Androgen Concentrations in Plasma and Testis of Developing Rats

SUMMARY Testosterone and androstenedione levels in plasma and testicular tissue of developing rats were measured using gas—liquid chromatography with electron capture detection. The major androgen of both the adult and early postnatal period of development was testosterone. Pooled plasma from 230 one-day-old male rats contained 0·027 μg. testosterone/100 ml. The concentration of testosterone in the testes at this age was 0·328 μg./g. wet tissue. With increasing age there was a decline in testosterone concentration in plasma as well as in gonadal tissue which lasted until about the age of 30 days. The period from 40 to 60 days was characterized by an increasing concentration of testosterone in the plasma and gonads. During adulthood, testosterone reached concentrations as high as 0·202 μg./100 ml. peripheral plasma. Androstenedione could not be detected in the circulation during the critical period of neonatal neural sexual differentiation, but it was present in the testes at this stage. In the pubertal and adult stages androstenedione was found in the plasma and testes. Its concentration, particularly in adulthood, was not as great as that of testosterone. These results indicate that testosterone is present in plasma and testicular tissue of the rat during the neonatal period when behavioural and physiological sexual differentiation is presumed to occur.