Studies of the human testis. XI. Leydig cell clusters and levels of intratesticular testosterone and 20 alpha-dihydroprogesterone.

Testosterone concentration in testes of 23 men, ages 51 to 90, was determined as 490 +/- 172 ng/g tissue (M +/- S.D.) and 20 alpha-dihydroprogesterone concentration as 10.0 +/- 2.3 ng/g tissue (M +/- S.D.) in 18 men of the same patient group. Leydig cells were estimated by the number of Leydig cell clusters per tubule. There was a high correlation (r = 0.88, p less than .001) of the Leydig cell index with intratesticular testosterone. It is proposed that the Leydig cell cluster index provides a direct index of steroid biosynthetic activity in the human testis as reflected in intratesticular testosterone levels. Although there was no significant correlation of 20 alpha-dihydroprogesterone levels in the testis with either the Leydig cell index or intratesticular testosterone, the high level of 20 alpha-dihydroprogesterone compared to peripheral levels suggests its production by the testis.