TERMINATION OF OBLIGATE ANESTRUS AND INDUCTION OF FERTILE OVARIAN CYCLES IN DOGS BY ADMINISTRATION OF PURIFIED PIG LH

The potential role of LH in the initiation of the follicular phase in dogs was investigated by treating anoestrous bitches with highly purif ied pig LH (n = 16) or saline (n = 8) three times a day for 7 days, be ginning in either early anoestrus (days 94-116 of the cycle) or mid-an oestrus (days 124-145). Treatment with LH induced pro-oestrus within 7 days (n = 16), and oestrus (n = 12) and fertile ovulations (n = 7) at 16 + 3 days, while pro-oestrus in bitches treated with saline did not occur until 46-166 days after the start of treatment. Six of the seve n ovulating bitches whelped normal litters. The bitches in which pro-o estrus but not oestrus occurred were all treated in early anoestrus. D uring treatment, plasma oestradiol in bitches treated with LH increase d from 8 + 2 pg ml(-1) to 20 + 5 pg ml(-1) within 1 day, and reached h igher peak values (45 + 7 pg ml(-1)) (P < 0.05) than those observed in saline-treated controls (9 + 3 ng ml(-1). These results demonstrate t hat LH treatment alone can terminate anoestrus by inducing a normal fo llicular phase ir dogs. The results also suggest that, in normal cycli c bitches, anoestrus is the result of insufficient LH secretion, and t hat spontaneous pro-oestrus could be the result of increased LH secret ion in the presence of already adequate concentrations of FSH.