Growth hormone releasing factors and secretion of growth hormone in sheep, calves and pigs

Abstract

Human pancreatic growth hormone releasing factors (hpGRF) (1–40) and (1–44) were administered iv in sheep, pigs and calves to determine their effectiveness in stimulating GH release in these species. Both peptides produced a rapid increase in plasma GH concentration in all three species at dose levels ranging from .0065 to .65 nmol/kg. Moreover, there was no difference in the GH-secretory response observed between hpGRF(1–44)NH 2 and (1–40)OH in sheep. Sheep also responded to hpGRF(1–40)NH 2 and (1–40)OH as well as [his 1]- and [tyr 1]-hpGRF(1–40)NH 2 in a similar manner. Rat hypothalamic GRF was less effective than [his 1]-hpGRF(1–40), while the response to bGRF was not significantly different from hpGRF(1–40) in stimulating GH secretion in sheep. Although all three species responded to hpGRF, the elevation in plasma GH levels above baseline were greater after hpGRF injection in sheep than in pigs or calves. Subcutaneous injection of hpGRF in sheep was an effective mode of administration of the peptide, although the effect was not as long-lasting as that after iv injections and higher doses were required to stimulate GH secretion.