Suppressed release of LH in ovariectomized post-partum ewes

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Abstract
The patterns of LH [luteinizing hormone] 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 anestrous (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 < 0.05) at 14 days after ovariectomy, and plasma LH concentrations were greater (P < 0.05, 0.01) at 14 and 33 days, respectively, than in control ewes. The hypothalamo-pituitary 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 LHRH.

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