The acute effect of prolactin on bone 45Ca 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 in 45Ca 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.

The acute effect of prolactin on bone 45Ca 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 in 45Ca 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.

Abstract.In an attempt to evaluate the acute effect of PRL on bone turnover, experiments were performed in sexually mature female Wistar rats which were given an intraperitoneal (ip) administration of 1.25 mM CaC12 solution containing 6 ,uCi 45Ca. Dose response study showed a two fold higher rate of 45Ca uptake in 30 min by control trabecular bones (sternum and vertebrae 5-6) compared with control compact bones (femur and tibia). Femur exhibited a dose dependent increase in 45Ca uptake in response to pharmacological doses of 0.01 and 0.02 mg PRL/100 g body weight but was less responsive to 0.04 mg PRL / 100 g body weight. Tibia only responded with increased 45Ca uptake to 0.02 and 0.04 mg PRL / 100 g body weight while trabecular bones were unresponsive. By varying the intervals between administration of 45Ca (0 min) and PRL (0, 30 or 60 min) and bone harvesting (30, 60 or 90 min), it was found that 0.01 mg PRL/100 g body weight had a biphasic action on 45Ca movement. It initially enhanced 45Ca influx into femur by 30 min followed by an accelerated 45Ca efflux from femur back to the circulation.It could be concluded that PRL acutely stimulated calcium turnover in compact bone.