PRESENCE AND DISTRIBUTION OF GONADOTROPIN AND THYROTROPIN IN PARS DISTALIS OF LIZARD ANOLIS-CAROLINENSIS

Partial hypophysectomy and bioassay of pituitary extracts were used to study the presence and distribution of thyrotropin (TSH) and gonadotropin within the pars distalis of the adult male lizard (Anolis carolinensis). Removal of different regions of the pars distalis indicated that gonadotropin was produced throughout the gland, whereas TSH was produced primarily by the caudal region of the gland. Injections of extracts of either rostral or caudal halves of the pars distalis stimulated testicular growth and interstitial cell activity in hypophysectomized Anolis, and the concentration of gonadotropin appears to be approximately equal in the two regions. The existence of two separate gonadotropins in reptiles is questioned. Hypophysectomy produced a gradual decline in the rate of radioiodine uptake by the thyroid; 24-hr uptake values 11 days after hypophysectomy were only 20% of control values, and after 21 days they were only about 2% of controls. A reduced rate of urinary 131I excretion also occurred in hypophysectomized animals. Chromatographic analysis of hydrolyzed thyroid homogenates and plasma indicated a relatively high rate of T4 production and secretion by the thyroids of intact animals, suggesting that the reptilian thyroid is not as sluggish as previously described. Hypophysectomy significantly reduced the rate of thyroid hormone biosynthesis. Only the caudal half of the pars distalis appeared to have TSH activity as judged by the radioiodine uptake and labeling of T4 in hypophysectomized Anolis injected with pituitary extracts. Animals injected with caudal tissue also showed significantly more lean growth than the other hypophysectomized animals. These results are discussed in relation to histological studies of pituitary cell types. Previous identification of pituitary thyrotropes and gonadotropes appear incorrect and a tentative scheme for the functional identification of the 5 recognized cell types in the pars distalis is proposed in light of recent bioassays of the pituitary hormones in reptiles. © 1970.