Maintenance of Normal Serum Calcium Level in the Hyperprolactinaemic Rat

Abstract

The effect of experimentally induced chronic hyperprolactinaemia in male rats on the serum levels of calcium has been examined. Chronic elevation of circulating prolactin levels had no significant effect on the serum calcium levels and normal blood calcium homeostasis was still maintained.There is evidence that prolactin is involved in calcium metabolism. In the rat, acute infusion of a low dose of prolactin results in hypercalcaemia and hypercalciuria [Mahajan, Robinson and Horrobin, 1974]. Prolactin administration to rats has also been reported to increase intestinal calcium absorption [James, Makeen, Foley, Stevens and Robinson, 1977]. The work of Spanos, Pike, Haussler, Colston, Evans, Goldner, McCain and Maclntyre, [1976] indicates that prolactin may modulate vitamin D metabolism in the chick. Furthermore, many of the metabolic effects of prolactin are similar to those of growth hormone which is known to play a role in calcium metabolism [McGarry and Beck, 1972].Although the studies of Mahajan et al. [1974] show that acute elevation of prolactin may influence the blood calcium levels, it has been shown that normal circulating levels of prolactin do not affect blood calcium homeostasis in the rat [Tan and Tan, 1978]. Physiologically, circulating prolactin levels become markedly elevated during pregnancy and lactation [Amenomori, Chen and Meites, 1970] and it has recently been suggested that prolactin may play a major role in producing the changes in vitamin D and calcium metabolism that occur during these states [Anon., 1977].In view of the possible important relationship between prolactin and calcium metabolism, we have undertaken an investigation of the long term effects of hyperprolactinaemia on blood calcium homeostasis in the rat. MethodsIn a preliminary study, chronic elevation of prolactin was induced in male rats by subcutaneous injection of perphenazine [Schering, Code 991571]