The secretory patterns of growth hormone in pregnant and hysterectomized ewes

This work was undertaken to determine the secretory patterns of GH during pregnancy, and to evaluate the effect, if any, of hysterectomy during early pregnancy on subsequent secretion of GH in ewes. The concentrations of GH were determined in the plasma of jugular blood samples collected at 15-min intervals during a 6-h period on days 20, 40, 60, 80, 100 and 120 post-mating, and three times per week between days 29 and 120 post-mating from 5 pregnant ewes and from 5 ewes from which the gravid uterus was removed on day 30 post-mating. A pulse analysis program (Pulsar) was used to analyse the secretory patterns of GH in individual profiles of the serial sampling period. In the two groups of ewes, peripheral concentrations of GH fluctuated in an episodic manner during the frequent blood sampling of any stage of the post-mating period examined. The overall GH concentrations, the basal GH concentrations, the frequency and the amplitude of GH pulses remained fairly stable between days 20 and 120 post-mating in the two groups of ewes. The parameters of GH secretion were not different between the two groups of ewes. The secretory patterns of GH, as determined in plasma of blood collected three times per week between days 29 and 120 post-mating were also not different between the two groups of ewes. In conclusion, results of this study show that (i) the pulsatile secretion of GH does not change as pregnancy advances, and (ii) hysterectomy performed during early pregnancy does not subsequently affect the secretory patterns of GH. These findings suggest that the gravid uterus and/or the feto-placental unit secretory products are unlikely to be involved in the control of GH secretion during pregnancy in the ewe.