Patterns of body weight change in rats following neonatal hormone manipulation: a "critical period" for androgen-induced growth increases.
The development of sexual behaviour and gonadal function is largely determined by the early postnatal hormone environment in the rat; testosterone propionate (TP) treatment in the neonatal female will stimulate development of predominantly masculine functional characteristics. On the other hand, removal of the testes from neonatal males results in feminization of these characteristics. It has been shown that an optimal neonatal steroid hormone environment is also essential for normal growth. We now report the effects of different doses of TP (10, 30, 90, or 270 mug) given on postnatal days 2, 3, 4, or 5 on growth as measured primarily by body weight. Only treatment in the 30-270 mug range on days 2 or 3 was effective in causing significant growth changes, however, these same doses caused sterility and impaired female sexual behaviour when given on days 4 or 5. Therefore, there appears to be a "critical period" before the fourth postnatal day when TP can affect processes leading to increased growth. Removal of the neonatal testes retards growth to the levels of the androgenized females. The ovaries of the female TP treated rats still have a restraining influence on growth since their removal produces an increment in body weight similar to, though not as great as, that of the normal ovariectomized rat. These findings suggest that neonatal TP administration may possibly reduce the responsiveness of rats to the growth depressing effect of ovarian steroids by action at a site functionally different from that producing sterility and impaired sexual behaviour.
D000367:Age Factors; D000818:Animals; D001835:Body Weight / Q000187:drug effects*; D002369:Castration; D003864:Depression, Chemical; D004305:Dose-Response Relationship, Drug; D004958:Estradiol / Q000494:pharmacology; D005260:Female; D005298:Fertility / Q000187:drug effects; D008297:Male; D010053:Ovary / Q000187:drug effects / Q000502:physiology; D051381:Rats; D012726:Sexual Behavior, Animal / Q000187:drug effects; D013268:Stimulation, Chemical; D013737:Testis / Q000502:physiology; D013739:Testosterone / Q000008:administration & dosage / Q000494:pharmacology*
D013739:Testosterone; D004958:Estradiol