Mode of androgen action at male and female calf pituitary level

Abstract

The microcalorimetric method was used to study the specific reaction between 5α-dihydrotestosterone (5α-DHT), progesterone (P) and testosterone (T) with their receptors in the pituitary of male and female calves, at the age of 8–10 weeks. Experiments for measuring the binding affinity were performed at 37°C. Molar enthalpy changes for 5α-DHT are −92.11 ± 1.26 kJ/mol of 5α-DHT for female and −66.99 ± 0.58 kJ/mol of 5α-DHT for male calves, respectively. For P molar enthalpy changes are −56.94 ± 0.54 kJ/mol of P for female and −63.63 ± 0.54 kJ/mol of P for male calves. If we suppose that the molar enthalpy change or the liberated heat is a measure for the number of binding sites, then the ratio of molar enthalpy change for 5α-DHT: P is near 2:1 in females and 1:1 in males, at 37°C. T binding, either to female or male pituitary, is an endothermic process, molar enthalpy changes are +8.79 ± 0.46 kJ/mol of Tin females and +6.28 ± 0.86 kJ/mol of T in male pituitary. This finding raise the question of the possibility of spontaneous formation of T-receptor complex at calf pituitary level. At pituitary level in male rats, T is mainly converted to 5α-DHT and 5α-androstan-3α,17β-diol, under the influence of Six-reductase and 3α-hydroxysteroid dehydrogenase systems. In comparison, in male calf at pituitary level T is converted mainly to 4-ene-androsten-3,17-dione (574 α 36 pg/mg wt) under the influence of 17β-hydroxysteroid dehydrogenase and futher on to 5α-andostan-3,17-dione (159 ± 23 pg/mg wt). In female calf at pituitary level enzymic systems are more like the one at pituitary level in male rats: T is mainly converted to 5α-DHT (427 ± 51 pg/mg wt) and futher on to 5α-androstan-3α, 17β-diol (242 ± 26 pg/mg wet tissue).