Content of LH, FSH, and growth hormone in the pituitaries of pregnant and anestrous sheep.

The total content of LH, FSH, and growth hormone was measured in pituitaries from anestrous ewes and from ewes at known stages of pregnancy. LH content was lower in the pregnant ewes than in the anestrous group. Compared with the anestrous group, a significant drop in mean LH content was seen by days 40-50 of pregnancy (894 vs 350 mug, P less than 0.001), and it reached its lowest value by 120-135 days of pregnancy (43 mug, P less than 0.001). In sheep 148 days of pregnant, mean LH content was higher than in the latter group (155 mug). The correlation coefficient between the stage of gestation and the LH content was 0.63 (P less than 0.01). There was no significant change in mean FSH content in ewes up to 135 days pregnant (range 1196-1550 mug) compared with anestrous ewes (1023 mug). In the group 148 days pregnant (531 mug), a significant decrease was seen compared with ewes at other stages of pregnancy (P less than 0.05). Stage of gestation and FSH content were poorly correlated (r = 0.07). No significant differences in growth hormone content were seen in any of the groups. The results suggest that the progressive reduction in LH response to synthetic GnRH which has been reported for pregnant sheep may be due to selective inhibition of LH biosynthesis.