LH release, induction of oestrus and fertile ovulations in response to pulsatile administration of GnRH to anoestrous dogs.

In one study in 33 bitches, in which each of seven doses of GnRH were injected into six anoestrous bitches each, doses of > or = 400 ng kg-1 released LH consistently, and doses of < or = 200 ng kg-1 did not. In a second study, GnRH was administered in pulses of 15-500 ng kg-1 every 90 min for 7-9 days to 36 anoestrous bitches, four prepubertal bitches and three luteal phase bitches. In 36 anoestrous bitches, GnRH pulses resulted in pro-oestrus, oestrus, ovulation and pregnancy in 26, 20, 16 and 12 bitches, respectively. Mean time for pro-oestrus onset, oestrus, ovulatory LH surge and parturition were 5.1 +/- 0.4, 11.2 +/- 0.7, 14.0 +/- 9.0, and 77.3 +/- 1.0 days, respectively, from start of treatment. In response to GnRH, pro-oestrus and pregnancy occurred in two of four prepubertal bitches, and pro-oestrus but not ovulation occurred in one of three luteal phase bitches. Efficacy in anoestrous bitches was dose dependent with high doses of > 280 ng kg-1 (n = 12) versus intermediate 85-270 ng kg-1 (n = 12) and low < 85 ng kg-1 doses (n = 12) resulting in a higher incidence of pro-oestrus (100 versus 80 and 33%), oestrus (92 versus 50 and 25%), ovulation (84 versus 42 and 8%) and pregnancy (58 versus 33 and 8%). With few exceptions, failed or weak responses were related to inadequate LH release, as measured in frequently collected samples following successive pulses on selected days of treatment; vaginal cornification, oestrous behaviour, and LH response were similar in oestrus without ovulation and fertile oestrus except for the lack of an ovulatory LH surge.