Prostanoid synthesis by human umbilical artery.

A discrepancy between published values of PGI2 production by human umbilical artery in vitro measured by platelet bioassay, compared with values of 6-oxo-PGF1 alpha by radioimmunoassay, raised the possibility that another anti-aggregatory prostanoid was produced by this tissue. To test this hypothesis, umbilical artery rings were incubated in buffer and PGI2 determined by platelet bioassay and by a more specific radioimmunoassay based on comparison of 6-oxo-PGF1 alpha in hydrolysed and non-hydrolysed samples. 6-oxo-PGF1 alpha, PGF2 alpha and TXB2 were also measured by gas chromatography negative ion chemical ionisation mass spectrometry. PGI2 concentrations by radioimmunoassay and bioassay were significantly correlated (r = 0.92, p less than 0.01). There was no difference between them, disproving the presence of an additional antiaggregatory substance. PGI2 production determined by bioassay (mean 1.21 ng/mg wet weight/h, range 0.59-1.53 ng/mg/h) differed from previously reported values (range 70-325 ng/mg/h). 6-oxo-PGF1 alpha concentrations were confirmed by gas chromatography negative ion chemical ionisation mass spectrometry. Previous determinations of PGI2 production by this tissue overestimated it by approximately 100 times.