Three-day old Sprague-Dawley rats were treated with graded doses, 1.25 to 5.0 mg, of progesterone. Other experimentals received testosterone propionate alone or in combination with progesterone; controls were either injected or non-injected.

Within 50 days 40% to 90% mortality was observed among the progesterone-treated groups. At 100 days the surviving males were given a series of weekly sexual performance tests during which a variety of behavioral components was recorded.

Ejaculation occurred in significantly fewer 5 mg progesterone-treated males than among controls, and the latency of those which did ejaculate was longer than among the controls. The frequency of mounting and ano-genital licking was greater in progesterone males although the time occupied by these components was not a factor in the longer latencies to ejaculation. Those progesterone-treated males which were able to ejaculate were as effective in fathering litters as were the controls.

Female rats receiving neonatal progesterone showed a significantly higher incidence of persistent vaginal estrus and subsequent infertility than controls. This combination of effects is similar to that resulting from testosterone treatment. Gonadal weights of both males and females treated with progesterone were lighter than controls although the lightest testes were found in the testosterone males.

This work shows a dose-response relationship between neonatally administered progesterone and mortality. Further, early progesterone treatment is capable of modifying adult sexual performance as has been previously shown for testosterone and estrogen.

(Supported by grant HD02326 and HD-03394 from the U.S.P.H.S.)


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