Testis-like steroidogenesis in the ovotestis of the European mole, Talpa europaea

The female European mole (Talpa europaea) presents a vivid paradox in relat ion to our contemporary understanding of mammalian sexual differentiation. These animals are exceptional among female mammals in that they possess bil ateral ovotestes. The ovotestis contains a morphologically normal ovarian c omponent that develops during the spring breeding season and a histological ly defined testicular region, the interstitial gland, which enlarges during autumn when the ovarian component decreases in size. In correlation with t his unusual gonadal situation, the female mole displays a penile clitoris t raversed by a urethral canal. Although the histology of the ovotestis is we ll documented and has recently been extended to an additional three species of the genus Talpa, there have been no clear indications of the physiologi cal function, particularly androgen production, of the ovotestis in these f emale moles. This paper presents the first clear evidence of seasonal varia tion in plasma testosterone concentrations, which parallel the growth and r egression of the "testicular" interstitial gland, in T. europaea. Plasma an drostenedione did not show significant seasonal variation, but plasma testo sterone (1.06 +/- 0.2 ng/ml) and gonadal testosterone concentration (1.57 /- 0.65 mu g/mg protein) in females in autumn were significantly higher (p < 0.02) than plasma (0.4 +/- 0.2 ng/ml) and gonadal (0.24 +/- 0.21 mu g/mg) concentrations in pregnant or immediately postpartum females in spring. Ou r data also reveal selective metabolic production of testosterone from radi olabeled steroid precursors (progesterone and androstenedione) by these ova rian interstitial tissues and male testes; estradiol is produced by ovarian tissue but not interstitial gland or testis.