Age-related differences in testicular microcirculation.

Different aspects of testicular microcirculation were studied in rats aged 20, 24 or 90 days, in order to determine if maturational changes in the testis could influence its vasculature. Using laser Doppler flowmetry, it was found that vasomotion was not present in 20-day-old rats, but it could be induced by hCG-treatment given 32 h prior to flow measurements. In rats aged 24 days vasomotion was present in the testis but it was not influenced by hCG treatment, in contrast to adult rats in which testicular vasomotion disappeared after hCG treatment. In all age-groups, hCG treatment induced an increase in testicular interstitial fluid (IF) volume, which was most pronounced in young rats. In young rats, as in adults, there was an increase in the volume density of polymorphonuclear (PMN) leucocytes in testicular blood vessels after hCG treatment. However, rats aged 20 or 24 days did not exhibit any significant extravascular migration of leucocytes as occurred in adult rat testis after hCG injection. The deposition of colloidal carbon particles observed in adult rats after hCG-treatment was also not seen in young rats. It is concluded that the vasculature of the immature rat testis responds to hCG stimulation with an increase in IF volume. However, when compared to adult rats, different mechanisms may be operating because no evidence for opening of inter-endothelial cell gaps was observed in the testis of young rats.