Abstract
Summary
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 revealed 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 hypernatremia nor hyperphospha-temia directly altered TCT secretion.
The findings are in accord with previous suggestions that although cations other than calcium are capable of increasing TCT secretion, probably only calcium plays an important role in the physiological regulation of TCT secretion. Nevertheless, other effective agents, such as those reported here, may constitute useful pharmacological tools for studying the mechanisms involved in secretion of TCT.
The author thanks Drs. Paul L. Munson, Philip F. Hirsch, and Tai-Chan Peng for advice in the course of the experiments and preparation of the manuscript. The fine technical assistance of Mr. Johnny F. Obie, Mr. Sanford C. Garner, Mrs. Debris B. Alston, and Mr. John R. Hagaman, Jr. also is appreciated. The pure porcine TCT used in this study was donated by Armour Pharmaceutical Co. through the courtesy of Dr. Robert Schlueter.
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