EXCRETION PATTERN OF LABELLED SPERMATOZOA AND THE TIMING OF SPERMATOZOA FORMATION AND EPIDIDYMAL TRANSIT IN RABBITS INJECTED WITH THYMIDINE-3H

Abstract

Sixteen rabbits were injected with thymidine-H3 and tissue sections or spermatozoa smears were evaluated by autoradiography. Two successive ejaculates were collected every 2nd day. Analyses of labelled germ cells in 24 testes taken 1 hr. to 32 days post-injection showed that 1 cycle of the seminiferous epithelium required 10. 7 [plus or minus] 0. 5 days and that labelled spermatozoa should enter the caput epididy-midis 31. 4 days post-injection. Labelled spermatozoa were found in the proximal portion of 4 capita epididymidum 32 days and 1 caput 33 days post-injection, but not in 11 other capita epididymidum 28 to 31 days post-injection. Labelled spermatozoa 1st were detected in ejaculated semen from 5 rabbits on Days 38, 39, 41, 42 and 42. The mean number of grains/spermatozoon in autoradiograms of successive samples agreed closely with the scintillation count activity curve. However, neither curve represented the excretion pattern of spermatozoa labelled as preleptotene spermatocytes. The 1st samples containing labelled spermatozoa had a low percentage of highly labelled spermatozoa while, through mixing with spermatozoa labelled as spermatogonia, subsequent ejaculates contained up to 55% labelled spermatozoa but individual cell activity was lower. Labelled spermatozoa were excreted over a period of 2 to 3 weeks. Epididymal spermatozoa transit time averaged 9. 0 days, but it ranged from 6. 6 to 10. 6 days even with a uniform semen collection schedule. Combined with autoradio-graphic evaluation of tissue sections or semen smears, intravenous injection of 0. 1 to 0. 3 mc/kg body weight of thymidine-H3 should be adequate for experiments of this type.