Bull sperm as a potential model system for cytotoxicity testing in vitro

The possibility of using frozen/thawed bovine sperm as a model system for cytotoxicity was explored using progressive motility (EC(50)), ATP content (ATP(50)) and cell death (CD(50)) as endpoints. ATP content and motility of sperm were relatively constant after 15 min in culture, enabling measurements to be made over the following 30 min. ATP content was lower in an 'extender' (1.4 x 10(-16) mol/sperm) than in the final diluent (2.3 x 10(-16) mol/sperm), which was Eagle's minimum essential medium (MEM) containing 5% (v/v) foetal calf serum. Nonylphenoxypolyethoxyethanol (nonoxynol-9), Gynol II((c)) containing 2% (v/w) of this surfactant, and dl-propranolol were the toxicants chosen for the evaluation. There was little difference between the three endpoints for Gynol II((c)) and nonoxynol-9 but the former caused a relatively greater effect on motility. dl-Propranolol (ATP(50) 1.39 mg/ml) was considerably less toxic than nonoxynol-9 (ATP(50) 53 mug/ml) but its CD(50) could not be measured for technical reasons. Results with Gynol II((c)) suggested that the effectiveness of the active ingredient of this compound, nonoxynol-9, was reduced by the excipients. It has been claimed that this compound causes membrane ultrastructural damage but, at 75 mug/ml, no disruption was observed under the scanning electron microscope. Measurement of sperm ATP content is the preferred assessment for cytotoxicity because it is automated and can give clues to the mechanism of toxic action.