Search results for "Histamine H2 receptor"

Effect of histamine and histamine analogues on human isolated myometrial strips.

1992

1. The effect of histamine and histamine H1- and H2-receptor agonists on isolated myometrium strips of premenopausal women has been examined. The effect of acetylcholine was also determined. 2. Histamine, 2-pyridylethylamine, 4-methylhistamine and acetylcholine, but not dimaprit, produced a concentration-related contractile response in human isolated myometrial strips. Histamine also produced a further contraction in human isolated myometrial strips precontracted with KCl (55 mM). 3. The contractile response to histamine was antagonized by the histamine H1-receptor antagonist, clemizole (0.1 microM) but was potentiated by the histamine H2-receptor antagonist, ranitidine (10 microM). Clemizo…

Mealtime versus nighttime acid inhibition

1992

This study was carried out in order to compare the effects of mealtime and bedtime regimens of ranitidine on gastric acidity. Fifteen duodenal ulcer patients in clinical remission were randomized to receive in single-blind fashion either placebo, ranitidine 300 mg at night (2200 hr) or ranitidine 150 mg three times a day given before each of the three daily meals (1800, 0800 and 1200 hr). Over 24 hr, the two active treatments produced a significantly greater acid inhibition than placebo, while the single daily regimen was superior to the three times a day regimen of ranitidine in terms of both rise in pH values (P less than 0.001) and duration of action expressed as time spent above 3.0 pH …

Absence of tolerance in duodenal ulcer patients treated for 28 days with a bedtime dose of roxatidine or ranitidine

1996

There is much experimental work on the occurrence of tolerance to the antisecretory effect of H2-receptor antagonists in healthy subjects, while data on its development in patients with duodenal ulcer are poor and conflicting. Moreover, this phenomenon has not been studied previously with 24 h gastric pH-metry in patients with active duodenal ulcer. For these reasons, we carried out a prospective pharmacodynamic investigation in 48 patients with endoscopically proven duodenal ulcer using the well-established once daily dosing schedule of H2 blockers. They were studied by means of 24 h continuous endoluminal pH-metry which was performed before, on d1 and d28 after receiving an oral bedtime d…

Influence of hormonal treatment on the response of the rat isolated uterus to histamine and histamine receptor agonists.

1992

The response of the isolated uterus to histamine and histamine agonists was investigated in progesterone- and oestrogen-treated rats. The uterine inhibitory responses to histamine and 4-methylhistamine (a histamine H2 receptor agonist) were similar in KCl-contracted uteri from progesterone- and oestrogen-treated rats. The histamine H1 receptor agonist, 2-pyridyl-ethylamine, produced a relaxant response only in progesterone dominant uterus. This was inhibited by the histamine H1 receptor antagonist. In the rat isolated uterus which was not preconstricted by KCl, neither histamine, 4-methylhistamine, nor 2-pyridyl-ethylamine produced any effect in the presence or absence of ranitidine. Raniti…

Effects of histamine on dentate granule cells in vitro

1990

Abstract Hippocampal slices from rat brain were exposed to histamine and related substances in a perfusion chamber. Granule cells of the dentate gyrus were studied with conventional extra- and intracellular recording and a single electrode voltage clamp. Histamine caused, through activation of H 2 -receptors, a small depolarization, an increase in the number of synaptic and action potentials, a block of the long lasting (but not the early) component of spike afterhyperpolarizations and a reduction of the accommodation of action potential firing. These effects were mimicked by forskolin (suggests activation of adenylate cyclase). In voltage clamp, histamine blocked a long lasting calcium-dep…

CLONIDINE, A PARTIAL AGONIST OF THE HISTAMINERGIC H2 RECEPTORS?

1978

Histamine binding to H2 receptors stimulates phospholipid methylation in mast cells

1982

Rat peritoneal mast cells incubated in vitro in the presence of L-[methyl-3H] methionine and exposed to histamine undergo a rapid but transient increase in phospholipid methylation. By using specific H1- and H2-receptor antagonists, and histamine analogues differing in their H2-receptor agonist potency, it has been demonstrated that this metabolic event is dependent on histamine binding to H2-receptors.

Responses to histamine and selective H2-receptor agonists in lung parenchymal strips from normal and sensitized guinea-pigs.

1989

Histamine produces concentration-dependent contractions of lung parenchyma strips obtained from normal and sensitized guinea-pigs. The responsiveness of the sensitized lung strips to histamine was significantly increased compared to normal tissues. Clemizole (0.1 microM) was equally effective as an H1-antagonist in normal (dose-ratio 9.12) and sensitized (dose-ratio 9.77) tissues. The concentration-response curves to histamine were displaced to the left by cimetidine (0.1 microM to 0.1 mM) with similar dose-ratios in normal and sensitized tissues. Cimetidine enhanced maximal responses to histamine only in normal lung strips. The effects of submaximal equieffective concentrations of histamin…

Structure-activity relationship of histamine H2-receptor agonists

1978

As demonstrated by the results the active C-5(4) substituted histamines and Nα-methyl-histamines are to various extents selective H2-receptor agonists.

H2-antihistaminics. 20. Structure-activity relationships in H2-receptor antagonists containing a 4-pyrimidone moiety.

1984

In a series of 5,6-substituted 4- pyrimidones 1 a-v the H2-antihistaminic activity was determined (guinea-pig atrium) and lipophilicity data are given in form of Rmo -values. The influence of different substituents at position 5 or 6 of a pyrimidone moiety has been studied. Quantitative structure-activity analyses showed the importance of lipophilicity for drug activity. Additionally other physicochemical substituent-properties may play a major role.