Ultrastructural changes in the adenohypophysis during the ovarian cycle of the viviparous teleost Poecilia latipinna. II. The thyrotrophic cells and the thyroid gland.

Electron microscopical observations were made on the thyrotrophic (TSH) cells during the monthly cycle of oocyte development and pregnancy in female sailfin mollies. Parallel light microscopic studies were made on the thyroid gland. By morphological criteria, TSH secretion and thyroid activity run in parallel, and the findings indicate that TSH secretion and thyroid hormone output are higher during vitellogenic oocyte growth than during earlier oocyte development and during pregnancy. Measurements of TSH cell area and nuclear area and of thyroid epithelial cell height confirm this pattern. The results are discussed in the light of what is known of thyroid hormone involvement in teleostean ovarian physiology.