Hormonal and radiation effects on osteoclastic proliferation

Abstract

The past century of research on bone physiology has established that the osteoclast is involved in the resorption of bone. The presence of parathyroid hormone in the circulating body fluids causes the calcium concentration in these fluids to increase and there is an accompanying increase in osteoclastic activity in the bone tissue. The metabolic processes, which result in crystal removal from bone, are mediated by parathyroid activity and are necessary for maintenance of specific calcium levels in all land-dwelling vertebrates. This study shows various hormonal and radiation effects on osteoclastic proliferation and the relationship between the activity of these cells and the maintenance of calcium concentrations in the rat. The proliferation of the osteoclasts was produced by the technique of continuous peritoneal lavage and/or nephrectomy. The experimental work consisted of: (1) altering the circulating calcium concentration by acidosis, peritoneal administration of NeF, or supplying exogenous calcium; (2) studying the effects of hypophysectomy, adrenalectomy or estrogen administration to male rats; and (3) producing changes in bone by internal radiation with Ca45 or Pu239. The results show that although wide variations are found ia the osteoclast numbers produced by the various experimental conditions, the calcium levels are uniformly maintained. This would indicate either a constantly changing level of parathyroid activity, a change in activity of the osteoclasts present, or that the calcium concentration in the body fluids can be maintained without the necessity of osteoclastic proliferation.