Metabolic effects of calcitonin in the newborn.

Calcitonin was injected in newborn rats and newborn lambs to study the metabolic effects of the hormone. Subcutaneous injection of salmon calcitonin (140 MRC U/kg) induced a clearing effect on plasma from suckling newborn rats that was naturally lactescent. A lower dose given by the same route (14 MRC U/kg) strongly decreased plasma triglyceride and amino acid levels in suckling newborn rats. This was mainly the result of gastric emptying inhibition. The gastrointestinal action of calcitonin in suckling newborn rats was substantiated by the absorption of [14C]triolein and 14C-labeled amino acids. Hormonal changes that were associated were a decrease in plasma insulin level and an increase in plasma growth hormone concentration. Intravenous calcitonin at a physiological dose (0.03 MRC U/kg) injected into newborn lambs inhibited increases in total plasma lipids, amino acids, and blood-glucose levels at the time of the first suckling period without changing serum calcium levels. One of the physiological roles of calcitonin in the newborn may be the regulation of nutrient absorption from milk rich in lipids.