Lipids and lipid-transporting proteins in Chrysemys picta: role of gonadal steroids and growth hormone in intact and hypophysectomized turtles

Abstract

In the freshwater turtle, the homeostatic control of plasma lipids and lipid-transporting proteins may be coordinately regulated by ovarian steroids and pituitary hormones such as growth hormone (GH). In order to elucidate the role of these hormones in the regulation of vitellogenesis and ovarian growth, we have investigated lipid metabolic changes in normal male and female turtles, and in hypophysectomized females with and without GH injections, in response to combinations of exogenously administered gonadal steroids (estradiol (E2), progesterone (P), and testosterone (T)). Determinations of total plasma triglycerides, cholesterol, vitellogenin, and apoA-I were performed. We have demonstrated that E2 alone and in combination with P significantly increased plasma apoA-I and triglyceride levels in both intact female and male turtles. Testosterone administered alone to males had no effect on any of the parameters measured. In hypophysectomized females, plasma apoA-I, vitellogenin, and triglyceride levels were all significantly elevated in animals which received GH and E2, compared to controls (sham and hypox) and those which received GH alone.