A Comparative Study of TSH and FSH Secretion in Rat and Guinea Pig: Effects of Gonadectomy and Goitrogens

Abstract

A comparative cytophysiologic study of the adenohypophysis revealed significant similarities and differences in the dynamics of TSH [thyroid-stimulating hormone] and FSH [follicbe-stimulating hormone] secretion in rat and guinea pig. TSH levels in serum and pituitary and thyroid activity were reduced in gonadectomized rats (both sexes). No significant change in pituitary-thyroid function developed in guinea pigs up to 1 yr. after ovariectomy. Pituitary TSH content declined gradually in normal, aging female rats. This relationship was not observed in the guinea pig. Bio-assay data indicated marked quantitative differences in pituitary hormone potency of these rodents. TSH and FSH content of adenohypophyses in rats were 15-30 and 3 times greater, respectively, than in guinea pigs. Chronic propylthiouracil (PTU) treatment of the latter elevated TSH levels in blood and hypophysis 600-800%. The rise was paralleled by an increase in size and numbers of glycoprotein-granulated, polyhedral-shaped basophils similar to the "thyro-trophs" of the rat pituitary. A similar relationship between basophil cell response and FSH secretion could not be demonstrated. Pituitary potency of FSH in guinea pigs oophorectomized for 1 yr. increased 3-fold but remained only a small fraction of that in ovariectomized rats. Cytologic changes in pituitary basophils of gonadectomized guinea pigs were moderate in degree, long delayed and qualitatively similar to those seen in thyroid-deficient states. Castration did not influence TSH hypersecretion and goitrogenesis in the chronically hypothyroid guinea pig. The results do not justify separation of the pituitary basophils in this species into separate TSH- and FSH-secreting categories as has been done for the rat.