Effect of bromocriptine administration on maintenance of late pregnancy in the pig

Plasma concentrations of prolactin, luteinizing hormone (LH) and progesterone were determined in pregnant gilts (n = 6) administered bromocriptine from 67-72 days of pregnancy. Blood samples were taken daily at 2 h intervals from 60 to 80 days of pregnancy. Bromocriptine treatment reduced prolactin from 9.7 +/- 1.4 before to 1.9 +/- 0.6 ng/ml during the treatment (p less than or equal to 0.05) and then returned to the pre-treatment concentrations (10.5 +/- 2.0) following cessation of bromocriptine. Bromocriptine increased LH from 1.4 +/- 0.2 before treatment to 2.9 +/- 0.5 ng/ml (p less than or equal to 0.01) during administration and maintained elevated (3.0 +/- 0.7) in the post-treatment period (p less than or equal to 0.05). Administration of bromocriptine did not alter progesterone concentration in plasma (7.5 +/- 1.2; 7.2 +/- 1.6 and 6.6 +/- 1.6 ng/ml in pretreatment, treatment and post-treatment periods, respectively). This study shows that decrease of prolactin level by bromocriptine treatment does not cause depletion of progesterone secretion in late pregnant pigs.