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Thymidine-3H-labelled spermatozoa were obtained in the sixth week after injection of males with a single or repeated doses of thymidine-3H, in amounts of 3.5 to 50 muCi per gramme body weight. Mouse ova were fertilized in vivo or in vitro by such labelled spermatozoa. It was found by means of autoradiography that heavily labelled spermatozoa compete successfully with non-labelled ones in performing fertilization. The distribution of relative levels of activity in fertilizing spermatozoa was similar to that in the population of inseminated spermatozoa. The early development of ova fertilized by generally labelled spermatozoa (followed up to the first cleavage) was not impaired. It is concluded that spermatozoa labelled with thymidine-3H in their DNA to a level sufficient for autoradiographic detection may be probably used in the studies of the cytology of fertilization without greater precautions regarding possible radiation-induced artefacts.

Breakdown of the germinal vesicle (GV) was studied in bovine follicular oocytes cultivated in vitro. The intact GV of control oocytes did not correspond to the findings in porcine oocytes (GV I). Instead it was characterized by a nuclear membrane and a few chromocenters in finely granular nucleoplasm (GV II). After two and three hours of cultivation, GV III predominated (50% and 64% respectively). Faintly-staining chromatin and after a longer interval in the form of filaments also appeared round the chromocenters. After four hours, 35.8% of the oocytes were still at stage GV III but the GV of 46.6% of the oocytes already contained filamentous bivalents (GV IV). After five hours, GV IV (59.7%) was typical, with a less distinct nuclear membrane and condensing bivalents. GV breakdown was completed in 30.4% of the oocytes after five hours of cultivation and in 92.5% after six hours.

On the basis of progesterone determination on plasma or blood after RIA and the kit method respectively and consecutive scanning performed on a total number of 31 mares the following features were demonstrated: The overall material shows that in 20 mares (64.5%) embryonic vesicles were demonstrated. Of these mares 16 have conceived after service in the 1st estrous cycle and 3 mares in the 2nd estrous cycle. 18 mares were scanned in the time interval 13th-26th day after the latest service, while 2 mares were scanned on day 46 and 41 respectively. A total of 14 scanning positive mares were examined for progesterone by the RIA as well as by the kit method. For these mares (100%) agreement was found between the progesterone analyses as well as with the scanning results. For 19 mares (100%) there was agreement between kit and scanning results. 15 RIA progesterone determinations are in agreement with the scanning results. Progesterone values after the RIA method performed on 15 scanning positive mares were in average 8.40 +/- 2.79 ng/ml plasma. A total of 9 out of 10 scanning negative mares have been examined by the RIA as well as by the kit method. In 6 of these mares with 7 estrous cycles agreement has been found between progesterone analyses and the scanning results (77.8%). In 2 mares (no. 2 and 4) discrepancy has been found in the 2nd estrous cycle between RIA, kit and scanning results. For 1 mare (no. 7) discrepancy has been found in the 1st and 3rd estrous cycle between RIA and scanning.(ABSTRACT TRUNCATED AT 250 WORDS)