Vascular Responsiveness in the Unstressed Borderline Hypertensive Rat

This study compares vascular responses of unstressed borderline hypertensive rats (BHR) to age-matched Wistar-Kyoto (WKY) and spontaneously hypertensive rats (SHR). Rings of thoracic aorta were mounted for isometric force determinations in tissue baths. Cumulative additions of phenylephrine (PE) or serotonin (5-HT) produced contractile responses in BHR aorta that were less than WKY but greater than SHR. Removing the endothelium increased force development to both agonists, with BHR showing the greatest increase. Based on EC50 determinations, no differences in PE sensitivity existed between groups, although in response to 5-HT, rings from SHR were significantly more sensitive than WKY. While the sensitivity of all rings increased with denuding, BHR showed a greater relative increase in sensitivity than WKY or SHR (intact EC50 divided by denuded EC50) to both PE and 5-HT. This suggests that there may be greater endothelium-derived relaxation in BHR than in WKY or SHR. In rings precontracted with 1 μM PE, th...