Comparative Stimulation of Growth Hormone Secretion in Anaesthetized Chickens by Human Pancreatic Growth Hormone-Releasing Factor (hpGRF) and Thyrotrophin-Releasing Hormone (TRH)

Harvey, S.; Scanes, Colin G.

doi:10.1159/000123998

Cited by 56 publications

(34 citation statements)

References 31 publications

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“…injection of peptide or the 0·9% (w/v) NaCl vehicle (1 ml/kg body weight). Each peptide was administered at a dose of 10 µg/kg, since this is the maximally effective dose of TRH and GHRH in chickens (Harvey & Scanes 1984) and is comparable to doses of ghrelin that stimulate GH release in rats (4-20 µg/kg in rats, Hosoda et al 2000b) and humans (5 µg/kg, Takaya et al 2000;33-66 µg/kg, Peino et al 2000). Venous blood samples were collected from each bird 10 min after injection, at the time of the maximal GH response to TRH and GHRH (Harvey & Scanes 1984).…”

Section: Gh-releasing Activitymentioning

confidence: 99%

Ghrelin: a hypothalamic GH-releasing factor in domestic fowl (Gallus domesticus)

Ahmed¹,

Harvey²

2002

Journal of Endocrinology

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Ghrelin, a recently discovered peptide in the mammalian hypothalamus and gastrointestinal tract is thought to be the endogenous ligand for the GH secretagogue (GHS) receptor and it stimulates GH release in rats and humans. The possibility that ghrelin is present in birds was therefore assessed, since a GHS receptor is present in the chicken pituitary gland.Although immunoreactive ghrelin is readily detectable in the rat stomach and ileum, ghrelin immunoreactivity could not be detected in the chicken proventriculus, stomach, ileum or colon, whereas somatostatin immunoreactivity, in contrast and as expected, was readily detectable in the chicken gastrointestinal tract. Ghrelin immunoreactivity was, however, present in the chicken hypothalamus, although not in the arcuate (infundibular) nucleus, as in rats. Discrete parvocellular cells and neuronal fibers with ghrelin immunoreactivity were present in the anterior medial hypothalamus. This immunoreactivity was specific and completely abolished following the preabsorption of the antibody with an excess of human ghrelin. Ghrelin immunoreactivity was also present in clusters of large ovoid magnocellular cells in the nucleus magnocellularis preopticus pars medialis, nucleus magnocellularis preopticus supraopticus and in the chiasmaopticus. Immunoreactivity for ghrelin was restricted to the cytoplasm of the perikarya and their axonal sprouts. Immunoreactivity for ghrelin was not seen in any other hypothalamic nuclei.In a preliminary experiment, circulating GH concentrations in conscious immature chicks were promptly increased following bolus i.v. administration of human ghrelin. The increase in GH concentration (approximately three times that in the controls) was comparable with that induced by the same dose (10 µg/kg) of human GHreleasing hormone, although less than that (approximately sixfold) induced by thyrotropin-releasing hormone.These results demonstrate the presence of a ghrelin-like protein in the chicken hypothalamus and suggest that it participates in the regulation of GH secretion in birds.

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Section: Gh-releasing Activitymentioning

confidence: 99%

Ghrelin: a hypothalamic GH-releasing factor in domestic fowl (Gallus domesticus)

Ahmed¹,

Harvey²

2002

Journal of Endocrinology

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“…TRH also releases GH in vertebrates including birds (Harvey, 1990). The sensitivity and responsiveness of avian somatotrophs to mammalian TRH stimulation in vivo exceeds that to mammalian GHRHs (Harvey and Scanes, 1984). The potent GHreleasing activity of TRH in young chicken, however, is well in contrast with the small or no increase in adult chickens (Harvey et al, 1981).…”

mentioning

confidence: 99%

Regulation of growth hormone expression by thyrotropin-releasing hormone through the pituitary-specific transcription factor Pit-1 in chicken pituitary

Careghi

Bruggeman

et al. 2004

Acta Veterinaria Hungarica

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Pit-1 is a pituitary-specific POU-domain DNA binding factor, which binds to and trans-activates promoters of growth hormone-(GH), prolactin-(PRL) and thyroid stimulating hormone beta-(TSHβ) encoding genes. Pit-1 has been identified in several mammalian and avian species. Thyrotropin-releasing hormone (TRH) is located in the hypothalamus and it stimulates TSH, GH and PRL release from the pituitary gland. In the present study, we successfully developed a competitive RT-PCR for the detection of Pit-1 expression in the chicken pituitary, that was sensitive enough to detect picogram levels of Pit-1 mRNA. Applying this method, the effect of TRH injections on Pit-1 mRNA expression was determined in the pituitary of chick embryos and growing chicks. In both 18-day-old embryos and 10-day-old male chicks the Pit-1 mRNA expression was significantly increased following TRH injection, thereby indicating that the stimulatory effects of TRH on several pituitary hormones is mediated via its effect on Pit-1 expression. Therefore, a semi-quantitative RT-PCR method was used to detect possible changes in GH levels. TRH affected the GH mRNA levels at both developmental stages. These results, combined with the data on Pit-1 mRNA expression, indicate that Pit-1 has a role in mediating the stimulatory effects of TRH on pituitary hormones like GH.

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“…Birds were anesthetized with sodium pentobarbitone (30 mg/kg; i.v.) 60 min before experimentation, to produce a low, stable plasma G H level [ 14] and to reduce the varia bility of the GH response to exogenous TRH [14,15] The ability of various doses and combinations of TRH or its metabolites to affect GH secretion was further examined in anesthetized chicks. Blood samples were obtained 10 min follow ing challenge, a time which has previously been established to be that when TRH evokes a maximal increase in the plasma GH con centration [15,16].…”

Section: Methodsmentioning

confidence: 99%

“…In addition, in view of the rapid enzymic degradation of TRH by plasma from mammals and the changes in TRH degrading activity with age [I, 25-27, 34] and other physiological states [3,6, 18, 27], the catabolic activity of plasma from young and adult chickens has also been investigated. Adult birds, par ticularly anesthetized fowl, are responsive to TRH stimula- tion in vivo [12,15], although they are less responsive than neonatal chicks [12, 16,36]. The possibility that this may be due to age-related differences in the degradation of TRH has therefore also been assessed.…”

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confidence: 99%

TRH Stimulation of in vivo GH Release in the Domestic Fowl

Scanes

Harvey

1985

Neuroendocrinology

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Thyrotropin-releasing hormone (TRH) stimulated in vivo growth hormone (GH) release in conscious and anesthetized young domestic fowl. The administration of the presumed metabolites of TRH, deamido-TRH (TRH-OH) and histidyl-proline diketopiperazine (HPD), was followed by small but significant (p < 0.05) increases in the plasma concentrations of GH in both conscious and anesthetized chicks. However, the ability of TRH-OH or HPD to stimulate GH secretion was less than that observed with a 100-fold lower dose of TRH. The administration of either TRH-OH or HPD with TRH increased the GH response over that observed with TRH alone. The ability of chicken plasma to degrade exogenous TRH in vitro was determined by measuring immunoreactive TRH (IR-TRH) content and by assessing the ability of the incubated samples to increase the plasma concentration of GH when administered to young fowl. The in vitro half-life of TRH was estimated to be 9.8 (by immunoassay) and 9.6 (by a biological index) min for plasma from adult male chickens and 23.9 (by immunoassay) and 20.2 (by biological index) min for plasma from 6-week-old chicks. This difference in degradation may account, at least in part, for the observed age-related decrease in the plasma concentration of GH in birds and for the diminished GH responsiveness of adult birds to exogenous TRH.

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Comparative Stimulation of Growth Hormone Secretion in Anaesthetized Chickens by Human Pancreatic Growth Hormone-Releasing Factor (hpGRF) and Thyrotrophin-Releasing Hormone (TRH)

Cited by 56 publications

References 31 publications

Ghrelin: a hypothalamic GH-releasing factor in domestic fowl (Gallus domesticus)

Ghrelin: a hypothalamic GH-releasing factor in domestic fowl (Gallus domesticus)

Regulation of growth hormone expression by thyrotropin-releasing hormone through the pituitary-specific transcription factor Pit-1 in chicken pituitary

TRH Stimulation of in vivo GH Release in the Domestic Fowl

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