Effects of prolactin inhibition during late gestation on the immunity of gilts and foetuses

The goal of the present study was to determine the effects of inhibiting prolactin (PRL) synthesis for three consecutive 20-d periods during the second half of gestation, on the immune status of gilts and their foetuses. Crossbred gilts were randomly assigned as controls (n = 12) or received 10 mg of bromocriptine orally three times daily from days 50 to 69 (BR50, n = 12), days 70 to 89 (BR70, n = 12), or days 90 to 109 (BR90, n = 12) of gestation. All gilts were injected subcutaneously with ovalbumin (OVA) on days 53 and 72 of gestation. Blood samples were collected on days 50, 60, 70, 90 and 109 of gestation to evaluate the antibody response. Cellular immunity, as measured by lymphocyte proliferative response and production of interferon-gamma, was characterized on controls and BR50 gilts until the end of gestation. Six foetuses from five litters per treatment were selected and their thymus and spleen were excised and weighed. Splenocytes and thymocytes were assayed to characterize lymphocyte sub-populations and to evaluate splenocyte responses to mitogenic stimulation. Average spleen weight in foetuses from BR90 gilts was significantly lower (P < 0.05) than that of foetuses from control or BR70 gilts. In all gilts treated with bromocriptine, percentages of CD4(+) and CD8(+) lymphocyte populations in foetus spleens were numerically reduced compared with those obtained in foetus from control gilts but the differences were not significant. In BR50 gilts, inhibition of PRL synthesis did not affect the proliferative response of lymphocytes to mitogenic stimulations compared with control group, but tended (P = 0.13) to increase the production of interferon-gamma. A time effect showed that production of interferon-gamma by leukocytes was reduced (P < 0.02) on days 80 and 100 compared with days 50 and 70, regardless of bromocriptine treatment. The antibody response of gilts to OVA was not affected by bromocriptine treatments. In conclusion, inhibition of PRL synthesis by bromocriptine did not significantly affect immune response of pregnant gilts. In foetuses, although the differences between treatments were not significant, data suggest that the foetal development of immune tissues seems to be impaired by bromocriptine treatment.