Cyclic AMP and cyclic GMP concentrations in, and efflux from, preimplantation cattle embryos

Basal embryonic cAMP and cGMP concentrations and cAMP and cGMP accumulation in embryos and in the incubation medium were measured in cattle blastocysts recovered at days 14 (n = 23), 15 (n = 29) and 16 (n = 23) of pregnancy. Cyclic AMP and cGMP concentrations were measured by radioimmunoassay and the results expressed per μg of protein, which was determined by the Pierce Micro BCA protein assay. Cyclic AMP and cGMP were present on each day. Basal embryonic cAMP was similar on days 14, 15 and 16, at 2.3, 2.5 and 2.6 fmol per μg protein, respectively, while the concentration of cGMP was higher at day 14 (0.14 fmol per μg protein) than at either day 15 or 16 (0.06 and 0.05 fmol per μg protein, respectively; P < 0.05), which were similar (P > 0.10). Basal embryonic cAMP concentrations were 15 to 60-fold higher than cGMP concentrations. Following a 2 h culture period in the presence or absence of the phosphodiesterase (PDE) inhibitor, isobutylmethylxanthine (IBMX), the accumulated concentrations of cAMP and cGMP were measured in the embryos and in the incubation medium. IBMX did not affect the concentrations of either cAMP or cGMP in the embryos but increased the concentrations of cAMP (P < 0.005) and cGMP (P < 0.01) in the incubation medium. There was no effect of day on either embryonic or medium cAMP, but both embryonic and medium cGMP were higher at day 14 than at day 15 (P<0.05) or 16 (P<0.005). Differences between embryonic and medium cAMP and cGMP accumulation were examined. There was no effect of day or treatment. cGMP accumulation in the medium was higher than in the embryos (P < 0.005) whereas cAMP accumulation in the medium was lower than in the embryos (P < 0.05). Whether the efflux of cAMP and cGMP is active or passive is not clear but it may indicate a possible role in embryo-maternal signalling.