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).

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.