Some Observations on Calcium-induced Mitogenesis in Rapidly Dividing Tissues of the Rat

Abstract

Magnesium ions stimulate mitosis in rat lymphopoietic and hematopoietic tissue in males and females. This is achieved by a different mechanism than that by which calcium ions promote division, since although calcium is able to elicit full mitogenic potential in the male, this action is impeded in the intact female. Replacement of sex steroids in ovariectomised rats revealed that calcium injections enhanced mitosis if progesterone was given, but failed to be effective in the presence of oestrogen. This inhibitory action of oestrogen on the response to calcium injections is not a consequence of some interference with the calcium homeostatic hormones, since a similar regime of injections did not provoke mitosis in the thyroparathyroidectomised female. A direct action of oestrogen in preventing calcium influx to the cell is inferred, which is supported by in vitro observations. Even though oestrogen impedes calcium-induced mitogenesis in the female, the mitotic rhythm throughout the oestrous cycle, showing maximal activity at oestrus and minimal at pro-oestrus, correlated plasma total calcium concentration. These observations are discussed in the light of the slower proliferative responses that occur in those tissues. of the female Another rapidly renewing tissue, the mucosa of the small intestine, was studied to establish another tissue influenced by physiological fluctuations in extracellular calcium ion concentration in the male. However, cell renewal in this tissue was unaffected by such changes. Even though a derangement of calcium metabolism exists in diabetic tissue, no evidence was obtained to substantiate a role for calcium in the pathogenesis of intestinal hyperplasia of such animals. Nevertheless, polar metabolites of vitamin D3, which are intimately linked with the intestinal handling of calcium, enhance division in normal animals, and an abnormal metabolites of vitamin D3 could well account for the cellular changes observed in the diabetic intestine.