Abstract
Clark 1 recently reported that in rats gonadectomized at 1 or 2 days of age and assayed 16 to 18 days later the gonad-stimulating potency of the pituitaries was approximately the same in both sexes. Since in normal control animals of that age (17 to 20 days) the sex-stimulating potency of the female pituitary exceeds that of the male, she concluded that castration at 1 or 2 days produced a relatively greater increase in gonadotropic potency than spaying. The following series of preliminary experiments indicates that if gonadectomy is delayed for a week the pituitary of the castrated male does not gain as much in gonadotropic potency as that of the spayed female in the same period of time.
Littermate male and female rats 7 to 9 days of age were gonadectomized and after 17 to 19 days their pituitaries were injected into immature female rats 23 to 26 days of age. Normal males and females, littermates of the gonadectomized series, served as control donors. A host series consisted of 4 littermate females. Three donor glands were weighed, minced, and injected by means of a fine glass pipette, according to the method of Smith and Engle, 2 into the leg muscle of each host. The hosts, and usually a control litter-mate, were killed 4 days after injection and the ovaries weighed and fixed. Various factors intervened to prevent obtaining complete results for all series. Donors often were not born in adequate numbers of both sexes, maternal cannibalism caused blanks in several series, and in a few cases fatalities occurred among prospective or actual hosts. Out of 14 series, full results were obtained in only 4, and the present report is limited to these with the exception of case 13 for which the hosts, although not littermates, were of the same age and very uniform in body weight. Table I gives the data for the 5 series. The inclusion of all fragmentary series with the present data would not change the general results.
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