Analyses of DNA content of living spermatozoa using flow cytometry techniques

A two-dimensional fluorescence analysis of spermatozoa stained with Hoechst 33342 was carried out using an Epics V flow cytometer. This analysis involved the measurement of fluorescence both in the conventional manner at 90 degrees and at a narrow forward angle (nominally 0 degree) to the direction of the interrogating laser beam. The arrangement provided an optical means of distinguishing the orientation of flattened particles passing through the interrogation system and enabled the verification and reinterpretation of one-dimensional (90 degree) fluorescence histogram data obtained previously. We now consider that the distinction between live and dead spermatozoa was over simplified and that the observed differences are due partly to an artefact of orientation. It has been confirmed that our earlier use of the low fluorescence peak, consisting of (bull, rabbit, sheep and pig) spermatozoa passing through the interrogation point obliquely to both detectors, as criterion for sorting X- from Y-bearing spermatozoa, is more practical than the use of a very much smaller subpopulation, based on limits imposed by selecting only spermatozoa accurately orientated with their narrow edges to one detector, while measurement of total fluorescence (DNA content) was made simultaneously from a broad face by the other detector. We report marked differences in the rate of staining and in attainment of a staining equilibrium between spermatozoa from different animals or from different ejaculates collected on the same or different days from the same animal. This variation introduces an element of subjectivity into the use of flow cytometry for sorting X- and Y-spermatozoa.(ABSTRACT TRUNCATED AT 250 WORDS)