Failure to relate thyroid hormones and in vitro 5′-monodeiodination activity to oocyte development and sex steroids in the giant swamp frog Dicroglossus occipitalis at the equator

Abstract

Females of the giant swamp frog Dicroglossus occipitalis were captured in Zaïre close to the equator in the course of 1 month. During this period, females with fully developed eggs were found, together with females of which the eggs were still in the first developmental stages. A close relationship was established between the maturation of the eggs and the studied gonadal factors: the gonadosomatic index, the oviduct weight, plasma estradiol-17β (E 2) concentrations, plasma testosterone concentrations, and the total ovarian E 2 concentrations. At the level of the thyroidal axis, the studied factors (plasma thyroxine (T 4), plasma triiodothyronine (T 3), plasma T 3 T 4 ratio, T 4 and T 3 concentrations, and the T 3 T 4 ratio in the thyroids and the 5′-monodeiodination activity (5′-D-activity) in the skin and kidney homogenates) did not show parallel changes with the maturation process of the eggs. These results indicate that no causal relation has to exist between the annual variation in thyroid hormones and the annual reproductive patterns as found in frogs from the tropical or temperate climatic region.