Biological profile of a bioactive aortic substance (BAS), released by vessel rings from indomethacin-treated rats

The biological activity of a stable unknown material(s), generated by aortic rings (bioactive aortic substance = BAS) isolated from rats injected with a high dose of indomethacin, was explored on contractions of several smooth muscle preparations from normal rats and its effects compared with those elicited by prostacyclin (PGI2) or by 6-keto-prostaglandin F1 alpha (6-k-PGF1 alpha). The BAS evoked, as did PGI2 or 6-k-PGF1 alpha, positive inotropism in strips from rat stomach, ileum and urinary bladder, but failed to influence uterine contractions as did prostacyclin or its non-enzymatic metabolite. When tested in rat aortic strips both, PGI2 and the BAS produced relaxation, whereas 6-k-PGF1 alpha was not active. Moreover, lipid substances present in the incubates of aortic rings, were extracted and explored for effects on contractions of rat aortic strips and on arachidonate-evoked human platelet aggregation. These extracts were devoid of influence on both parameters. On the contrary, dried aqueous residues, after the lipid extraction of the supernatants of aortic ring incubates, exhibited human platelet antiaggregatory capacity as well as the ability to evoke positive and negative inotropism similar to those triggered by the BAS in different smooth muscle preparations. Experiments with BAS were also performed employing smooth muscle strips exposed to indomethacin, atropine, propranolol, phentolamine and cyproheptadine. The presence of these antagonists of several neuromodulators and of indomethacin failed to alter de BAS-induced inotropic capacity observed in controls. The findings suggest that the effects attributable to the BAS are not subserved by prostacyclin or other prostanoids, nor by acetylcholine, norepinephrine, histamine or 6-OH-tryptamine.