Effect of different growth hormone-releasing factors on the concentrations of growth hormone, insulin and metabolites in the plasma of sheep maintained in positive and negative energy balance

Abstract

Three experiments were conducted to compare the ability of different preparations of growth hormone-releasing factor (GRF) to stimulate GH secretion in sheep maintained in positive and negative energy balance. In experiment 1 five sheep were injected (i.v.) with three preparations of human pancreatic GRF (hpGRF-44, hpGRF-40, hpGRF-29-NH2) and one preparation of rat hypothalamic GRF (rhGRF-29-NH2) all at 98.0 pmol/kg, or control vehicle, in a Latin square design when the animals either had free access to food or were fed half their maintenance requirements. Analysis of plasma samples, obtained before and for 150 min after injection, revealed that the reduced food intake resulted in the expected changes in body weight and circulating GH, insulin, glucose, urea and non-esterified fatty acids. The maximum post-injection concentrations of GH did not differ between either the two levels of feeding or the four GRF preparations but the mean post-injection concentration of GH was significantly higher for all GRF treatments on the restricted ration (P less than 0.001). The mean post-injection response to rhGRF-29-NH2 was less than that obtained with hpGRF-44 for sheep with food available ad libitum (P less than 0.05) and was clearly more persistent for all GRF treatments in animals fed the reduced diet (P less than 0.001). In experiment 2 the same five sheep were injected i.v. with rhGRF-29-NH2 (98.0 pmol/kg) when they had free access to food and after food had been withdrawn for 3 days.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of intravenous bovine growth hormone or human pancreatic growth hormone-releasing factor on milk production and plasma hormones and metabolites in sheep

“…injection of hpGRF-44 into lactating ewes was similar to that pre¬ viously determined using four GRF analogues in castrated sheep (Hart, Chadwick, Coert et al 1985). Previous work in rats ) and sheep (LC.…”

Responses to administration of growth hormone releasing hormone and glucose in steers receiving stair-step and extended restriction on feeding

“…This increase may have been caused by restricted feeding. Compared to well-fed sheep, sheep fed a restricted diet showed a higher GH response to the GHRH injection; this is attributable to the decrease in the secretion because of somatostatin (GH-inhibiting hormone; GRIH) from the hypothalamus during the oligotrophic state (Hart et al, 1985). Therefore, the increase in GH secretion by GHRH in the extended restriction group (T2) in this study may have been caused by the oligotrophic state.…”

Influence of parasitism on plasma concentrations of growth hormone, somatomedin-C and somatomedin-binding proteins in calves

“…Effects of this infection per se, beyond those attributable to nutrition alone, on insulin and thyroid hormone status and urinary excretion of creatinine, hydroxyproline and n-methylhistidine (Elsasser, Hammond, Rumsey & Fayer, 1986) suggest a meta¬ bolic readjustment to shunt nutrients away from growth to support febrile responses by infected ani¬ mals. Plasma concentrations of growth hormone (GH) and insulin-like growth factor-I (somatomedin-C; SM-C) are responsive to changes in nutrient intake (Merimee, Zapf & Froesch, 1982;Prewitt, D'Ercole, Switzer & Van Wyk, 1982;Isley, Underwood & Clemmons, 1984;Hart, Chadwick, Coert et al 1985). …”