Fluid and electrolyte reabsorption in the ductuli efferentes testis.

The efferent ducts of mammals are a series of ducts that are arranged in parallel and reabsorb most of the fluid released with spermatozoa from the testis. This function is essential for spermatogenesis, and for sperm maturation and storage in the epididymis. There is evidence for the involvement of three major transport processes in the bulk reabsorption of water and low molecular weight solutes from the ducts: active solute transport, passive (presumably paracellular) diffusion and fluid phase endocytosis. A small back-flux into the ducts via anion secretion also appears to occur. Control of fluid reabsorption by the efferent ducts is emerging as a complex process with multiple components. Reabsorption is flow dependent which provides local control of reabsorption with a rapid response to changes in luminal conditions. Sex steroids (oestrogen as well as androgen), but not mineralocorticosteroids, are involved in the chronic control of reabsorption in the ducts. Control of epithelial transport in the efferent ducts appears to be mediated by cAMP and probably other signal transduction systems.