Control of mesenteric arterial tone in vitro in humans and rats

The majority of the findings concerning arterial physiology and pathophysio logy originate from studies with experimental animals, while only limited i nformation exists about the functional characteristics of human arteries. T herefore, the aim of the present work was to compare the control of vascula r tone in vitro in mesenteric arterial rings of corresponding size (outer d iameter 0.75-1 mm) from humans and Wistar-Kyoto rats. The relaxations to ac etylcholine (ACh) were clearly less marked in the mesenteric arteries of hu mans when compared with rats. However, when calcium ionophore A23187 was us ed as the vasodilator, the endothelium-mediated relaxations did not signifi cantly differ between these species. The NO synthase inhibitor N-G-nitro-L- arginine methyl ester (L-NAME) attenuated the relaxations to ACh and A23187 in both groups. The endothelium-independent relaxations to the beta-adreno ceptor agonist isoprenaline and the nitric oxide (NO)-donor nitroprusside w ere somewhat lower in human arteries, while vasodilation induced by the Kchannel opener cromakalim was similar between humans and rats. Arterial con tractile sensitivity to noradrenaline and serotonin was slightly lower in h uman vessels, whereas contractile sensitivity to KCI was similar between th ese species. The contractions induced by cumulative addition of Ca2+ with n oradrenaline as the agonist were effectively inhibited in both groups by th e calcium channel blocker nifedipine, the effect of which was clearly more pronounced in human arteries. In conclusion, the control of vascular tone o f isolated arteries of corresponding size from humans and rats appeared to be rather similar The most marked differences between these species were th e impaired endothelium-mediated dilation to ACh and the more pronounced eff ect of nifedipine on the Ca2+-induced contractions in human arteries.