Physiology of the sexual segment of the kidney in reptiles

Abstract

The sexual segment represents the hypertrophied secondary and tertiary collecting duct tubules of the kidney in lizards and snakes. This organ is present only in the males and is secretory when the testes are spermatogenically active; it is regressed during testicular quiescence or following castration, and is stimulated to a secretory state by androgens. Secretions of the sexual segment are rich in phospholipids and contain acid phosphatase. The levels of the lipids of the sexual segment vary during different months of the year, and it appears that lipids of the kidney and liver are utilised by the sexual segment for resynthesis of its lipids. Incorporation of radioactive inorganic orthophosphate is differential and markedly higher in the sexual segment than in the kidney during different months of the year and is apparently regulated by changing patterns of testicular endocrine activity. Androgens stimulate selectively synthesis of lipid-rich secretions in the sexual segment. These secretions are mixed with sperm and are released into the female genital tract during copulation. It is presumed that the secretions of the sexual segment are utilised by the spermatozoa in the female genital tract. The function and homologies of the sexual segment are discussed. It is suggested that the sexual segment may be homologous with the seminal vesicles of mammals.