Rat aortic strip as a bioassay tissue for thromboxane A2 and rabbit aorta contracting substance (RCS) released from guinea pig lung by bradykinin or anaphylaxis

Rat aortic strips and rabbit aortic strips were superfused in series with Krebs solution. Comparison of the sensitivity of the tissues to thromboxane A₂ (TXA₂), generated by mixing prostaglandin (PG)H₂ with human platelet microsomes (HPM), indicated that the rat aorta was just as sensitive an assay tissue as the rabbit aorta. Furthermore, it was equally selective in that it did not respond to low levels of the other metabolites of arachidonic acid. When the two tissues were used simultaneously to assay aortic contracting activity released from perfused guinea pig lung by bradykinin, both tissues detected activity that could be matched with similar known amounts of TXA₂. However, when ovalbumin was used to release aortic contracting activity from sensitized guinea pig lung, the amounts of TXA₂ needed to match the responses of the assay tissues often differed by 2–3 fold. This suggested that other substances, as well as TXA₂, released during anaphylaxis can affect the aortic strips and thus influence the bioassay of TXA₂. This discrepancy in assay of TXA₂ can be detected only when more than one assay tissue is used. In the series of experiments in which we used the assay tissues to detect TXA₂ released by bradykinin, we noted that bradykinin released more TXA₂ from unsensitized lungs than from sensitized ones. Although the significance of this observation remains unclear, it suggests that there are quantitative differences in the PG biosynthetic pathways induced by the sensitization process.