Ability of several cations to promote secretion of thyrocalcitonin in the pig-1-2 (38559).

Various ions were tested to see whether or not at pharmacological plasma levels they affected TCT secretion from the pig thyroid gland in vivo. Test solutions were infused either systemically (femoral vein) or directly into the thyroid artery for brief (10-12 min) periods. Infusions of large doses of magnesium, potassium, strontium and barium, as well as calcium, produced increases in TCT in thyroid venous plasma ranging from two- to tenfold. Blood analyses reveled that levels of these stimulatory cations produced in plasma during the infusions indeed were high. In contrast, infusions of sodium and phosphate suggested that neither hypernatermia nor hyperhosphatemia directly altered TCT secretion. The findings are in accord with previous suggstions that although cations other than calcium are capable of increasing TCT secretion, probably only calcium plays an important role in the physical regulation of TCT secretion. Neverthless, other effective agents, such as those reported here, may consitute useful pharmacological tools for studying the mechanisms involved in secretion of TCT.