Prostaglandin endoperoxides, serotonin and the superfused rabbit aorta: Possible pitfalls in the bio-assay of rabbit aorta contracting substance (RCS)

Abstract

The specificity of the isolated rabbit aorta for identification and assay of prostaglandin endoperoxides, formed during aggregation of platelet rich plasma (PRP) from rats, was investigated in the superfused organ cascade. The use of cumulative dose-response curves in this design is quicker than conventional step-wise dosing while delivering identical results. On the rabbit aorta, in contrast to the rat fundus strip, methysergide is too weak an antagonist to rule out responses due to 5-HT. After pretreatment with phenoxybenzamine, in the presence of methysergide, the rabbit aorta retains its sensitivity towards oxygenated fatty acids, while being virtually unreactive towards 5-HT. The prostaglandin endoperoxide PGH₂ is more potent than prostaglandin E₂ when assayed on the rabbit aorta, while on the rat fundus the situation is reversed. Combining the rabbit aorta and rat fundus strip with pre-filtration on Amberlite^® XAD-2 columns showed that during collagen induced aggregation rat PRP generated both a labile RCS-most probably a prostaglandin endoperoxide—and a lipophylic prostaglandin-like material, along with 5-HT.