68 STEROIDOGENIC CONTROL OF INTRAUTERINE SEXUAL DIFFERENTIATION IN SPIX’S YELLOW-TOOTHED CAVY, GALEA SPIXII

Abstract

The Spix’s yellow toothed (SYT) cavy is a species of rodent that lives in Caatinga vegetation of northeast Brazil. The SYT is utilised as a protein source by inhabitants of that region and has zootechnic potential. SYT cavies have been bred in captivity for studies related to reproductive biology. The presence of a penile clitoris trespassed by the urethra was described in the adult female. The aim of this research is describe sexual differentiation events in the male and female conceptus and relate molecular mechanisms of androgen and oestrogen metabolism of the placenta with the differentiation of external genitalia. Conceptuses after 15, 22, 30, 40, >50 (full term) days of gestation (DG; n = 9 males and 9 females at each gestational period) from 30 pregnant females, which were paired with 10 males, were used. After detection of copulation, the above described DG were awaited prior to the day of euthanasia. We performed anatomical description and light and scanning electron microscopy on the genital organs in the conceptus; concentration of testosterone (T) and oestradiol (E) by radioimmunoassay in the pregnant females; and described the immunoreactivity (by immunoblotting and immunohistochemistry) of enzymes: cytochrome P450 aromatase, cytochrome P450c17, 17-β-HSD, and 3-β-HSD in placentas of male and female conceptus. The genital organs emerge from a pair of undifferentiated gonads and a genital tubercle at 15 DG. These gonads differentiate into a pair of testicles or a pair of ovaries at 22 DG. The other internal genital organs arise from the urogenital sinus and Müllerian ducts in females or Wolffian ducts in males after 22 DG. The undifferentiated genital tubercle forms the penis in males with the urethra channeling at 30 DG. In females, the urethra channeling is complete after 40 DG with the closure of the urethral groove, and at >50 DG the clitoris has characteristics of a pseudo-penis. Those that are pregnant undergo an increase of E (from 5.456 ± 1.599 pg mL^–1 at 22 DG to 107.186 ± 15.966 pg mL^–1 at >50 DG) and T (from 122.444 ± 15.799 pg mL^–1 at 22 DG to 718.555 ± 67.407 pg mL^–1 at >50 DG) concentrations during the gestational period. The concentration of T was a minimum 5-fold higher than the E concentration at the moment of external sexual differentiation. The placentas from the male and female conceptus are immunoreactive for the enzyme 3-β-HSD producing progesterone throughout pregnancy, but these placentas are not immunoreactive for the oestrogen-producing enzyme cytochrome P450 aromatase throughout pregnancy. Conversely, the cytochrome P450c17 and 17-β-HSD enzymes are immunoreactive in the placentas of the male and female conceptus throughout pregnancy, producing androgen hormones. The absence of enzymes that produce oestrogen hormones in the placenta of SYT cavies indicate that testosterone from pregnant reaches the fetal circulation, and associated with the presence of enzymes that produce androgens, may act to increase androgen hormone concentration in the pregnant, which may act in the virilization process of the female external genitalia.