Spermatogenesis and immune responsiveness to sheep red blood cells in guinea pigs treated with cyproterone acetate and testosterone.

The synthetic steroid antiandrogen, cyproterone acetate, and the androgen, testosterone isobutyrate, were injected subcutaneously into adult male and female guinea pigs of two outbred strains (laboratory coloured and albino Pirbright-Harley stocks). Cyproterone acetate was given as 1, 10 and 20 daily 5-mg doses (body-weight matched with immunosuppressively effective doses in mice) and as 30 doses of 15 micrograms/100 g b.w. (body-weight matched with those used in the long-term human male contraception), testosterone as 1 and 10 doses of 5 mg/100 g b.w. The guinea pigs of the two stocks used showed different sensitivity: with the same doses of CA albino guinea pigs compared to the coloured ones declined in weight, had lower viability, reduced thymus weight, diminished capacity for SRBC haemolysin formation, a lower testes weight and inhibited spermatogenesis. Both stocks reacted by similar lymphopoenia, however. Testosterone neither inhibited haemolysin formation nor produced lymphopoenia but induced a more marked reduction of thymus weight than did CA and, in addition, produced greater depletion of cortex lymphocytes in albino guinea pigs. The thymus of albino guinea pigs was more sensitive to testosterone than to cyproterone acetate. Sexual dimorphism was apparent in some criteria in albino guinea pigs following cyproterone acetate and testosterone. Cyproterone acetate in the lowest doses had no inhibitory effect on thymus or SRBC formation but also did not affect spermatogenesis in albino guinea pigs. The hitherto accepted classification of animal species according to which guinea pigs (and also man) belong to steroid-resistant species is discussed and questioned, and the potential risks of application of sexual steroids in male contraception are stressed.