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The pressor activity of burimamide: a relationship between chemical constitution and pressor activity of burimamide and related histamine H2-receptor antagonists.

Burimamide, a histamine H2-receptor antagonist, has been shown to cause pressor responses in pithed rats. The response can be prevented by prior removal of the adrenal glands or by pretreatment with the alpha-adrenoceptor antagonist, phentolamine, 5 mg/kg, suggesting that the pressor response to burimamide is due to release of catecholamines from the adrenal glands. The pressor activity of burimamide has been compared with that of metiamide and two close chemical analogues, methylburimamide and thiaburimamide, in order to identify which chemical features of the compounds are necessary for this activity. Methylburimamide was the most potent pressor agent, followed by burimamide, metiamide and thiaburimamide. The pressor effects (and presumably catecholamine-releasing activities) appear to be related to the basicities of the compounds. We conclude that the release of catecholamines by these histamine H2-receptor antagonists is probably due to their cationic (imidazolium) forms.

Animals

Effects of the histamine H2-receptor blocking drugs burimamide and cimetidine on noradrenergic transmission in the isolated aorta of the rabbit and atria of the guinea-pig.

1 In rabbit aortic strips, concentration-response curves to noradrenaline (NA) were shifted to the right in a parallel and concentration-dependent manner by the alpha-adrenoceptor blocking drug, phentolamine and also by the histamine H(2)-receptor blocking drugs, burimamide and cimetidine. Responses to 5-hydroxytryptamine were not affected by these drugs.2 Burimamide had the properties of a competitive antagonist of noradrenaline, possessing about one-hundredth the potency of phentolamine. Cimetidine was weaker than burimamide and did not fulfil the requirements for competitive antagonism of noradrenaline.3 In guinea-pig isolated atria, in which noradrenergic transmitter stores were labelled with [(3)H]-noradrenaline, phentolamine (3 muM), burimamide (30 muM) and cimetidine (30 muM), in decreasing order of effectiveness, each enhanced stimulation-induced efflux of [(3)H]-noradrenaline, indicating that their blocking effects on prejunctional alpha-adrenoceptors in this tissue are in the same order of relative potency as on postjunctional alpha-adrenoceptors in rabbit aortic strips.4 In the concentrations used (30 muM), neither burimamide nor cimetidine interfered with the neuronal uptake of noradrenaline. Burimamide, and to a much lesser extent, cimetidine, increased the resting efflux of [(3)H]-noradrenaline from guinea-pig atria.5 The effect of clonidine, a partial agonist on prejunctional alpha-adrenoceptors in guinea-pig atria, in increasing stimulation-induced efflux of [(3)H]-noradrenaline when stimulated with 150 pulses at 5 Hz was blocked by cimetidine (30 muM) and reversed by phentolamine (3 muM) and burimamide (30 muM).

Animals

The pharmacology of burimamide and metiamide, two histamine H2-receptor antagonists.

Burimamide and metiamide are two histamine H2-receptor antagonists. Evidence is presented that indicates the competitive nature and the specificity of the antagonism. Metiamide is about ten times more potent than burimamide and is also more effective than burimamide when given orally. Both compounds inhibit gastric secretion and the evidence is consistent with this inhibition being due to competitive antagonism of H2 receptors in the gastric mucosa. Burimamide, unlike metiamide, causes release of catecholamines even at dose levels that are just sufficient to produce H2-receptor antagonism. Burimamide, but not metiamide, has alpha-adrenoceptor blocking activity. In certain models for inflammation, particularly rat paw edema induced by compound 48/80, burimamide in combination with the H1-receptor antagonist mepyramine shows anti-inflammatory activity. This may, in part, be associated with the catecholamine-releasing properties of the compound. Metiamide is less active in this respect.

Animals

An indirect sympathomimetic effect of burimamide on kitten isolated atria.

1. Burimamide (34-1080 muM) caused a concentration-dependent increase in the force and frequency of contraction of kitten isolated atria. 2. Metiamide (467 muM) had no stimulant action on kitten atria and did not modify the effects of burimamide. 3. The atrial stimulation produced by burimamide was reduced by (-)propranolol (34-68 nM) and by cocaine (3 muM). 4. The atrial stimulant effect of burimamide was prevented by pretreatment of kittens with reserpine (1 mg/kg, 24 h before the experiment). 5. It is concluded that burimamide causes atrial stimulation by releasing catecholamines.

Animals

Electrophysiological effects of burimamide and 16,16-dimethyl prostaglandin E2 on the canine gastric mucosa.

The electrophysiological effects of two potent inhibitors of gastric acid secretion, burimamide and 16,16-dimethyl prostaglandin E2 (dm-PGE2), were determined in an in vivo histamine-stimulated canine stomach preparation and an in vitro canine gastric mucosal preparation. In the in vivo stomach preparation, intravenous burimamide caused a decrease in acid secretion, an increase in transmucosal potential difference (PD) and the relative resistance (R) was essentially unchanged. Intravenous dm-PGE2 also inhibited acid secretion and increased PD but, in contrast to burimamide, increased R. In the in vitro preparation, the unidirectional flux of sodium from mucosa to serosa increased after dm-PGE2 but not after burimamide. Passive sodium fluxes and unidirectional chloride fluxes were not altered after either agent. These findings suggest that increased active transport of sodium from mucosa to serosa is at least partially responsible for the observed increase in transmural PD with dm-PGE2, an agent which also decreases hydrogen ion transport. With burimamide the increased PD was due primarily to inhibition of hydrogen ion secretion.

Animals

In vitro anaphylaxis in guinea-pig skin: amplification by burimamide.

The effects of burimamide, an H2-antihistamine, on the anaphylactic reaction in the skin of ovalbumin-sensitized guinea pigs were studied in vitro. Burimamide enhanced the concentration of histamine in the supernatant fraction of antigen-challenged sensitized guinea-pig skin in a dose-related way, but did not alter the concentration of residual histamine in the skin after antigen challenge. The enhanced histamine concentration in the supernatant was not due to increased histamine synthesis by the target cells during the reaction because the increase was not inhibited by a histidine decarboxylase inhibitor, Brocresine. In further experiments it was shown that guinea-pig skin possesses potent histamine degrading enzyme activity which is inhibited by burimamide. We suggest that inhibition of these degrading enzymes leads to the increase in histamine concentration in the presence of burimamide.

Anaphylaxis

Effect of the H2-receptor antagonists (burimamide and metiamide) on gastric secretion stimulated by histamine and its methyl derivatives.

This study was done to determine the comparative effectiveness of burimamide and metiamide as antagonists of gastric secretion stimulated by histamine and its methyl derivatives, Nalpha-methylhistamine, N-alpha,N-alpha-dimethylhistamine and 4-methylhistamine, in dogs with vagally denervated (Heidenhain pouches) and vagally innervated gastric mucosal septal pouches (Pavlov-type pouches). The secretagogues were always given by continuous i.v. infusion to produce steady states of secretory activity in the fasted conscious dogs; the antagonists were given by either rapid "bolus" i.v. injection or continuous i.v. infusion. With bolus injections, both antagonists promptly inhibited the secretion produced by histamine and its methyl derivatives. When control secretory rates were similar, 40 mumol of burimamide per kg and 4 mumol of metiamide per kg produced the same degree of inhibition. When the antagonists were also given by continuous i.v. infusion, the difference between them was greater, metiamide being 15 to 17 times more potent than burimamide. The effectiveness of the antagonists was not changed by vagal denervation. Symptoms of toxicity to burimamide developed at doses in excess of 30 mumol/kg/hr; none occurred with doses of metiamide ranging from 1.8 to 7.5 mumol/kg/hr.

Animals

A Quantitative study of histamine H2-receptor bockade by burimamide in isolated artica.

The onset of burimamide inhibition of histamine stimulation of rabbit atria is rapid, and a near steady-state blockade occurs at approximately 15 min ( larger than or equal to 90% complete). The blockade is reversible but requires several washings suggesting the disassociation is slow. The administration of histamine may accelerate the decay of the burimamide effect. Reciprocal plots (rate response versus histamine concentration) of dose-response curves are linear for both rabbit and guinea pig atria. In the presence of low concentrations of burimamide; (2.4 times 10-5 M), the displacement of curves suggests a competitive type of inhibition both for rabbit and guinea guinea pig atria. The apparent association constants calculated from these curves are: K1 (rabbit) 3.7 times 10-6M and K-1 (guinea pig) 6.7 times 10-6M. These results for guinea pig atria are in satisfactory agreement with the value obtained in another laboratory (2). At higher concentrations of burimamide, inhibition curves showed distinct evidence of departure from competitive character for both guinea pig and rabbit atria.

Animals

Effects of the H1-antagonist promethazine and the H2-antagonist burimamide on chronotropic, inotropic and coronary vascular responses to histamine in isolated perfused guinea-pig hearts.

On guinea-pig atria part of the inotropic response to histamine is attributable to a concomitant increase of the frequency [7]. Since the chronotropic effect of histamine is mediated by a stimulation of H2-receptors a direct interaction of histamine with H1-receptors a direct interaction of histamine with H1-receptors mediating the inotropic response on heart may be overlooked. For this reason the ability of the H1-antagonist promethazine and the H2-antagonist burimamide to inhibit the positive chronotropic, inotropic and coronary vascular responses to histamine was determined in spontaneously beating and electrically driven perfused guinea-pig hearts. (1) Burimamide produced a competitive blockade of the positive chrono- and inotropic responses to histamine. (2) On the other hand, promethazine in concentrations that had no effect on cardiac function by itself, proved to be ineffective against the positive chrono- and inotropic responses produced by histamine on spontaneously beating and electrically driven heart preparations. (3) The predominant coronary vasodilation observed after infusion with histamine was competitively antagonized by promethazine and burimamide. This blockade was not attributable to an interaction with myocardial H2-receptors mediating increases in heart rate and contractility and was, therefore, direct in nature. (4) Based upon the present study and former investigations [7] the following distribution of different histamine receptors in the guinea-pig heart does exist: H1-receptors are present in the atrial muscle and the coronary vascular bed. H2-receptors are located in the sinus node, the ventricular myocardium and the coronary vessels.

Animals

Liberation of histamine by compound 48/80, tolazoline, betahistine and burimamide from isolated spontaneously beating guinea pig and rabbit atrial pairs.

Tolazoline, betahistine, burimamide and compound 48/80 release histamine from isolated guinea pig atria resulting in histamine concentrations that stimulate H2-receptors. Tolazoline, burimamide and 48/80 also release histamine from rabbit atria but do not result in histamine concentrations that will stimulate either H1- or H2-receptors. However, betahistine (which does not release histamine from rabbit atria) and tolazoline stimulate the rabbit atrial chronotropic response by releasing catecholamines.

Animals

The effects of burimamide and metiamide on basal gastric function in the cat.

1 Burimamide injected intravenously in the anaesthetized or conscious cat produced significant increases in gastric acid secretion: in the anaesthetized cat it produced increased gastric mucosal blood flow. 2 Metiamide, in doses which inhibited pentagastrin-stimulated acid secretion, produced no increase in gastric acid secretion in conscious animals, or gastric acid secretion or gastric mucosal blood flow in the anaesthetized cat. 3 Metiamide did not influence the amount of acid which diffused out of the stomach when instilled at pH values between 1.5 and 6.0. 4 The possible mode of action of burimamide in increasing basal gastric secretion is discussed.

Anesthesia

Histamine H2-receptors in the sheep bronchus and cat trachea: the action of burimamide.

Histamine-induced relaxation of the sheep bronchus was antagonized by burimamide but not by mepyramine, indicating the presence of H(2)-receptors. Mepyramine or burimamide alone produced partial antagonism of histamine-induced relaxation of the cat trachea. Both inhibitors added simultaneously effectively abolished the histamine response, suggesting that both H(1)- and H(2)-receptors are active in relaxing the cat trachea.

Animals

Anaphylaxis in the guinea-pig isolated heart: selective inhibition by burimamide of the positive inotropic and chronotropic effects of released histamine.

1. Anaphylaxis was induced in the isolated heart of the guinea-pig in the presence of burimamide at concentrations of 4 x 10(-5)M and 2.7 x 10(-4)M.2. Burimamide did not affect the immunological release of histamine; however, it selectively antagonized the positive inotropic and chronotropic effects of released histamine. The antagonism of the positive chronotropic effect was concentration-dependent.3. Neither the negative dromotropic effect nor the decrease in coronary flow rate occurring during anaphylaxis were inhibited by burimamide.4. The results are in agreement with the double histamine receptor theory and suggest that, in the heart of the guinea-pig, H(2)-receptors are involved in the positive inotropic and chronotropic effects of released histamine, and H(1)-receptors in the negative dromotropic effect.

Anaphylaxis

The inhibition of histamine uptake and metabolism by burimamide in the guinea-pig atrium and in mouse neoplastic mast cells, in vitro.

Burimamide, an H(2)-receptor blocking agent, has been shown capable of blocking the uptake and metabolism of [(14)C]-histamine, both in the guinea-pig isolated atrium and in murine neoplastic mast cells. This occurs even at concentrations far below the dose range capable of blocking the positive chronotropic effect of histamine in the isolated atrium. In the atrium, very low concentrations of burimamide were found capable of blocking histamine metabolism.

Animals

Stimulation of rat gastric adenylate cyclase by histamine and histamine analogues and blockade by burimamide.

Histamine, 4-methylhistamine, 3-(beta-aminoethyl)-1,2,4 triazole and betazole, in that order, stimulated adenylate cyclase prepared from rat gastric tissue in a dose-dependent manner. Burimamide, an H(2)-receptor blocking agent, in concentrations of 1-5 x 10(-6) M antagonized this effect. The data lend some support to the hypothesis that elevated levels of cyclic adenosine 3',5'-monophosphate may be involved in histamine-stimulated gastric secretions and that H(2)-receptors are associated with adenylate cyclase.

Adenylyl Cyclases

Effect of mepyramine, a histamine H1-, and burimamide, a histamine H2-receptor antagonist, on ovum implantation in the rat.

Systemic administration to rats of a combination of mepyramine, a histamine H1-, and burimamide, a histamine H2-receptor antagonist, over a period which included the time of implantation (late Day 5 to early Night 5), increased the number of blastocysts recovered from the uterus and reduced the number and intensity of Pontamine Sky Blue (PSB) sites obtained at autopsy on Night 5. Histological examination of the PSB sites taken on Night 5 from animals receiving the histamine antagonists revealed that the stromal oedema, which is characteristic of the attachment phase of pregnancy, had been inhibited.

Animals