Effects of acute and long-term administration of prolactin on bone⁴⁵Ca uptake, calcium deposit, and calcium resorption in weaned, young, and mature rats

Abstract

The acute effect of prolactin on bone45Ca uptake and the long-term effect on calcium turnover in femur, tibia, sternum, and lumbar vertebrae 5 and 6 were evaluated in weaned, young, and mature female Wistar rats. A dose-dependent increase in45Ca uptake at 60 min after intraperitoneal administration of 0.01 and 0.02 mg prolactin/100 g body weight was seen in femur of mature rats and in femur, tibia, and vertebrae of weaned rats. In contrast, bones of young rats were less responsive and responded only to the higher dose of prolactin. Daily subcutaneous injection of 0.25 mg prolactin/100 g body weight for 2 weeks in weaned rats enhanced calcium deposit in femur while increasing calcium resorption in all four bones. Young rats responded to prolactin only by enhancing calcium deposit in femur, tibia, and sternum. Mature rats, on the other hand, responded by increasing calcium resorption from all four bones while enhancing calcium deposit in femur, tibia, and sternum. It could be concluded that effects of prolactin varied with bone type and age of animals. Prolactin, in general, enhanced calcium turnover in both compact and trabecular bones of mature rats. Young rats responded to prolactin by increasing the rate of calcium deposit, whereas weaned rats increased calcium release. Nevertheless, all three age groups exhibited a net gain in calcium after 2 weeks of prolactin administration.