Differential effects of passive immunization with somatostatin antiserum on adenohypophysial hormone secretions in starved rats

1986 ◽  
Vol 109 (2) ◽  
pp. 169-174 ◽  
Author(s):  
J. N. Hugues ◽  
A. Enjalbert ◽  
E. Moyse ◽  
C. Shu ◽  
M. J. Voirol ◽  
...  
Keyword(s):  
Binding Capacity ◽  
Hormone Secretion ◽  
Plasma Concentrations ◽  
Passive Immunization ◽  
Negative Control ◽  
Prolactin Secretion ◽  
Male Rats ◽  
Minimal Effective Dose ◽  
Gh Secretion

ABSTRACT The role of somatostatin (SRIF) on adenohypophysial hormone secretion in starved rats was reassessed by passive immunization. Because of the absence of pulsatile GH secretion in starved rats, the effects of the injection of SRIF antiserum on GH levels can be clearly demonstrated. To determine whether starvation modifies the sensitivity of the adenohypophysis to SRIF, we measured 125I-labelled iodo-N-Tyr-SRIF binding. There was no difference in the dissociation constant (Kd) nor in the maximal binding capacity (Bmax) in fed (n = 15) and starved (n = 15) animals (Kd = 0·38 ± 0·09 (s.e.m.) and 0·45 ± 0·09 nmol; Bmax = 204 ± 39 and 205 ± 30 fmol/mg protein respectively). Administration of SRIF antiserum resulted in a dose-dependent increase in plasma concentrations of GH, TSH and prolactin. The minimal effective dose of SRIF antiserum was 50 μl for GH, 100 μl for TSH and 200 μl for prolactin. Our results show that: (1) starvation does not modify adenohypophysial SRIF-binding sites, (2) in starved male rats endogenous SRIF exerts a negative control on prolactin secretion in vivo and (3) sensitivity to endogenous SRIF seems to be different for each hypophysial cell type. J. Endocr. (1986) 109, 169–174

Immunization against vasoactive intestinal peptide does not affect thyroid hormone secretion or thyroid blood flow

1994 ◽  
Vol 266 (6) ◽  
pp. E905-E913
Author(s):  
M. Michalkiewicz ◽  
L. J. Huffman ◽  
M. Dey ◽  
G. A. Hedge
Keyword(s):  
Thyroid Hormone ◽  
Thyroid Hormones ◽  
Vasoactive Intestinal Peptide ◽  
Iodine Deficiency ◽  
Binding Capacity ◽  
Hormone Secretion ◽  
Passive Immunization ◽  
Male Rats ◽  
Blood Levels ◽  
Blood Flows

Vasoactive intestinal peptide (VIP) is present in thyroid parasympathetic nerves. To assess the involvement of endogenous VIP in the regulation of thyroid function, blood levels of thyroid hormones and thyroid blood flows (TBF) were measured after systemic immunization against VIP or after transection of the superior laryngeal nerves in male rats, which reduced the thyroid content of VIP but did not affect blood levels of thyroid hormones or TBF. Anti-VIP monoclonal antibody or anti-VIP serum was used for immunization against VIP in normal rats. In addition, VIP antibody was given to rats fed an iodine-deficient diet for 5 days to examine the involvement of this peptide in iodine deficiency-induced increases in TBF. Effects were measured at different times (90 s, 30 min, 1 h, and 5 days) after immunoneutralization, but none of these treatments changed blood levels of thyroid hormones or TBF in normal or iodine-deficient rats. However, passive immunization against VIP was associated with a high binding capacity of rat plasma to VIP, and this treatment reduced blood levels of prolactin as well as blood flows to the duodenum, stomach, and lung. These findings suggest that the VIP present in thyroid nerves is not involved in maintaining basal thyroid hormone secretion or TBF and that this neuropeptide does not mediate thyroid vascular adjustments to dietary iodine deficiency.

scholarly journals Obestatin Partially Affects Ghrelin Stimulation of Food Intake and Growth Hormone Secretion in Rodents

Endocrinology ◽  
2007 ◽  
Vol 148 (4) ◽  
pp. 1648-1653 ◽  
Author(s):  
Philippe Zizzari ◽  
Romaine Longchamps ◽  
Jacques Epelbaum ◽  
Marie Thérèse Bluet-Pajot
Keyword(s):  
Food Intake ◽  
Hormone Secretion ◽  
Growth Hormone Secretion ◽  
Male Rats ◽  
Pituitary Cells ◽  
Gh Secretion ◽  
Freely Moving ◽  
Stimulation Of

Administration of ghrelin, an endogenous ligand for the GH secretagogue receptor 1a (GHSR 1a), induces potent stimulating effects on GH secretion and food intake. However, more than 7 yr after its discovery, the role of endogenous ghrelin remains elusive. Recently, a second peptide, obestatin, also generated from proteolytic cleavage of preproghrelin has been identified. This peptide inhibits food intake and gastrointestinal motility but does not modify in vitro GH release from pituitary cells. In this study, we have reinvestigated obestatin functions by measuring plasma ghrelin and obestatin levels in a period of spontaneous feeding in ad libitum-fed and 24-h fasted mice. Whereas fasting resulted in elevated ghrelin levels, obestatin levels were significantly reduced. Exogenous obestatin per se did not modify food intake in fasted and fed mice. However, it inhibited ghrelin orexigenic effect that were evident in fed mice only. The effects of obestatin on GH secretion were monitored in superfused pituitary explants and in freely moving rats. Obestatin was only effective in vivo to inhibit ghrelin stimulation of GH levels. Finally, the relationship between octanoylated ghrelin, obestatin, and GH secretions was evaluated by iterative blood sampling every 20 min during 6 h in freely moving adult male rats. The half-life of exogenous obestatin (10 μg iv) in plasma was about 22 min. Plasma obestatin levels exhibited an ultradian pulsatility with a frequency slightly lower than octanoylated ghrelin and GH. Ghrelin and obestatin levels were not strictly correlated. In conclusion, these results show that obestatin, like ghrelin, is secreted in a pulsatile manner and that in some conditions; obestatin can modulate exogenous ghrelin action. It remains to be determined whether obestatin modulates endogenous ghrelin actions.

scholarly journals Ghrelin-induced growth hormone secretion in humans

2000 ◽  
pp. R11-R14 ◽  
Author(s):  
R Peino ◽  
R Baldelli ◽  
J Rodriguez-Garcia ◽  
S Rodriguez-Segade ◽  
M Kojima ◽  
...  
Keyword(s):  
Growth Hormone ◽  
Total Dose ◽  
Dose Response ◽  
Hormone Secretion ◽  
Growth Hormone Secretion ◽  
Prolactin Secretion ◽  
Gh Secretion ◽  
Relevant Dose

Ghrelin is a novel growth hormone (GH) releaser acylated peptide that has recently been purified from stomach, and which potently binds to the GH secretagogue receptor. Ghrelin releases GH in vitro and in vivo in animal models, however its actions, potency and specificity in humans are unknown. In the present study, 12 healthy subjects were studied: 6 underwent four tests with ghrelin administered i.v. at the dose of 0 (placebo), 0.25, 0.5 and 1 microg/kg which corresponds to 0, 18, 37 and 75 microg total dose. A further 6 volunteers underwent two tests on different days with ghrelin at the dose of 3.3 or 6.6 microg/kg which corresponds to 250 microg and 500 microg total dose. Ghrelin-mediated GH secretion showed a dose-response curve, in which 1 microg/kg was the minimally effective dose in some individuals, but not as a group. On the contrary, the total doses of 250 microg and 500 microg elicited a powerful GH secretion, with a mean peak of 69.8+/-9.2 microg/l and 90.9+/-16.9 microg/l respectively, and areas under the curve of 4435+/-608 and 6125+/-1008 microg/l per 120 min respectively. All of them statistically significant vs placebo and vs the 1 microg/kg dose. Ghrelin administration also elicited a relevant dose-response mediated prolactin secretion suggesting no specificity of its actions. No relevant side effects were observed with ghrelin apart from a hyperhydrosis episode in two individuals tested with the higher ghrelin doses. In conclusion, ghrelin is a potent releaser of GH in normal individuals, with a dose-response pattern of operation. No saturating dose was observed.

Comparison of the feedback effect of magnesium and calcium on parathyroid hormone secretion in man

1987 ◽  
Vol 113 (1) ◽  
pp. 117-122 ◽  
Author(s):  
O. Ferment ◽  
P. E. Garnier ◽  
Y. Touitou
Keyword(s):  
Parathyroid Hormone ◽  
Urinary Excretion ◽  
Hormone Secretion ◽  
Plasma Concentrations ◽  
Magnesium Salt ◽  
Saline Injection ◽  
Molar Basis ◽  
Magnesium Salts ◽  
High Doses

ABSTRACT Administration of high doses of magnesium is known to produce a decrease in parathyroid hormone (PTH) secretion in human patients but the effect of magnesium on the secretion of PTH in healthy man is not known. We have looked at the effect of a relatively moderate i.v. dose of magnesium (7·08 mmol) in seven healthy men. In addition and for comparison the effect of calcium (4·25 mmol) was studied. Two magnesium salts were considered, magnesium sulphate (MgSO4) and magnesium pyrrolidone carboxylate (MgPC). Four i.v. injections were given at 08.00 h (MgPC, NaCl (control), MgSO4 and Ca gluconate), with an interval of 1 week between each injection. Whatever the magnesium salt the variations in plasma concentrations of magnesium were the same whereas no change in erythrocyte magnesium was observed. Plasma concentration of C-terminal PTH did not show significant variations after MgPC or saline injection. Both MgSO4 and Ca gluconate produced a statistically significant 30% decrease in plasma PTH levels 45 min after the injection. The effect was more sustained with calcium (2 h) than with magnesium (45 min). The urinary excretion of magnesium was significantly higher after injection of MgSO4 than after MgPC. These results suggest (1) that magnesium was, on a molar basis, less potent than calcium in regulating PTH secretion in vivo, (2) that the nature of the magnesium salt used must be kept in mind for the interpretation of the effect of magnesium on PTH secretion in vivo and (3) that the decrease in plasma PTH can partly explain the larger urinary excretion of magnesium after MgSO4 than after MgPC. J. Endocr. (1987) 113, 117–122

In vivo effects of flavonoid EMD 21388 on thyroid hormone secretion and metabolism in rats

1991 ◽  
Vol 261 (2) ◽  
pp. E227-E232 ◽  
Author(s):  
J. P. Schroder-van der Elst ◽  
D. van der Heide ◽  
J. Kohrle
Keyword(s):  
Thyroid Hormone ◽  
Hormone Secretion ◽  
Male Rats ◽  
Intact Male ◽  
Hormone Production ◽  
Iodide Uptake ◽  
Brown Adipose ◽  
In Vivo Effects

In vitro, the synthetic flavonoid EMD 21388 appears to be a potent inhibitor of thyroxine (T4) 5'-deiodinase and diminishes binding of T4 to transthyretin. In this study, in vivo effects of long-term administration of EMD 21388 on thyroid hormone production and metabolism were investigated. Intact male rats received EMD 21388 (20 mumol.kg body wt-1.rat-1.day-1) for 14 days. [125I]T4 and 3,5,3'-[131I]triiodotyronine (T3) were infused continuously and intravenously in a double-isotope protocol for the last 10 and 7 days, respectively. EMD 21388 decreased plasma thyroid hormone concentrations, but thyrotropin levels in plasma and pituitary did not change. Plasma clearance rates for T4 and T3 increased. Thyroidal T4 secretion was diminished, but T3 secretion was elevated. Extrathyroidal T3 production by 5'-deiodination was lower. T4 concentrations were markedly lower in all tissues investigated. Total tissue T3 was lower in brown adipose tissue, brain, cerebellum, and pituitary, tissues that express the type II 5'-deiodinase isozyme due to decreased local T3 production. Most tissues showed increased tissue/plasma ratios for T4 and T3. These results indicate that this flavonoid diminished T4 and increased T3 secretion by the thyroid, probably in analogy with other natural flavonoids, by interference with one or several steps between iodide uptake, organification, and hormone synthesis.

Somatostatin Inhibits prolactin secretion in the estradiol primed male rat

1981 ◽  
Vol 59 (10) ◽  
pp. 1082-1088 ◽  
Author(s):  
G. R. Cooper ◽  
S. H. Shin
Keyword(s):  
Hormone Secretion ◽  
Growth Hormone Secretion ◽  
Blocking Agent ◽  
Prolactin Secretion ◽  
Male Rats ◽  
Male Rat ◽  
Dependent Manner ◽  
Intact Male ◽  
Plasma Prl

Somatostatin inhibits not only growth hormone secretion, but also the secretion of several other hormones. The role of somatostatin in prolactin (PRL) secretion has not been clearly demonstrated. The present study was undertaken to examine the effects of somatostatin on rat PRL secretion in several different circumstances where the circulating PRL level is elevated: (1) the estradiol primed intact male rat, (2) normal and (3) estradiol primed rats pretreated with pimozide, (4) normal and (5) estradiol primed hypophysectomized male rats with adenohypophyses grafted under the kidney capsule (HAG rat). Blood samples (70 μL) were taken every 2 min via an indwelling atrial cannula from conscious, unrestrained animals. In the estradiol primed intact rats, a bolus injection of somatostatin (10, 100, and 1000 μg/kg) lowered PRL levels in a dose-dependent manner. When the PRL concentration was elevated by the administration of pimozide (3 mg/kg), a dopaminergic receptor blocking agent, somatostatin was ineffective in decreasing plasma PRL concentration but the PRL concentration was lowered by somatostatin when the rat had been primed with estradiol. Somatostatin had no effect on the normal HAG rats, but lowered the plasma PRL concentration in the estradiol primed HAG rats. Since somatostatin inhibits PRL secretion only in the estradiol primed rats, it is suggested that estradiol priming creates a new environment, presumably via new or altered receptors, which can be inhibited by somatostatin.

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

1996 ◽  
Vol 135 (4) ◽  
pp. 481-488 ◽  
Author(s):  
Antonio Torsello ◽  
Roberta Grilli ◽  
Marina Luoni ◽  
Margherita Guidi ◽  
Maria Cristina Ghigo ◽  
...  
Keyword(s):  
Growth Hormone ◽  
Mechanism Of Action ◽  
Direct Action ◽  
Male Rats ◽  
Surgical Ablation ◽  
Adult Rats ◽  
Gh Secretion ◽  
Plasma Gh

Torsello A, Grilli R, Luoni M, Guidi M, Ghigo MC, Wehrenberg WB, Deghenghi R, Müller EE, Locatelli V. Mechanism of action of Hexarelin. I. Growth hormone-releasing activity in the rat. Eur J Endocrinol 1996;135:481–8. ISSN 0804–4643 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 μg/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 μg/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 μg/kg, iv) induced a GH response greater (p < 0.05) than that induced by GHRH (2 μg/kg, iv). 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. Antonio Torsello, Department of Pharmacology, via Vanvitelli 32, 20129 Milano, Italy

Photic cues induce multiple neuroendocrine adjustments in testicular function

1986 ◽  
Vol 250 (2) ◽  
pp. R199-R206 ◽  
Author(s):  
J. L. Blank ◽  
C. Desjardins
Keyword(s):  
Luteinizing Hormone ◽  
Sperm Count ◽  
Hormone Secretion ◽  
Plasma Concentrations ◽  
Prolactin Secretion ◽  
Deer Mice ◽  
Testicular Function ◽  
Short Day ◽  
Environmental Lighting ◽  
Null Response

Neuroendocrine responses were evaluated in an outbred population of deer mice (Peromyscus maniculatus nebrascensis) after exposure to an inhibitory photoperiod (8:16 light-dark) for 10 wk. Deer mice were chosen as an animal model for this study because they are typical of naturally selected species that rely on environmental factors to signal the onset or cessation of annual reproductive effort. Short photoperiods induced multiple neuroendocrine adjustments as judged by three types of spermatogenic responses: normal, intermediate, and azoospermic individuals. Plasma concentrations of luteinizing hormone and testosterone coincided with gradations in spermatogenic activity. In contrast, plasma concentrations of follicle-stimulating hormone were unaffected. Prolactin secretion was lowered in all mice exposed to short day lengths, regardless of sperm count. These results demonstrate that short photoperiods engage at least three types of neuroendocrine adjustments: 1) a suppression in luteinizing hormone and testosterone secretion accompanying spermatogenic arrest, 2) a reduction in prolactin secretion independent of changes in testicular function, and 3) a null response in gonadotrophic hormone secretion in which spermatogenesis is unimpaired by short day lengths. The neuroendocrine subsets identified in this model provide new evidence that photic cues induce three types of adjustments in pituitary-testicular function. These subsets are readily identified, and they can be easily exploited to dissect and manipulate the suite of neural, endocrine, and metabolic adaptations triggered by environmental lighting among mammals with annual reproductive strategies.

Endogenous opioid peptide modulation of LH secretion in the ewe lamb: possible involvement of 5-hydroxytryptamine

1988 ◽  
Vol 116 (3) ◽  
pp. 403-411 ◽  
Author(s):  
S. C. Stansfield ◽  
P. G. Knight ◽  
C. M. Howles ◽  
F. J. Cunningham
Keyword(s):  
Limit Of Detection ◽  
Plasma Concentrations ◽  
Opioid Peptide ◽  
Prolactin Secretion ◽  
Endogenous Opioid ◽  
Concurrent Administration ◽  
Endogenous Opioid Peptide ◽  
Ewe Lambs

ABSTRACT Evidence from several species suggests that the endogenous opioid peptides participate in the regulation of gonadotrophin and prolactin secretion. The aim of the present study involving intact and ovariectomized prepubertal ewe lambs was to compare the effects in vivo of an opioid peptide agonist d-Ala2,N-Phe4,Met(0)ol5]-enkephalin (FK 33–824) and antagonist, naloxone, on concentrations of LH and prolactin in plasma, and levels of neurotransmitter metabolites in cerebrospinal fluid (CSF), with their effects in vitro on the release of gonadotrophin-releasing hormone (GnRH) and neurotransmitters from isolated median eminences. Infusion of FK 33–824 (0·5 mg/30 min) in vivo depressed plasma LH levels in both intact and ovariectomized lambs; this effect could be reversed by naloxone. In ovariectomized lambs, the inhibitory action of FK 33–824 on plasma LH levels was associated with a 13% rise in the concentration of the metabolite of 5-hydroxytryptamine, 5-hydroxyindolacetic acid (5-HIAA). Concurrent administration of naloxone resulted in an abrupt 33% fall in CSF levels of 5-HIAA. No significant changes in plasma concentrations of prolactin or CSF concentrations of the metabolites of dopamine were observed in response to the administration of FK 33–824 or FK 33–824 plus naloxone. That FK 33–824 inhibited LH release through a central mechanism was confirmed using superfused median eminences in vitro. Thus FK 33–824 (1 μmol/l) greatly diminished the release of GnRH induced by the introduction of a depolarizing stimulus (36 mmol K+/l) in tissue obtained from both intact and ovariectomized ewe lambs. Since neurotransmitter levels in superfusate samples were below the limit of detection of the high-performance liquid chromatography assay, it remains to be ascertained whether FK 33–824 concomitantly affected neurotransmitter release. These results lead us to conclude that FK 33–824 inhibits the secretion of LH, but not prolactin, in intact and ovariectomized prepubertal ewe lambs. The action of FK 33–824 is mediated, at the level of the median eminence, through a reduction of GnRH release. It is tentatively suggested that FK 33–824 may exert this inhibitory effect by stimulating the release of 5-hydroxytryptamine. J. Endocr. (1988) 116, 403–411

A possible relationship between serum transferrin, growth hormone secretion and height velocity in children

1980 ◽  
Vol 93 (2) ◽  
pp. 134-138 ◽  
Author(s):  
M. Donnadieu ◽  
R. M. Schimpff ◽  
P. Garnier ◽  
J. L. Chaussain ◽  
J. C. Job
Keyword(s):  
Growth Hormone ◽  
Growth Regulation ◽  
Hormone Secretion ◽  
Growth Hormone Secretion ◽  
Height Velocity ◽  
Obese Children ◽  
Gh Secretion ◽  
Growth Promoting

Abstract. Since transferrin (Tf) in vitro has a growth-promoting activity and is associated with NSILA properties, the aim of this work was to study in vivo the relationships between Tf, somatomedin activity (SM), growth hormone (GH) secretion, and height velocity in children. An iv infusion of ornithine hydrochloride was given to 23 controls; the induced rise of GH was accompanied by a simultaneous fall of SM (r = −0.711, P < 0.001) and was preceded by a fall of Tf (r = −0.610, P < 0.01). In 17 obese children SM was within the normal range, when Tf levels were higher and arginineinduced GH peaks lower than in the controls, and a negative correlation was found between Tf basal levels and GH peaks (r = −0.608, P < 0.01). In 9 children with confirmed hypopituitarism the Tf levels were significantly lower than in the controls. In 14 children with confirmed or suspected hypopituitarism a single im injection of hGH (6 mg) failed to induce Tf variations over 24 h. In 39 of these children the height velocity was significantly correlated with Tf basal levels (r = 0.701, P < 0.001). These data suggest that transferrin is involved in growth regulation, and that GH secretion is related to transferrin levels by a feed-back mechanism.

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