CALCIUM APPETITE OF PARATHYROIDECTOMIZED RATS USED TO BIOASSAY SUBSTANCES WHICH AFFECT BLOOD CALCIUM1

Abstract

31 parathyroidectomized rats kept on a low Ca diet but given access to Ca lactate soln. showed greatly increased Ca appetite. By increased Ca intake the rats survived and showed no tetany. Apparently they made an effort to maintain blood Ca at its normal level. In 5 parathyroidectomized rats increasing the Ca content of the food decreased the Ca appetite to approx. the normal. Parathyroid extract injected daily into 5 parathyroidectomized rats reduced the Ca appetite to normal level only when 100 U per day were administered, a dosage definitely toxic. Dihydrotachysterol (A-T-10) given to 8 parathyroidectomized rats, 0.035 mg. per day in food, reduced their Ca appetite to its normal level. Irradiated ergosterol and cholesterol and crystalline vits. D2 and D3, given to 4 groups of 4 or 5 parathyroidectomized rats each, in mimute amts.. 3000 to 8000 IU per kg. of body wt., sufficed to reduce the Ca lactate intake to its normal level. Cod liver oil given to 5 parathyroidectomized rats either in the food or by stomach tube could not be introduced in sufficiently large amts. to reduce the Ca appetite to its normal level. In terms of body wt. the effective doses of A-T-10 and of the vit. D preps. given to the rats were about the same as have been used for parathyroid-deficient patients. The doses of parathyroid extract were far greater. The A-T-10 and vit. D preps. may act directly on the Ca metabolism. The appetite method may be used for the bioassay of substances which affect Ca metabolism.