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Lack of effect of hormones and inducers of intracellular messengers on plasminogen activator production by bovine embryos in vitro

Summary. Several hormones and inducers of intracellular messengers, known to affect plasminogen-activator (PA) production in other systems, were investigated for putative effects on bovine embryos. Day 8 embryos were cultured for 5 days in a humidified atmosphere of 5% CO₂ in air at 37°C in media containing different concentrations of progesterone, oestradiol, dexamethasone, retinoic acid, dibutyryl cyclic AMP (dbcAMP) and phorbol myristate acetate (PMA). At intervals of 24 h, the medium was recovered for PA analysis and overall embryonic diameter was measured. While none of the hormones and agents tested affected PA production (P > 0·05), dimethyl sulfoxide, which was used to dissolve PMA, inhibited PA production during the first 72 h of culture (P < 0·05). PA production was affected by duration of culture (P < 0·05). Concentrations of plasminogen activator in the media were low during the first 48 h, had increased after 72 and 96 h in culture, and either remained high or decreased slightly toward the end of the culture period. With the exceptions of dbcAMP and PMA, the hormones tested in this study did not affect embryonic size. Dibutyryl cAMP caused a progressive decrease in embryonic diameter. PMA resulted in embryo death at high concentrations but at lower concentrations it enhanced overall embryonic diameter throughout the time of culture (P < 0·05). These results suggest that cultured bovine embryos produce PA in a fixed, time-dependent manner, independent of exogenous hormonal regulation.

Keywords: embryo; plasminogen activator; hormones; cow