Changes in the regulation of calcium metabolism and bone calcium content during growth in the absence of endogenous prolactin and during hyperprolactinemia: A longitudinal study in male and female Wistar rats

Abstract

Since endogenous prolactin has been shown to enhance food consumption, calcium absorption, and bone calcium turnover in the pregnant rat, the role of endogenous prolactin in the regulation of calcium metabolism was investigated in 3-day balance studies of female Wistar rats from the age of 3 to 11 weeks. The study was divided into two parts. In part I, calcium metabolism in males and females was compared. In part II, 3-week old female rats were divided into 5 groups: (i) control animals receiving 0.9% NaCl; (ii) animals receiving 6 mg bromocriptine/kg/day (- PRLendo group); (iii) animals receiving 2.5 mg ovine prolactin/kg/day (+PRLexo); (iv) sham-operated animals receiving 0.9% NaCl, and (v) animals with two extra pituitaries implanted under the renal capsule, receiving 0.9% NaCl (AP group). Results showed that rapid growth occurred between 3 and 6 weeks with maximum fractional calcium absorption and calcium retention at 5 weeks of age in both sexes. The data also showed a physiological significance of endogenous prolactin in enhancing calcium absorption and retention in 5 week old rats. In an absence of prolactin, peak calcium absorption was delayed in 7-week old animals, and vertebral calcium content of 11-week old animals was reduced by 18%. Hyperprolactinemia in the AP group was found to enhance fractional calcium absorption and calcium retention at 7, 9, and 11 weeks and increased the femoral calcium content by 16%. It could be concluded that a physiological role of prolactin is the stimulation of calcium absorption and maintainance of bone calcium content during growth and development.

Two-step stimulation of intestinal Ca2+absorption during lactation by long-term prolactin exposure and suckling-induced prolactin surge

“…Visual examination of the well-vascularized hypophyseal graft and immunohistochemical staining for PRL production were performed at the end of the experiments to confirm successful AP transplantation (10). At 4 wk after transplantation, plasma PRL levels are known to increase to 90 -100 ng/ml (28). Surgery and tissue collection.…”

High Physiological Prolactin Induced by Pituitary Transplantation Decreases BMD and BMC in the Femoral Metaphysis, but Not in the Diaphysis of Adult Female Rats

“…Besides the estrogen-dependent action, the effect of PRL on bone was also dependent on the circulating levels of PRL and duration of exposure [6,16]. We previously showed that the basal levels of PRL of ~7-10 ng/ml were necessary for the maintenance of the normal rate of bone turnover in nonmated adult female rats [6].…”

“…1). This technique has also been known to raise plasma PRL to 90-100 ng/ml (comparable to the levels during pregnancy) [16] and to suppress plasma estrogen below 50 pg/ml [17].…”

“…Within 15 days after two extra AP glands were transplanted from donors under the renal capsule of a recipient (i.e., distant from the hypothalamus), a continuous secretion of PRL from the AP allografts in the absence of the hypothalamic dopaminergic inhibition resulted in a sustained physiological hyperprolactinemia [16,18]. Other pituitary hormones were not secreted from the grafts because of the absence of their respective hypothalamic trophic factors.…”

“…In the present study, the anterior pituitary (AP) transplantation technique was used to induce the sustained high physiological PRL levels of 90-100 ng/ml [15][16][17], which were comparable to the levels during pregnancy in humans and rats [1]. Within 15 days after two extra AP glands were transplanted from donors under the renal capsule of a recipient (i.e., distant from the hypothalamus), a continuous secretion of PRL from the AP allografts in the absence of the hypothalamic dopaminergic inhibition resulted in a sustained physiological hyperprolactinemia [16,18].…”