Porcine diaphragmatic arteries. An in vitro comparative study

The purpose of the experiment was to determine whether diaphragmatic circulation could be compared to other skeletal muscle circulation or whether it has an originality of its own. Diaphragmatic (phrenic and costophrenic arcade arteries), coronary, femoral and cerebral arteries were taken up from anaesthetized pigs, cut into rings and suspended in organ chambers for isometric tension recording. Vasopressin induced a maximal contraction of the femoral artery, no significant changes in tone in cerebral and coronary arteries, and only minimal contraction (30% of the maximum) in diaphragmatic arteries. These results were obtained in a state of basal level of tension or in vessels contracted with prostaglandin F2 alpha. The endothelium did not influence the response in any of the vessels investigated. Norepinephrine induced a contraction in the femoral artery and a relaxation in the coronary artery which was not influenced by the endothelium. Isoproterenol could relax the coronary but not the femoral or the diaphragmatic arteries. The alpha 2-adrenoceptor agonist UK 14304 induced endothelium-dependent relaxation in the diaphragmatic and coronary arteries, but not in the femoral arteries. Phenoxybenzamine unmasked a small alpha-adrenoceptor reserve in the diaphragmatic arteries. These results suggest that diaphragmatic circulation has protective mechanisms in order to preserve a correct supply to the vital respiratory muscle it subserves.