The movement of fluid in the seminiferous tubules and rete testis

rat has been studied. Differences in ionic, steroid and protein concentrations in the two fluids suggest that two different fluids are secreted, but from the numbers of sperm and the concentrations of inositol, it now seems more likely that all the fluid is secreted in the seminiferous tubules but that its composition is modified as it passes through the tubuli recti or when it reaches the rete testis. The permeability of the rete to potassium is appreciably higher than that to sodium ; the latter is comparable to the permeability of the tubules to both ions. The potential difference from blood is similar at the two sites (approx. 5 mV lumen negative). Movements of fluid along the tubules have been observed using small oil droplets. Fluid moves in either direction and at widely varying rates from time to time. The observed rate of fluid flow supports the suggestion that most of the fluid is formed in the tubules. Focal lesions produced in one seminiferous tubule « progress » along the tubule and blockage of the lumen also causes a progressive degeneration. From studies on rats with depleted numbers of germ cells, it appears that secretion by the Sertolicellscan continue in the absence of germ cells, but that the composition of the secretion may be affected. The tubular luminal fluid is thus an important possible vehicle for interactions between germ cells and somatic cells inside the tubules.