Steroid hormone may modulate hepatic somatomedin C production in newborn calves.

We have studied the possible influence of steroid hormones and a beta-agonist (clembuterol) on hepatic insulin-like growth factor 1 (IGF1) production in young calves. For this purpose nine 20- to 40-day-old Holstein X Friesian male calves were fitted with chronically indwelling catheters in hepatic and portal veins and hepatic artery. Estradiol induced a simultaneous increase in plasma growth hormone (GH nmol/l) and IGF1 (nmol/l) levels (0.35 +/- 0.05 vs. 0.10 +/- 0.01 in control calves; 9.5 +/- 1.0 vs. 5.9 +/- 0.5 in controls, respectively). In the same way, 90 min after starting testosterone treatment, plasma GH levels increased from 0.21 +/- 0.08 to 1.30 +/- 0.40 while plasma IGF1 concentrations began to rise only 240 min after starting infusion (8.4 +/- 1.0) to reach maximal values at 300 min (10.7 +/- 1.1). Cortisol and clembuterol did not significantly modify either plasma GH levels or plasma IGF1 concentrations. Our results indicate that in young calves gonadal steroids exert their anabolic action through GH and IGF1.