Passage of leptin across the blood-testis barrier

Leptin is a 17-kDa protein, secreted by fat, that controls adiposity and ha s been proposed to have numerous effects on reproduction in the mouse. To a ssess whether the effects of leptin on testicular function are direct, we d etermined whether leptin can cross the murine blood-testis barrier. Multipl e time regression analysis showed that a small amount of blood-borne leptin is able to enter the testis but does so by a nonsaturable process. In addi tion, no significant expression of leptin receptors was found at the Leydig cells or Sertoli cells of the testis. This compares with the presence of a saturable transport system for leptin at the blood-brain barrier and abund ant receptors for leptin at the leptomeninges, neurons, and choroid plexus of the central nervous system (CNS). These results support the hypothesis t hat the effects of leptin on reproductive function are not mediated at the level of the testis but indirectly, probably through the CNS.