Isolation of pituitary proteins from Mexican axolotls (Ambystoma mexicanum COPE) by polyacrylamide gel electrophoresis. I. Assay for thyrotropic activity

Abstract

AbstractPituitaries from male, sexually mature neotenic axolotls were subjected to polyacrylamide gel electrophoresis (PAGE). Eight protein fractions were isolated from unstained gels. They were tested for thyrotropic activity in two different systems: 1) 131iodide uptake into the thyroids of hypophysectomized neotenic axolotls was followed over a 72‐hour period after pretreatment with the protein fractions (one pituitary‐equivalent per animal and day); 2) The thyroxine (T4)‐release in vitro from thyroid glands was measured by radioimmunoassay (RIA). PAGE fractions were added to the culture medium. Three fractions (A1, A2, and A4) were found to increase 131iodide uptake significantly. Specific release of T4 by axolotl thyroid glands was stimulated by only one fraction (B2), corresponding to the two fractions (A1 and A2) which caused the greatest 131I uptake. The T4‐release was dose‐dependent, and on a μg‐basis, axolotl‐TSH, (a‐TSH), B2, was approximately eight times more potent than the reference bovine TSH (b‐TSH), NIH‐TSH‐B8. It was shown the pituitary of neotenic axolotls contains proteins with high thyrotropic activity.