THE PRESENCE OF AN INHERENT REPRODUCTIVE CYCLE IN THE MALE LABORATORY RAT

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Abstract
SUMMARY: The data presented in this paper illustrate a distinct yearly cycle of activity in the capacity of the dorso-lateral prostate (d.l.p.) of the male laboratory rat to concentrate injected 65Zn. From 60 to 85% more 65Zn was taken up per mg of glandular tissue in the months of February-March and June-July than at other times of year. Studies of the corresponding weights of the d.l.p. showed trends towards lower glandular weights in January and in April; the maximum difference noted between high and low glandular weights was, however, only 28%. That this increased uptake of 65Zn by the d.l.p. in February-March and June-July was a strong inherent feature was illustrated by the fact that rats of various ages, from 8 weeks to 1½ years, showed this increased glandular activity at these times of year. Of all the animals tested only the immature rat of 5 weeks of age and the exhausted breeder did not manifest this seasonal activity.
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