Effect of long-term thyroidectomy on post-prandial plasma calcium changes in man

Abstract

Five totally thyroidectomized (TX) individuals were compared to age-matched controls and to 20 normal adults, 20 to 30 years of age. All subjects, after an overnight fast, were given a morning meal containing 563 mg calcium and an equal amount of phosphorus. In separate tests some of the young adults were given a meal containing only 280 mg of each of the two elements. Most individuals were studied twice: on one occasion salmon calcitonin (0.1 MCR U/kg body weight) was injected 30 min after the meal; on the other visit only the vehicle was injected. In normal individuals plasma calcium values fluctuated only slightly during the 8 hour post-prandial study period, showing no consistent deviation. In contrast, in the TX population, plasma calcium concentrations changed in a sigmoid pattern. They fell for the first hour after consumption of the meal, then rose gradually to a value statistically higher than controls by the fourth hour. This was followed by a drop in plasma calcium values to levels lower than those in their normal counterparts. A single injection of calcitonin reversed this sigmoid pattern to one not statistically different from normal. It is concluded that the post-prandial presence of calcitonin (secreted or injected) minimizes fluctuations in both directions in plasma calcium concentrations in human subjects.