EFFECTS ON MOUSE BLASTOCYSTS OF INVITRO EXPOSURE TO METHYLNITROSOUREA AND 3-METHYLCHOLANTHRENE

Abstract

Mouse blastocytes were exposed in vitro to various concentrations of N-methyl-N-nitrosourea and 3-methylcholanthrene. The incorporation of [3H]thymidine, [3H]uridine and [3H]leucine into the exposed blastocysts was determined immediately following exposure or after 18 h of culture. Concentrations of N-methyl-N-nitrosourea or 3-methylcholanthrene used had no effect on blastocyst viability in either situation. There was a concentration-dependent decrease in the incorporation of the precursors into blastocysts exposed to N-methyl-N-nitrosourea which appears to be more pronounced after 18 h in culture. This effect was not demonstrated for 3-methylcholanthrene, which requires metabolic activation for reactivity. Blastocysts exposed to N-methyl-N-nitrosourea were injected into the uterine horns of surrogate mothers; a significant increase in the resorption rate of these blastocytes was seen when compared to controls. Similar experiments were performed to determine birth rate. A dose-dependent decrease in birth rate was observed which correlated well with the effects on incorporation of thymidine, uridine and leucine but not with the effect on implantation rate.