Thyrocalcitonin and Age

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Abstract
The effect of increasing age in rats on the recovery from CaCl2-induced hypercalcemia, the hypocalcemic response to thyrocalcitonin (TC) released by cautery, and the response to increasing exogenous doses of TC were examined. The recovery from hypercalcemia was markedly retarded with advancing age. The maximum hypocalcemic response after cautery and after sc TC was largest, 3–5 mg/100 ml, in 38–39-day-old rats, smaller, 1.5–2.0 mg/100 ml, in 97–115-day-old rats, and smallest, about 1 mg/100 ml, in discarded breeders about 1 yr old. While the maximum response in discarded breeders could be increased from 1 to 1.5 mg/100 ml by repeated administration of TC, the maximum fall in serum calcium was still smaller than in younger rats. It is concluded that the delayed recovery from hypercalcemia and the smaller response to TC in old rats is due to a reduced rate of bone metabolism with advancing age. Evidence is also presented showing that in response to hypercalcemia TC is released in large amounts from the thyroid gland and that the presence of the thyroid gland restricted the hypercalcemia induced by parathyroid hormone in older as well as in young rats. Despite the lower hypocalcemic response to exogenous TC associated with advancing age, TC has the ability to protect against hypercalcemia in old rats and this may be its important physiological function at all age levels. (Endocrinology93: 1206, 1973)

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