Latency and duration of the effects of bromocriptine and prolactin on milk secretion in lactating rabbits

Milk yields were measured at 8h intervals in rabbits during early (days 11-14) and late (days 31-34) lactation. A single injection of 1 mg bromocriptine given to rabbits 30 min before sucking on days 11 or 31 caused a significant reduction in milk yield after approximately 8h. The depressant effect of the drug was then maintained over the next 24-36h. Recover of milk yield occurred in bromocriptine-treated rabbits during both early and late lactations 8-16h after a single injection of 3 mg prolactin. The recovery accelerated more in the rabbits in the early lactating group. Attainment of the maximal stimulatory effect occurred by 24h after prolactin injection during both early and late lactation although the improvement in milk yield lasted for a shorter period (8h compared with 24h) during late lactation compared with early lactation. These differences in response of the rabbit to prolactin during late lactation may contribute substantially to the declining milk yields characteristic of late lactation in this species.