EFFECTS OF ENDOTHELIAL CELL REMOVAL ON α‐ADRENOCEPTOR‐MEDIATED RESPONSES OF AORTAE OF PREGNANT RATS

The possibility that changes in sensitivity of the aorta occurring during pregnancy in the rat are due to changes in uptake mechanisms, alpha- and/or beta-adrenoceptor-mediated responses was investigated. 2. Thoracic aortic rings from 20 day pregnant rats showed increased sensitivity to the constrictor effects of phenylephrine, with increased maximum responses when compared with those from non-pregnant animals. Removal of endothelium caused leftward shifts of the log concentration-response curves with further increases in maxima to the same extent in rings of both non-pregnant and 20 day pregnant rats. 3. Propranolol, beta-oestradiol, and nisoxetine did not significantly alter the CR-curves to phenylephrine of endothelium-intact or denuded thoracic aortic rings obtained from either non-pregnant or 20 day pregnant rats. 4. BHT-920 failed to cause marked constriction of endothelium-intact rings. After removal of endothelium, significant constrictor responses to BHT-920 occurred which were of similar magnitude for rings from both non-pregnant and 20 day pregnant rats. 5. Relaxant responses to BHT-920 of endothelium-intact rings preconstricted with phenylephrine were not significantly different between those from non-pregnant and 20 day pregnant rats. Removal of endothelium resulted in rightward shifts of the curves together with decreased maximum responses. 6. These results support earlier suggestions that the endothelium plays a role in controlling vascular reactivity to phenylephrine. The increased maximum response of thoracic aortic rings to phenylephrine seen during pregnancy does not appear to be due to marked changes in amine uptake mechanisms or beta- or alpha 2-adrenoceptor-mediated responses.