Lysergic acid diethylamide stimulates cardiac human H 2 histamine receptors

Introduction: Lysergic acid diethylamide (LSD) is an artificial hallucinogenic drug. Thus, we hypothesized that LSD might act 5-HT 4 serotonin receptors and/or H 2 histamine receptors. Methods: We studied isolated electrically stimulated left atrial preparations, spontaneously beating right atrial preparations, and spontaneously beating Langendorff-perfused hearts from transgenic mice with cardiomyocyte-specific overexpression of the human 5-HT 4 receptor (5-HT 4 -TG) or of the H 2 -histamine receptor (H 2 -TG). For comparison, we used wild type littermate mice (WT). Finally, we measured isometric force of contraction in isolated electrically stimulated muscle strips from the human right atrium obtained from patients during bypass surgery. Results: LSD (up to 10 µM) concentration dependently increased force of contraction and beating rate in left or right atrial preparations from 5-HT 4 -TG (n=6, p<0.05) as a partial agonist in 5-HT 4 -TG atrial preparations. The inotropic and chronotropic effects of LSD were antagonized by 10 µM tropisetron in 5-HT 4 -TG. In contrast, LSD (10 µM) increased force of contraction and beating rate in left or right atrial preparations, from H 2 -TG as a full agonist. After pre-stimulation with cilostamide (1 µM), LSD (10 µM) increased force of contraction in human atrial preparations (n = 6, p < 0.05). The contractile effects of LSD in human atrial preparations could be antagonized by by 10 µM cimetidine. Conclusion: LSD leads to H 2 -histamine receptor mediated cardiac effects in humans. Significance LSD is undergoing a revival in clinical studies. New indications for LSD especially in psychiatric patients are being found. Hence, there is a clinical need to understand its cardiac effects and possibly cardiac side effects better. The present work uses a translational approach to address this research need.