Objective: The aim was to investigate the effect on the coronary network of the interaction between high arterial blood oxygen tension (Pao(2)) and stimulation by the or adrenergic agonist phenylephrine or by serotonin in an isolated, blood perfused rabbit heart preparation. Methods: Fresh pig erythrocytes in Krebs-Henseleit buffer were oxygenated to reach normal Pao(2) [19.4(SEM 0.7) kPa] or high Pao(2) [53.2(5.5) kPa]. Blood oxygen content was kept constant despite the higher Pao(2), by slightly reducing the haemoglobin concentration from 9.3(0.2) to 8.8(0.2) g.100 m(-1) (p<0.01). Coronary blood flow was kept constant throughout the study, so that the oxygen supply would not vary with the rise in Pao(2). Increases in coronary resistance were therefore reflected by increased perfusion pressure. Results: Switching from normal to high Pao(2) induced coronary vasoconstriction, reflected by enhanced perfusion pressure of +21(5)%. After pretreatment with the alpha adrenergic agonist phenyleprine, perfusion of a high Pao(2) solution increased coronary resistance by +35(7)% (p<0.05), a value significantly higher than that found without phenylephrine. Oxygen consumption and myocardial performance did not vary throughout the study. To determine whether this amplification of the response was specifically due to alpha agonist stimulation or could be observed with other vasoactive agents, we applied the same protocol using serotonin instead of phenylephrine. Here again, coronary vasoconstriction rose in response to high Pao(2) after serotonin infusion [+25(5)% versus +59(10)%]. Conclusions: The response of the coronary network to high Pao(2) is amplified by pretreatment with the alpha adrenergic agonist phenylephrine or with serotonin, regardless of any changes in metabolic status.
