Influence of nutritional status and oestradiol-17 beta on plasma growth hormone, insulin-like growth factors-I and -II and the response to exogenous growth hormone in young steers.

Plasma GH profiles and circulating concentrations of plasma insulin-like growth factors-I and -II (IGF-I and -II) were examined in 20 steers on either high (3% dry matter of body weight per day) or low (1% dry matter of body weight per day) planes of nutrition with or without an implant of oestradiol-17 beta. The response of plasma IGF-I and -II to a bolus injection of bovine GH (bGH) was also investigated. Reduced feeding significantly (P less than 0.01) increased the mean concentration, peak height and integrated area of plasma GH. Treatment of steers with oestradiol at low nutrition significantly increased baseline GH concentrations. Treatment of steers with oestradiol at high nutrition significantly (P less than 0.05) increased mean, baseline, peak height, and integrated area of plasma GH. GH pulse frequency was not changed by either nutritional plane or oestradiol treatment. Basal concentrations of plasma IGF-I were significantly (P less than 0.01) decreased by reduced feeding in both the oestradiol-treated and the control group. Treatment with oestradiol increased (P less than 0.01) basal plasma concentrations of IGF-I at both high and low levels of nutrition. After i.v. injection of bGH (0.1 mg/kg body weight), an increase in plasma IGF-I was observed only in steers at high nutrition. Basal concentrations of plasma IGF-II were not altered by nutritional manipulations but were significantly (P less than 0.001) increased by oestradiol treatment. After bGH infusion only steers at high nutrition showed an increase in plasma IGF-II.(ABSTRACT TRUNCATED AT 250 WORDS)