Fertile estrus induced in bitches by bromocryptine, a dopamine agonist: A clinical trial

The dopamine agonist bromocryptine, probably through amplifying gonadotroph (mainly FSH) secretion, was found to be suitable for provoking fertile est rus during the anestrous phase in bitches without functional cycles and/or ovarian activity. We studied estrus induction in 48 bitches after treatment with semisynthetic ergot alkaloid bromocryptine. For habituation a fractio nal dose of 0.3 mg/bitch was administered for three days followed by larger doses within the range of 0.6 to 2.5 mg/bitch by selecting dose rates on t he basis of individual responsiveness and body weight. The long-term daily bromocryptine dose did not exceed 0.6 mg/bitch and 2.5 mg/bitch in small an d large sized bitches, respectively. Gradual habituation and individual dos e rates have almost completely eliminated the unwanted side effect of emesi s. The period between treatment and onset of estrus varied but the average was 19 days. After the onset of estrus bromocryptine administration was usu ally continued for another 3 to 6 days. Occurrences of estrus, ovulation an d pregnancy were monitored by cytological evaluation of vaginal epithelium, rapid ELISA for plasma progesterone and ultrasonography, respectively. Sam ples for progesterone were taken on Days 7, 9, 12 and 15 and sonograms of o varian follicles and of fetuses were taken on Days 0, 22 and 35. The bitche s involved in the study either regular or irregular cycles. Bromocryptine t reatment induced estrus in all of the bitches including 40 of 48 (83%) with ovulation within a regular estrus and 6 of 48(12.5%) that showed estrus bu t did not ovulate. Mating or artificial insemination of bitches in their fe rtile periods twice at two day intervals resulted in an 83% pregnancy rate (40 cases) and 39 (97.5%) of them gave birth to puppies. However, the avera ge litter size was small with 4.8 +/- 1.6 pups. (C) 2001 by Elsevier Scienc a Inc.