Coronary artery reactivity in the mako shark, Isurus oxyrinchus

Vasoactivity was examined in isolated vascular rings from the coronary arteries of the mako shark, Isurus oxyrinchus, a representative of the athletic elite among elasmobranch fishes. Adenosine relaxed vascular rings. ADP contracted vascular rings at concentrations less than 0.1 mM and relaxed them at higher concentrations. Theophylline inhibited both the ADP-mediated contraction and adenosine-mediated relaxation. Prostaglandin F2α produced strong constrictions. Serotonin had no vasoactive effect. Adrenaline and noradrenaline produced relaxations, indicating a population of β-adrenoceptors. ACh produced weak relaxations at concentrations greater than 10 μM. With the notable exception of the response to adenosine, these vasoactive responses were similar to those previously observed for the coronary arteries in another elasmobranch, the rough skate (Raja nasuta).