Effect of elevated calcium concentration on fertilization of rat oocytes in vitro

The purpose of this study was to develop a modification of the medium of Toyoda and Chang which would permit high rates of fertilization in vitro in rats of our colony. Elevation of the calcium concentration from 1.71 to 3.42 mM increased the fertilization rate by 87%. Greater additions of calcium gave no further improvement. This effect was not due to reduction in phosphate activity, nor was it due to antagonism of heavy-metal contamination. Although calcium is known to enhance the fertilizing capacity of spermatozoa, our results suggest that it may also affect the oocyte.