Testosterone and Androstenedione Concentrations in Human Testis and Epididymis during the First Two Years of Life*

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Abstract
Testosterone and androstenedione were measured in testicular and epididymal tissue of 37 previously healthy infants between 1 and 24 mo. of age who died suddenly. In 1/2 of the patients elevated plasma levels of cortisol and androstenedione suggested preterminal stress. Plasma testosterone levels, however, did not differ from those in healthy infants. Testicular testosterone concentrations were maximal in boys from 1-3 mo. of age (median, 36.6 ng/g; range, 7-380 ng/g) with peak values similar to those found in pubertal or even adult testes. Testicular testosterone concentrations decreased and after the age of 6 mo. all values were below 12.5 ng/g, which corresponds to the low normal range of older prepubertal boys. Plasma testosterone and testicular testosterone correlated significantly (P < 0.001). On average the testicular concentrations were 36.4 times higher than the corresponding plasma concentrations. Testicular androstenedione was low but correlated significantly with testicular testosterone (P < 0.001). Epididymal testosterone concentrations were surprisingly high (1-3 mo.: median, 10.3 ng/g; range, 4-42.7 ng/g) and averaged 30% of the testicular testosterone concentration. Epididymal testosterone concentrations were significantly higher than the circulating plasma testosterone levels, indicating the capacity of the infant epididymis to accumulate androgens. Apparently high local testosterone concentrations during early infancy are important not only for the testis itself but particularly for the developing epididymis.