituitary hormones has largely been demonstrated to affect their biologic activity We evaluated the presence of different glycosylated gonadotropin isoforms using concanavalin A (Con-A) sepharose, a specific carbohydrate adsorbent, to separate glycosylated from nonglycosylated moieties, the former bound to Con-A and the latter eluted from Con-A. In stress-induced amenorrhea, although the LH elution pattern was similar in both patients and controls, the FSH eluted amounts were significantly higher in stress-induced amenorrhea than in controls because of more nonglycosylated FSH moieties with reduced biologic activity, accounting for gonadal failure with amenorrhea. This difference is corrected by exogen GnRH administration and suggests a relation between gonadotropin conformational alterations, with subse- quent reduction in biologic activity, and impairment of endogenous GnRH secretion as an expression of hypothalamic damage. These data were further evaluated in patients with anorexia nervosa in whom differences in gonadotropin evaluation were detected with both RIA and IRMA methods before and after Con-A, taking into account the influences of altered glycosyl- ation in these assays. These differences are not related to the percentage of weight decrease from ideal body weight or the body mass index or to the age of the patient or the duration of anorexia nervosa and they provide evidence of conformational alterations in gonadotropin isoforms in anorexic patients, likely accounting for the low biologic activity strongly suggested by clinical evidence of amenorrhea with low estrogen plasma levels. Again, the exogen GnRH acute stimulation test can correct for these RIA-IRMA differences, which are similar to those in hypothalamic hypothy- roidism with TSH molecular alterations. In conclusion, our data support the hypothesis that anorexic patients secrete fewer glycosylated molecules with decreased biologic activity. A deficiency in GnRH hypothalamic secretion, as suggested by the decreased gonadotropin pulses reported in women with weight loss-related amenorrhea, determines a low gonadotropin turnover and structural alterations with impaired biologic activity. Structural alterations in hormonal molecules may provide a further stress-mediated disease-determining mechanism.
NEUROENDOCRINE AXIS AND BEHAVIORAL STRESS
Valentino R;
1994
Abstract
Integrated neuroendocrine activation is necessary to successfully overcome stressful events. Neuroendocrine activation, part of the well-known biologic phase of stress adaptative responses, is not aspecifically generated by the organism, however, due to the effects of numerous factors, in part also genetically determined. Growing evidence shows the relevance of subjective cognitive and emotional modulation elaborated in cortical and subcortical structures of the brain in determining different individual strategies of stress response. The nervous system, where all stressful stimuli exert their initial effects, is well documented to play a crucial role in the generation of adequate stress responses by correctly integrating endocrine and immune system functions to maintain homeostasis of the organism. The specific individual pattern of stress response is also determined by modulation of emotional influences, as previously hypothesized by Mason. Emo- tional structures are located mainly in the modular neuronal network represented by the limbic system. The hypothalamus, in particular, with its connections to both central and peripheral nervous structures, and neuroendocrine integrated systems represents the limbic module more properly concerned with the organization of motivated behavioral and endocrine responses. Other limbic modules related to the emotional network are the amygdala, the area where emotional or affective quality are attributed to motivationally relevant stimuli, and the septum, one of the structures involved in the inhibition or selection of behavioral responses. In humans, neocortex cognitive influences, however, operate a superimposed control of cognitive influences on emotional structures, with various reciprocal interrelationships. Both endocrine and immune systems, in turn, feed back to the brain by closely affecting nervous system plasticity, its development, and its functions during adult life and aging. The presence of hormones and hormonal receptors in brain areas other than those typically involved in the control of endocrine function, such as the hypothalamus, supports the hypothesis that brain represents a direct target of hormonal effects. These bidirectional neuroendocrine interactions, classified as experiential hormonal effects, contribute to modulate neuroendocrine responses after different kinds of stressors, including psychological stress. As hormonal experiential effects are part of the individual experience, subsequent stress adaptative responses are so extremely variable as to be hardly predictable, accounting also for the emergence of variable degrees of pathologic states related to chronic stress exposure. Neuroendo- crine axis activation may vary in different species, taking into account the varying relevance of intermediate lobe metabolism of the proopiomelanocortin molecule, whereas in the same species it may closely depend on the specific stressors employed or the duration of stress exposure until the generation of dissociated neuroendocrine activation in particular pathologic states. The neuroendocrine cascade following the application of emotional stress is generally similar to that determined by other physical stressors, and several models of socially hierarchically organized animals provide suitable examples for evaluating such mechanisms. In humans, mental stress is known to induce pronounced and reproducible activation of the sympathoadrenal system, with elevation of plasma epinephrine and norepinephrine concentrations and subsequent hemodynamic changes (i.e., heart rate increase) and metabolic consequences, such as an increase in adipose tissue lipolytic activity and a reduction in adipocyte glucose uptake activity. Nevertheless, behavioral stress can also be a consequence of particular physical stressors, deeply affecting stress adaptative responses through modulation of cortical and subcortical cognitive and emotional neuronal circuits. In particular, stressors inducing a high degree of emotionality stimulate the sympathoadrenomedullary reflex, which, in turn, is responsible for complex modulation of the hypothalamus-pituitary- adrenal axis. Higher endocrine changes have been reported in athletes after an international race compared to a national one with similar duration and intensity of muscular work, likely due to the psychological stress of the greater agonistic effort associated with the international race. Examination or medical interview represents examples of acute psychological stress, with short duration of the particular emotional state and of subsequent endocrine changes. Conversely, inadequate coping with life's vicissitudes or adverse life situations, such as insufficient social network supports, retirement from work, and actual and impending losses and separations, represent examples of variable degrees of chronic psychological stress. Other examples of behavioral stress in humans are provided by studies of patients undergoing different kinds of medical treatment, such as surgery or chronic hemodialysis, or suffering variable acute or chronic traumatic lesions; in healthy volunteers the effects of psychological challenges, such as math and speech tests, or isolation during confine- ment have been evaluated. After brain perception of a specific stressor, the crucial event in neuroendocrine activation of stress responses is the triggering of CRH release from the paraventricular nucleus of the hypothalamus. Activation of the HPA axis with secretion of glucocorti- coids (GC), mainly cortisol, 18-hydroxycorticosterone, aldosterone, and dehydroepi- androsterone, is the end-point of the neuroendocrine cascade of events generated by hypothalamic CRH release. Glucocorticoids, in turn, may deeply affect brain cells by inducing neuronal and glial synthesis of proteins useful in generating adaptative responses. As previously noted, stress-induced HPA axis activation is further enhanced by the morphologic and functional linkage between CRH and the sympathoadrenal system either at central levels through brain alpha- and beta-adrenoceptors or at the peripheral level, through ascending adrenergic fibers of the brain stem. Glucocorti- coids affect the sympathoadrenal system, stimulating enzymatic conversion of norepi- neprine to epinephrine in the adrenal medulla. Besides its main role in controlling ACTH and GC secretion, CRH may be considered the central regulator of a series of other stress-induced body functions, including activation of the sympathoadrenomedullary axis, behavioral inhibition, appetite suppression, and reproductive In fact, apart from the paraven- tricular nucleus, CRH is also present in central nervous systems involved in behavior control, such as limbic areas, median raphe nuclei, locus coeruleus, and cortical interneuron circuits with known anxiogenic effects in animal models. Its content in the locus coeruleus is particularly increased by stressors, likely influencing its norepinephrine neurotransmitter function. Arginine vasopressin (AVP) is cosecreted with CRH from the paraventricular nucleus and interacts with CRH at the anterior pituitary levels to promote ACTH secretion, with similar negative and positive regulation exerted by GC and stressors, respectively. The relevance of CRH and AVP in the regulation of stress-induced ACTH secretion varies in the different species as well as with the type of tressor. In particular, in addition to the aforementioned species differences between rats and humans in neuroendocrine axis activation after acute cold exposure, chronic intermittent psychosocial stress in male rats has been reported to enhance AVP but not CRH synthesis in CRH-producing neurons and its storage in nerve terminals of the external zone of the median eminence with subsequent enhanced pituitary POMC mRNA expression and ACTH storage, thus shifting the hypothalamic CRH/AVP signal in favor of AVP. Autoradiographic mapping studies of hormone receptors reveal specific receptors of AVP and oxytocin in certain areas of the brain, such as the limbic lobe (gyrus fornicatus), likely responsible for the behavioral actions of neuropeptides; moreover, some vasopressinergic fibers have been described to project towards the locus coeruleus and, through the fornix and stria terminalis, towards the hippocampus and septum, thereby influencing social behavior, cognitive function, and memory. Opioid peptides, widely identified immunohistochemically in cerebral areas that specifically influence cognitive, affective, and behavioral processes, are consensually secreted with ACTH in response to CRH release at pituitary levels, playing a specific role in mediating the organism's response to mental stress in humans. The role of opioids in the modulation of neuroendocrine stress responses is complex because of the presence of multiple types of both opioid peptides and opioid receptors. However, opioids are known to inhibit HPA axis functional activity and are actually considered the counterregulatory system in controlling the organism's neuroendocrine responses to stress. In particular, delta receptors have been suggested to play a modulating role in neuroendocrine responses to stress, and beta-endorphins are supposed to modulate sensitivity to painful stimuli to avoid emotional interference in behavioral strategies of response to stressors. Although stress responses are relevant to successful adaptation of an organism by increasing readily available energy substrates to sustain brain and heart activity, chronic and prolonged exposure of individuals to stress may induce excessive exposure to the central and peripheral effects of GC, causing detrimental effects to the organism itself, so-called hormonal detrimental effects. This causes alterations in the complex neuroendocrine network underlying the stress adaptative response as well as damage to neural tissue. Similarly, age and age-related degenerative brain diseases also deeply affect the efficiency of stress-induced neuroendocrine secretive mechanisms. Degenerative alterations of the aging brain may be a useful example of disruption of the balance in the individual neuroendocrine responses to adequately counteract the perturbative event represented by the stressful stimulus, with impaired ability to cope with stress. In particular, an increased risk of developing premature atheroscle- rosis is associated with stress through the specific metabolic effects of GC in promoting the secretion of very low density lipoproteins and other metabolic changes related to insulin resistance with stress-induced increases in blood glucose levels that cannot be properly metabolized. Stress adaptative responses, however, involve activation of neuroendocrine axes other than the HPA, such as those controlling GH and prolactin release or those regulating thyroid and gonadal function. Elevated GH and prolactin plasma levels have been reported after various stressors, such as physical exercise, surgery, stressful interviews involving the effects of activa- tion of numerous monoaminergic pathways and the modulating effects of the opioid peptide system, the latter particularly concerning inhibition of dopaminergic control of prolactin secretion; however, common stressors, such as academic stress, are not always able to elicit the GH and prolactin response. Moreover, GH secretion is reduced after severe emotional stress. In particular, GC appear to play two opposite roles in GH control, facilitatory at pituitary levels with enhancement of GH gene transcription and an increase in GHRH receptor synthesis, and inhibitory due to enhancement of hypothalamic somatostatin release related to beta-adrenoceptor activity. This effect, however, requires more prolonged exposure, and accounts for the known development of psychosocial dwarfism. Circulating thyroid hormone levels are important regulators of cellular metabolism and energy expenditure; in this context, the hypothalamus-pituitary-thyroid (HPT) axis is strongly involved in the stress-adaptative response, with reduction in thyroid hormone levels after prolonged exposure to stress, likely due to the increased periph- eral thyroid hormone turnover. The HPT axis alteration is particularly evident in the presence of other neuroendocrine aberrations such as functional amenorrhea in athletic women. In such cases, despite the reduced negative feedback of thyroid hormones, no increase in 24-hour mean thyroid-stimulating hormone (TSH) plasma levels or any alteration in the circadian rhythm of TSH secretion was present as expression of the derangement in feedback regulation andor metabolism of thyroid hormones, the effects of prolonged GC exposure likely accounting for the reduced TSH response to thyroid-releasing hormone stimulation. Secondary hypothalamic amenorrhea is often associated with emotional stress, weight loss, excessive physical exercise, and eating disorders such as anorexia nervosa and bulimia. In primates as well as in rodents, GnRH pulsatility is negatively regulated by intrahypothalamic CRH-41. Evidence now exists that CRH-41 mediates its inhibitory action on GnRH neurons by activation of the hypothalamic opioids, with beta-endorphins being the most likely candidate. Furthermore, opioid peptides have also been hypothesized to mediate the known estrogen negative effects on luteinizing hormone (LH) release. We therefore evaluated gonadotropin qualitative and quantitative abnormalities in women affected by stress-induced amenorrhea and anorexia nervosa. Previous data in stress-induced amenorrhea and in patients with anorexia nervosa demonstrated LH pulses similar to those in the pre- and peripubertal period, with sleep-related nocturnal peaks and low and delayed luteinizing-hormone releasing-hormone (LHRH) LH responses, whereas follicle-stimulating hormone (FSH) response to LHRH appeared to be quantitatively normal, although delayed. Primary dysfunction of hypothalamic release of GnRH has been hypothesized to occur in patients with anorexia nervosa in terms of abnormalities of GnRH pulsatile rhythm with lower frequency and reduced amplitude45 and is related to stress-induced activation of the HPA axis, accounting for altered production of gonadotropin isoforms and for subsequent impaired ovarian stimulation, with amenorrhea and low 17 beta-estradiol plasma levels in the presence of apparently normal gonadotropin plasma levels evalu- ated by radioimmunoassay. Moreover, secretion of different gonadotropin isoforms with variability in the posttranslational conformational structure determines differences in gonadotropin evaluation using two different analytic methods, such as radioimmunoassay and immunoradiometric assay (IRMA), and suggests altered gonadotropin biologic activ- ity related to this alteration. Glycosylation of pituitary hormones has largely been demonstrated to affect their biologic activity We evaluated the presence of different glycosylated gonadotropin isoforms using concanavalin A (Con-A) sepharose, a specific carbohydrate adsorbent, to separate glycosylated from nonglycosylated moieties, the former bound to Con-A and the latter eluted from Con-A. In stress-induced amenorrhea, although the LH elution pattern was similar in both patients and controls, the FSH eluted amounts were significantly higher in stress-induced amenorrhea than in controls because of more nonglycosylated FSH moieties with reduced biologic activity, accounting for gonadal failure with amenorrhea. This difference is corrected by exogen GnRH administration and suggests a relation between gonadotropin conformational alterations, with subse- quent reduction in biologic activity, and impairment of endogenous GnRH secretion as an expression of hypothalamic damage. These data were further evaluated in patients with anorexia nervosa in whom differences in gonadotropin evaluation were detected with both RIA and IRMA methods before and after Con-A, taking into account the influences of altered glycosyl- ation in these assays. These differences are not related to the percentage of weight decrease from ideal body weight or the body mass index or to the age of the patient or the duration of anorexia nervosa and they provide evidence of conformational alterations in gonadotropin isoforms in anorexic patients, likely accounting for the low biologic activity strongly suggested by clinical evidence of amenorrhea with low estrogen plasma levels. Again, the exogen GnRH acute stimulation test can correct for these RIA-IRMA differences, which are similar to those in hypothalamic hypothy- roidism with TSH molecular alterations. In conclusion, our data support the hypothesis that anorexic patients secrete fewer glycosylated molecules with decreased biologic activity. A deficiency in GnRH hypothalamic secretion, as suggested by the decreased gonadotropin pulses reported in women with weight loss-related amenorrhea, determines a low gonadotropin turnover and structural alterations with impaired biologic activity. Structural alterations in hormonal molecules may provide a further stress-mediated disease-determining mechanism.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
