Effect of intravenous administration of growth hormone-releasing factor (hpGRF-44) and Tyr-d-Trp-Ala-Trp-d-Phe-NH2 on plasma hormones and metabolites in goats

Abstract

ABSTRACT It has recently been demonstrated that human pancreatic GH-releasing factor (hpGRF-44) and Tyr-d-Trp-Ala-Trp-d-Phe-NH2 (subsequently referred to as 'the peptide') release GH from rat pituitary glands maintained in vitro and, in the former case, increase circulating GH in rats and man. The commercial importance of discovering an agent capable of specifically enhancing GH secretion in ruminants stimulated the present study which examined: (1) the intravenous administration of both peptides on plasma GH, prolactin, insulin, glucose, urea and non-esterified fatty acids in goats and (2) the effect of the peptide on the release of GH from sheep pituitary glands maintained in vitro. The peptide was injected into the jugular vein of goats in three different forms and at several concentrations (dispersal by shaking, 0·07 μg/kg; 0·7 μg/kg; ball-milled, 7·0 μg/kg, 70 μg/kg; dimethyl sulphoxide (5%), 7·0 μg/kg, 70 μg/kg). None of the treatments stimulated a significant increase in circulating GH. Nevertheless the peptide (20 μg/ml medium) was found to stimulate a 50–60% increase in the production of GH from sheep pituitary glands maintained in vitro. The effect of intravenously injecting hpGRF-44 (1·0 pg/kg) was investigated in the present and absence of passive immunization with sheep anti-somatostatin immunoglobulin G (IgG) (a bolus of 600 mg, 3 h before treatment with hpGRF-44). Plasma GH was increased (P<0·001) within 15 min of treatment and the magnitude of the response was the same for both the immunized and non-immunized goats. A second peak was measured after approximately 75 min which was only significant (P < 0·05) in the immunized group. Although circulating insulin tended to increase after treatment with sheep anti-somatostatin IgG, neither passive immunization, nor hpGRF-44 nor the peptide stimulated any change in the plasma concentrations of the other parameters which were measured. J. Endocr. (1984) 103, 173–178