Calorimetric approach to the study of 5α-dihydrotestosterone and estradiol receptors in rat hypothalamus cytosol

Abstract

The hypothalamus and pituitary are the sites through which androgen and estrogen hormones perform the feedback control of gonadotropic mechanism. The microcalorimetric method was used to study the specific reaction between 5α-dihydrosterone (5α-DHT) and Estradiol (E 2) and their receptors in the hypothalamus of male and female rats at the age of 28 d. In order to compare binding affinity, experiments were performed at 4° and 37°C. Molar enthalpy changes for E 2 at 37°C are −43.96 ± 0.453 kcal/mol for female and −25.04 ± 0.222 kcal/mol for male rats, respectively. At 4°C molar enthalpy changes are approximately 50% higher for female and 25% higher for male rats. For 5α-DHT molar enthalpy changes at 37°C are −26.67 ± 1.221 kcal/mol for female and −18.60 ± 0.512 kcal/mol for male rats. At 4°C increase for female rats is over 60% and for male rats 40%. The effect of sex difference is much better expressed for E 2 than for 5α-DHT. Possible binding of E 2 and 5α-DHT to hypothalamus receptors in the female and male rats could be in some connection with the mechanism in regulation of gonadotropic feedback system. Ratios of molar enthalpy changes for E 2: 5α-DHT are 2:1 in females and 1:1 in males, at 4°C. Difference between these ratios could be an answer for the physiological sex difference.