Effects of prolactin suppression with cabergoline on the pregnancy of the bitch

Abstract

Twenty-one mated bitches were used, some of them repeatedly, to study the effect of an ergot alkaloid derivative, cabergoline (CAB), on ovarian endocrine function during early- to mid-luteal phase and late-luteal phase of gestation. In a blind trial, twelve bitches were bred three times; six of them received a daily dose of 5 mcg/kg body weight (BW) for 28 d, starting the day after the third breeding; the remaining six bitches received a placebo. In open trials, three bitches were given 15 mcg/kg CAB, and one bitch was given 5 mcg/kg daily for 5 d, around four wk of pregnancy (mid-luteal phase). Bight bitches were given 5 mcg/kg CAB once daily for 5 d, around 6 to 7 wk of pregnancy (late-luteal. phase). All dogs treated during the early- to mid-luteal phase maintained pregnancies. However, abortion resulted during or after CAB treatment during the late-luteal phase. Prolactin levels were determined in four bitches (late-luteal phase), and they showed a drop to baseline levels within 24 h after the first treatment with CAB. Progesterone blood levels always dropped in response to CAB treatment, but they reached baseline levels within 48 h only in bitches treated after mid pregnancy. These results indicate that CAB is not sufficiently luteolytic during the first half of pregnancy; however, it is fully luteolytic during the second half and can be used as an abortifacient during this period.