Thyroid and gonadal function in hypophysectomized hagfish, Eptatretus stouti

Abstract

Use of a surgical hypophysectomy procedure which produces complete removal of the neuro- and adenohypophysis, and which permits survival of a large proportion of treated hagfish, has made possible an extensive study of the tropic relations of the hagfish pituitary gland. As long as 7 months after complete hypophysectomy, although some abnormalities were found in both testes and ovaries, gametogenesis still appeared to go to completion, indicating independence of the hagfish gonad from hypophysial gonadotropic control. There was similar lack of morphological evidence for thyrotropic control in these animals. Analysis of plasma levels of testosterone, estradiol and thyroxine also revealed no evidence of relation to presence of the pituitary gland. Subcutaneous multiple implants of pituitary glands did not affect plasma levels of the sex steroids, but were associated with a significant elevation of plasma T 4, suggesting a thyrotropic function of the implants. A negative correlation of plasma testosterone and body length in female hagfish was found, and implications of this finding are discussed. It was concluded that no clear evidence for hypophysial gonadotropic or thyrotropic function can be found in hypophysectomy experiments in hagfish. Evidence of thyrotropic activity by multiple subcutaneous transplants requires further study.