Development of the blood-testis barrier and changes in vascular permeability at puberty in rats.

The effectiveness of the blood-testis barrier to water-soluble substances was assessed in rats of various ages by measuring the volumes of distribution of Cr-EDTA and albumin, and estimating the proportion of the testis made up by interstitial tissue and tubular lumen by morphometric techniques on cryostat sections of frozen tissue. The interstitial tissue volume fell from 15 days to reach adult values at about 30 days of age. A lumen was present in some animals at 15 days, and it enlarged progressively to reach adult levels at about 45 days of age. The 1-h Cr-EDTA space began to fall after 25 days, and reached adult values by 33 days; in rats aged 25 and 30 days, the Cr-EDTA space was almost twice the measured interstitial tissue volume, but even in the older rats, the Cr-EDTA space remained appreciably greater than the interstitial tissue volume. The 20-h albumin space did not begin to fall until after 33 days, and had still not reached adult values in rats aged 44 days. Thus, the functional barrier to water-soluble markers develops later and more gradually than the barrier to electron-opaque markers as used by previous authors, and its appearance correlates more closely with enlargement of the tubular lumen than with formation of the inter-Sertoli cell junctions. The rate at which the albumin space approached its final value was used to calculate the vascular permeability to albumin. This rose to a maximum between 25 days and 33 days of age, and then fell again, although adult values had still not been reached by 44 days of age.