The Effect of Thyrotropin-Releasing Hormone (TRH) and Somatostatin (GHRIH) on Growth Hormone and Prolactin Secretion <i>in vitro</i> and <i>in vivo</i> in the Domestic Fowl (<i>Gallus domesticus</i>)

Abstract

The effects of thyrotropin-releasing hormone (TRH) on growth hormone (GH) and prolactin (Prl) secretion have been investigated in vitro and in vivo in domestic fowl. In both conscious and anaesthetized immature chickens the administration (i.v.) of TRH (2.5 and 25 μg/kg) significantly increased the concentration of plasma GH. The simultaneous administration of somatostatin (GHRIH), 2.5 μg/kg, to conscious birds significantly reduced the magnitude of the GH response to TRH treatment, but had no effect on the basal levels of plasma GH. The repeated injection of TRH (10 μg/kg) every 20 min over a 100-min period failed to maintain the concentration of plasma GH at a high level. Prl secretion was not stimulated in any of these experiments, and in anaesthetized birds TRH (2.5 and 25 μg/kg) treatment was followed by a depression in the level of plasma Prl. The effects of TRH and GHRIH on GH secretion by an in vitro dispersed pituitary cell suspension system were very similar to the in vivo studies. TRH stimulated Prl release in vitro, in contrast to the in vivo studies, and the response was dose related. GHRIH had no effect on the basal release of Prl in vitro but significantly inhibited the response to TRH treatment.

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

“…Since TRH directly affects the chicken pituitary, TRH pituitary receptors are likely to mediate the effect of TRH on GH and TSH secretion (Harvey and Baidwan, 1989). TRH also has an effect on the PRL secretion of domestic fowl in vitro and in vivo (Harvey et al, 1978). All the actions of TRH on PRL (Yan et al, 1991) and TSHβ (Steinfelder et al, 1992) secretion and gene expression are known to be mediated through Pit-1 in mammalian species.…”

The influence of thyrotropin-releasing hormone (TRH) on growth rate and thyroid activity in broiler chicks

“…In females, TRH had no effect on growth parameters. Previous observations on chickens (Harvey et al, 1978;Burkę, 1983;Leung et al, 1984;Lauterio and Scanes, 1987) and ducks (Folzer-Joudaione et al, 1988) established that TRH not only stimulates the release of thyroid hormones but also is a potent stimulant of GH secretion. Remarkable differences in GH response between małe and female broilers were seen in the form of higher plasma GH concentrations in males (Harvey et al, 1977;Johnson et al, 1990).…”

Ghrelin-induced GH secretion in domestic fowl in vivo and in vitro

“…Controls were similarly injected with the saline vehicle (1·0 ml/kg). Heparinized blood samples (0·5-1·0 ml) were then collected from the contralateral vein after 10 min (the time of the maximal GH response to other GH secretagogues; , or at additional intervals (20, 30 and 60 min) following injection, in accordance with previous in vivo studies (Harvey et al 1978 and in compliance with the University of Alberta's Policy on Animal Welfare. Following centrifugation and separation, the plasma was stored at 20 C prior to GH radioimmunoassay, using NIADD reagents (Bethesda, MD, USA, kindly provided by Dr A F Parlow), as previously described (Ahmed & Harvey 2002).…”

“…Dispersed pituitary cells The GH-releasing activity of human ghrelin was assessed using freshly dispersed pituitary cells, as outlined by Harvey et al (1978) for the GH-releasing activity of thyrotrophin-releasing hormone (TRH). Briefly, anterior pituitary glands from the heads of 6-week-old broiler fowl (obtained from Lillydale, Edmonton, Alberta, Canada) were collected into ice-cold Medium 199 (Gibco, Burlington, Ontario, Canada) and pituitary cells were obtained after a 2-h incubation at 39 C in 0·02% (w/v) collagenase (type III, fraction A; Sigma Chemical Company, St Louis, MO, USA).…”