THE INFLUENCE OF REPRODUCTIVE CONDITION UPON GROWTH IN THE FEMALE RAT

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Abstract
Data are presented on the age and weight of [female] rats at the time of vaginal opening which demonstrate that the vagina opens in the absence of the ovaries but at a greater wt. and age. The factors influencing growth are also concerned with vaginal opening. Ovariectomized [female] [female] grow more rapidly early in life than virgins or breeding animals, but the growing period is no longer than for the virgins. Animals breeding but not lactating grow more rapidly than lactating animals or virgins and grow for a longer time than virgins. Breeding, lactating animals grow more rapidly than virgins and for a longer time but do not approach the growth rate of ovariectomized or breeding-non-lactating [female][female]. They grow for a longer time than the ovariectomized rats. Virgins grow slower and reach a plateau in growth earlier than breeding animals. They grow slower than ovariectomized rats but these 2 groups reach their plateau at the same age. Early bred animals may have a set-back from the drain of lactation early in life, but they reach the same adult size as animals bred later. Even after the rat has reached the growth plateau, breeding stimulates growth. Late bred animals never attain adult size equal to other breeding animals but they surpass the virgins. The residual growth influence is probably less at this time. Estrogens inhibit growth possibly through an inhibiting action upon the pituitary, the corpus luteum removing this inhibition. Ovariectomy has a similar effect by direct removal. Ovariectomized rats experience the pre-mortal loss of wt. at an earlier age than other rats.