1987 Volume 54 Issue 2 Pages 109-117
The effect of testosterone on plasma GH secretory profiles was examined in unrestrained adult female Wistar rats. Some of the rats were ovariectomized. One or 2mg testosterone propionate was injected sc daily for 21 days starting 3 weeks after the ovariectomy. The control rats received Sesame oil. Four to 5 days prior to use, all of the rats were provided with two indwelling cannulae, one in the right atrium for undisturbed blood collection and the other in the inferior vena cava for vehicle or synthetic human GH-releasing factor [1-44] NH2, (GRF) infusion. Vehicle or GRF was administered by infusion pump (0.6ml/h) at a dose of 50ng/kg BW/min for 6h. Serial blood specimens were obtained every 20 min.
In intact female rats, pulsatile GH secretion occurred irregularly at 1-2h intervals and GH values at the trough period fluctuated during a 6-h vehicle infusion. During a 6-h GRF infusion, a striking elevation of basal GH levels was observed and the number of pulsatile GH secretion increased. GH secretory profiles during a 6-h vehicle and GRF infusion in the ovariectomized rats did not differ from those observed in the intact female rats. A dramatic change in plasma GH secretory profile was observed in the ovariectomized rats that had received testosterone. In these rats, pulsatile GH secretion occurred regularly every 3-3.2h during a 6-h vehicle infusion and trough GH values were maintained at a low level with little fluctuations. Among ovariectomized rats that had received testosterone, the amplitude of pulsatile GH secretion was augmented significantly while GH secretion during the trough period was markedly inhibited. These effects of testosterone on GH secretory profiles were dose dependent.
The results suggest that testosterone increases the release of somatostatin, which mediates intermittent tonic inhibition on GH secretion, and thereby alters plasma GH secretory profiles in female rats.
