Effect of human growth hormone-releasing hormone on GH secretion in Cushing's syndrome and non-endocrine disease patients treated with glucocorticoids

Association of IGF-1 Level with Low Bone Mass in Young Patients with Cushing's Disease

Purpose

Few related factors of low bone mass in Cushing's disease (CD) have been identified so far, and relevant sufficient powered studies in CD patients are rare. On account of the scarcity of data, we performed a well-powered study to identify related factors associated with low bone mass in young CD patients.

Methods

This retrospective study included 153 CD patients (33 males and 120 females, under the age of 50 for men and premenopausal women). Bone mineral density (BMD) of the left hip and lumbar spine was measured by dual energy X-ray absorptiometry (DEXA). In this study, low bone mass was defined when the Z score was -2.0 or lower.

Results

Among those CD patients, low bone mass occurred in 74 patients (48.37%). Compared to patients with normal BMD, those patients with low bone mass had a higher level of serum cortisol at midnight (22.31 (17.95-29.62) vs. 17.80 (13.75-22.77), p=0.0006), testosterone in women (2.10 (1.33-2.89) vs. 1.54 (0.97-2.05), p=0.0012), higher portion of male (32.43% vs. 11.54%, p=0.0016) as well as hypertension (76.12% vs. 51.67%, p=0.0075), and lower IGF-1 index (0.59 (0.43-0.76) vs. 0.79 (0.60-1.02), p=0.0001). The Z score was positively associated with the IGF-1 index in both the lumbar spine (r = 0.35153, p < 0.0001) and the femoral neck (r = 0.24418, p=0.0057). The Z score in the femoral neck was negatively associated with osteocalcin (r = -0.22744, p=0.0229). Compared to the lowest tertile of the IGF-1 index (<0.5563), the patients with the highest tertile of the IGF-1 index (≥0.7993) had a lower prevalence of low bone mass (95% CI 0.02 (0.001-0.50), p=0.0002), even after adjusting for confounders such as age, gender, duration, BMI, hypertension, serum cortisol at midnight, PTH, and osteocalcin.

Conclusions

The higher IGF-1 index was independently associated with lower prevalence of low bone mass in young CD patients, and IGF-1 might play an important role in the pathogenesis of CD-caused low bone mass.

The association between insulin-like growth factor 1 levels within reference range and early postoperative remission rate in patients with Cushing's disease

INTRODUCTION

The relationship between growth hormone (GH)/insulin-like growth factor 1 (IGF-1) and glucocorticoids (GC) was examined in various studies. Long-term GC treatment was shown to decrease GH concentration and, interestingly, to increase IGF-1 concentration. We performed a retrospective study in order to examine how preoperative IGF-1 concentrations vary within the reference range and if tertiles of age- and sex-adjusted normal IGF-1 are predictive for early postoperative remission in the patients with Cushing's Disease (CD).

PATIENTS AND METHODS

Patients diagnosed with CD were retrospectively evaluated. After the exclusion of 67 patients, a final cohort of 250 CD patients were included. Age- and sex-adjusted normal IGF-1 levels were divided into tertiles (T1, T2 and T3). Early postoperative remission was defined as a nadir morning cortisol concentration measured within the first 3 consecutive days following surgery of less than 5 µg/dL (138 nmol/L).

RESULTS

Early postoperative remission rate was the lowest in T1 and highest in T3; 49.1% (n = 28) versus 77.3% (n = 75), p = .001, respectively. Binary logistic regression analysis showed the remission rate in T3 was three times higher than that in T1 (p = .003). Cortisol and ACTH concentration were significantly higher and GH concentrations were significantly lower in T1 compared to those in the other two tertiles.

CONCLUSIONS

As the first study evaluating the correlation between early postoperative remission rate in patients with CD and the tertiles of normal age- and sex-adjusted IGF-1 levels, we have shown that higher IGF-1 levels could predict better outcome in CD.

Elevated insulin-like growth factor-1 in Cushing's disease

OBJECTIVE

To determine if patients with untreated Cushing's disease have higher serum insulin-like growth factor-1 (IGF-1) compared to matched controls, and if IGF-1 decreases following remission of Cushing's disease.

DESIGN

Retrospective case-control study matching Cushing's disease cases to control patients for adenoma size, age, sex, diabetic and gonadal status, body mass index and serum IGF-1 measured within one year. Paired analysis of pre-operative (untreated) and >3 months post-operative (remission) serum IGF-1 for cases.

PATIENTS AND MEASUREMENTS

All patients were investigated at the Princess Alexandra Hospital Endocrine Unit between 2005 and 2017. Serum IGF-1 was measured in 25 cases and 49 controls, 23 case-control pairs and 13 cases pre- and post-operatively.

RESULTS

Mean serum IGF-1 in cases was significantly higher compared to controls-32 ± 12 nmol/L compared to 25 ± 8 nmol/L, (P = 0.005). The proportion of cases with elevated serum IGF-1 above an age-adjusted reference range was higher compared to 1:1 matched controls (8/23 (35%) vs 1/23 (4%), P = 0.02). In 13 cases in remission post-operatively, serum IGF-1 decreased significantly from 31 (IQR 29-40.5) nmol/L to 23 (IQR 15-28.5) nmol/L, (P < 0.001), despite no difference in the prevalence of pre- vs post-operative pituitary hormone dysfunction (P = 0.47).

CONCLUSION

Patients with untreated Cushing's disease may have elevated IGF-1, which decreases following remission. Mildly elevated IGF-1 in Cushing's disease does not imply pathological growth hormone (GH) excess.

Effect of one month ketoconazole treatment on GH, cortisol and ACTH release after ghrelin, GHRP-6 and GHRH administration in patients with cushing’s disease

GH responses to ghrelin, GHRP-6, and GHRH in Cushing’s disease (CD) are markedly blunted. There is no data about the effect of reduction of cortisol levels with steroidogenesis inhibitors, like ketoconazole, on GH secretion in CD. ACTH levels during ketoconazole treatment are controversial. The aims of this study were to compare the GH response to ghrelin, GHRP-6, and GHRH, and the ACTH and cortisol responses to ghrelin and GHRP-6 before and after one month of ketoconazole treatment in 6 untreated patients with CD. Before treatment peak GH (mg/L; mean ± SEM) after ghrelin, GHRP-6, and GHRH administration was 10.0 ± 4.5; 3.8 ± 1.6, and 0.6 ± 0.2, respectively. After one month of ketoconazole there was a significant decrease in urinary cortisol values (mean reduction: 75%), but GH responses did not change (7.0 ± 2.0; 3.1 ± 0.8; 0.9 ± 0.2, respectively). After treatment, there was a significant reduction in cortisol (mg/dL) responses to ghrelin (before: 30.6 ± 5.2; after: 24.2 ± 5.1). No significant changes in ACTH (pg/mL) responses before (ghrelin: 210.9 ± 69.9; GHRP-6: 199.8 ± 88.8) and after treatment (ghrelin: 159.7 ± 40.3; GHRP-6: 227 ± 127.2) were observed. In conclusion, after short-term ketoconazole treatment there are no changes in GH or ACTH responses, despite a major decrease of cortisol levels. A longer period of treatment might be necessary for the recovery of pituitary function.

Decreased GH secretion and enhanced ACTH and cortisol release after ghrelin administration in Cushing's disease: comparison with GH-releasing peptide-6 (GHRP-6) and GHRH

GH responsiveness to GH secretagogues (GHS) is blunted in Cushing's disease (CD), while ACTH/cortisol responses are enhanced, by mechanisms still unclear. Ghrelin, the endogenous ligand for GHS-receptors (GHS-R), increases GH, ACTH, cortisol and glucose levels in humans. This study evaluated the GH, ACTH, cortisol and glucose-releasing effects of ghrelin in CD in comparison with GHRP-6. GHRH-induced GH release was also studied. Ten patients with CD (BMI 26.9+/-1.0 kg/m(2)) and ten controls (BMI 24.4+/-1.1 kg/m(2)) received ghrelin (1 microg/kg), GHRP-6 (1 microg/kg) and GHRH (100 microg) separately. GH, ACTH, cortisol and glucose levels were measured. In CD ghrelin-induced GH (microg/L; mean +/- SE) release (peak: 7.2+/-3.0) was higher than seen with GHRP-6 (2.7+/-1.0) and GHRH (0.7+/-0.2), but lower than in controls (ghrelin: 58.3+/-12.1; GHRP-6: 22.9+/-4.8; GHRH: 11.3+/-3.7). In controls ACTH (pg/mL) release after ghrelin (79.2+/-26.8) was higher than after GHRP-6 (23.6+/-5.7). In CD these responses (ghrelin: 192+/-43; GHRP-6: 185+/-56) were similar, and enhanced compared to controls. The same was observed with cortisol. Glucose levels failed to increase after ghrelin in CD, differently than in controls. Our data suggests that hypothalamic and pituitary pathways of GH release activated by ghrelin, GHRP-6 and GHRH are deranged in chronic hypercortisolism. The increased ACTH/cortisol responses to ghrelin and GHRP-6 in CD could be mediated by overexpression of GHS-R in ACTH-secreting adenomas. Hypercortisolism apparently impairs the ability of ghrelin to increase glucose levels.

Growth hormone secretion in primary adrenal Cushing's syndrome is disorderly and inversely correlated with body mass index

To evaluate the impact on the somatotropic axis of endogenous cortisol excess in the absence of primary pituitary disease, we investigated spontaneous 24-h growth hormone (GH) secretion in 12 adult patients with ACTH-independent hypercortisolism. Plasma GH concentration profiles (10-min samples) were analyzed by deconvolution to reconstruct secretion and approximate entropy to quantitate orderliness of the release process. Comparisons were made with a body mass index (BMI)-, age-, and gender-matched control group and an age- and gender-matched lean control group. GH secretion rates did not differ from BMI-matched controls but were twofold lower compared with lean subjects, mainly due to a 2.5-fold attenuation of the mean secretory burst mass (P = 0.001). In hypercortisolemic patients, GH secretion was negatively correlated with BMI (R = -0.55, P = 0.005) but not cortisol secretion. Total serum IGF-I concentrations were similar in the three groups. Approximate entropy (ApEn) was increased in patients with Cushing's syndrome compared with both control groups (vs. BMI-matched, P = 0.04; vs. lean, P = 0.001), denoting more irregular GH secretion patterns. ApEn in patients correlated directly with cortisol secretion (R = 0.77, P = 0.003). Synchrony between cortisol and GH concentration series was analyzed by cross-correlation, cross-ApEn, and copulsatility analyses. Patients showed loss of pattern synchrony compared with BMI-matched controls, but copulsatility was unchanged. We conclude that hyposomatotropism in primary adrenal hypercortisolism is only partly explained (approximately 30%) by increased body weight and that increased GH secretory irregularity and loss of synchrony suggest altered coordinate regulation of GH release.

Pulsatile secretion pattern of growth hormone in dogs with pituitary-dependent hyperadrenocorticism

The amplitude and frequency of growth hormone (GH) secretory pulses are influenced by a variety of hormonal signals, among which glucocorticoids play an important role. The aim of this study was to investigate the pulsatile secretion pattern of GH in dogs in which the endogenous secretion of glucocorticoids is persistently elevated, i.e. in dogs with pituitary-dependent hyperadrenocorticism (PDH). Blood samples for the determination of the pulsatile secretion pattern of GH were collected at 10-min interval between 08:00 and 14:00 h in 16 dogs with PDH and in 6 healthy control dogs of comparable age. The pulsatile secretion patterns of GH were analyzed using the Pulsar program. GH was secreted in a pulsatile fashion in both dogs with PDH and control dogs. There was no statistical difference between the mean (+/-S.E.M.) basal GH level in dogs with PDH (0.7+/-0.1 microg/l) and the control dogs (0.6+/-0.1 microg/l). The mean area under the curve (AUC) for GH above the zero-level in dogs with PDH (4.6+/-0.6 microg/l per 6 h) was significantly lower than that in the control dogs (7.3+/-1.0 microg/l per 6 h). Likewise, the mean AUC for GH above the base-level in dogs with PDH (0.6+/-0.1 microg/l per 6 h) was significantly lower than that in the control dogs (3.7+/-1.0 microg/l per 6 h). The median GH pulse frequency in the dogs with PDH (2 pulses/6 h, range 0-7 pulses/6 h) was significantly lower (P = 0.04) than that (5 pulses/6 h, range 3-9 pulses/6 h) in the control group. The results of this study demonstrate that PDH in dogs is associated with less GH secreted in pulses than in control dogs, whereas the basal plasma GH concentrations were similarly low in both groups. It is discussed that the impaired pulsatile GH secretion in dogs with PDH is the result of alterations in function of pituitary somatotrophs and changes in supra-pituitary regulation.

Effect of withdrawal of somatostatin plus growth hormone (GH)-releasing hormone as a stimulus of GH secretion in Cushing's syndrome

OBJECTIVE

Somatostatin (SS) may not merely be inhibitory to GH secretion but, under appropriate temporal conditions, may act in a paradoxically positive manner to sensitize somatotroph responsiveness to GHRH. SS infusion withdrawal (SSIW) produces a rebound GH rise in humans and increases GHRH-induced GH release. Theoretically SSIW leaves the somatotroph cell in a situation of low endogenous SS. In Cushing's syndrome, GH secretion appears blunted to all stimuli. The mechanisms by which glucocorticoids impair GH secretion in Cushing's syndrome are unknown. There are no data evaluating GH responsiveness to SSIW plus GHRH in Cushing's syndrome patients. The aim of the present study was to evaluate the GH response to SSIW plus GHRH in a group of Cushing's syndrome patients, in order to further understand the deranged GH secretory mechanisms in Cushing's syndrome.

PATIENTS AND MEASUREMENTS

Eight female patients with Cushing's syndrome were studied. As a control group, eight normal subjects of similar age and sex were studied. Three tests were done. On one day, SS intravenous (i.v.) infusion (500 micro g for 0-90 min) was performed followed by placebo i.v. bolus at min 90 after SS withdrawal (SSIW). On another day, SS i.v. infusion (500 micro g for 0-90 min) was performed followed by GHRH (100 micro g) i.v. bolus at min 90 after SS withdrawal. On a third day, slow infusion of 150 mmol/l NaCl administration was performed followed by GHRH (100 micro g) i.v. bolus at min 90 after the start of the infusion. Blood samples were taken at appropriate intervals for determination of GH.

RESULTS

GHRH-induced GH secretion in normal subjects showed a mean peak of 15.4 +/- 2.1 micro g/l (conversion factor: 1 micro g/l = 1.2 mUI/l). Normal control subjects had a mean peak of 3.3 +/- 1.6 micro g/l after SSIW-induced GH secretion. When GHRH was administered after SSIW there was increased GH secretion with a mean peak of 23.7 +/- 4.2 micro g/l significantly greater than the response after SSIW alone (P < 0.05) and GHRH alone (P < 0.05). The patients with Cushing's syndrome had a blunted GH response after GHRH administration with a mean peak of 1.4 +/- 0.4. After SSIW, Cushing's syndrome patients had a mean peak of 1.0 +/- 0.5 micro g/l. When GHRH was administered after SSIW there was a similar GH response with a mean peak of 1.7 +/- 0.6 micro g/l, not statistically different than the response after SSIW alone (P = ns) and GHRH alone (P = ns). When we compare the response of normal subjects and Cushing's syndrome patients, after SSIW plus GHRH, it was decreased in Cushing's syndrome patients (P < 0.05), with a mean GH peak of 23.7 +/- 4.2 micro g/l and 1.7 +/- 0.6 micro g/l for normal subjects and Cushing's syndrome patients, respectively.

CONCLUSIONS

This study has demonstrated a significantly blunted peak GH response to somatostatin infusion withdrawal plus GHRH in Cushing's syndrome patients. In this theoretical situation of decreased somatostatinergic tone there is persistence of GH hyposecretion in Cushing's syndrome, suggesting the existence of a pituitary defect responsible for the decreased GH secretion in Cushing's syndrome.

Glucocorticoids regulate pituitary growth hormone secretagogue receptor gene expression

Glucocorticoids regulate growth hormone (GH) secretion by modulating both hypothalamic and pituitary function. At the level of the pituitary, glucocorticoids increase GH and GH-releasing hormone receptor (GHRH-R) gene expression. To test if glucocorticoids might also regulate the pituitary expression of the recently identified GH secretagogue (GHS) receptor, GHS-R; adult male rats were adrenalectomized or sham operated, and treated with the synthetic glucocorticoid (dexamethasone, 200 microg/day) or vehicle for 8 days. Pituitary GHS-R mRNA levels were assessed by reverse transcriptase polymerase chain reaction (RT-PCR). Adrenalectomy decreased pituitary GHS-R mRNA to 45% of vehicle-treated, sham-operated rats (P < 0.05). Administration of dexamethasone increased GHS-R mRNA levels in sham-operated as well as in adrenalectomized rats (199 +/- 24% (P < 0.05) and 369 +/- 48% (P < 0.01) of vehicle-treated controls). Addition of dexamethasone to primary rat pituitary cell cultures increased GHS-R mRNA levels in a dose- and time-dependent manner while the transcriptional inhibitor, actinomycin D, completely blocked the stimulatory action of dexamethasone. Taken together, these results suggest glucocorticoids directly increase pituitary GHS-R mRNA levels by stimulating GHS-R gene transcription.

Integrity of the growth hormone/insulin-like growth factor system is maintained in patients with chronic fatigue syndrome

GH deficiency states and chronic fatigue syndrome (CFS) share several characteristics, and preliminary studies have revealed aspects of GH dysfunction in CFS. This study assessed indexes of GH function in 37 medication-free CFS patients without comorbid psychiatric illness and 37 matched healthy controls. We also assessed GH function before and after treatment with low dose hydrocortisone, which has been shown recently to reduce fatigue in CFS. We measured basal levels of serum insulin-like growth factor I (IGF-I), IGF-II, IGF-binding protein-1 (IGFBP-1), IGFBP-2 and IGFBP-3 together with 24-h urinary GH excretion. We also performed 2 dynamic tests of GH function: a 100-microg GHRH test and an insulin stress test using 0.15 U/kg BW insulin. There were no differences between patients and controls in basal levels of IGF/IGFBP or in urinary GH excretion. GH responses to both the GHRH test and the insulin stress test were no different in patients and controls. CFS patients did have a marginally reduced suppression of IGFBP-1 during the insulin stress test. Hydrocortisone treatment had no significant effect on any of these parameters. There is no evidence of GH deficiency in CFS. At the doses used, hydrocortisone treatment appears to have little impact on GH function.

IGF-I levels rise and GH responses to GHRH decrease during long-term prednisone treatment in man

Glucocorticoid excess is associated with a blunted GH response to GHRH. IGF-I levels in hypercortisolism are controversial and have been reported as low, normal or high. The aim of this study was to evaluate longitudinally time-dependent changes in the GH response to GHRH, IGF-I, IGFBP-3 and albumin values in patients during corticotherapy. Six patients received GHRH before and after one week and one month of prednisone administration (20-60 mg/d, orally). IGF-I, IGFBP-3 and albumin were determined in each test, at time 0. Ten normal controls were also evaluated in one occasion. There were no differences in basal GH values, GH response to GHRH, IGF-I and IGFBP-3 levels between controls and patients before starting corticotherapy. Albumin (g/l; mean+/-SE) values were lower in patients before treatment (31+/-4) than in controls (43+/-1). After one week of prednisone administration there was a significant decrease in peak GH (microg/l) levels (before: 18.8+/-7.4; 1 week: 5.0+/-1.3), which was maintained after one month (8.1+/-3.5). IGF-I (microg/l) levels increased significantly, from 145+/-23 to 205+/-52 after one week of therapy, reaching levels of 262+/-32 after one month. IGFBP-3 (mg/l) values did not increase significantly (before: 2.1+/-0.2; 1 week: 2.5+/-0.3; 1 month: 2.8+/-0.2). Albumin levels showed a significant rise both after one week (36+/-4) and one month (42+/-3) of corticotherapy. In summary, we observed a marked decrease in the GH response to GHRH after one week and one month of prednisone administration associated with an increase in circulating IGF-I and albumin values. The physiological implications of these findings are still uncertain. It is possible that glucocorticoids increase hepatic IGF-I and albumin synthesis, although other mechanisms may have a role.

Growth hormone responses to growth hormone-releasing hormone and clonidine in dogs with Cushing's syndrome

The effects of clonidine, a growth hormone (GH) secretagogue, acting at the hypothalamic level and synthetic GH-releasing hormone (GHRH), a physiological stimulus of somatotrophs, on GH secretion were measured in 11 dogs with Cushing's syndrome. Eight healthy dogs served as controls. After the administration of GHRH the dogs with hyperadrenocorticism had a mean (SEM) GH peak of 11.2 (2.5) ng ml-1 which was significantly lower than the peak of 48.6 (13.4) ng ml-1 observed in the healthy dogs. Similarly, the GH response to clonidine was inhibited in the dogs with hyperadrenocorticism, the mean GH peak being 9.3 (3.3) ng ml-1 compared with 135.6 (43.3) ng ml-1 in the control dogs. No significant difference between the GH responses to GHRH and clonidine was observed in the dogs with Cushing's syndrome, the areas under the response curves being 567.9 (78.2) and 478.0 (102.6) ng.min ml-1, respectively. These results demonstrate that the function of somatotrophs is abnormal in dogs with Cushing's syndrome. There is evidence that the likely action of clonidine in dogs is to inhibit the release of somatostatin and the results therefore suggest that the effect of an excess of glucocorticoid in the dog is probably not mediated through an increase in somatostatin tone.

Relation between growth hormone and cortisol spontaneous secretion in children

OBJECTIVE

Dual effects of corticoids upon GH release in man have been described: a rapid, potentiating effect and a delayed suppressive one. Many investigators have used pharmacological doses of glucocorticoids in an attempt to detect this interaction of corticoids and GH. The aim of the present study was to determine the relationship between GH and cortisol spontaneous secretion in children under physiological conditions.

DESIGN AND PATIENTS

Nine children aged 7.5-13.5 years with different growth rates were evaluated over a 24-hour period. Four were of normal stature (+/- 2 SD) and five were below 2 SD (familial or constitutional short stature). Blood samples were obtained at 20-minute intervals over a 24-hour period.

MEASUREMENTS

GH and cortisol concentrations were measured by radioimmunoassay in each of the 73 samples collected.

RESULTS

A significant correlation was obtained between mean 24-hour cortisol concentration and mean 24-hour GH concentration (r = 0.83; P < 0.01), the sum of 24-hour GH pulse amplitudes (r = 0.85; P < 0.01) and the highest 24-hour GH concentration (r = 0.88; P < 0.01). A significant positive correlation was also detected between mean 24-hour cortisol concentration and the number of GH pulses over a 24-hour period (r = 0.70; P < 0.05). However, there was no significant correlation between mean 24-hour GH concentration and number of cortisol pulses over a 24-hour period. The correlation between number of cortisol pulses and number of GH pulses was also non-significant.

CONCLUSION

These data suggest an interplay of spontaneous GH and cortisol secretion in children. Physiological plasma cortisol levels may play a role in brain-pituitary regulatory mechanisms of GH secretion.

Effect of the combined administration of galanin and clonidine on serum growth hormone levels in normal subjects and in patients under chronic glucocorticoid treatment

Aim of our study was to investigate the effect of clonidine and galanin (alone or in combination) on growth hormone (GH) secretion in normal subjects and in adult patients with increased somatostatin tone due to chronic daily immunosuppressive glucocorticoid treatment. We studied 7 adult patients undergoing long-term (no less than 6 months) immunosuppressive glucocorticoid treatment for non endocrine diseases (4F, 3M; age 49.7 +/- 6.3 years). Six normal adult nonobese subjects (3F, 3M; age 34 +/- 2.7 years) served as controls. All subjects underwent the following three tests in random order: 1) iv infusion of clonidine, 150 micrograms in 10 mL of saline, from time 0 to 10 min; 2) iv infusion of synthetic porcine galanin, 500 micrograms in 100 mL of saline from -15 to 30 min; 3) iv infusion of clonidine from 0 to 10 min combined with synthetic porcine galanin iv infusion from -15 to 30 min. Blood samples for GH assay were taken at -15, 0, 15, 30, 45, 60, 90, 120 min. No significant differences in GH absolute values were observed at any time between the three different tests within each group of subjects. Normal subjects showed significantly (p < 0.05) higher GH peaks and GH absolute values from 15 to 90 min after galanin alone, clonidine alone and clonidine+galanin with respect to the glucocorticoid-treated patients. The absence of any either synergistic or at least additive effect on GH secretion of galanin and clonidine in conditions of both normal and increased somatostatin tone suggests that also in man, as well as in the rat, the action of galanin on the GH axis may be mediated through alpha-adrenergic pathways.

Growth hormone secretion: the role of glucocorticoids

Glucocorticoids (GCs) modulate the somatotropic axis at a genomic and a non-genomic level. Critical concentrations of steroids not only determine somatotrope differentiation but also enhance growth hormone (GH) gene expression. At a cellular level GH-releasing hormone (GHRH) and somatostatin (SS) are the two principal neuropeptides involved in the release of GH. In vitro data indicates that steroids enhance GH release by altering the affinity and the density of GHRH receptors. In addition, they reduce the sensitivity of the somatotrope to SS and decrease IGF-1 induced negative feedback on GH secretion. The net effect is an enhancement of GH release.

Effect of galanin on the growth hormone (GH) response to GH-releasing hormone in patients with Cushing's disease

Attenuated plasma GH secretion during sleep and blunted GH responses to provocative stimuli have been observed in patients with Cushing's disease. Synthetic porcine galanin elicits GH secretion when given alone, and enhances the GH response to GHRH in normal human subjects. The aim of our study was to investigate the effects of galanin on the GH response to GHRH in patients with Cushing's disease. We studied 5 female subjects with untreated active Cushing's disease caused by micro-pituitary adenomas (age 43 +/- 6.7 years; BMI 30 +/- 0.7 kg/m2). Four normal adult females, matched for age and body weight with the patients with Cushing's disease, were studied as controls. Subjects underwent in random order: (1) infusion of synthetic porcine galanin IV, 500 micrograms in 100 mL; (2) infusion of saline, IV, 100 mL. A bolus of human GHRH(1-29)NH2 (Geref, Serono, Italy), 100 micrograms in 1 mL saline, was injected IV at 0 minutes. Patients with Cushing's disease showed blunted GH peaks after GHRH (1.2 +/- 0.4 micrograms/L) during saline infusion, as compared to normal controls (24.6 +/- 4.6 micrograms/L; p < 0.05). During galanin infusion a significantly enhanced GH response to GHRH, as compared with saline infusion, was observed in control subjects (GH peak: 51.4 +/- 9.8 micrograms/L; p < 0.05), but not in patients with Cushing's disease (GH peak: 2.3 +/- 0.6 micrograms/L). GH levels were significantly lower both after saline and after galanin in patients with Cushing's disease as compared to normal controls. Our data demonstrate that galanin is not able to enhance the GH response to GHRH in patients with Cushing's disease. That galanin cannot reverse this effect suggests that the mechanism of action of galanin is not via a decrease in somatostatin release by the hypothalamus.

Effects of pyridostigmine on spontaneous and growth hormone-releasing hormone stimulated growth hormone secretion in children on daily glucocorticoid therapy after liver transplantation

OBJECTIVES

We aimed to investigate both nocturnal spontaneous and morning growth hormone (GH)-releasing hormone (GHRH)-induced GH secretion in children on daily glucocorticoid treatment after liver transplantation and to evaluate the effect of pyridostigmine (an acetylcholinesterase inhibitor thought to reduce hypothalamic somatostatin tone) on GH secretion in these patients.

DESIGN

We performed a randomized, single-blind, cross-over study.

PATIENTS

We studied three male and three female juvenile patients, within a year of orthotopic liver transplantation and under immunosuppressive glucocorticoid therapy (mean dose +/- SEM, 5.92 +/- 0.63 mg/day) and five normal children (four males, one female).

MEASUREMENTS

Both nocturnal spontaneous and morning GHRH-induced GH secretion were evaluated after administration of placebo, 1 tablet p.o., or pyridostigmine, 2 mg/kg p.o.

RESULTS

Spontaneous GH. Placebo: in liver transplanted children nocturnal GH secretion (mean GH level 10.8 +/- 2.0 mU/l) was not significantly different with respect to normal children (mean GH level 12.8 +/- 1.2 mU/l); pyridostigmine: nocturnal GH secretion was significantly increased as compared to placebo in subjects with liver transplantation but not in normal children. GHRH test. Placebo: liver transplanted patients showed a blunted GH response to GHRH with respect to normal children; pyridostigmine: the GH responses to GHRH (P less than 0.05) increased as compared to placebo and did not differ significantly in the two groups.

CONCLUSIONS

Our data suggest a steroid-mediated increase in hypothalamic somatostatin tone in liver transplanted children.

Pyridostigmine does not reverse dexamethasone-induced growth hormone inhibition

Glucocorticoids inhibit the growth hormone (GH) response to a variety of stimuli, including GH-releasing hormone (GHRH) in vivo, but they increase GHRH-stimulated GH secretion when added, in vitro, to animal and human pituitary cells. This discrepancy has led to the hypothesis that glucocorticoids act in vivo by increasing somatostatin secretion from the hypothalamus. To examine this hypothesis, we used a cholinergic drug, pyridostigmine (PD), which reduces hypothalamic somatostatin secretion. Eight normal volunteers were studied. They underwent four tests: (1) GHRH test; (2) Dex + GHRH (GHRH test after treatment the night before, with dexamethasone (Dex)); (3) PD + GHRH; (4) Dex + PD + GHRH. Dex significantly inhibited the GH response to GHRH expressed as area under the GH/time curve (AUC, microgram/1/min) (mean +/- SEM = 895.2 +/- 196.6 vs 1970.9 +/- 600.1, P less than 0.05). PD significantly increased the AUC of GH secretion in PD + GHRH compared with GHRH alone (3541.2 +/- 571.3 vs 1970.9 +/- 600.1, P less than 0.01) but by no means restored completely the normal GH response to GHRH, when given to Dex-pretreated subjects. Furthermore, the mean AUC of Dex + PD + GHRH was significantly lower than that of PD + GHRH (1621.7 +/- 500.6 vs 3541.2 +/- 571.3, P less than 0.01), demonstrating that Dex continues to exert its inhibitory effect on GH secretion in the presence of PD. These results suggest that glucocorticoid-induced GH inhibition does not act solely through an increase in hypothalamic somatostatin secretion.

Psychiatric implications of altered limbic-hypothalamic-pituitary-adrenocortical activity

Hormones of the limbic-hypothalamic-pituitary-adrenocortical (LHPA) system are much involved in central nervous system regulation. The major LHPA neuropeptides, corticotropin-releasing hormone (CRH), vasopressin (AVP) and corticotropin (ACTH) do not only coordinate the neuroendocrine response to stress, but also induce behavioral adaptation. Transcription and post-translational processing of these neuropeptides is regulated by corticosteroids secreted from the adrenal cortex after stimulation by ACTH and other proopiomelanocortin derived peptides. These steroids play a key role as regulators of cell development, homeostatic maintenance and adaptation to environmental challenges. They execute vitally important actions through genomic effects resulting in altered gene expression and nongenomic effects leading to altered neuronal excitability. Since excessive secretory activity of this particular neuroendocrine system is part of an acute stress response or depressive symptom pattern, there is good reason to suspect that central actions of these steroids and peptides are involved in pathophysiology determining the clinical phenotype, drug response and relapse liability. This overview summarizes the clinical neuroendocrine investigations of the author and his collaborators, while they worked at the Department of Psychiatry in Mainz. The major conclusions from this work were: (1) aberrant hormonal responses to challenges with dexamethasone, ACTH or CRH are reflecting altered brain physiology in affective illness and related disorders; (2) hormones of the LHPA axis influence also nonendocrine behavioral systems such as sleep EEG; (3) physiologically significant interactions exist between LHPA hormones, the thyroid, growth hormone, gonadal and other neuroendocrine systems; (4) hormones of the LHPA axis constitute a bidirectional link between immunoregulation and brain activity; and (5) future psychiatric research topics such as molecular genetics of affective disorders, familial risk studies, drug response analysis and neurobiology of aging will benefit from extended knowledge of neural corticosteroid effects at a clinical, cellular, and molecular level.

Dexamethasone treatment increases neuropeptide Y levels in rat hypothalamic neurones

Immunoreactive glucocorticoid receptors (GR) have previously been demonstrated in neuropeptide Y (NPY) neurones of the rat hypothalamus. To determine whether NPY synthesis is influenced by glucocorticoids, the effect of dexamethasone (DEX) on the levels of immunoreactive NPY in rat hypothalamic neurones was investigated in vivo and in vitro. Daily injections of DEX (0.1 mg/day) for 5 days increased the NPY content of the mediobasal hypothalamus in female rats by 117% (p less than 0.002). Primary cultures of hypothalamic neurones were also sensitive to the effect of glucocorticoids. Intracellular NPY levels were significantly increased (p less than 0.001) compared to control values by 151%, 222% and 268% when cultures were maintained in a defined serum free medium containing DEX 10(-9), 10(-8) and 10(-7) M respectively.