The renal sex segment (RSS) is a unique nephric region found only in male lizards and snakes.
The RSS enlarges seasonally in response to changes in plasma androgens, being hypertrophied and
secretory during the mating period. Embryologically, the RSS is homologous to the mammalian
prostate and bulbo-urethral glands. The function of the RSS remains uncertain, but secretory
material forms a significant portion of the seminal mass that is transferred at copulation. RSS
secretory products stain strongly with beibrich scarlet and are presumed to be rich in arginine.
Poly-acrylamide gel electrophoresis of RSS material indicates that the major protein has a
molecular weight of 39,000 daltons. A histochemically similar secretory protein is synthesised
by the lizard epididymis, but the molecular weight of this material is 78,000 daltons, almost
certainly a dimeric form of the RSS protein.
Hypertrophy and secretory activity of the RSS occurs rapidly following testosterone administration
in Sceloporus jarrovi. Significant cellular enlargement is exhibited by RSS tubules within
three days of subcutaneous testosterone implant placement, secretory activity being maximal by 14
days of testosterone exposure. RSS and epididymal products make up the bulk of the seminal fluid
in lizards. During copulation, male-derived secretory granules are deposited into the female cloaca.
Sperm swim out of this seminal material and enter the oviducts, and are eventually held in vaginal
storage crypts. Male secretory granules are endocytosed by the transitional epithelium of the cloaca.
Many aspects of RSS function remain unknown, but this material may initiate supression of the female
immune system, thereby enhancing the likelihood that stored sperm will survive to fertilise ova.