Porcine Blood and Hypophyseal Prolactin Values

SUMMARY Blood serum and hypophyseal prolactin determinations were made, using the double antibody radioimmunoassay, on 4 groups of pluriparous sows during various phases of reproduction and 1 group of virgin gilts (5 pigs per group). The groups of sows included sows at midgestation, sows at 112 days' gestation, and postpartum sows (2 groups). The effect of nursing on the quantities of prolactin in serum and hypophysis was demonstrated by sows designated as suckled and nonsuckled. The serum prolactin concentrations of postpartum nonsuckled sows had a significant decrease (115.3 ± 9.1 ng/ml) compared with those of postpartum suckled sows (167.1 ± 15.35 ng/ml). A lack of the nursing stimulus was related to the reduced quantity of circulating hormone. Significant differences in circulating prolactin were not seen among the virgin gilts (151.0 ± 8.2 ng/ml), the sows at midgestation (140.7 ± 8.8 ng/ml), and the sows at the 112th day of gestation (148.3 ± 7.7 ng/ml). Hypophyseal content of prolactin was closely related to the activity of the mammary gland. The hypophysis of prepuberal virgin gilts contained the largest amount of prolactin (122.7 ± 14.9 μg) of all groups of sows. The amount of hypophyseal prolactin decreased progressively as size and activity of the mammary gland increased. The hypophyseal prolactin content of sows at midgestation (78.5 ± 4.1 μg) was significantly different from that of sows at 112 days' gestation (64.8 ± 1.62 μg). Postpartum nonsuckled sows had lesser amounts of hormone in the hypophysis (55.8 ± 4.7 μg), and postpartum suckled sows had the least amounts (46.7 ± 3.5 μg). The stimulus of suckling produced measurable decrease in the content of prolactin in the hypophysis.