The effect of paracrine/autocrine interactions on the in vitro culture of bovine preimplantation embryos.

Bovine preimplantation embryos develop more successfully when cultured in groups, proibably because of the increased production of, and exposure to, embryotrophic autocrine and paracrine factors. Using a novel embryo culture technique, this study had two aims: 1. to determine the distance over which potential paracrine interactions affect bovine embryo development in terms of blastocyst and hatching rates, cell counts and carbohydrate metabolism; 2. to investigate the effect of platelet-activating factor (PAF) supplementation on bovine embryo development and metabolism. Groups of 16 presumptive zygotes were attached to the bottom of a culture dish by the cell adhesive Cell-Tak in a 4 x 4 equidistant array. The distance between individual embryos in each group was 0-689 microm. Optimal blastocyst formation rate occurred when embryos were cultured 165 microm apart compared with control non-attached zygotes (Kruskal-Wallis followed by Mann-Whitney U test post-hoc; P < 0.05). Increasing the distance between embryos resulted in a further decline in blastocyst rate, which reached zero at 540 microm apart. Blastocyst cell number, pyruvate/glucose uptake and lactate production decreased as the interembryo distance increased from 240 to 465 microm (P < 0.05). Supplementation with PAF during conventional group culture enhanced blastocyst cell number, hatching rates and the oxidative metabolism of pyruvate and glucose. The data indicate that the distance between individual bovine embryos in culture influences preimplantation development, in particular blastocyst formation, cell number and metabolism. It is suggested that diffusible paracrine/autocrine factors, such as PAF, are in part responsible for the regulation of early embryo development.