High-affinity binding of progesterone, testosterone and cortisol in normal and androgen-treated guinea pigs during various reproductive stages: relationship to masculinization.

TLDR: Sera from normal and androgen-treated female guinea pigs obtained during the estrous cycle, pregnancy and puerperium were analyzed for binding affinity toward progesterone, testosterone and cortisol by multiple equilibrium dialysis using radiolabeled steroids.

Abstract: Sera from normal and androgen-treated female guinea pigs were obtained during the estrous cycle, pregnancy and puerperium. They were analyzed for binding affinity toward progesterone, testosterone and cortisol by multiple equilibrium dialysis using radiolabeled steroids. Cortisol levels were also determined. A marked increase in binding activity for all 3 steroids, especially progesterone and testosterone, was found during pregnancy; the cortisol concentration rose concomitantly. By the end of the puerperium all parameters measured had returned toward estrous cycle levels. Testosterone treatment of the cycling females greatly lowered the cortisol-binding activity of the serum as well as the peripheral cortisol values, and resulted in a slight decrease of the binding activity for testosterone. Sera from pregnant guinea pigs receiving testosterone had lower peripheral cortisol levels than the pregnant controls; the binding activity toward progesterone and testosterone was generally greater than in the untre...