Efficiency of Liquid Scintillation Counting and Autoradiography for Detecting Tritium in Spermatozoa

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Abstract
Assays by autoradiography (grain counts) and liquid scintillation (disintegrations per minute, dpm) were made on semen samples collected from 5 rabbits for 63 days following injection with H3 -thymidine. The mean grain counts and mean dpm determined on semen samples containing radioactive spermatozoa were highly correlated (r = 0.93, P< 0.001). With this high relationship it was possible to calculate a meaningful regression of mean grain counts on dpm. It was found that 5.8 disintegrations were required per grain observed in NTB-3 emulsion for an autoradiographic efficiency of 17.3%. Utilizing direct sample preparation, liquid scintillation counting was demonstrated as a rapid method to detect initial appearance of H3-labeled spermatozoa. The correlation coefficient calculated for counts obtained on duplicate subsamples was 0.99. The efficiency of the procedure was estimated by means of external standards to range from 9.8 to 12.5%. Inclusion of thixotropic gel reduced errors in counting, but actual solidification of the mixture was not necessary, as nongelled samples averaged 1293 and 1202 dpm, respectively.

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