Effect of gonadotrophin-releasing hormone agonist treatment on growth hormone secretion in women with polycystic ovarian syndrome

The suppression of the pituitary-gonadal axis by the administration of gonadotrophin-releasing hormone agonists (GnRH-a) is used occasionally as an adjunct therapy with gonadotrophins for ovulation induction in women with polycystic ovarian syndrome (PCOS). A number of recent clinical studies have suggested that women with polycystic ovaries (PCO) may have disturbances of normal growth hormone (GH) kinetics and alterations in the GH/insulin-like growth factor (IGF)-I system. The purpose of this study was to determine the effect of GnRH-a administration on GH-releasing hormone (GHRH)-stimulated GH release in women with PCOS. Eight women with PCO and six control women were studied before and after 2 months of treatment with the long acting GnRH-a triptoreline (3.75 mg monthly injections). GHRH was given as a single i.v. injection and blood samples for GH measurements were obtained at -15, 0, 30, 60, 90 and 120 min. The GH responses were expressed as the area under the curve (AUC) or the differences from the basal value (delta(max)). The GH response to GHRH (mean +/- SEM) was lower in women with PCO (AUC 114.9 +/- 43.1 versus 206.2 +/- 28.7 ng/ml/120 min, P < 0.05 and delta(max) 31.6 +/- 8.2 versus 49.4 +/- 5.8 ng/ml, P < 0.05). After treatment with the GnRH-a, the GH response to GHRH was significantly smaller than before treatment in both groups (PCO AUC 34.6 +/- 9.0 ng/ml/120 min and delta(max) 12.4 +/- 3.1 ng/ml; controls AUC 148.8 +/- 28.4 ng/ml/120 min and delta(max) 31.2 +/- 6.1 ng/ml), but the PCO group had a significantly smaller response. These data demonstrate that women with PCO have a reduced GH response to GHRH compared with normal controls and that GnRH-a administration causes a further GH reduction in both groups. Women with PCO have a greater suppression of GH response to GHRH during treatment with GnRH-a. This suggests that a different level of sensitivity in the somatotrophic axis exists in PCOS.      

Lymphocyte subset distribution and natural killer activity in growth hormone deficiency before and during short-term treatment with growth hormone releasing hormone

Natural killer (NK) cell activity was assessed in the peripheral blood of 20 patients with growth hormone (GH) deficiency due to a hypothalamic deficit of GH-releasing hormone (GHRH). All patients failed to respond to at least two provocative tests of GH secretion (GH below 7 ng/ml) but responded to a single GHRH iv bolus injection (1 microgram/kg body wt). In 14 of the 20 patients (20 determinations), lymphocyte subsets were also measured; in all patients the distribution of lymphocyte subsets was within the normal range. More importantly, NK cell activity in the 20 patients was significantly lower than in controls (P less than 0.01). To assess the in vivo effect of GH and GHRH on NK activity and lymphocyte subset distribution, immunologic tests were performed (i) before and after a single iv bolus injection of GHRH (1 microgram/kg body wt) in six patients; (ii) before and after 3 weeks of GHRH treatment (3-9 micrograms/kg body wt, one to four times daily) in five patients; and (iii) after 6 weeks of GH treatment (5 IU sc every alternate day) in one patient. Neither NK activity nor the distribution of lymphocyte subsets was altered during short-term GHRH administration. In conclusion, low NK activity is found in GH-deficient patients, and short-term administration of GH or GHRH fails to restore this immunological abnormality. This result suggests that the hypothalamus may be a regulator of NK activity in the human and that patients with hypothalamic deficiencies should be monitored for the development of discrete immunodeficiencies.     

Growth hormone secretion in Alzheimer's disease: 24-hour profile of basal levels and response to stimulation and suppression studies.

The 24-h growth hormone secretory pattern and GH response to growth hormone releasing hormone, the alpha 2-adrenoceptor agonist clonidine and the somatostatin-analogue SMS 201-995 were evaluated in 9 patients with Alzheimer's disease and 9 age- and body body-matched control subjects. The secretory profile did not differentiate between patients and controls. Both secreted the largest amount of GH during the early nighthours between 22.00-02.00, whereas the majority of daytime GH levels were below the assay's detection limit (0.4 ng/ml). No difference was found in GH response to GHRH between patients and controls. All subjects showed significantly enhanced GH secretion after GHRH. Dividing the patients into two groups according to age-of-onset (less than 60 years greater than), there was a trend toward larger GH responses to GHRH for the early-onset group. No other parameter differentiated the groups. GH levels after clonidine were blunted in all subjects but one AD patient, probably due to an age-dependent attenuation frequently observed in subjects over 45 years of age. Finally, the administration of the somatostatin-analogue did not render conclusive results, since spontaneous decline of GH concentration was already beginning 2 hours before the drug was given and continued steadily throughout the observation period. In conclusion, patients with only mild to moderate degree of Alzheimer's disease have no prominent changes in GH regulation.     

Plasma growth hormone-releasing hormone levels in type 1 (insulin-dependent) diabetic children following a mixed meal

Summary Following a mixed meal, plasma hormone responses were measured in four type 1 diabetic children and in eight short normal children. Between 60 and 150 min after ingestion of the mixed meal there was a significant increase in circulating growth hormone-releasing hormone values both in diabetic and in normal children. Mean plasma GHRH peak values were not different between diabetic patients (27.0±3.9 ng/l) and controls (24.6±4.9 ng/l). No time relationship to spontaneous growth hormone peaks was observed. Whereas normal children showed a characteristic biphasic plasma somatostatin response, somatostatin plasma levels in diabetic children did not change. In normal children plasma insulin values increased between 30 and 150 min, but remained unchanged in type 1 diabetic patients. Blood glucose response was more pronounced in diabetic children than in short normal children. These results indicate that circulating growth hormone-releasing hormone does not play a dominant role in the regulation of insulin and somatostatin.Abbreviations GHRH growth hormone-releasing hormone - GH growth hormone - SRIF somatotropin inhibiting factor - RIA radioimmunoassay - SEM standard error of the mean This study was supported by the Deutsche Forschungsgemeinschaft (Ro 717/1-1)     

Somatotropic axis and body weight in pre-menopausal and post-menopausal women: evidence for a neuroendocrine derangement, in absence of changes of insulin-like growth factor binding protein concentrations

The altered function of the somatotropic axis observed in perimenopause may underlie the changes in body weight and fat distribution. The aim of the present study was to evaluate, in pre-menopausal and post- menopausal women with body mass index (BMI) > or = or <25, the basal plasma levels of growth hormone (GH), insulin-like growth factor (IGF)- I and -II, IGF binding protein (IGFBP)-1 and -3, and the response of GH and IGFBP-1 and -3 to GH releasing hormone (GHRH) and GHRH plus arginine tests. GH and IGF-I basal concentrations were significantly higher in pre-menopausal than in post-menopausal women, while IGF-II, IGFBP-1 and IGFBP-3 concentrations did not vary significantly. IGFBP-1, but not IGFBP-3, concentrations were higher in lean than in obese patients. Insulin concentrations were significantly higher in obese patients, while no differences were observed between pre-menopausal and post-menopausal women. In all subjects, GH concentrations increased significantly during GHRH test; pre-menopausal and lean women showed a higher response compared to post-menopausal and obese women. The GHRH plus arginine test stimulated GH response in all women, irrespective of age and BMI. IGFBP-1 and -3 concentrations did not vary in response to GHRH or GHRH plus arginine tests. The somatotropic axis undergoes modifications in post-menopausal women, apparently not involving IGFBP- 1 and -3. Arginine infusion restores the response of GH to GHRH, in both post-menopausal and obese subjects. A somatostatinergic hyperactivity at the climateric period may underlie the changes both in body weight and somatotropic axis.      

Growth hormone secretion is impaired but not related to insulin sensitivity in non-obese patients with polycystic ovary syndrome

BACKGROUND: The aim of the study was to elucidate the relationship between growth hormone (GH) secretion and insulin resistance in polycystic ovary syndrome (PCOS) patients. In order to exclude the influence of obesity on these parameters, only non-obese PCOS patients were studied. METHODS: Eleven PCOS patients and 11 controls with a body mass index (BMI) 相似文献   

Growth hormone response to thyrotrophin releasing hormone in women with polycystic ovarian syndrome.

Recent clinical studies have suggested that women with polycystic ovarian syndrome (PCOS) may have disturbances of growth hormone (GH) kinetics and the GH/insulin-like growth factor (IGF)-I system. The knowledge that in various metabolic abnormalities there is a paradoxical sensitivity of pituitary somatotrophs to thyrotrophin releasing hormone (TRH) administration led to this investigation of the GH secretory response to TRH in women with PCOS. Twenty-four women with PCOS and 18 control women were studied. TRH was given as a single i.v. injection (time 0) and blood samples for GH measurements were obtained at -15, 0, 15, 30, 60 and 90 min. The GH responses were expressed as the area under the curve (AUC) or the differences from the basal value (Deltamax). The GH response to TRH (mean +/- SEM) was greater in women with PCOS (Deltamax 2.47 +/- 1. 73 versus 0.47 +/- 0.06 ng/ml, P < 0.05 and GH AUC 8.05 +/- 2.10 versus 2.58 +/- 0.18 ng/ml/90 min, P < 0.05). According to GH response to TRH, two PCOS subgroups were identified: (i) normal responders (n = 14) who showed Deltamax GH response (0.36 +/- 0.06 ng/ml)and GH AUC (1.93 +/- 0.64 ng/ml/90 min) similar to that in the controls and (ii) over-responders (n +/- 10) who showed a paradoxical increase in GH concentrations in response to TRH (Deltamax GH response 5.43 +/- 1.27 ng/ml and GH AUC 16.62 +/- 3.51 ng/ml per 90 min) that was significantly higher than in normally responding PCOS patients (P < 0.0001) or in controls (P < 0.0001). These data demonstrate an enhanced GH response to TRH administration in a subgroup of women with PCOS.     

Secretion of growth hormone and thyroid-stimulating hormone in patients with dementia

We studied the growth hormone (GH) response to GH-releasing hormone (GHRH) and the thyroid-stimulating hormone (TSH) response to thyrotropin-releasing hormone (TRH) in four groups of patients with dementia and examined whether GH and TSH secretion is altered in patients with Alzheimer's disease. The four groups included those with Alzheimer's disease (n=28), parkinsonism with dementia (n=10), progressive supranuclear palsy with dementia (n=10), and dementia of vascular origin (n=28). The results showed no differences among the four groups in GH response to GHRH (12.2 ± 2, 10.7 ± 2, 8.9 ±1.1, and 9.9 ± 1.9 g/ml, respectively); there was no correlation between GH response to GHRH and sex, stage of the disease, or cerebral atrophy. The proportion of patients with exaggerated, normal, or lower GH response was similar in the four groups. There were also no differences among the groups in terms of TSH response to TRH (9.2 ±0.9, 11.1 ± 1, 11.1 ± 1, and 10.3 ± 1 mU/ml, respectively), nor was there a correlation between TSH response to TRH and sex, stage of the disease, cerebral atrophy, or GH response to GHRH. The proportion of those with exaggerated, normal, or lower TSH response was similar in the four groups. Cerebrospinal somatostatin levels were similar in Alzheimer's disease and vascular dementia patients. These findings indicate that neither GH response to GHRH nor TSH response to TRH provides a useful diagnostic adjunt in Alzheimer's disease patients.Abbreviations AD Alzheimer's disease - PD parkinsonism with dementia - PSP progressive supranuclear palsy - VD dementia of vascular origin - GH growth hormone - GHRH growth hormone releasing hormone - TRH thyrotropin releasing hormone - TSH thyroid stimulating hormone Correspondence to: J.M. Gomez     

Study on growth hormone and insulin secretion in myotonic dystrophy

Growth hormone (GH) levels were measured in 12 patients with myotonic dystrophy (MD; 7 men and 5 women, aged 21–49 years) and 14 volunteers after administration of 100 g GH-releasing hormone (GHRH; 1–29). A 75-g oral glucose tolerance test was carried out to determine glucose, insulin, plasma C-peptide, and urinary C-peptide. The GH level in six MD patients responded normally to GHRH (group I), with a peak of 17.1 ± 1.46 g/l, compared withcontrols (27.8 ± 19.6 g/l, NS), and that in the other six patients responded subnormally, with a peak of 3.15 ± 1.46 g/l, lower than in controls and in group I patients (P < 0.001). In group I the insulin response to the glucose tolerance test showed hyperinsulinism and was lower than that in group II patients; stimulated C-peptide was also higher in group II than in group I and in controls; urinary C-peptide levels were parallel to those in previous data. In all MD patients there were a negative correlation between absolute values of GH response to GHRH and insulin response to glucose tolerance test (r = - 0.79, P < 0.001). Our data suggest that the failure in GH release and peripheral insulin action is due to a generalized defect in cellular membrane function in MD patients.Abbreviations BMI body mass index - GH Growth hormone - GHRH growth hormone releasing hormone - MD myotonic dystrophy Correspondence to: J. M. Gomez Saez     

A pilot study of the long-term effects of acipimox in polycystic ovarian syndrome

BACKGROUND: To evaluate the effects of long-term acipimox administration on glucose-induced insulin secretion and peripheral insulin sensitivity in polycystic ovarian syndrome (PCOS), 20 PCOS subjects (eight lean and 12 obese) and 14 body mass index-matched controls (seven lean and seven obese) were investigated. METHODS: Fasting blood samples were collected for basal hormone and lipoprotein assays, after which patients underwent an oral glucose tolerance test (OGTT). The following day a euglycaemic-hyperinsulinaemic clamp was performed. After 4-6 weeks of treatment with acipimox at a dose of 250 mg given orally three times a day, the patients repeated the study protocol. RESULTS: No significant differences were found in the glucose, insulin or C-peptide responses to OGTT before and after anti-lipolytic drug administration in any group, nor was there any effect on insulin sensitivity. Concerning the lipid profile, acipimox administration led to a significant decrease of cholesterol and low-density lipoprotein levels in obese PCOS patients as well as in obese and lean controls. Lower triglycerides were found after the drug administration in both obese groups. Post-treatment free fatty acid levels were not significantly different when compared with basal values. CONCLUSIONS: Acipimox does not appear to be an effective insulin-lowering drug in PCOS, even if it can be used in obese women with PCOS as an additional therapeutic agent to ameliorate the atherogenic lipid profile of the syndrome.     

Difference in growth hormone response to growth hormone-releasing hormone (GHRH) testing following GHRH subacute treatment in normal aging and growth hormone-deficient adults: Possible perspectives for therapeutic use of GHRH or its analogs in elderly subjects?

The somatotroph axis function shows a decline in the elderly (somatopause). In particular growth hormone (GH) response to GH-releasing hormone (GHRH) is reduced in aged man but less than that observed in GH-deficient adults (GHDAs). Plasma GH response to GHRH (1 µg/kg BW) was significantly lower in four GHDAs than in seven healthy aged men 30, 60, and 90?min after acute GHRH administration. To verify whether a priming regimen might be able to increase the reduced GH response to GHRH, both healthy aged men and GHDA patients underwent repetitive administration of GHRH (100 µg GHRH intravenously as a single morning dose, every 2 days for 12 days). After the GHRH-priming regimen, plasma GH values 30, 60, and 90?min after the acute GHRH test were significantly higher than values at the corresponding time points before priming regimen in healthy aged men but not in GHDA patients. These findings confirmed that somatotroph cells become less sensitive to GHRH with normal aging and demonstrate that repetitive administration of GHRH restores the attenuated response only in healthy aged men but not in GHDA patients. This could support the possible use of GHRH or its analogs instead of recombinant human GH in elderly patients with the advantage of preserving the endogenous pulses of GH with the secretion of the different isoforms of GH. However, concerns arise about the possible role of these molecules in tumorigenesis and tumor growth promotion.     

Neural networks in the analysis of episodic growth hormone release

Pulsatile secretion of growth hormone (GH) has been observedin healthy controls as well as acromegalic patients. In healthyadults, highly regulated secretory pulses of GH occur 4-8 timeswithin 24 h. This episodic pattern of secretion seems to berelated to the optimal induction of physiological effects atthe peripheral level. In contrast to normal subjects, acromegalicpatients demonstrate an irregular pattern of excessive GH release.This pattern of secretion is responsible for many systemic effects,such as the stimulation of connective tissue growth, cardiovascularand cerebrovascular disease, diabetes mellitus and arthritis.Standard methods for the analysis of pulsatile patterns of hormonesecretion did not consistently separate the temporal dynamicsof GH release in healthy controls and acromegalic patients undervarious study conditions. Using the cutting edge technologyof artificial neural networks for time series prediction, wewere able to achieve significant separation of both groups undervarious conditions by means of the predictability of their GHsecretory dynamics. Improving the predictive results by usinga more refined system of multiple neural networks acting inparallel (adaptive mixtures of local experts), we found thatthis system performed a self-organized segmentation of hormonepulsatility. It separated phases of secretory bursts and quiescencewithout any prior knowledge of the form of a GH pulse or a modelof secretion. Comparing the predictive results for the GH dynamicswith those for computer-simulated stochastic processes, we wereable to define the irregular pattern of GH secretion in acromegalyas a random autonomous process. The introduction of neural networksto the analysis of dynamic endocrine systems might help to expandthe existing analytical approaches beyond counting frequencyand amplitude of hormone pulses.     

Endurance exercise modulates levodopa induced growth hormone release in patients with Parkinson's disease

Acute levodopa (LD) application and exercise release human growth hormone (GH). An earlier trial showed, that combined stimulus of exercise and LD administration is the best provocative test for GH response in healthy participants. Objective was to show this combined effect of LD application and exercise on GH response and to investigate the impact on LD metabolism in 20 previously treated patients with Parkinson's disease (PD). We measured GH- and LD plasma concentrations following soluble 200 mg LD/50 mg benserazide administration during endurance exercise and rest on two separate consecutive days. GH concentrations significantly increased on both days, but GH release was significantly delayed during rest. LD metabolism was not altered due to exercise in a clinical relevant manner. Exercise induced a significant faster LD stimulated GH release in comparison with the rest condition. We did not find the supposed increase of LD induced GH release by endurance exercise. We assume, that only a limited amount of GH is available for GH release in the anterior pituitary following an acute 200 mg LD administration. GH disposal also depends on growth hormone releasing hormone (GHRH), which is secreted into hypothalamic portal capillaries. During the exercise condition, the resulting higher blood pressure supports blood flow and thus GHRH transport towards the GH producing cells in the pituitary. This might additionally have caused the significant faster GH release during exercise.     

Abnormal responsiveness of growth hormone to human corticotropin-releasing hormone in major depressive disorder

Plasma growth hormone (GH) release after injection of 100 micrograms synthetic human corticotropin-releasing hormone (hCRH) was investigated in 11 patients with major depressive disorder and normal controls matched for gender, age, body weight and ovarian status. In contrast to controls, who exhibited no significant GH response to CRH, depressed patients showed a significant net increase in GH secretion following CRH administration. The abnormal GH response to CRH was not correlated with baseline corticotropin (ACTH) and cortisol nor with CRH-induced ACTH and cortisol response. The implications of these findings are discussed with reference to such factors as alpha-adrenergic hyperactivity, hypothalamic-pituitary system dysregulation, drug interference, non-specific stress responses and abnormal neuroendocrine circadian rhythms in major depression.     

Deletion of 20p 11.23----pter with normal growth hormone-releasing hormone genes

Using a molecular analysis of the DNA from a patient with a deletion of chromosome 20 [46,XX,del(20)(p 11.23)], we have excluded the growth hormone-releasing hormone (GHRH) gene from the region 20p11.23----pter. The patient had minor facial anomalies. Rieger eye anomaly, a congenital heart defect, severe failure to thrive, and a neurosecretory problem in growth hormone (GH) secretion. Since the GHRH gene was previously mapped to chromosome 20, we used molecular genetic methods to determine whether the growth abnormalities were due to the deletion of this gene. DNAs of the patient and 2 normal control subjects were analyzed by quantitative Southern blotting using a DNA probe for the GHRH gene and 2 reference DNA probes mapping to chromosome 21. The GHRH gene was found to be present in 2 copies in the patient. This indicates that the gene for GHRH maps to the region outside the patient's deletion, in 20p11.23----qter. Furthermore, our results suggest that genes other than GHRH on 20p are important for developmental steps leading to normal neurosecretory function of GH and may also be involved in generating Rieger eye anomaly. Finally, GH deficiency and Rieger eye anomaly should be sought in other patients with deletions of 20p.     

Effects of growth hormone releasing hormone on rat ovarian steroidogenesis

During the last decade, it has been shown that each part ofthe somatotrophic axis can influence granulosa cell function.Growth hormone releasing hormone (GHRH) may be effective throughthe release of hypophyseal growth hormone (GH) and the subsequentincrease of insulin-like growth factors (IGF). There is alsosome evidence that GHRH could act directly on ovarian function.The aim of this study was to determine the mechanism throughwhich GHRH affects granulosa cell steroidogenesis in the ovary.Granulosa cells were obtained from immature, oestrogen-treatedrats supplemented with or without follicle stimulating hormone(FSH) in vivo and were cultured for 48 h to evaluate steroidproduction. GHRH was administered either in vivo at the sametime as FSH, or in vitro in the presence or absence of testosteroneand FSH. Our results show that co-treatment with GHRH and FSHin vivo induced significant increases in plasma IGF-I concentrationsand steroid production by cultured granulosa cells. The additionof GHRH to culture medium did not significantly alter steroidproduction by either non-differentiated (no FSH in vivo) ordifferentiated (FSH in vivo) granulosa cells. In contrast, treatmentin vitro with IGF-I significantly increased steroidogenesisha both cases. Our results suggest that any physiologicallysignificant effect of GHRH on ovarian function is probably tobe exerted via activation of the somatotrophic axis and thesubsequent amplification of ovarian FSH responsiveness by IGF-I.     

Deletion of 20p 11.23→pter with normal growth hormone-releasing hormone genes

Using a molecular analysis of the DNA from a patient with a deletion of chromosome 20 [46,XX,del(20)(p11.23)], we have excluded the growth hormone-releasing hormone (GHRH) gene from the region 20p11.23→pter. The patient had minor facial anomalies, Rieger eye anomaly, a congenital heart defect, severe failure to thrive, and a neurosecretory problem in growth hormone (GH) secretion. Since the GHRH gene was previously mapped to chromosome 20, we used molecular genetic methods to determine whether the growth abnormalities were due to the deletion of this gene. DNAs of the patient and 2 normal control subjects were analyzed by quantitative Southern blotting using a DNA probe for the GHRH gene and 2 reference DNA probes mapping to chromosome 21. The GHRH gene was found to be present in 2 copies in the patient. This indicates that the gene for GHRH maps to the region outside the patient's deletion, in 20p11.23→qter. Furthermore, our results suggest that genes other than GHRH on 20p are important for developmental steps leading to normal neurosecretory function of GH and may also be involved in generating Rieger eye anomaly. Finally, GH deficiency and Rieger eye anomaly should be sought in other patients with deletions of 20p.     

Activity of growth hormone-releasing peptide-2 in cultured human pituitary adenoma cells and its interaction with growth hormone-releasing hormone and somatostatin

Experiments on primary cultures of human pituitary adenoma cells producing growth hormone (GH) or GH and prolactin showed that similarly to GH-releasing hormone (GHRH) synthetic hexapeptide GH-releasing peptide-2 (GHRP) directly enhance secretion of GH but not of prolactin by human pituitary cells. The effect of various doses of GHRP and GHRH applied in combination was additive or slightly synergistic in nature. Somatostatin inhibits secretion of GH induced by GHRP, GHRH, or their combination. A dissociation is found between the inhibitory effects of somatostatin on basal and stimulated GH secretion. Translated fromByulleten' Eksperimental'noi Biologii i Meditsiny, Vol. 125, No. 2, pp. 207–212, February, 1998     

Corticotropin-releasing hormone (CRH)-immunoreactive (IR) axon varicosities target a subset of growth hormone-releasing hormone (GHRH)-IR neurons in the human hypothalamus

It is a general consensus that stress is one of the major factors that suppresses growth. Previous studies revealed that the catecholaminergic and neuropeptide Y (NPY) systems, involved in the activation of stress-related neuronal circuits, influence growth hormone (GH)-release via modulating growth hormone-releasing hormone (GHRH) secretion. Indeed, catecholaminergic and NPY-immunoreactive (IR) axon varicosities abut on the surface of the GHRH neurons forming contacts. These juxtapositions appear to be real synapses and may represent the morphological substrate of the impact of stress on growth. In addition to catecholamines and NPY, there is a vast amount of evidence that corticotropin-releasing hormone (CRH), a major stress hormone, also influences GH secretion. Whether this modulatory effect is direct, or indirect, via the hypothalamic GHRH system, has not been elucidated yet.In the present study, we examined the possibility that CRH influences GH secretion via modulating the GHRH release by direct synaptic mechanisms. Since the verification of these synapses by electron microscopy is problematic in human due to the long post mortem time, in order to reveal the putative CRH-GHRH juxtapositions, light microscopic double label immunohistochemistry was utilized. In the infundibular nucleus, a subset (6%) of the GHRH perikarya received abutting CRH fiber varicosities forming multiple contacts while passing by. No gaps appeared between the contacting elements. The morphology of these CRH-GHRH juxtapositions suggests that, among other neurotransmitters/neuromodulators, CRH influences growth by modulating the hypothalamic GHRH secretion via direct synaptic mechanisms.     

Differential effects of in vivo estrogen administration on hypothalamic growth hormone releasing hormone and somatostatin gene expression.

The aim of this study was to investigate the effect of in vivo estrogen administration on hypothalamic growth hormone releasing hormone (GHRH) and somatostatin (SS) gene expression. We found that estrogen administration (estradiol valerate 250 micrograms/every 3 days, subcutaneously) to male rats induced a decrease in both hypothalamic GHRH mRNA levels and GHRH content, that was significant after 3 and 8 days of treatment. In contrast SS mRNA levels were transiently elevated after 1 and 3 days of estrogen administration, returning to normal values after 8 days of treatment. These data suggest that the existence of sexual dimorphism in GH secretion in the rat could be mediated to some extent by gonadal hormones regulating somatostatin and GHRH gene expression in the hypothalamus.