Effect of bromocriptine administration during mid-pregnancy on the ovary function in the pig

Plasma concentrations of prolactin, luteinizing hormone (LH), progesterone, estradiol-17 beta and androgens testosterone with dihydrotestosterone were determined in pregnant gilts (n = 6) administered bromocriptine (BR) from 37-42 days of pregnancy. Blood samples were daily taken at 2h-intervals from day 34 to 45 of pregnancy. BR treatment reduced (p less than 0.001) prolactin secretion from 14.8 +/- 0.9 ng/ml to 8.6 +/- 1.1 and 5.5 +/- 0.7 during the initial 1-3 and 4-6 days of treatment, respectively. Following cessation of BR treatment prolactin returned to the pre-treatment concentrations (14.5 +/- 1.0). BR did not alter LH during the first 3 days of treatment but decreased LH on days 4-6 (1.5 +/- 0.1 vs 2.1 +/- 0.2, p less than 0.05). Bromocriptine evoked a 20% increase (p less than 0.05) in estradiol-17 beta during days 1-3 following onset of treatment, however it suppressed androgen concentrations from 10.7 +/- 1.2 to 5.6 +/- 0.4 pg/ml in the same period. Suppression of prolactin from day 37-42 with a concurrent decrease of LH from day 40-42 of gestation did not affect maintenance of pregnancy and surprisingly was associated with a temporary elevation of progesterone. We conclude that prolactin has no luteotrophic properties during midpregnancy in gilts.