Some effects of histamine in the depolarized rat uterus

Abstract

Summary1. The relaxant effect of histamine in the isolated rat uterus remained after the preparation was depolarized in a potassium Ringer. 2. The effect was abolished by the calcium-chelating agent, ethyleneglycol bis-aminoethyl ether-tetraacetic acid (EGTA). 3. Histamine caused relaxation during calcium-induced contractures in a depolarized uterus treated with EGTA, but did not produce relaxation during barium-induced contractures. 4. While responses of a normally polarized rat uterus to acetylcholine were inhibited by histamine, those of a depolarized uterus were enhanced by histamine. The inhibitory effects of isoprenaline and papaverine on acetylcholine responses were maintained in depolarized preparations. 5. Both the enhancing effect of histamine on responses to acetylcholine and the relaxation of calcium-induced contractures were abolished by burimamide, indicating that H2-receptors mediate the effects of histamine in the depolarized tissue. 6. A reduction in the rate of exchange of calcium across the depolarized cell membrane was demonstrated with high concentrations of histamine. 7. The results are consistent with the hypothesis that in the rat uterus, the stimulation of H2-receptors by histamine is accompanied by a reduction in calcium exchange across the membrane which may result in a decrease in the concentration of free intracellular calcium available to stimulate contraction of the myofilaments. Histamine may act by increasing the binding of calcium within the cell. IntroductionThe receptors for histamine in the rat uterus are similar to those involved in histamine-stimulated gastric secretion (Black, Duncan, Durant, Ganellin & Parsons, 1972). A knowledge of the immediate consequences of H2-receptor stimulation in the rat uterus would not only help to explain how histamine exerts its relaxant effect on this tissue, but may provide information about the mechanisms involved in gastric secretion.It has been shown (Blyth, 1972) that histamine keeps the resting membrane potential of the rat uterus at the normal level and suppresses spike discharge.

Pharmacological investigations into the effects of histamine and histamine analogs on guinea pig and rat uterus

“…1). This confirms the previous findings of BLACK et al [12], BLYTn [31] and McNEmL and VERNA [32] of the presence of H2-receptors in the rat uterus. In …”

Effect of histamine on the longitudinal and circular muscle of the oestrogen dominated rat uterus

“…Goyal and Verma [15] described that histamine produced the uterine inhibitory effect mediated only by histamine H2-receptors, but that they act indirectly through the release of noradrenaline. Our results with reserpine in both uterine layers of the oestrogenized-treated rats contrast with those results, but agree with others described in our laboratory [10,11] and by others [17,18]. Although the existence of excitatory histamine H 1-receptors in the rat uterus was suggested by Viggiano et al [19], in this study neither histamine nor 2-pyridylethylamine, in the presence of ranitidine, caused any contraction of the longitudinal and circular layers of the isolated diethylstilboestrol-treated rat uterus.…”

Cimetidine as pre-anesthetic agent for cesarean section: perinatal effects on the infant, the placental transfer of cimetidine and its elimination in the infants

“…Histamine H 2 receptors are present in many organs including the heart and the uterus. Animal experiments have not revealed any influence of cimetidine on the contractility pattern of the uterine muscles [2] and, following a single bolus injection, no electrocardiographic changes were observed [5]; however, arrhythmias have been described following repeated doses administered to already ill and hypovolemic patients [3]. During the study, no pathological changes related to cimetidine were found in the contractility pattern of the uterus, the cardiotocographic tracings or blood samples from the infants.…”