Leptin stimulates growth hormone secretion via a direct pituitary effect combined with a decreased somatostatin tone in a median eminence-pituitary perifusion study

The aim of this study was to examine the effect of recombinant human leptin on growth hormone (GH) secretion in perifused anterior pituitary slices from adult pigs. Anterior pituitary slices from sows were perifused and treated with recombinant human leptin (10 nM) and GH-releasing hormone (GHRH; 1 nM). In some experiments, pituitary slices were coincubated with stalk median eminence (SME). In a subset of the coincubation experiments, immunoneutralization of endogenous GHRH and somatostatin (SRIH) release was performed with antisera to GHRH and SRIH. Leptin increased GH secretion in pituitary slices alone (up to 100% vs. control at 40 min) as well as in pituitary slices coincubated with SME (up to 122% vs. control at 40 min). A significant difference was observed in GH secretion from pituitary slices when the tissue was coincubated with leptin and GHRH at a low concentration (0.1 nM), but not when GHRH was used at 1 and 10 nM. Furthermore, anti-SRIH antiserum increased GH release from pituitary slices in coincubation experiments with SME. Finally, SRIH secretion was significantly reduced by leptin (down by 35% vs. control from 0 to 30 min of treatment) in cultured SME. These data show that leptin is effective in stimulating GH secretion by acting at two different levels: (1) it stimulates GH secretion directly from pituitary slices, and (2) it reduces SRIH tone from the median eminence and, indirectly, increases GH secretion from the pituitary. These results support the hypothesis that leptin may be an interesting hormonal mediator of growth and related metabolic effects by acting directly on the hypothalamic-pituitary axis.

Long-term effects on bone of postnatal immunization against GHRH in female and male rats

The effects of neonatal passive immunization against GHRH on bone was examined in male and female rats. Pups were treated subcutaneously with GHRH-antiserum (GHRH-Ab) from day 1 to day 10 of age. Bone mineral content (BMC) and bone mineral density (BMD) were evaluated at monthly intervals until 7 months. Markers of bone resorption (urinary lysylpyridinoline, LP), bone formation (serum osteocalcin, OC) and serum IGF-I were measured at 2, 3 and 7 months. In male rats, GHRH-Ab did not modify BMC and BMD when compared with controls. In contrast, female rats demonstrated lower whole body and femoral BMC and BMD from 2 to 7 months of age. Reduced bone growth in the females was associated with lower IGF-I levels than controls at 2 and 3 months of age, whereas in males IGF-I titers did not change during the period of the study. LP excretion was higher in GHRH-Ab-treated rats at 2 and 3 months in both sexes. In females, no difference in OC values was recorded, whereas in GHRH-Ab-treated males, there was an increase in OC levels at 2 and 3 months. These data indicate that transient GHRH deprivation induces an osteopenic effect in female rats which is not evident in male rats.

Differential GH-releasing hormone regulation of GHRH receptor mRNA expression in the rat pituitary

To understand the capacity of growth hormone-releasing hormone (GHRH) to regulate expression of the GHRH receptor, we studied the effects of GHRH on GHRH receptor mRNA expression in immature and adult rats by use of pituitary cell culture and immunoneutralization approaches. Pituitary cell cultures from neonatal (2-day-old) and adult (70-day-old) rats were treated with GHRH for 4, 24, or 72 h. The effect of GHRH on GHRH receptor mRNA expression depended on the duration of GHRH exposure in both age groups; short-term (4 h) GHRH treatment significantly reduced GHRH receptor mRNA expression (P < 0.05), whereas intermediate treatment (24 h) restored GHRH receptor mRNA to basal levels, and long-term treatment (72 h) stimulated GHRH receptor mRNA expression (P < 0.02). The long-term stimulatory effect of GHRH on GHRH receptor mRNA expression required the presence of serum in the culture medium, and, in the absence of serum, the stimulatory effect was completely abolished. Moreover, the capacity of the pituitary to increase GHRH receptor mRNA expression in response to 72-h GHRH treatment was age dependent, with neonatal pituitaries exhibiting a much greater stimulatory effect than adult pituitaries (P < 0.025). Immunoneutralization of endogenous GHRH significantly reduced GHRH receptor mRNA expression in neonatal (P < 0.004), juvenile (P < 0.003), and mature (P < 0.004) pituitaries compared with age-matched controls. Taken together, these results indicate that GHRH is a potent regulator of GHRH receptor gene expression in immature and mature pituitaries; however, the nature and direction of GHRH regulation of its receptor depend significantly on several variables, including the duration of GHRH exposure, the presence of permissive components in serum, and the developmental stage of the pituitary.

Acute and chronic galanin administration decreases hypothalamic galanin synthesis in both male and female adult rats: evidence for a long-loop galanin autofeedback

The secretion of growth hormone (GH) in both male and female rats is controlled by two main neuropeptides, GH-releasing hormone (GHRH), which is stimulatory, and somatostatin, which is inhibitory. Recently, it has been shown that galanin (GAL) also stimulates GH secretion, although the underlying mechanism is still unknown. It was the aim of this study to begin to elucidate if and how GAL regulates its own production at the hypothalamic and pituitary level. Rats underwent the following experimental trials. In experiment 1, adult male and female rats had blood samples collected at -15 minutes, -7.5 minutes, and immediately preceding a subcutaneous (s.c.) injection of GAL at a dose of either 50 or 200 microg/kg. Blood samples were collected at 5, 10, 15, 30, and 60 minutes, and the GH concentration was measured using a radioimmunoassay. The tissues were collected and analyzed for mRNA levels of hypothalamic and pituitary GAL. In experiment 2, adult male and female rats were treated long-term with 200 microg/kg GAL for 7 days s.c., and the pituitary and hypothalamus were analyzed for GAL mRNA. Serum GH concentrations were significantly increased in acutely dosed male and female rats regardless of the dosage level. For the male and female animals acutely dosed with both 50 and 200 microg/kg GAL, hypothalamic GAL mRNA was decreased, whereas pituitary GAL mRNA was affected by 200 microg/kg GAL only in females (increased). For the animals treated long-term with GAL, hypothalamic GAL mRNA was decreased while mRNA for pituitary GAL was increased. We conclude that regardless of the dosage and duration of treatment, administration of GAL negatively regulates hypothalamic GAL mRNA in a non-gender-specific way. Pituitary GAL synthesis appears to be stimulated particularly during chronic SCGAL administration.

The effects of a continuous infusion of hexarelin on pulsatile growth hormone release, growth axis and galanin gene expression and on the response of the growth axis to growth hormone-releasing hormone

The effect of a 6 hour continuous infusion of Hexarelin (100 micrograms/hour) on GH peak frequency, amplitude and duration, GH trough concentrations, the interval between successive peaks and the pituitary responsiveness to GHRH, as well as GH axis and galanin mRNA contents, were examined in conscious adult male rats. Plasma GH concentrations peaked within 15 minutes after the initiation of Hexarelin infusion, but returned to baseline levels by 60 minutes. No significant differences between Hexarelin and saline infused rats were noted for any of the parameters of pulsatile GH release analyzed. However, following a 6 hour infusion, rats treated with Hexarelin demonstrated a greater GH responsiveness to GHRH (delta GH: 57 +/- 16 ng/ml for Hexarelin infused; 21 +/- 7 ng/ml for saline infused; p < 0.05). Furthermore, the rats infused with Hexarelin demonstrated decreased GHRH and increased hypothalamic galanin mRNA contents as compared to the saline infused rats, while hypothalamic somatostatin and pituitary GH mRNA contents appeared unchanged. Rats infused with Hexarelin had lower pituitary galanin mRNA content than did the rats which were infused with saline. Collectively, these results suggest that Hexarelin may not act via alteration of somatostatin synthesis and that suppression of somatostatin's action at the pituitary can not be excluded. The current study also suggests that other hypothalamic pathways aside from those currently defined for the growth axis may be involved in the mechanism by which Hexarelin and the other GH-releasing peptides elicit GH release.

Pituitary somatostatin receptor (sst)1-5 expression during rat development: age-dependent expression of sst2

The capacity of the pituitary to suppress hormone secretion in response to somatostatin (SRIF) is markedly age dependent. Immature pituitaries are relatively resistant to SRIF effects, and increasing sensitivity to SRIF with advancing age is believed to cause characteristic developmental changes in pituitary hormone secretion in mammals. However, the cellular mechanism(s) underlying this developmental pattern of response to SRIF are not understood. Because somatostatin receptors (ssts) are critical mediators of SRIF's actions on target tissues, we investigated the expression of sst1, sst2, sst3, sst4, and sst5 messenger RNA (mRNA) in pituitaries of developing and mature rats. Animals were studied at embryonic day 19.5, and at postnatal days 2, 12, 30, 45, 70, and 1 yr; these ages correspond to major changes in circulating GH levels and pituitary responsiveness to SRIF. Pituitary levels of sst2 mRNA increased strikingly and progressively with advancing age after birth (F = 30.92, P < 0.0001). Compared with 2-day-old pituitaries, sst2 mRNA abundance rose 3.25-fold by 12 days of age and 6-fold by 70 days of age. Moreover, Western blot analysis indicated a marked increase in pituitary expression of sst2A protein with advancing age. By contrast, pituitary abundance of sst1, sst3, sst4, and sst5 mRNAs did not differ with age. To assess the role of endogenous SRIF in regulating perinatal sst2 gene expression, we also administered a well-characterized SRIF antiserum (or NSS as controls; 10 microl/10 g) sc daily from postnatal days 2 to 12 of life. Treatment with SRIF antiserum raised GH levels but did not alter pituitary sst2 mRNA abundance, compared with controls. Taken together, these data indicate that 1) the perinatal rat pituitary expresses the same complement of ssts as the adult pituitary; 2) expression of ssts is developmentally regulated in a highly subtype-specific manner; 3) pituitary sst2 mRNA and sst2A protein increase markedly and progressively with advancing age after birth; and 4) the perinatal rise in sst2 mRNA levels is unlikely to be regulated by endogenous SRIF. The finding of subtype-specific, developmentally determined sst expression indicates a novel and potentially fundamental mechanism of sst regulation, and suggests a molecular mechanism underlying developmental maturation in the capacity of the pituitary to respond to SRIF.

Short-term glucocorticoid administration decreases both hypothalamic and pituitary galanin synthesis in the adult male rat

Galanin (GAL) is a peptide that has been implicated in the regulation of the growth axis. It is generally accepted that GAL can increase serum growth hormone (GH) levels, although the underlying mechanism for this increase is unknown. It is well known that long-term glucocorticoid treatment alters in vivo GH secretion, since there is a decrease in serum GH in response to stimuli. It has previously been shown in our laboratory that administration of GAL can overcome the effects of glucocorticoid administration on GH secretion. The aim of the present study was to determine the effects of long-term glucocorticoid administration on the regulation of hypothalamic and pituitary GAL mRNA levels. Adult male rats were treated for 72 hours with the synthetic glucocorticoid dexamethasone ([DEX] 40 microg/kg/d intraperitoneal injections). RNase protection assays were performed on both the hypothalamus and pituitary for the presence of GAL mRNA. As expected, DEX significantly decreased somatic growth, as evidenced by a decrease (50%) in the weight gain of glucocorticoid-treated versus control animals. It was also demonstrated that in both the hypothalamus and pituitary, glucocorticoid treatment reduced the level of GAL mRNA (to 11% and 6.5%, respectively) compared with the control condition. We conclude that the decrease in GAL mRNA may lead to a decrease in GAL secretion, which in turn may be involved in the glucocorticoid-induced inhibition of GH secretion.

Effects of repeated doses and continuous infusions of the growth hormone-releasing peptide hexarelin in conscious male rats

We have previously shown that hexarelin, a novel GH-releasing peptide (GHRP), is able to elicit GH release when administered i.v., s.c. or by mouth and that it is a more potent GH secretagogue than GHRP-6. In the current study, we investigated the effects of hexarelin administered as repeated doses at 2 h intervals or as a continuous 6, 30 or 174 h infusion to conscious male rats. In the first experiment, adult male Sprague-Dawley rats were prepared with dual indwelling jugular catheters. On the day of experimentation, these animals received three 25 micrograms/kg i.v. boluses of hexarelin at 2 h intervals with blood sampling at 5, 10, 15, 30, 60, 90 and 120 min after each dose. The mean peak GH response and the mean area under the GH response curve (AUC) for the 30 min after each administration were calculated and are reported as the mean +/- S.E.M. For both the peak and AUC results there was a significant (P < 0.05) difference in the GH response noted between the first (peak 301 +/- 37 ng/ml; AUC 5585 +/- 700 ng/ml per 30 min) and second (peak 149 +/- 47 ng/ml; AUC 3056 +/- 908 ng/ml per 30 min) injections of hexarelin, but not between the first and third (peak 214 +/- 49 ng/ml; AUC 3862 +/- 844 ng/ml per 30 min). In a second series of experiments, adult male Sprague-Dawley rats received continuous infusions (100 micrograms/h) of hexarelin or saline (1 ml/h) for 6, 30 or 174 h. Blood samples were collected every 20 min for the duration of the 6 h infusion and for the last 6 h of the two longer hexarelin infusions. Plasma GH concentrations peaked within 40 min of the initiation of infusion, but soon returned to basal levels. Mean plasma GH concentrations did not differ between any of the treatment groups, nor did any of the parameters of pulsatile hormone release analyzed. No significant differences in plasma corticosterone concentrations were noted between any of the treatment groups. On the other hand, while neither the 6 h (941 +/- 70 ng/ml) nor the 30 h (954 +/- 70 ng/ml) hexarelin infusions resulted in a significant increase in the plasma IGF-I concentrations over those noted in the saline controls (935 +/- 65 ng/ml), a 174 h hexarelin infusion did elicit a significant increase (1289 +/- 42 ng/ml; P < 0.05). Thus it appears that, while continuous exposure to hexarelin does not disrupt normal GH cycling, it may (after up to 174 h of exposure) alter other components of the growth axis. In addition, since the character of pulsatile GH release remained unaltered in response to the hexarelin infusion, it appears that this GHRP may not act by suppression of functional somatostatin tone as has been suggested previously.

Maturation of the regulation of growth hormone secretion in young males with hypogonadotropic hypogonadism pharmacologically exposed to progressive increments in serum testosterone

To study the onset of the action of gonadal sex steroids on the GH axis in spontaneous puberty, which is prolonged and sparingly predictable, we present a clinical investigative paradigm in which six previously untreated boys with isolated hypogonadotropic hypogonadism were exposed to progressively higher testosterone levels designed to mimic the androgen environment recognized during the early stages of puberty. We administered three incremental doses of testosterone (25-, 50-, and 100-mg im injections), each over a period of 4 weeks. Studies of overnight pulsatile GH secretion and GH responses to GHRH alone or combined with L-arginine (a functional somatostatin antagonist) were performed before testosterone administration and after each dose of testosterone. Serum testosterone, but not estrogen, levels increased progressively in all subjects during therapy. Deconvolution analysis of GH release profiles disclosed that GH secretory burst mass was stimulated significantly even by 25 mg testosterone. This parameter was not altered further by higher doses of testosterone. Spontaneous GH secretory burst number and amplitude increased significantly only after the 50- and 100-mg testosterone treatments, after which the serum GH response to GHRH and arginine also rose significantly. In contrast, the GH response to GHRH alone was not significantly affected by any dose of testosterone. Serum testosterone levels correlated significantly with the primary parameters of nocturnal GH secretion. In summary, our experimental model suggests that in males even very small increases in circulating testosterone occurring during the earliest stages of puberty are able to amplify pulsatile GH secretion. Our concomitant secretagogue data further suggest that testosterone exerts its action at different sites in the hypothalamo-somatotropic axis, i.e. directly at the pituitary level, and also at hypothalamic loci, possibly increasing both GHRH and somatostatin release.

Glutamate decarboxylase autoimmunity and growth hormone secretion in type I diabetes mellitus

Insulin-dependent (type I) diabetic patients are known to have an exaggerated growth hormone (GH) response to GH-releasing hormone (GHRH), which is hypothesized to be due to a decrease in somatostatin tone. The aim of the study was to ascertain the influence of the presence and activity of the autoimmune process involving a key enzyme (glutamic acid decarboxylase [GAD]) in the synthetic pathway of a neurotransmitter regulating somatostatin secretion, ie, gamma-aminobutyric acid (GABA), on the GH response to GHRH alone or combined with an acetylcholinesterase inhibitor, pyridostigmine (PD), in patients with type I diabetes mellitus. Twenty non-obese type I diabetic patients and 17 normal subjects underwent an intravenous (IV) injection of 100 micrograms GHRH(1-29)NH2. Twelve of 20 diabetic subjects and all of the control subjects also underwent a second experimental procedure, administration of 120 mg oral PD 60 minutes before IV injection of 100 micrograms GHRH. Diabetic subjects with serum GAD antibody (GADA) levels more than 3 U (n = 10) showed significantly higher serum GH levels after GHRH injection as compared both with diabetic patients with GADA less than 3 U (n = 10) and with normal controls, whether expressed as absolute or peak values. GH peaks after GHRH were significantly (rs = .46, P < .05) correlated with the level of GADA in the whole population of type I diabetic subjects studied. PD significantly enhanced the GH response to GHRH, in terms of both absolute and peak values, in patients without GADA (n = 6) and in normal subjects. On the contrary, PD failed to enhance the GH response to GHRH in diabetic patients with GADA (n = 6). Our findings suggest that autoimmunity may play a key role in determining the exaggerated GH response to GHRH in type I diabetes mellitus. The mechanism underlying this effect is hypothesized to be the production of antibodies to GAD, a key enzyme in the synthesis of GABA, and in turn a reduced GABAergic stimulatory tone on somatostatin production at the hypothalamic level.

Hexarelin stimulation of growth hormone release and mRNA levels in an infant and adult rat model of impaired GHRH function

Hexarelin, a GH-releasing peptide, is an effective GH secretagogue in man and a variety of experimental animals. In the present study, we sought to characterize the effects of short-term Hexarelin treatment on GH release and GH mRNA levels in infant and young-adult rats and in rats of either age passively immunized with an antiserum against GHRH (GHRH-Ab). Hexarelin (80 micrograms/kg, b.i.d. s.c.), administered for 3, 5 or 10 days to 8-, 6- and 1-day-old rats, respectively, induced a progressive enhancement of the plasma GH rise elicited by a subsequent acute Hexarelin (80 micrograms/kg s.c) challenge when pups were 10 days old. As expected, GHRH-Ab treatment decreased GH concentrations in 10-day-old pups. In GHRH-Ab-treated pups, Hexarelin administration for 3-10 days significantly enhanced the GH response to the acute Hexarelin injection, though the mean plasma GH values remained significantly lower than in the respective control group. Hexarelin treatment did not alter GH mRNA levels in control pups. In GHRH-Ab-treated pups Hexarelin treatment for 3 and 5 days, but not 10 days, restored GH mRNA levels to control values. In young-adult male rats, regardless of antiserum treatment, Hexarelin administration for 5 or 10 days significantly suppressed the GH response to a subsequent acute challenge with the peptide. Yet, 5-10 days of Hexarelin treatment did not alter GH mRNA in control young-adult rats. In adult rats GHRH-Ab also decreased GH mRNA levels, but 10 days of Hexarelin treatment were necessary to return GH mRNA back to normal levels. These results indicate that: (1) the effects of Hexarelin on GH release and GH mRNA levels may be unrelated events; (2) deprivation of GHRH function discloses the ability of Hexarelin to stimulate GH mRNA levels; (3) age plays a crucial role in setting the pituitary responsiveness to short-term Hexarelin treatment, and (4) the different ability of Hexarelin to stimulate GH release and GH synthesis in neonatal and young-adult rats may have clinical relevance in the chronic administration of the peptide.

Effects of food deprivation on the GH axis: immunocytochemical and molecular analysis

Neuroendocrine mechanisms governing growth hormone (GH) secretion are sensitive to nutritional status since the normal pulsatile pattern of GH release is disrupted during conditions of food deprivation or malnutrition. A reasonable hypothesis for this occurrence is the alteration of somatostatin and GH-releasing hormone (GHRH) synthesis, storage and secretion. In this study, we investigated the effects of food deprivation on GH, GHRH, hypothalamic and pituitary galanin (GAL), and somatostatin through immunocytochemical and mRNA analysis. Adult male rats were subjected to 72 h of food deprivation, during which an average of 18% total body weight was lost. ICC studies were performed on brain sections from the rostral, middle and caudal regions of the median eminence of the hypothalamus using the avidin-biotin-peroxidase method. Immunocytochemical results were generated for the percent area and optical density (intensity) of immunostaining in the median eminence. Messenger RNA analyses were performed using sense and antisense riboprobes produced from cDNA clones for GH, GHRH, somatostatin and GAL. Food deprivation decreased somatostatin immunostaining in middle and caudal regions of the median eminence; similarly, food deprivation resulted in decreased GHRH immunostaining in rostral and middle sections of the median eminence of the hypothalamus. mRNA levels for somatostatin, GHRH and GH and GAL were also reduced by food deprivation. Our data suggest that suppressed GH secretion in food-deprived rats may reflect a general downregulation of the neuroendocrine and pituitary GH axis.

Modulation of growth axis gene expression by in utero and lactational exposure to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) in the weaning Holtzman rat

While thein utero and lactational effects of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) on both male and female reproductive systems appear to be severe, little is known about its effects on the developing growth axis. The objective of this study was to describe changes in growth axis gene expression that accompany exposure to TCDD duringin utero and lactational development. Pregnant Holtzman rats were administered 1 μg TCDD/kg maternal body weight or vehicle control on gestational day 15 by gavage. Using ribonuclease protection assays, we compared mRNA levels measured in 21-d-old female pups exposed to TCDD with levels measured in control animals for the following genes: somatostatin, growth hormone-releasing hormone (GHRH), hypothalamic and pituitary galanin (GAL), growth hormone (GH), and insulin-like growth factor-I (IGF-I). Serum GH concentrations measured by radio-immunoassay were significantly increased, although GH mRNA levels were unchanged from controls by TCDD exposure. Hypothalamic GAL mRNA was decreased in TCDD-treated animals, whereas pituitary GAL mRNA in TCDD-treated animals was not altered. GHRH mRNA was increased in hypothalami from TCDD-exposed animals. IGF-I mRNA in the liver was decreased to 67% of controls. These data indicate that the growth axis is sensitive to the effects of TCDD delivered during critical periods of development. The alterations observed in growth axis gene expression with exposure to TCDD add to the body of data demonstrating a potent effect of this compound on the fetal and neonatal endocrine system.

Mechanism of action of Hexarelin. I. Growth hormone-releasing activity in the rat

We have reported Hexarelin (HEXA), an analog of growth hormone-releasing peptide 6 (GHRP-6), potently stimulates growth hormone (GH) secretion in infant and adult rats. This study was undertaken to further investigate Hexarelin's mechanisms of action. In 10-day-old pups, treatments with HEXA (80 micrograms/kg, b.i.d.) for 3-10 days significantly enhanced, in a time-related fashion, the GH response to an acute HEXA challenge. Qualitatively similar effects were elicited in pups passively immunized against growth hormone-releasing hormone (GHRH) from birth. In adult male rats, a 5-day pretreatment with HEXA (150 micrograms/kg, b.i.d.) did not enhance the effect of the acute challenge, and the same pattern was present after a 5-day pretreatment in male rats with surgical ablation of the mediobasal hypothalamus (MBH-ablated rats). In addition, in adult sham-operated rats, Hexarelin (300 micrograms/kg, i.v.) induced a GH response greater (p < 0.05) than that induced by GHRH (2 micrograms/kg, i.v.). However, in MBH-ablated rats 7 days after surgery, GHRH was significantly (p < 0.05) more effective than HEXA, and 30 days after surgery HEXA and GHRH evoked similar rises of plasma GH. Finally, the in vitro Hexarelin (10(-6) mol/l) effect was transient while GHRH (10(-8) mol/l) induced a longer lasting and greater GH release. Three different mechanisms, not mutually exclusive, are postulated for Hexarelin stimulation of GH secretion in vivo: a direct action on the pituitary, though of minor relevance; an indirect action that involves release of GHRH, of relevance only in adult rats; and an action through the release of a still unknown hypothalamic "factor", which in infant and adult rats elicits GH release acting sinergistically with GHRH.

Immunocytochemical and molecular analysis of the effects of glucocorticoid treatment on the hypothalamic-somatotropic axis in the rat

Glucocorticoids are potent inhibitors of linear growth and growth hormone (GH) secretion when secreted or administered in pharmacological amounts in vivo. The mechanisms involved require further clarification although enhanced somatostatin tone has been suggested to play a role. In this study, we investigated the effects of excess glucocorticoids on pituitary GH, hypothalamic GHRH and hypothalamic somatostatin through immunocytochemical (ICC) and mRNA analysis. Twelve adult male rats were injected daily with dexamethasone (40 micrograms/day, i.p.) or saline for 4 days. ICC studies were performed on brain sections from the rostral, middle and caudal regions of the median eminence of the hypothalamus using the avidin-biotin-peroxidase method. Messenger RNA analyses were performed using sense and antisense riboprobes produced from GH, GHRH and somatostatin cDNAs. Immunocytochemical results were generated for the percent area and intensity (optical density) of immunostaining in the median eminence. Glucocorticoids increased somatostatin immunostaining of the rostral, middle and caudal regions of the median eminence while GHRH staining was only reduced in the rostral region of the median eminence and unchanged in the other hypothalamic regions. GH and somatostatin mRNA levels dramatically increased following glucocorticoid treatment concomitantly with a decrease in GHRH mRNA levels. Our data suggest that increased somatostatin synthesis and storage and a decrease in GHRH mRNA synthesis play a major role in the GH inhibitory effects of glucocorticoids.

Hypothalamic control of growth hormone (GH) secretion in type I diabetic men: effect of the combined administration of GH-releasing hormone and hexarelin, a novel GHRP-6 analog

Insulin dependent (type I) diabetic patients show abnormal growth hormone (GH) secretion. Hexarelin is an analog of GHRP-6 which releases GH in part via somatostatin inhibition. The aim of our study was to evaluate the effects of hexarelin and GHRH, administered either alone or in combination, on GH secretion in 10 type I diabetic and 7 normal men. All the subjects were administered: 1) human GHRH (1-29) NH2 100 micrograms i.v. bolus at 0 min; 2) hexarelin 100 micrograms i.v. bolus at 0 min; 3) hexarelin 100 micrograms + hGHRH 100 micrograms i.v. bolus at 0 min. In type I diabetic patients significantly greater GH responses to GHRH and hexarelin have been observed with normal subjects. Hexarelin caused a significantly (p < 0.05) greater GH response as compared to GHRH in both diabetic and control subjects. After the administration of hexarelin+GHRH, a significant increase in both GH absolute and peak levels as compared to hexarelin or GHRH alone was found in all the subjects. However, the GH responses to the combined stimuli were not significantly different in diabetics as compared to normals; moreover, the interaction of GHRH and hexarelin was synergistic in controls and additive in diabetics. We hypothesize that a reduction in the hypothalamic somatostatin inhibitory tone combined with increased pituitary GH production may be responsible for the pattern of the GH responses to hexarelin and GHRH observed in our type I diabetic patients.

Incidence of dog bites in Milwaukee, wis

Dogs are everywhere. The incidence of and injuries caused by dog bites have grown to such epidemic proportions in certain parts of the United States that they are now considered a major public health concern. Playful Rover is no longer a harmless pet. Uncontrolled, he now can be considered a public nuisance. In this study, we evaluated the epidemiology of dog bites recorded in Milwaukee, for calendar years 1989-1991. This assessment included anatomical location of bites, victims' ages, behavioral antecedents, leading up to the bite incidents, season of the year, and animal ownership. The evaluation also measured the correlation coefficient between the frequency of dog bite incidents and median household income distribution within the city. During the 3-year period, a total of 3,926 animal bites, including 3,244 (83%) dog bites, were reported to the City of Milwaukee Department of Health. Of all the dog bites reported, 60% were on the upper extremities. Children less than 15 years old sustained 44% of the injuries, mostly to the head and face. Provocation by the victim accounted for 19% of the cases. The majority of the incidents (67%) occurred during the spring and summer months. In 49% of all cases, the victims families or neighbors owned the animals involved in the biting. Researchers also observed a significant negative correlation between bites and median household income distribution. Study results suggest a need to educate the public about the magnitude of dog-bite problems, enforce leash laws and impound stray dogs as an integral part of prevention programs.

Influence of thyroid hormones on the regulation of growth hormone secretion

The effects of thyroid hormones on GH secretion and the mechanisms underlying their action are very similar in man and the laboratory animal. We feel that it is possible to organize the available data into a unique pathophysiological model explaining these complex interactions (Table 1). In summary, physiological levels of circulating thyroid hormones are necessary to maintain normal pituitary GH secretion owing to their direct stimulatory actions. When the serum concentrations of thyroid hormone increase above the normal range there is an increase in hypothalamic somatostatin tone, which in turn suppresses pituitary GH secretion and overrides any stimulatory effects. The suppression of GH secretion by thyroid hormones may be mediated at the hypothalamic level also by a decrease in GHRH release.

Adrenergic and cholinergic involvement in basal and growth hormone-releasing hormone-stimulated growth hormone secretion in glucocorticoid-treated rats

Glucocorticoids are known to inhibit GH secretion via somatostatin. The aim of our study was to elucidate the involvement of somatostatin in the GH-releasing action of the alpha 2 agonist clonidine and the cholinergic agent pyridostigmine in conscious, freely-moving rats chronically treated with dexamethasone. After seven days of chronic glucocorticoid treatment, animals received an i.v. injection of either saline (1 ml/kg) or clonidine (150 micrograms/kg) or pyridostigmine (100 micrograms/kg) at -15 min. Three blood samples were then drawn (-10 min, -5 min, and 0 min) to assess the GH response to either clonidine or pyridostigmine alone. After the 0 min sample, saline (1 ml/kg) or GNRH (500 ng/kg) was injected i.v. and additional blood samples were drawn from 5 to 30 min. The GH response to clonidine alone or combined with GNRH in rats treated with dexamethasone was significantly lower (p < 0.05) as compared to vehicle-treated rats. The GH response to pyridostigmine alone or combined with GNRH did not significantly differ between vehicle- and dexamethasone-treated rats. These data suggest that in the rat the mechanism of action of clonidine is mainly to stimulate endogenous GNRH secretion, while pyridostigmine appears to predominantly act by decreasing hypothalamic somatostatin.

Comparison of the effects of growth hormone-releasing hormone and hexarelin, a novel growth hormone-releasing peptide-6 analog, on growth hormone secretion in humans with or without glucocorticoid excess

The aim of our study was to investigate the effect of hexarelin, a novel GH-releasing peptide-6 analog, and GH-releasing hormone (GHRH) (alone or in combination) on GH secretion in adult patients with increased somatostatin tone due to chronic glucocorticoid excess. We studied seven adult patients undergoing long-term (no less than 6 months) immunosuppressive glucocorticoid treatment for non-endocrine diseases (six females and one male, age range 42-68 years) and one subject (female, age 31 years) with endogenous hypercortisolism due to adrenal adenoma. Six normal subjects (four females and two males) matched for sex and age with the patients and not undergoing any therapy served as controls. All the subjects underwent the following three tests in random order: (1) human GHRH (1-29)NH2 (100 micrograms in 1 ml saline) injected as an i.v. bolus at 0 min, (2) hexarelin (100 micrograms in 1 ml saline) injected as an i.v. bolus at 0 min and (3) hexarelin (100 micrograms in 1 ml of saline) plus GHRH (100 micrograms in 1 ml saline) injected as an i.v. bolus at 0 min. After GHRH alone the patients with glucocorticoid excess showed a blunted GH response as compared with normal subjects (median delta GH: 0.9, range 0-5.6 micrograms/l vs 7:1, range 0.3-14.9 micrograms/l). No significant differences were observed in the steroid-treated group with respect to normal subjects after hexarelin alone (median delta GH: 15.5, range 1.9-45.2 micrograms/l vs 17.9, range 5.5-53.9 micrograms/l).(ABSTRACT TRUNCATED AT 250 WORDS)

Changes in the growth hormone axis due to exercise training in male and female rats: secretory and molecular responses

GH secretion is altered by exercise in humans. In an attempt to investigate the underlying mechanisms, we developed a rodent model. GH secretion was assayed in male and female rats that were sedentary (not exercised), acutely exercised, and chronically exercised. Sedentary males showed typical pulsatile GH secretion. The acutely exercised males had low GH concentrations during the exercise bout, but showed partial recovery of GH pulses during the 5.5-h postexercise period. GH secretion in the chronically exercised males was low during both the exercise and postexercise periods. Sedentary females displayed the typical pattern of GH secretion for this sex. The acutely exercised females had low GH concentrations during the exercise period; the pulsatile pattern of GH secretion did not return during the postexercise period. In contrast, the chronically exercising females had suppressed GH secretion during the exercise bout, but concentrations immediately returned to normal during the postexercise bout. The effects of exercise on GH, GH-releasing hormone (GHRH), and somatostatin messenger RNA (mRNA) levels using Northern and slot blot analyses were also determined. Acutely and chronically exercised male rats had decreased levels of GH mRNA compared to sedentary male rats. The acutely exercised female rats had increased levels of GH mRNA compared to the sedentary females, whereas the chronically exercised females had decreased levels. GHRH mRNA levels in acutely exercising male rats was decreased and in chronically exercising male rats was increased compared to those in the sedentary controls. The pattern of GHRH mRNA in female rats was the opposite of this. Somatostatin mRNA levels decreased in acutely exercised male rats and were not affected in chronically exercised male rats. This signal increased in both acute and chronically exercised female rats. These studies suggest that GH secretion is suppressed in response to exercise in the rat. This contrasts with the increase observed after exercise in humans.

Galanin counteracts the inhibitory effects of glucocorticoids on growth hormone secretion in the rat

The aim of our study was to investigate the effect of galanin on baseline and growth hormone (GH)-releasing hormone (GHRH)-stimulated GH concentrations in conscious, freely moving rats receiving long-term glucocorticoid treatment. Animals were treated for 7 days with an intraperitoneal injection of either vehicle or dexamethasone ([dex] 40 micrograms/d). Rats underwent the following experimental trials: at -15 minutes animals received an intravenous injection of saline or galanin (12.5 micrograms/kg), and at 0 minutes rats received a second intravenous injection of saline or rat GHRH (500 ng/kg). Blood samples were drawn every 5 minutes from -15 to +15 minutes and then at 30 minutes. The GH response to saline + GHRH alone was significantly higher (P < .05) in chronically vehicle-treated rats as compared with chronically dex-treated ones. In contrast, galanin + saline increased serum GH levels in a similar fashion in both chronically vehicle- and dex-treated rats. The response to galanin + GHRH was similar to galanin + saline in chronically vehicle-treated rats, but was significantly enhanced in chronically dex-treated rats. These results suggest that galanin-mediated GH release in rats may involve somatostatinergic pathways.

Effects of recombinant human growth hormone (GH) on bone and intermediary metabolism in patients receiving chronic glucocorticoid treatment with suppressed endogenous GH response to GH-releasing hormone

Glucocorticoids, when administered over prolonged periods of time, cause protein wasting, osteoporosis, elevation of total cholesterol, and carbohydrate intolerance. Human GH is a potent anabolic agent known to stimulate protein synthesis and osteoblast activity. Chronic hypercortisolemia is associated with impaired GH secretion. The aim of our study was to evaluate the effects of short term administration of human recombinant GH on bone and fuel metabolism in patients receiving chronic glucocorticoid treatment and with suppressed GHRH-stimulated GH peaks (< 10 micrograms/L). We studied nine nonobese adult patients more than 70 yr of age (seven females and two males; age range, 41-68 yr; body mass index, 26 +/- 1.3 kg/m2) undergoing long term glucocorticoid therapy for nonendocrine diseases. After a 3-day stabilization period in the hospital, several parameters were evaluated in all patients: 1) protein, 2) bone, 3) lipid, 4) carbohydrate metabolism, and 5) immune system function under baseline conditions. At 1800 h on the fifth day of hospitalization, the patients began treatment with a daily sc injection of 0.1 IU/kg (0.037 mg/kg) recombinant human GH (Humatrope, Eli Lilly Co.) for 7 days. GH administration caused a significant increase in nitrogen balance (from -0.12 +/- 0.04 to -0.03 +/- 0.02 g/kg.day; P < 0.05), osteocalcin, carboxy-terminal propeptide of type I procollagen, and carboxy-terminal telopeptide of type I collagen with respect to basal levels. After GH administration, total, high density lipoprotein, and low density lipoprotein cholesterol levels were significantly lowered, and serum triglyceride levels were increased in all patients. Normal blood glucose levels during GH administration were observed in our patients concomitantly with a slight increase in insulin secretion. After GH treatment, the T-helper/T-suppressor cell ratio significantly increased with respect to basal levels (2.5 +/- 0.4 vs. 2.2 +/- 0.3; P < 0.05). Our data suggest that in patients receiving chronic glucocorticoid treatment, GH administration may significantly antagonize several side-effects of long term glucocorticoid administration, such as protein wasting, osteoporosis, and hyperlipidemia.

Mechanism of action of hexarelin and GHRP-6: analysis of the involvement of GHRH and somatostatin in the rat

We have recently reported oral and parenteral bioactivity for a new GH-releasing peptide, hexarelin. In the present study, we have examined the neuroendocrine mechanism by which hexarelin and GHRP-6, two GH-releasing peptides, mediate their actions. Although previous studies have looked at the role of growth hormone-releasing hormone (GHRH) and somatostatin in regulating the action of GHRP-6 in culture and in stressed animals, our study looked at the role of both somatostatin and GHRH in regulating the action of hexarelin as well as GHRP-6 in conscious and freely-moving, nonstressed rats. Adult male rats, prepared with indwelling jugular catheters, were pretreated i.v. with either control antiserum (CTLas), growth hormone-releasing hormone antiserum (GHRHas), somatostatin antiserum (SSas), or both GHRHas and SSas. Animals were then treated i.v. with 25 micrograms/kg of either hexarelin or GHRP-6 4 h after i.v. antisera pretreatment. Blood samples were collected every 20 min for the 3 h prior to peptide treatment and at 5, 10, 15, 20, 40 and 60 min following hexarelin or GHRP-6 injection. The peak plasma GH responses in rats pretreated with CTLas were 552 +/- 125 ng/ml following hexarelin administration and 386 +/- 132 ng/ml following GHRP-6 administration. Rats pretreated with SSas exhibited peak GH responses following hexarelin or GHRP-6 of 702 +/- 115 and 312 +/- 42 ng/ml, respectively. These plasma GH responses were similar to those observed in the CTLas-pretreated animals.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of GHRP-6 and GHRH on GH secretion in rats following chronic glucocorticoid treatment

The aim of our study was to investigate the effects of His-DTrp-Ala-Trp-Phe-Lys-NH2 (GHRP-6) on baseline and growth hormone-releasing hormone (GHRH) stimulated growth hormone (GH) release in conscious, freely-moving rats receiving chronic glucocorticoid treatment. Animals were treated daily for seven days with either vehicle or dexamethasone (dex, 40 micrograms/day). On the day of experimentation, rats received an i.v. injection of saline or GHRP-6 followed 15 min later by an i.v. injection of saline or rat GHRH. Three doses of GHRP-6 were evaluated, 1 microgram, 4 micrograms and 25 micrograms/kg; one dose of GHRH was evaluated, 500 ng/kg. GHRP-6 increased plasma GH levels over baseline concentrations in a dose-dependent fashion both in vehicle- and dex-treated rats. The GH response to GHRP-6 and GHRH was significantly less in dex-treated rats as compared to vehicle-treated rats. The combined administration of GHRP-6 and GHRH did not result in any change in plasma GH levels which could not be predicted from the administration of either peptide alone. Our results show that GHRP-6 is able to stimulate GH secretion in glucocorticoid-treated rats but it is unable to counteract the glucocorticoid-induced inhibition of GH secretion.

Reciprocal relationship between the level of circulating cortisol and growth hormone secretion in response to growth hormone-releasing hormone in man: studies in patients with adrenal insufficiency

The aim of our study was to elucidate the relationship between the level of circulating cortisol and the GH responsiveness to GHRH in six hypoadrenal patients (one male and five females; age range, 35-67 yr; body mass index range, 18-31 kg/m2). Twenty-four hours after taking the last dose of replacement therapy, each patient underwent the following experimental trials on nonconsecutive days: 1) saline, and 2) 12.5 mg, or 3) 25 mg, or 4) 250 mg hydrocortisone hemisuccinate in 250 mL saline constant iv infusion from 0-180 min. On each occasion, 1 micrograms/kg human GHRH-(1-29)NH2 was injected as an iv bolus at 60 min. During GHRH and saline infusion, serum cortisol levels were always less than the detection limit of the assay (55 nmol/L). During 12.5-, 25-, and 250-mg hydrocortisone infusions (from 15-180 min), serum cortisol averaged 413.8 +/- 19.3, 772.5 +/- 46.9, and 1520.2 +/- 110.4 nmol/L, respectively. The GH peaks after GHRH treatment during the various infusions of hydrocortisone were compared to the GH peaks observed after saline, which were normalized to 100% in each subject. GH peaks after GHRH and 25 mg hydrocortisone (70 +/- 11%) and GHRH and 250 mg hydrocortisone (69 +/- 7%) were significantly (P < 0.05) lower than the GH peaks after GHRH and saline or GHRH and 12.5 mg hydrocortisone (83 +/- 15%). No significant differences were observed between the GH peaks after GHRH and 12.5 mg hydrocortisone or GHRH and saline. Our data demonstrate that in hypoadrenal patients, the acute absence of circulating cortisol does not impair the GH secretory response to GHRH with respect to the eucortisolemic state. Moreover, our data suggest that 700 nmol/L is the approximate threshold serum cortisol concentration above which a decrease in the GH responsiveness to GHRH is observed in humans. Further increases in serum cortisol levels above this threshold value do not cause a proportional decrease in the GH responsiveness to GHRH.

Somatotropic dysfunction in growth hormone-releasing hormone-deprived neonatal rats: effect of growth hormone replacement therapy

In a previous work, we reported that passive immunization with anti-growth hormone-releasing hormone (GHRH) antibodies (GHRH-Ab) in neonatal rats caused disruption of somatotropic function that was still present 60 d posttreatment. We studied the reversibility of this condition by growth hormone (GH) replacement therapy. Neonatal rats received GHRH-Ab (50 microL/rat, s.c.) or normal rabbit serum every second day from birth up to postnatal d 10 and received hGH (0.4 microgram/g body weight, s.c., b.i.d.) or vehicle in a 2 x 2 factorial design. Animals were studied on d 11 of age. In GHRH-Ab-treated rats, GH therapy 1) counteracted the reduced body weight and low plasma IGF-I levels; 2) failed to modify the reduced pituitary weight and GH content; 3) further reduced the low plasma GH levels; 4) partially restored the defective GH responsiveness to GHRH; 5) failed to modify the reduced hypothalamic somatostatin and increased GHRH gene expression in the hypothalamus; and 6) reverted the decreased pituitary somatostatin binding. Morphologic and morphometric evaluation of the pituitary gland from GHRH-AB+GH pups showed that the number of GH-labeled structures was lower than in normal rat serum-GH-treated pups, whereas the total GH immunoreactivity per unit surface, an index of intracellular hormone concentration, was slightly higher than in vehicle-GH or GHRH-Ab pups. As determined by electron microscopy, somatotropes from GHRH-Ab+GH pups had morphologic features of high cellular activity. It appears that in GHRH-deprived pups GH replacement therapy can normalize most but not all altered indices of the somatotropic function.(ABSTRACT TRUNCATED AT 250 WORDS)

Growth hormone (GH) deprivation induced by passive immunization against rat GH-releasing factor does not disturb the course of sexual maturation and fertility in the female rat

The importance of normal GH secretion for the onset of sexual maturation is a subject of controversy. Also, the need to achieve a minimal body size or body fat content has been postulated to be of importance for determining the timing of the onset of puberty. To evaluate the importance of GH secretion on the onset of sexual maturation in the female rat, GH deprivation has been induced by treating prepubertal rats with antirat GRF serum to passively immunize these animals against GRF. Chronic administration of anti-GRF serum produced in all series an impressive reduction in growth rate (from 5 to 2 g/day), resulting in a body weight averaging 50-60% the normal value at 50 days of life. Despite this deficit in growth, sexual maturation, as established by vaginal opening and first estrous cycles, occurred at the normal age in three of four series of rats; in one series, however, sexual maturation was delayed by 4 days, but thereafter, all parameters indicated that the gonadotropic axis was normally activated. In one series, fertility was tested at 59 days of age in females with a body weight corresponding to 51% of the control weight; these females conceived and delivered a reduced number of pups (9.4 +/- 0.7 instead of 14.2 +/- 0.8 in control dams), but the pups were of normal size. In a second experimental approach, the effect of GH deprivation was evaluated in a model of late sexual maturation obtained by severe food restriction followed by a switch to ad libitum feeding. Severe food restriction initiated at approximately 28 days, when the body weight was 75 g, drastically reduced the growth rate and completely prevented sexual maturation. A switch to ad libitum feeding at 50 days provoked an important compensatory growth and the occurrence of sexual maturation 4 days later. Passive immunization against GRF during this recovery phase did reduce the growth rate, but did not delay sexual maturation. Plasma insulin-like growth factor-I (IGF-I) secretion was very low in food-restricted rats and in each situation with induced GH deprivation. During food restriction, plasma IGF-binding protein-3 (IGFBP-3) and to a lesser extent IGFBP-1 were decreased, and IGFBP-2 was increased; after switching to ad libitum feeding, plasma levels of IGFBP-2 normalized, but levels of IGFBP-1 and IGFBP-3 remained low in the face of normalized plasma IGF-I levels.(ABSTRACT TRUNCATED AT 400 WORDS)

Growth hormone-releasing hexapeptide is a potent stimulator of growth hormone gene expression and release in the growth hormone-releasing hormone-deprived infant rat

The growth hormone-releasing hexapeptide (GHRP-6) specifically stimulates growth hormone (GH) secretion in several animal species and humans. The mechanism of action of GHRP-6 is largely unknown, although experimental evidence indicates that it may modulate growth hormone-releasing hormone (GHRH) and somatostatin actions at the pituitary or hypothalamic level. To gain more insight into the mechanism(s) of action of GHRP-6, we studied the infant rat, an animal model highly responsive to GH-releasing stimuli. In 14-d-old rats GHRP-6 (32-600 micrograms/kg, s.c.) induced a marked and dose-dependent rise in plasma GH concentrations, maximal stimulation occurring with the dose of 300 micrograms/kg. Neither GHRH nor somatostatin antiserum prevented or modified the GH release elicited by GHRP-6. In pups passively immunized with GHRH antibodies, a 5-d treatment with GHRP-6 (80 micrograms/kg, s.c., twice daily) completely counteracted the inhibitory effect of GHRH deprivation on GH mRNA expression. In vitro GHRP-6 (10(-7) and 10(-6) M) induced a small and transient stimulation of GH release from cultured pituitary cells. These results indicate the following: 1) GHRP-6 is a potent stimulator of GH release in rat pups; 2) it stimulates GH gene expression in the GHRH-deprived pup; 3) during the neonatal period its action is not mediated by GHRH or somatostatin; and 4) its actions are not directed at the somatotrophs.

Effect of pyridostigmine on the hydrocortisone-mediated decrease of circulating growth hormone levels in acromegaly

The aims of our study were to investigate the effect of the acetylcholinesterase inhibitor pyridostigmine (PD) administration on growth hormone (GH) secretion in acromegaly and to investigate the effects of PD on GH levels following an i.v. infusion of hydrocortisone in acromegaly. We studied five adult patients with active acromegaly, three men and two women with a mean age of 60 +/- 5 years (range 47-71 years) and a mean BMI of 27 +/- 0.7 kg/m2 (range 24-28 kg/m2). All the patients underwent: 1) placebo, 2 tablets po or 2) PD, 120 mg po, at time -60 plus a bolus i.v. injection of 100 mg hydrocortisone succinate in 2 ml saline at time 0 followed by an i.v. infusion of 250 mg hydrocortisone succinate in 250 ml saline from 0 to 120 min, or 3) PD, po or 4) placebo, po at time -60 plus a bolus i.v. injection of 2 ml saline followed by an i.v. infusion of 250 ml saline from 0 to 120 min. Serum GH values did not significantly change after PD administration compared to those during placebo treatment and with respect to baseline levels. In all of the acromegalic patients during hydrocortisone succinate infusion, GH values clearly decreased with respect to basal levels in varying degrees, with a nadir between 90 and 180 minutes after the beginning of hydrocortisone infusion.(ABSTRACT TRUNCATED AT 250 WORDS)

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 neuroregulation in diabetes mellitus

GH secretion is markedly altered in diabetic rats and humans. Diabetes in the rat, whether occurring spontaneously or after streptozotocin administration, results in depressed GH secretion. This defect is likely caused by an increase in hypothalamic somatostatin tone and decreased pituitary GH. The effects of diabetes in humans depend upon the etiology of the disease. In type-1 diabetes, GH secretion is increased and in type 2 it is decreased. Again, these changes are hypothesized to be due to opposite alterations in hypothalamic somatostatin. Current evidence suggests that GH hypersecretion in human type-1 diabetes may be relevant to important metabolic and angiopathic complications of the disease.

Effect of hydrocortisone on the growth hormone response to growth hormone-releasing hormone in acromegaly

Our recent data show that acute and sustained hypercortisolism decreases circulating growth hormone (GH) levels in acromegaly with respect to saline infusion. It has been hypothesized that in acromegalic patients, as well as in normal subjects, short-term increases in serum cortisol levels may be able to cause an enhancement of hypothalamic somatostatin secretion, which in turn may be responsible for the glucocorticoid mediated GH inhibition. The aim of our study was to investigate the acute effects of an intravenous infusion of hydrocortisone on the GH response to growth hormone-releasing hormone (GHRH) in acromegaly. We studied 6 adult patients with active acromegaly (3 M, 3 F; mean age 60.5 +/- 4.1 years; mean body mass index 27.1 +/- 0.6 kg/m2). All the patients underwent: (1) a bolus intravenous injection of 100 mg hydrocortisone succinate in 2 ml saline, at time -60 followed by a 120-min intravenous infusion of 250 mg hydrocortisone succinate in 250 ml saline, from -60 to 60 min; (2) a bolus intravenous injection of human GHRH 1-29NH2 100 micrograms in 1 ml saline, 60 min after initiation of a 2-hour hydrocortisone infusion; (3) a bolus intravenous GHRH injection 60 min after initiation of a 2-hour saline infusion. In all of the acromegalic patients during hydrocortisone succinate infusion, GH values clearly decreased with respect to basal levels (mean nadir 47 +/- 8.6%, p < 0.05 with respect to basal levels). After GHRH injection and saline infusion all the patients showed a significant increase in GH levels (mean peak 231.5 +/- 52.8%, p < 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Long-term changes of somatotrophic function induced by deprivation of growth hormone-releasing hormone during the fetal life of the rat

We have studied the effects of intra-amniotic administration of an anti-GH-releasing hormone serum (GHRH-Ab) on day 16 of fetal life in the rat, when the ontogenetic development of the GHRH neuronal system occurs. Control animals received normal rabbit serum. Following delivery, body weight was monitored for the next 30 days as an index of somatic growth, and the following indices of somatotrophic function were determined: plasma and pituitary GH, pituitary GH mRNA, hypothalamic GHRH and somatostatin mRNA, and the in vivo GH responsiveness to GHRH. At birth, GHRH-Ab-treated rats had a body weight that was equivalent to that of control rats but, starting from postnatal day 6 up to day 30, they had a significantly reduced body weight. Pituitary weight, the absolute pituitary GH content and GH mRNA levels were lower in experimental compared with control rats, while pituitary GH concentrations were similar in the two groups, thus implying that there was a defect, not only in GH synthesis, but also in GH release. In agreement with this theory, basal GH levels and GHRH-stimulated GH secretion were reduced in GHRH-Ab-treated rats but, in contrast, hypothalamic regulation of GH secretion appeared to be working in these rats as they were still able to respond to the low plasma GH by increasing GHRH and decreasing somatostatin mRNA levels. These findings indicate that deprivation of GHRH during fetal life induces long-lasting changes of growth rate and somatotrophic function.(ABSTRACT TRUNCATED AT 250 WORDS)

Variability in the growth hormone response to growth hormone-releasing hormone alone or combined with pyridostigmine in type 1 diabetic patients

In man the GH response to GHRH is variable within and between subjects. Pyridostigmine (PD), an acetylcholinesterase inhibitor, has been shown to reduce the variability of the GH response to GHRH in normal subjects. The aim of this study was to assess the existence of either inter- or intraindividual variability in the GH response to GHRH in type 1 diabetic patients. Moreover, we investigated the effect of PD on such variability in the same patients. Seven (4 females-3 males) nonobese type 1 diabetic patients underwent two experiments performed in consecutive days according to a single-blind protocol: 1) 120 mg oral PD 60 min before iv injection of human (h) GHRH-(1-29) NH2, 100 micrograms in 2 ml of sterile water; 2) oral placebo 60 min before iv injection of 100 micrograms hGHRH. The two experiments were then repeated, following the same procedure, one and two weeks after the start of the study. The GH peaks after GHRH were variable within different subjects but also in the same subject on different occasions. However, the mean GH peak levels after GHRH in the three tests were not significantly different (14.2 +/- 3.5, 15.3 +/- 3, 16.5 +/- 6.4 micrograms/L, respectively), the coefficient of variation for each test was 65%, 51.8%, 102.4%, respectively (mean 73.1 +/- 15.1%). The GH response to GHRH was always significantly enhanced by PD administration: the mean GH peak levels in the three tests were 31.9 +/- 7.1, 44.8 +/- 10.4, 49.9 +/- 13.1 micrograms/L, respectively, without significant differences between tests.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of metoclopramide on the growth hormone response to galanin in normal man

One of the most prominent metabolic effects of the systemic administration of the synthetic neuropeptide galanin in man is the increase in growth hormone (GH) secretion. This stimulating action of galanin is thought to occur directly at the hypothalamic level through the release of GHRH. Recently, it has been shown that also dopaminergic drugs may elicit GH secretion through an increase in hypothalamic GHRH secretion. The aim of this study was to investigate if the action of galanin on GHRH and consequently on GH release may be mediated via dopaminergic pathways evaluating the effects of a potent central dopaminergic receptor blocker, metoclopramide (MCP), on the galanin-induced growth hormone (GH) secretion in normal subjects. We studied seven young non obese healthy subjects (three females and four males). GH secretion was evaluated after 45 min iv infusion of porcine galanin (0.5 mg in 100 ml of saline) from 0 to 45 min combined with a 60 min iv infusion of a) saline (100 ml) or b) MCP (10 mg in 100 ml of saline) from -15 to 45 min. In all the seven subjects, during galanin infusion, GH values increased with respect to baseline with peaks occurring between 30 and 60 min after the beginning of galanin infusion. Peak GH values ranged between 3.5 and 15.4 micrograms/l (mean 10.4 +/- 1.6 micrograms/l). During MCP infusion no significant differences in the GH response to galanin with respect to saline were observed both when absolute GH levels and GH AUC were examined.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of galanin and arginine, alone or in combination, on growth hormone secretion in adult patients treated with glucocorticoids

Glucocorticoids are known to decrease growth hormone (GH) secretion in man. Galanin, a 29-amino acid peptide, and arginine stimulate GH secretion through different hypothalamic mechanisms. The aim of our study was to investigate the effect of arginine and galanin (alone or in combination) on GH secretion in 7 adult patients with nonendocrine diseases receiving chronic daily immunosuppressive glucocorticoid treatment (5 F, 2 M; mean age 48.4 +/- (SEM) 3.7 years). Five normal adults (3 F, 2 M; mean age 34.6 +/- 2.2 years) served as controls. All subjects underwent in random order: (1) infusion of arginine hydrochloride (30 g i.v. in 100 ml saline) from -30 to 0 min; (2) infusion of synthetic porcine galanin (500 micrograms i.v. in 100 ml saline) from -15 to 30 min; (3) intravenous infusion of arginine hydrochloride from -30 to 0 min combined with synthetic porcine galanin from -15 to 30 min. In normal subjects GH peak after arginine (8.6 +/- 3.3 micrograms/l) and galanin (6.6 +/- 3.2 micrograms/l) did not show significant differences; the GH peak after arginine + galanin (21.4 +/- 6.1 micrograms/l) was significantly higher with respect to galanin or arginine alone. In glucocorticoid-treated patients the GH peak after arginine (4.6 +/- 1.5 micrograms/l) was significantly (p < 0.05) higher with respect to galanin (1.8 +/- 1.0 micrograms/l); after arginine + galanin the GH peak (8.2 +/- 2.3 micrograms/l) was significantly (p < 0.05) enhanced with respect to either galanin or arginine alone. The GH response to arginine was not significantly different in normal and glucocorticoid-treated patients.(ABSTRACT TRUNCATED AT 250 WORDS)

Arginine blocks the inhibitory effect of hydrocortisone on circulating growth hormone levels in patients with acromegaly

In patients with acromegaly, circulating growth hormone (GH) levels and GH responses to GH-releasing hormone (GHRH) are decreased by long-term administration of pharmacological doses of glucocorticoids. The aim of our study was to investigate the acute effects of intravenous (i.v.) infusion of hydrocortisone combined either with saline or arginine infusion on circulating GH levels in acromegaly. We studied five adult patients with acromegaly, two men and three women aged 54.6 +/- 4 years having a body mass index of 25.9 +/- 1.2 kg/m2. On two randomized occasions, patients underwent a bolus i.v. injection of 100 mg hydrocortisone succinate at time 0 followed by a 120-minute i.v. infusion of 250 mg hydrocortisone in 250 mL saline, combined with a 90-minute (from -15 to 75 minutes) i.v. infusion of (1) 60 g arginine hydrochloride in 200 mL saline, or (2) 200 mL saline. In all of the acromegalic patients during the infusion of hydrocortisone alone, serum GH levels clearly decreased (nadir range, 26.4% to 68.1%) with respect to GH levels before hydrocortisone administration (mean of time -15 and 0, basal level), with a nadir between 90 and 180 minutes after the beginning of the infusion. After arginine pretreatment, GH levels were significantly enhanced compared with levels attained with hydrocortisone saline, and they were also significantly increased (peak, 167.5% +/- 27.7%) with respect to basal levels. Our data show that arginine blocks the inhibitory effect of acute and sustained hypercortisolism on circulating GH levels in acromegaly.(ABSTRACT TRUNCATED AT 250 WORDS)

Clinical evaluation of the BackMate lower lumbar rehabilitation system: results of a preliminary study

Back pain profoundly affects daily activities and quality-of-life parameters. It was the intent of the present study to evaluate a procedure of stretching and strengthening the lower back musculature with the aid of a pelvic stabilization device, the BackMate, for the treatment of lower back pain. Subjects suffering from chronic back pain (> 3 months in duration) were studied. The treatment program consisted of three therapy sessions per week for 3 weeks. Sitting time, walking distance, and lower back pain, parameters reported by the subjects, significantly improved regardless of age and sex of the subjects. Similarly, objective parameters, including forward bend, straight leg raise, and hamstring flexibility, significantly improved. This preliminary experience suggests that stretching and strengthening procedures performed with the aid of a pelvic stabilization device may prove to be a significant addition to current clinical treatment procedures for lower back pain.

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.

Picotamide, a dual TXB synthetase inhibitor and TXB receptor antagonist, reduces exercise-induced albuminuria in microalbuminuric patients with NIDDM

We investigated the short-term effect of the TXB inhibitor picotamide on albuminuria induced by exercise in 15 microalbuminuric (i.e., with UAE at rest between 20 and 200 micrograms/min) type II diabetic patients (12 men and 3 women, age 56 +/- 2, BMI 28 +/- 1 kg/m2) and in six normal age-matched control subjects. The diabetic subjects performed five submaximal exercise tests (90% of theoretical heart rate) on a cycle ergometer: the first two under basal conditions; the third and fifth after subjects had received picotamide (900 mg/day) or placebo (3 tablets/day) for 10 days; the fourth exercise always was performed after 10 days of wash-out. Control subjects performed two exercises: the first in baseline conditions and the second after 10 days of picotamide administration (900 mg/day). When diabetic patients were untreated, a significant (P < 0.05) increase in UAE with respect to baseline levels was observed immediately after and 1 h after the exercise test. After picotamide administration, UAE significantly decreased (P < 0.05) immediately after and 1 h after exercise, as compared with diabetic patients given a placebo. In normal subjects, exercise was followed by a slight increase in UAE, which was not significantly affected by picotamide administration. Our results show that short-term administration of picotamide is associated with a reduction in UAE after exercise in type II diabetes patients with microalbuminuria while at rest. Picotamide, a TXB synthetase and receptor inhibitor, may decrease exercise-induced albuminuria in diabetic patients through a reduction in circulating TXB levels and inhibition of TXB action, which in turn may act by lowering glomerular capillary hydraulic pressure.

Hypothalamic regulation of growth hormone secretion during food deprivation in the rat

Suppressed pulsatile GH secretion in food-deprived rats has been hypothesized to be due to an increase in hypothalamic somatostatin secretion. We investigated this hypothesis and the role of GHRH in regulating GH secretion during food deprivation using two different models. In experiment one, rats were food deprived for 72h during which time they received a saline infusion (n = 5). At the same time rats were normal fed for 72h during which time they received a somatostatin infusion (5 micrograms/h, n = 7). After the 72h infusion period, all rats received two iv injections of GHRH (1 microgram/rat) at 2h intervals. GH concentrations in food-deprived rats rose from approximately 10 ng/ml to 400-800 ng/ml in response to both GHRH injections. This increase was significantly greater (p < 0.01) than the GH response (100-400 ng/ml) observed in somatostatin-infused animals. The significantly higher GH response observed in food-deprived rats as compared to somatostatin-infused, normal-fed rats suggests that somatostatin concentrations may decrease during food deprivation. In experiment two, rats were infused for 5h with either saline (n = 6) or GHRH (10 micrograms/h, n = 9) at the end of a 72h fast. GH concentrations did not change in saline-infused animals. In contrast, GH concentrations significantly increased (p < 0.01) upon initiation of the continuous GHRH infusion. Yet, this release of GH was pulsatile in nature. Pulsatile GH secretion in the presence of a constant GHRH infusion suggests that pulsatile somatostatin release from the hypothalamus is maintained during food deprivation. These studies suggest that during food deprivation in the rat 1) absolute concentrations of somatostatin decrease, but its pattern of secretion remains pulsatile, and 2) decreased GHRH release may be responsible for the absence of spontaneous GH pulses.

Electromyographic analysis of four popular abdominal exercises

This study was designed to evaluate the effects of four specific sit-up exercises on muscular activity of the rectus abdominis. Pairs of surface electrodes were placed unilaterally on four quadrants of the rectus abdominis, delimited by tendinous inscriptions, in four male subjects. Electromyographic (EMG) recordings were taken while the subjects performed four different abdominal exercises. Each abdominal exercise was hypothesized to have a specific effect on one of the four quadrants of the rectus abdominis. The four exercises analyzed were: 1) long lying crunch, 2) bent knee crunch, 3) leg raise, and 4) vertical leg crunch. Analysis of the standardized EMG recordings demonstrated no significant differences in the mean muscle activity between the four different quadrants, in the mean muscle activity between the four different exercises, and in interactions between the exercises and the quadrants of the rectus abdominis. We conclude that none of the four abdominal exercises studied are specific for strengthening individual muscle quadrants of the rectus abdominis.

Galanin does not affect the growth hormone-releasing hormone-stimulated growth hormone secretion in patients with hyperthyroidism

Patients with hyperthyroidism have reduced spontaneous and stimulated growth hormone (GH) secretion. The aim of our study was to evaluate the effects of galanin, a novel neuropeptide which stimulates GH secretion in man, on the GH response to GHRH in patients with hyperthyroidism. Eight untreated hyperthyroid patients with Graves' disease (6F, 2M, aged 25-50 years) and six healthy volunteers (3F, 3M, aged 27-76 years) underwent from -10 to 30 min in random order: (i) porcine galanin, iv, 500 micrograms in 100 ml saline; or (ii) saline, iv, 100 ml. A bolus of human GHRH(1-29)NH2, 100 micrograms, was injected iv at 0 min. Hyperthyroid patients showed blunted GH peaks after GHRH+saline (10.2 +/- 2.5 micrograms/l) compared to normal subjects (20.7 +/- 4.8 micrograms/l, p < 0.05). GH peaks after GHRH+galanin were also significantly lower in hyperthyroid subjects (12.5 +/- 3 micrograms/l) compared to normal subjects (43.8 +/- 6 micrograms/l, p < 0.05). That galanin is not able to reverse the blunted GH response to GHRH in hyperthyroidism suggests that hyperthyroxinemia may either increase the somatostatin release by the hypothalamus or directly affect the pituitary GH secretory capacity.

Vibrio-associated gastroenteritis in the lower Cross-River Basin of Nigeria

A total of 120 Vibrio species were isolated from 588 patients with acute diarrheal disease during an outbreak of gastrointestinal tract infections at different locations in the lower Cross River Basin of Nigeria. Vibrio cholerae O1, biotype El Tor, serotype Ogawa, was the prominent organism isolated from the Vibrio-associated diarrheal cases. During the 3 months of study, V. cholerae non-O1 was recovered from 10 patients while Vibrio parahaemolyticus was recovered from 19 patients. The significance of this study is the recognition that there is an ecological niche which supports V. cholerae non-O1 and V. parahaemolyticus in the Cross River Basin of Nigeria.

The role of glucocorticoids in the regulation of Growth Hormone secretion: mechanisms and clinical significance

Glucocorticoids are well known to inhibit growth and GH secretion in humans and animals, yet in vitro these steroids stimulate GH synthesis and secretion. These opposite actions appear to be mediated at different sites. The inhibition involves modulation of hypothalamic somatostatin and the stimulation involves direct actions on the pituitary. Current evidence suggests that the predominant action in vivo is through the inhibitory influences of somatostatin.

Long-term failure of compensatory growth in rats following acute neonatal passive immunization against growth hormone-releasing hormone

Interruption of hypothalamic growth hormone-releasing hormone (GHRH) secretion by administration of antiserum against GHRH (GHRH-ab) decreases growth hormone (GH) secretion and inhibits growth in rats. The present study was undertaken to investigate whether there is a period of accelerated or catch-up growth following a period of growth arrest induced by GHRH-ab treatment. Neonatal male and female rats were injected daily on days 1-14 of age. Animals received normal rabbit serum (NRS) or GHRH-ab subcutaneously at a dose of 5 microliters/10 g body weight. Body weight, serving as an index of somatic growth, was monitored over the next 3 months. The increase in absolute body weight and growth velocity of GHRH-ab-treated rats, regardless of gender, was lower than the increase of NRS-treated animals. Significant decreases were observed by day 13 of age in the female rats and day 17 in the male rats. The percent differences and absolute difference in weight between the two treatment groups clearly demonstrated that the GHRH-ab-treated rats did not demonstrate any period of catch-up growth. A second group of animals was treated in a similar fashion to evaluate serum GH concentrations at three months of age. Pulsatile GH secretion, as assessed by peak frequency and amplitude, was normal in all of the rats, suggesting that the failure of catch-up growth in the GHRH-ab-treated animals was not due to decreased GH secretion.(ABSTRACT TRUNCATED AT 250 WORDS)

Arginine normalizes the growth hormone (GH) response to GH-releasing hormone in adult patients receiving chronic daily immunosuppressive glucocorticoid therapy

Glucocorticoids are thought to inhibit GH secretion through an enhancement of endogenous somatostatin tone. The aim of our study was to evaluate the effect of arginine, a secretagogue that increases GH secretion acting at the hypothalamic level, probably by decreasing somatostatin tone, on GH-releasing hormone (GHRH)-induced GH secretion in three male and five female adult patients with nonendocrine disease who were receiving daily immunosuppressive glucocorticoid therapy. Six normal subjects (four males and two females) served as controls. GHRH-induced GH secretion was evaluated after 30-min iv infusion of saline (100 mL) or arginine (30 g) in 100 mL saline. After saline administration, steroid-treated patients showed a blunted GH response to GHRH (GH peak, 8.7 +/- 2.4 micrograms/L) compared to that of normal subjects (GH peak, 23.8 +/- 3.9 micrograms/L). The GH responses to GHRH increased (P less than 0.05) after pretreatment with arginine compared to saline pretreatment in both normal subjects (GH peak, 36.6 +/- 4.0 micrograms/L) and steroid-treated patients (GH peak, 28.4 +/- 5.5 micrograms/L). The GH responses to GHRH plus arginine were not significantly different in steroid-treated and normal subjects. Thus, arginine is able to normalize the GH response to GHRH in patients receiving chronic glucocorticoid treatment. Our data are evidence that the stimulatory action of arginine and the inhibitory action of glucocorticoids on GH secretion are mediated by opposite effects on hypothalamic somatostatin tone.