An in vivo model for testing somatostatin suppression of growth hormone release in sheep

To investigate the suppressive effect of somatostatin on growth hormone secretion, a consistent, potent stimulus to growth hormone release is required. The antilipolytic compound 3,5-dimethylpyrazole (DMP) gave a rapid rise in plasma immunoreactive growth hormone following iv administration to fasting sheep. The dose response relationship for iv DMP was defined in 12 sheep, and a rise in growth hormone levels from a baseline of 2.1 +/- 0.4 ng/ml (mean +/- SE) to 38.9 +/- 3.9 ng/ml was achieved in 40 min with 0.1 mg/kg bw of DMP given as a bolus. Infusion of graded doses of somatostatin (50, 100 and 200 micrograms) in 4 sheep over a 90 min period resulted in a dose-dependent suppression of the DMP-provoked growth hormone secretion below the responses observed during saline infusion. This experimental model should facilitate further studies of the inhibitory effects of somatostatin, its analogues and other drugs which suppress growth hormone secretion.