Evidence for a common defect associated with pressure in the aorta of two hypertensive rat strains

1, Thoracic aortas of normotensive (Wistar-Kyoto (WKY) and Lyon normotensiv e (LN) and hypertensive (spontaneously hypertensive rats (SHR) and Lyon hyp ertensive (LH) rats from tno groups (Japanese (WKY rats and SHR) and Lyon ( LN and LH rats) were compared using organ chambers. Changes in endothelium and smooth muscle reactivity to noradrenaline (NA), carbamylcholine and N-o mega-nitro-L-arginine (L-NNA) were analysed to distinguish between changes in reactivity, that are associated with the presence of hypertension and th ose that are dependent on group (Japanese vs Lyon), 2, Aortas of hypertensive rats had lower pot values for NA than aortas from normotensive rats. These differences were associated with hypertension (P< 0.005 and P<0.01) and group (P < 0.005 and P < 0.005) in presence or absenc e of endothelium, respectively, whereas no difference was seen in the maxim al developed tension in response to NA. 3, Aortas also differed by a reduced ability to relax in response to carbam ylcholine in hypertensive rats; this effect is hypertension (P < 0.05) and group (P < 0.005) dependent, without any change in carbamylcholine pD(2) va lues. 4. Changes in maximum developed tension in the presence of L-NNA were found to be endothelium dependent and pressure and group independent. Furthermor e, the change in tension induced by L-NNA appears significantly more pronou nced in SHR than in LH rats (P < 0.05). 5, These results indicate that the common defect associated with hypertensi on appears to be linked to the endothelium through cw-adrenoceptors and mus carinic receptors in both the Japanese and Lyon groups. However, SHR differ s markedly from LH rats by having a higher developed tension in response to NA, this increased tension being counterbalanced by the release of nitric oxide, as observed in the presence of L-NNA.