Abstract
The luteinizing hormone (LH) activity of pituitary glands from three orders of Reptilia was studied by means of the induction of ovulation in vitro from the ovaries of the frogs Hyla regilla and Xenopus laevis. Representatives from several families including both suborders of Chelonia (turtles) and several Crocodilia had relatively high concentrations of LH activity in the pituitary. In contrast, ovulation could not be induced with pituitaries from any of the Squamata (snakes and lizards) tested, although these glands had high levels of gonadotropins in other bioassays. Thus, there appears to be a major dichotomy between Squamata and other reptiles either in the levels at which LH is stored in the gland, in the structure of the LH molecule, or in whether LH exists. The lack of bioassayable LH in snakes and lizards distinguishes them from all other orders of tetrapods examined. Previous cytological studies of the reptilian pituitary indicated a regional distribution of LH-cells (luteotropes), but measurement of LH in different regions of the pars distalis from three families of turtles revealed a uniform distribution of this hormonal activity.
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