Growth hormone response to long-term GH-RH administration in lambs

Abstract

The pattern of long-term GHRH administration capable of stimulating GH release without depleting pituitary GH content has been investigated using two experimental approaches. In experiment 1, recently weaned male lambs were treated for 3 weeks as follows: Group A) control; B) subcutaneous (sc) continuous infusion of GHRH (1200 mg/day) using a slow release pellet; C) the same as B plus 1 daily sc injection of long acting somatostatin (SS) (octreotide, 20 mg) ; D) 3 daily sc GHRH (250 mg) injections ; E) 2 daily sc injections of GHRH (250 mg) and 2 of natural SS (250 mg). In experiment 2, recently weaned male lambs were continuously GHRH-treated using sc osmotic minipumps (900 mg/day) alone or combined with a daily sc injection of octreotide (20 mg) for 4 weeks. Basal plasma GH levels were increased after chronic pulsatile GHRH treatment but not after any kind of continuous GHRH administration. This increment was maintained during the 3 weeks of experimentation and appeared accompanied by a pituitary GH content similar to controls. A marked GH response to the iv GHRH challenge was observed in controls and in lambs receiving both types of continuous sc GHRH infusions, whereas pulsatile sc GHRH-treated animals did not respond to the iv GHRH challenge in the first and second weeks of the study but did so in the third week of treatment. These data demonstrate that long-term pulsatile GHRH administration is capable of stimulating GH release in growing male lambs, without producing pituitary desensitization.

Hypothalamic arcuate neuropeptide Y-neurons decrease periventricular somatostatin-neuronal activity before puberty in the female lamb: Morphological arguments

“…In a recent study in ewes, numerous afferents containing various neuropeptides, including orexin, galanin and GHRH, were observed on ir somatostatin PEV neurons (Iqbal et al, 2005). In sheep, galanin, orexin and GHRH stimulate GH release (Spencer et al, 1994;Pé rez-Romero et al, 2000;Molik et al, 2008), but no evidence of their effect on the somatostatincontaining neurons has been found.…”

The chronic oral administration of arginine aspartate decreases secretion of IGF‐1 and IGFBP‐3 in healthy volunteers

“…Growth hormone receptors desensitization has been shown in sheep and rats [4,5]. In addition, GH secretion is regulated by the negative feedback of GH and insulin‐like growth factor‐1 (IGF‐1) [6,7].…”