Induction of plasma LH surges and normal luteal function in acyclic post-partum ewes by the pulsatile administration of LH-RH.

Plasma LH surges, similar to preovulatory surges in cyclic ewes (N = 9), were induced in 11/15 acyclic ewes, 19-26 days post partum, treated with LH-RH (100 ng i.v. every 3 h for 24 h, every 2 h for 24 h, then every 1 h for 24 h) (Group PPrh ), and in 11/15 LH-RH-treated acyclic ewes pretreated with progesterone (s.c. implant for 11 days) (Group PPprh ). Plasma progesterone, indicating subsequent luteal function, was detected in 10/11 Group PPrh ewes and in 9/11 Group PPprh ewes. The mean and peak plasma progesterone concentrations in these ewes were similar to those in cyclic ewes (2.0 +/- 0.2 and 3.1 +/- 0.4 ng/ml). The periods over which plasma progesterone was detected were similar in cyclic (11.7 +/- 0.5 days) and in Group PPprh ewes (12.2 +/- 0.8 days), but less in Group PPrh ewes (9.6 +/- 0.4 days). After regression of the induced corpus luteum more Group PPprh ewes (6/9) than Group PPrh ewes (2/10) showed oestrus and continued cycling. These results show that an appropriate pattern of pulsatile LH-RH treatment of post-partum acyclic ewes, pretreated with progesterone, can lead to plasma LH surges, luteal function, and subsequent ovarian cyclicity similar to that found in cyclic ewes. This suggests that ovarian acyclicity in post-partum ewes is a reflection of an inadequate pattern of pulsatile release of LH-RH from the hypothalamus.