Lysergic acid diethylamide stimulates cardiac human H₂ histamine and cardiac human 5-HT₄-serotonin receptors

Lysergic acid diethylamide (LSD) is an artificial hallucinogenic drug. Thus, we hypothesized that LSD might act 5-HT₄ serotonin receptors and/or H₂ histamine receptors. 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-HT₄ receptor (5-HT₄-TG) or of the H₂-histamine receptor (H₂-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. LSD (up to 10 µM) concentration dependently increased force of contraction and beating rate in left or right atrial preparations from 5-HT₄-TG (n = 6, p < 0.05) in 5-HT₄-TG atrial preparations. The inotropic and chronotropic effects of LSD were antagonized by 10 µM tropisetron in 5-HT₄-TG. In contrast, LSD (10 µM) increased force of contraction and beating rate in left or right atrial preparations, from H₂-TG. 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 10 µM cimetidine and 1 µM GR 125487. LSD leads to H₂-histamine receptor and 5-HT₄-receptor mediated cardiac effects in humans.