Autoregulation of central and peripheral growth hormone receptor mRNA in domestic fowl

Abstract

Growth hormone (GH) regulates numerous cellular functions in many different tissues. A common receptor is believed to mediate these tissue-specific effects, suggesting that post-receptor signalling molecules or tissue sensitivity to GH may differ between tissues. Tissue sensitivity depends upon the abundance of GH receptors (GHRs), thus tissue-specific GHR regulation could enable tissuespecific GH actions. The comparative autoregulation of GHR gene transcription in central (whole brain or hypothalami) and peripheral (liver, bursa, spleen and thymus) tissues was therefore examined in domestic fowl. In all tissues, a 4·4 kb GHR gene transcript that encodes the full-length GHR was identified. The abundance of this transcript was inversely related to endogenous GH status; it was lower in males with high circulating concentrations of GH and higher in females with lower basal concentrations of plasma GH. The abundance of this transcript was also rapidly downregulated in response to a bolus systemic injection of recombinant chicken GH, designed to mimic an episodic burst of endogenous GH release. This autoregulatory response was observed within 2 h of GH administration and was of greater magnitude in the brain than in peripheral tissues. Intracerebroventricular injections of GH also downregulated GHR gene expression in the brain, although hepatic GHR transcripts were unaffected 24 h after central administration of GH. In contrast, the induction of hyposomatotropism by passive GH immunoneutralization increased the abundance of the GHR transcript in the thymus, but not in other central (brain) or peripheral (bursa, liver) tissues. GH is not the sole regulator of GHR abundance, however; hypersomatropism induced by hypothyroidism was associated with an increase in GHR mRNA. The expression of the GHR gene in the domestic fowl would thus appear to be autoregulated by GH in a tissue-specific way.

Blood-Brain Barrier for Human Growth Hormone and Insulin-like Growth Factor-I

“…Neuropeptide-Y neurons, which are closely located to GHRH neurons, do express GH receptors and act in a paracrine manner on the GHRH neurons 61 ' 62 . Plasma levels of GH (measured by radioimmunoassay) correlated negatively with the density of binding sites in the choroid plexus and hypothalamus, but not in other brain regions 11,63 .…”

“…High levels of GH in the cerebrospinal fluid of some acromegalic patients are well known 10 . Receptors for GH have been identified throughout the brain 11 , mainly in the choroid plexus, and were shown to decrease with age 12,13 . There are GH receptors in some neurons and astrocytes 14 , but they cannot differentiate the ligands produced outside and inside the BBB 15 Although such accumulated indications suggest the crossing of the BBB by GH, an active transport mechanism for GH still has to be proven.…”

Effects of growth hormone over-expression on reproduction in the common carp Cyprinus carpio L.

“…There are reports on GH effects on GHR expression showing that there exists autoregulation of GH on GHR in the target cell with both down-regulatory effects (Hull and Harvey, 1998;Maiter et al, 1988) and up-regulatory effects (Hull and Harvey, 1996) in some vertebrate species. In fish, GH effects on GHR expression are still unclear.…”

Growth Prior to Thermogenesis for a Quick Fledging of Adélie Penguin Chicks (Pygoscelis adeliae)

“…Furthermore, GH concentration has been positively shown to control the expression of its receptor in avian skeletal muscle satellite cell cultures [14]. However, at the whole organism level, an apparent inverse relationship between plasma GH levels and avGHR expression is evident from ontogeny studies of commercial broiler chickens [15,16,30]. Although we were unable to access plasma pulsatile GH concentrations in Adélie chicks, it is therefore tempting to speculate that the rapid decline in avGHR expression corresponds to the sharp rise in plasma GH, which generally starts immediately before hatching in domestic birds [15].…”