Evidence that prolactin stimulates alpha-lactalbumin production in mannary tissues from premenarcheal rhesus monkeys.

PRL was found to stimulate marked increases in alpha-lactalbumin production in six of eight specimens of mammary tissue from premenarcheal rhesus monkeys, and a lesser increase was seen in a seventh. Even without added PRL, low concentrations of this milk protein (mean total alpha-lactalbumin production, 1.9 ng/dish) were released into the organ culture medium bathing these relatively immature tissues; most of the epithelial elements were ductal. Under similar conditions, significantly higher concentrations of alpha-lactalbumin (mean total production, 23.4 ng/dish) were released from tissues of sexually mature animals in which lobulo-alveolar elements were abundantly present in addition to ducts. When tissues from premenarcheal animals were exposed to ovine PRL, alpha-lactalbumin concentration in medium and tissue homogenates were increased significantly. Overall, mean total alpha-lactalbumin production rose to 12.9 (P less than 0.02) and 40.5 (P less than 0.02) ng/dish in response to 100 and 1000 ng/ml ovine PRL, respectively. In those cases in which both medium and tissue homogenates were analyzed, increases were parallel. These findings indicate that PRL has a lactogenic effect on mammary tissue from sexually immature and mature rhesus monkeys.