The direct excitatory effects of cimetidine on the smooth muscle of guinea pig ileum

Acute cardiovascular effects of intravenous cimetidine

To assess the acute cardiovascular effects of cimetidine--a widely used histamine-H(2)-receptor antagonist--cuff arterial blood pressure, M-mode echocardiogram of the left ventricle and systolic time intervals were recorded in 10 healthy volunteers before and after 200 mg of cimetidine or isotonic saline given intravenously in a double-blind cross-over manner. Neither echocardiograms nor systolic time intervals revealed any significant effects of cimetidine on the left ventricular performance. However, cimetidine decreased slightly the systolic arterial pressure. The maximal effect of cimetidine (7 +/- 1 mmHg, mean +/- SEM) differed significantly from that of saline (3 +/- 1 mmHg, p less than 0.02). When compared with the pre-injection level, the calculated total peripheral resistance decreased significantly after cimetidine (p less than 0.01), whereas saline induced no such change. We conclude that a bolus injection of cimetidine does not impair cardiac performance but may induce transient hypotension due to reduction of the total peripheral resistance. This reduction can explain the hypotensive effect of i.v. cimetidine reported in acutely ill patients.

Histamine receptors: subclasses and specific ligands

In this review the three main types of histamine receptors are discussed together with their specific ligands. For the classical H1-receptors much emphasis is put on the mechanism by which the receptor is stimulated. For the H1- and H2-receptor the review includes information on the several models available for establishing agonistic or antagonistic activity. In the section on the H3-receptor the ligands are discussed as well as the possible physiological role of this receptor. In the final paragraphs some less well defined activities are presented.

Cholinergic effects of cimetidine and ranitidine

Cimetidine and ranitidine were submitted to eight in vitro assays: their intrinsic activity was evaluated on guinea-pig auricles and ileum, acetylcholine synergism on guinea-pig tracheal muscle, frog rectus abdominis, guinea-pig vas and rat phrenic nerve diaphragm, and antagonism on guinea-pig auricles and rat jejunum estimated at a range of concentrations. Ranitidine alone opposed 1-hyoscyamine antagonism in guinea-pig ileum when acetylcholine was the agonist, but not when the agonist was bethanechol.