Hyperthermia Augments the H1-Histamine Receptor-Mediated Force in the Human Atrium

It was unknown whether hyperthermia increased the efficacy of histamine to raise the force of cardiac contractions via human H1-histamine receptors. To that end, we measured the force in isolated human atrial preparations (HAPs) excised from the right atrium of patients who underwent cardiac surgery due to severe two- or three-vessel coronary heart disease. For comparison, we also measured the force in paced (1 Hz) left and spontaneously beating right atrial preparations of transgenic mice overexpressing cardiac human H1-histamine receptors (H1-TG). Histamine (100 µM) was less efficient in raising the force in left atrial preparations from H1 TG mouse atria under hyperthermia than under hypothermia. Oppositely, histamine was more efficient in augmenting force during hyperthermia than during hypothermia in isolated electrically stimulated (1 Hz) HAPs. In sum, the contractile response to activation of H1-histamine receptor in H1-TG mice and in HAPs are opposite with regard to hyperthermia dependence. In patients with fever, histamine might thus be important, to preserve cardiac contractile function as a compensatory mechanism.