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R. GOLDSTEIN and S. PAVEL

Institute of Endocrinology, Bucharest, Rumania

(Received 29 March 1977)

The mammalian pineal gland contains (Pavel, 1965) and synthesizes (Pavel, Goldstein, Ghinea & Calb, 1977) the nonapeptide arginine-vasotocin (AVT). Since luteinizing hormone releasing hormone (LH–RH), thyrotrophin releasing hormone (TRH) and growth hormone release-inhibiting hormone (somatostatin, SRIF) have now been localized not only in the brain, but also in the pineal gland (White, Hedlund, Weber, Rippel, Johnston & Wilber, 1974; Pelletier, Le Clerc, Dube, Labrie, Puviani, Arimura & Schally, 1975), we investigated the effects of these peptides on the release of AVT into the cerebrospinal fluid (CSF) of cats.

Intracarotid injections of 0·1 μg LH-RH, TRH (Hoechst, Frankfurt), SRIF (Serono, Rome) or oxytocin (Syntocinon, Sandoz Ltd, Basel) in 0·5 ml saline were given to urethane-anaesthetized male cats weighing 3–4 kg. Controls received an equal volume of saline only. The pineal glands were removed 60 min after the injections, quickly homogenized, and extracted

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I Shimon and S Melmed

Introduction

The two naturally occurring bioactive peptides, somatostatin (SRIF)-14 and SRIF-28 are physiological regulators of pituitary growth hormone (GH), pancreatic endocrine secretions, and gastrointestinal motility and hormone secretion (Brazeau et al. 1972, Mandarino et al. 1981). These biological effects are mediated through specific high-affinity G-protein-coupled receptors containing seven transmembrane domains. Five distinct SRIF receptor (SSTR) subtypes are located on different chromosomes (Bruno et al. 1992, Yasuda et al. 1992, Roher et al. 1993, Xu et al. 1993, Yamada et al. 1992a,b, 1993), and consist of 364–418-amino acid proteins (39–46 kDa) which display 42–60% identity among the different subtypes and 81–97% homology with rodent receptors (Reisine & Bell 1995). The SSTRs interact with different G-proteins (Rens-Domiano et al. 1992, Law et al. 1993) to inhibit adenylate cyclase activity. Receptor subtypes are also associated with other signal-transduction mechanisms, including cationic channel conductance reduction and tyrosine phosphatase activation (Reisine & Bell

Free access

CD McMahon, LT Chapin, RP Radcliff, KJ Lookingland and HA Tucker

After a meal, somatotropes are temporarily refractory to growth hormone-releasing hormone (GHRH), the principal hormone that stimulates secretion of growth hormone (GH). Refractoriness is particularly evident when free access to feed is restricted to a 2-h period each day. GH-releasing peptide-6 (GHRP-6), a synthetic peptide, also stimulates secretion of GH from somatotropes. Because GHRH and GHRP-6 act via different receptors, we hypothesized that GHRP-6 would increase GHRH-induced secretion of GH after feeding. Initially, we determined that intravenous injection of GHRP-6 at 1, 3 and 10 microg/kg body weight (BW) stimulated secretion of GH in a dose-dependent manner. Next, we determined that GHRP-6- and GHRH-induced secretion of GH was lower 1 h after feeding (22.5 and 20 ng/ml respectively) than 1 h before feeding (53.5 and 64.5 ng/ml respectively; pooleds.e.m.=8.5). However, a combination of GHRP-6 at 3 microg/kg BW and GHRH at 0.2 microg/kg BW synergistically induced an equal and massive release of GH before and after feeding that was fivefold greater than GHRH-induced release of GH after feeding. Furthermore, the combination of GHRP-6 and GHRH synergistically increased release of GH from somatotropes cultured in vitro. However, it was not clear if GHRP-6 acted only on somatotropes or also acted at the hypothalamus. Therefore, we wanted to determine if GHRP-6 stimulated secretion of GHRH or inhibited secretion of somatostatin, or both. GHRP-6 stimulated secretion of GHRH from bovine hypothalamic slices, but did not alter secretion of somatostatin. We conclude that GHRP-6 acts at the hypothalamus to stimulate secretion of GHRH, and at somatotropes to restore and enhance the responsiveness of somatotropes to GHRH.

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S G Cella, V Locatelli, M L Broccia, E Menegola, E Giavini, V De Gennaro Colonna, A Torsello, W B Wehrenberg and E E Müller

Abstract

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. In addition, when comparing these changes with those in rats given GHRH-Ab postnatally, it would appear that deprivation of GHRH affects different regulatory levels of the hypothalamo-pituitary-somatotroph axis depending on when the deprivation occurs.

Journal of Endocrinology (1994) 140, 111–117

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H. M. Charlton, R. G. Clark, I. C. A. F. Robinson, A. E. Porter Goff, B. S. Cox, C. Bugnon and B. A. Bloch

ABSTRACT

Mutations in animals have provided insight into many aspects of normal and pathological human physiology. This paper reports the discovery and initial characterization of a new mutant dwarf rat. The mutation, inherited as an autosomal recessive, arose spontaneously in a breeding colony of Lewis rats at the Medical Research Council Cellular Immunology Unit, Sir William Dunn School of Pathology, Oxford, U.K., in 1985 and the strain has now been established both in Oxford and at Mill Hill. Body growth in the mutant is retarded such that at 3 months of age both males and females weigh approximately 40% less than their normal litter-mates, and continue to grow at a slower rate.

The mutants show a selective reduction in pituitary GH synthesis and storage (pituitary GH concentrations were approximately 10% of normal in males and 6% in females). The concentration of their anterior pituitary trophic hormones (LH, TSH, prolactin and ACTH) were within the normal range in dwarf animals. Exogenous GH treatment for 5 days resulted in an increase in growth rate from 1·5 ± 0·3 to 3·9 ± 0·4 g/day in male mutants, and 0·8 ± 0·2 to 3·1 ±0·1 g/day in females. Longitudinal bone growth rates were more than doubled by this treatment from 49 ± 5 to 100 ±10 μm/day in females and from 52 ± 11 to 131 ± 16 μm/day in males.

Dot blot and Northern blot analysis of pituitary mRNA extracts revealed that the GH message in mutants was between 20 and 25% of normal, and that the GH transcript was of normal size.

Immunoreactive GH-releasing factor (GRF) and somatostatin were present in the dwarf hypothalamus, and exogenous GRF released small amounts of GH in vivo but in proportion to the pituitary GH content. This mutant rat, which shows a selective pituitary GH deficit, may provide a useful new model for studying the endocrinology of growth.

J. Endocr. (1988) 119, 51–58

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J. J. Bass, P. D. Gluckman, R. J. Fairclough, A. J. Peterson, S. R. Davis and W. D. Carter

ABSTRACT

The effect of immunizing against somatostatin (SRIF), with SRIF conjugated to bovine thyroglobulin, was examined in cross-bred sheep fed either cut pasture or lucerne pellets. Plasma concentrations of GH were unaffected by SRIF immunization, but were lower in pellet-fed sheep. Plasma concentrations of insulin-like growth factor I (IGF-I) increased after immunization in sheep on both diets. Pasture-fed sheep had lower plasma concentrations of IGF-I than those on pellets. Sheep showed a small increase in growth rate in response to immunization. Immunization had no effect on carcass composition and did not affect plasma concentrations of IGF-II, free fatty acids or glucose. The results show that even though SRIF immunization increases plasma concentrations of IGF-I, it does not necessarily result in a large increase in growth rate.

J. Endocr. (1987) 112, 27–31

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GM Portela-Gomes and A Hoog

Insulin-like growth factor II (IGF-II) appears to play an important role during fetal life in cell growth and differentiation in several organs, including the pancreas. In the present study we investigated the cellular localization of IGF-II in human fetal pancreas at 16, 18 and 22 embryonic weeks and compared it with adult pancreas. Single and double immunofluorescence methods were used to study co-localization of IGF-II with the four major islet hormones - insulin, glucagon, somatostatin, pancreatic polypeptide - and with islet amyloid polypeptide (IAPP). Distinct IGF-II immunoreactive (IR) cells were found in the endocrine, but not in the exocrine, pancreas. The intensity of IGF-II immunoreactivity was more pronounced in the fetal than in the adult pancreas. In fetal pancreas IGF-II immunoreactivity was observed in virtually all insulin-IR cells and in subsets of the glucagon, somatostatin and IAPP cells. In the adult pancreas, IGF-II immunoreactivity was found in insulin/IAPP cells only. Our results suggest a broader effect of IGF-II in fetal endocrine pancreatic cells than in the adult.

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J. Rabii, L. Knapp, A. De La Guardia, P. Zafian, T. J. Lauterio and C. G. Scanes

ABSTRACT

To study brain sites involved in the regulation of GH secretion in the domestic fowl, lesions were placed in and around the hypothalamus of 1-week-old cockerels. Circulating concentrations of GH were then measured at weekly intervals for 4 weeks after the placement of lesions. At the termination of the experiment, histological procedures were used to determine the exact site of the lesion in each bird. Although a fair degree of overlap existed between the lesion sites leading to stimulation and those causing an inhibition of GH secretion, a clear distinction could be made in the overall distribution of stimulatory and inhibitory sites of GH control. A high concentration of lesion sites resulting in GH decline (presumed GH-releasing factor-rich areas) appeared to reside in the general area of the ventromedial and the arcuate nucleus of the hypothalamus. Lesion sites causing a GH rise (presumed somatostatin-rich areas), on the other hand, seemed to have a more caudal distribution. In addition, some evidence of an anterior hypothalamic distribution of these presumed 'somatostatin' neurones was observed. These agree with the existing immunohistochemical data on the distribution of somatostatin and constitute experimental evidence for localization of presumed GH-releasing factor sites within the avian brain.

J. Endocr. (1984) 103, 327–332

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C. J. Bailey, L. C. Wilkes, P. R. Flatt, J. M. Conlon and K. D. Buchanan

ABSTRACT

The effect of synthetic human growth hormone-releasing hormone(1–40) (hGHRH-40) on the function of the endocrine pancreas and on glucose homeostasis in lean and genetically obese-diabetic (ob/ob) mice and normal rats has been examined. The addition of 1 μmol hGHRH-40/1 to incubated islets from normal lean mice increased insulin release by 90 and 37% at 5·6 and 16·7 mmol glucose/l respectively. Lower concentrations of hGHRH-40 did not affect insulin release. hGHRH-40 (1 μmol/l) increased pancreatic polypeptide release by 50% at 5·6 mmol glucose/l. A range of concentrations of hGHRH-40 (1 nmol/l–1 μmol/l) reduced glucagon release by 42–73% at 5·6 mmol glucose/l, and by 38–70% at 16·7 mmol glucose/l. Somatostatin release was increased (eightfold) by 1 μmol hGHRH-40/1 at 5·6 mmol glucose/l, but at 1 nmol hGHRH-40/l somatostatin release was reduced (by > 50%). At 16·7 mmol glucose/litre 0·01–1 μmol hGHRH-40/l increased somatostatin release (three- to fourfold), but 1 nmol hGHRH-40/l produced a reduction of 50%. In vivo, administration of hGHRH-40 (50 μg/kg body weight i.p.) to fasted lean and ob/ob mice did not alter basal plasma concentrations of glucose and insulin, or the glucose and insulin responses to a concomitant i.p. glucose challenge. Intravenous injection of hGHRH-40 (20 μg/kg body weight) to anaesthetized rats increased plasma concentrations of insulin in the hepatic portal vein. A lower dose of hGHRH-40 (0·2 μg/kg) was ineffective, and neither dose of hGHRH-40 altered plasma glucose. The results indicate that hGHRH-40 exerts dose-dependent effects on the secretion of islet hormones, but this does not appear to be sufficient to produce measurable effects on plasma glucose homeostasis.

Journal of Endocrinology (1989) 123, 19–24

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Caiyun Sun, Da Duan, Bo Li, Chaobin Qin, Jirong Jia, Bin Wang, Haiyan Dong and Wensheng Li

Urotensin II (UII) is a cyclic peptide that was originally extracted from the caudal neurosecretory system (CNSS) of fish. UII is well known to exhibit cardiovascular, ventilatory, and motor effects in vertebrates. Studies have reported that UII exerts mitogenic effects and can act as an autocrine/paracrine growth factor in mammals. However, similar information in fish is limited. In this study, the full-length cDNAs of UII and its receptor (UT) were cloned and characterized in the orange-spotted grouper. UII and UT were expressed ubiquitously in various tissues in grouper, and particularly high levels were observed in the CNSS, CNS, and ovary. A functional study showed that UT was coupled with intracellular Ca2 + mobilization in HEK293 cells. Studies carried out using i.p. injections of UII in grouper showed the following: i) in the hypothalamus, UII can significantly stimulate the mRNA expression of ghrh and simultaneously inhibit the mRNA expression of somatostatin 1 (ss1) and ss2 3 h after injection; ii) in the pituitary, UII also significantly induced the mRNA expression of gh 6 and 12 h after injection; and iii) in the liver, the mRNA expression levels of ghr1/ghr2 and igf1/igf2 were markedly increased 12 and 3 h after the i.p. injection of UII respectively. These results collectively indicate that the UII/UT system may play a role in the promotion of the growth of the orange-spotted grouper.