Testosterone production and metabolic clearance rates in sexually mature male and female skate (Raja radiata).

Abstract

Testosterone production and metabolic clearance rates (MCR) were measured in skate to evaluate their role in maintaining the high testosterone levels found in the plasma of this fish. The results indicate that testosterone production rates in the skate are very low and that the high levels of plasma testosterone are primarily the result of a low metabolic clearance rate. Metabolic clearance rates were determined by the method of continuous infusion. The mean plasma MCR obtained for females (10.4 ±0.42 ml/kg/hr) was significantly higher thanthat of the males (7.93 ±0.57 ml/kg/hr). Plasma testosterone was determined using gas-liquid chromatography after prior purification by thinlayer and paper chromatography. Testosterone levels in plasma samples taken at 9:30 AM were significantly higher than in 5 :30 PM samples. At 9:30 AM, the mean plasma testosterone concentration in the males (5.8 ±1.1 μg/100 ml) did not differ significantly from that of the females (3.8 ±0.73 μg/100 ml). However, at 5:30 PM the values obtained for the sexes were significantly different (males 3.6 ±0.45 μg/100 ml, females 1.8 ±0.39 μg/100 ml). Testosterone production rates were determined as the product of the MCR and the plasma concentration of the steroid. No significant differences were observed between the production rates of the 2 sexes. The average testosterone production rates obtained were 0.38 ±0.07 μg/Kg/hr for the males and 0.33 ±0.05 μg/kg/hr for the females. (Endocrinology85: 552, 1969)