Suppressed release of LH in ovariectomized post-partum ewes

The patterns of LH release were studied in 5 ewes, ovariectomized when 3 days post partum, at 4, 14, 33, 47 and 61 days after ovariectomy. These patterns were compared with those in 4 seasonally anoestrous (control) ewes ovariectomized and sampled at the same times. In the control ewes regular pulsatile release of LH was apparent 4 days after ovariectomy: plasma LH concentrations and LH pulse frequencies, but not pulse amplitudes, then declined. In the post-partum ewes all indices of LH release were lower than those in the control ewes at 4 days after ovariectomy, but then they increased: pulse amplitude was greater (P less than 0.05) at 14 days after ovariectomy, and plasma LH concentrations were greater (P less than 0.05, 0.01) at 14 and 33 days than in control ewes. These results indicate that the hypothalamopituitary axis of lactating ewes has a reduced capacity to release LH for only a short period after ovariectomy early in the post-partum period. This probably reflects the time needed for recovery from the inhibitory effects of ovarian and placental hormones, and may reflect reduced secretion of LH-RH.