Responses of rabbit portal vein to histamine

Histamine and H1 -histamine receptors faster venous circulation

The study has analysed the action of histamine in the rabbit venous system and evaluated its potential role in contraction during increased venous pressure. We have found that a great variety exists in histamine sensitivity and H(1) -histamine receptor expression in various types of rabbit veins. Veins of the extremities (saphenous vein, femoral vein, axillary vein) and abdomen (common iliac vein, inferior vena cava) responded to histamine by a prominent, concentration-dependent force generation, whereas great thoracic veins (subclavian vein, superior vena cavas, intrathoracic part of inferior vena cava) and a pelvic vein (external iliac vein) exhibited slight sensitivity to exogenous histamine. The lack of reactivity to histamine was not due to increased activity of nitric oxide synthase (NOS) or heme oxygenase-1. H(1) -histamine receptor expression of veins correlated well with the histamine-induced contractions. Voltage-dependent calcium channels mediated mainly the histamine-induced force generation of saphenous vein, whereas it did not act in the inferior vena cava. In contrast, the receptor-operated channels were not involved in this response in either vein. Tyrosine phosphorylation occurred markedly in response to histamine in the saphenous vein, but not in the inferior vena cava. Histamine induced a prominent ρ kinase activation in both vessels. Protein kinase C and mitogen-activated protein kinase (MAPK) were not implicated in the histamine-induced intracellular calcium sensitization. Importantly, transient clamping of the femoral vein in animals caused a short-term constriction, which was inhibited by H(1) -histamine receptor antagonist in vivo. Furthermore, a significantly greater histamine immunopositivity was detected in veins after stretching compared to the resting state. We conclude that histamine receptor density adapts to the actual requirements of the circulation, and histamine liberated by the venous wall during increased venous pressure contributes to the contraction of vessels, providing a force for the venous return.

Presinusoidal vessels predominantly contract in response to norepinephrine, histamine, and KCl in rabbit liver

In rabbit livers, it is not well known which segments of the hepatic vasculature are predominantly contracted by various vasoconstrictors. We determined effects of histamine, norepinephrine, and KCl on hepatic vascular resistance distribution in isolated rabbit livers perfused via the portal vein with 5% albumin-Krebs solution at a constant flow rate. Hepatic capillary pressure was measured by double vascular occlusion pressure (Pdo) and was used to determine portal (Rpv) and hepatic venous (Rhv) resistances. A bolus injection of either histamine or norepinephrine dose-dependently increased portal venous pressure but not Pdo, resulting in a dose-dependent increase in Rpv and no changes in Rhv. KCl (50 mM), when injected in anterogradely perfused livers, contracted the presinusoidal vessels selectively with liver weight loss. Although KCl significantly increased Rhv in retrogradely perfused livers, the increase in Rpv by 400% of baseline predominated over the increase in Rhv by 85% of baseline. In the retrogradely perfused livers, KCl produced an initial liver weight loss followed by a profound weight gain. We conclude that histamine and norepinephrine selectively contract the presinusoidal vessels. The results on KCl effects suggest that this selective presinusoidal constriction might be possibly due to predominant distribution of functionally active vascular smooth muscle in the presinusoidal vessels rather than the hepatic vein in rabbit livers.

Characterization of histamine-induced contraction in rat isolated aorta

High concentrations of histamine (greater than 10 microM) contract rat aortic rings and the effect is greatly enhanced when the endothelium is removed. The present study was aimed at characterizing the histamine-induced contractions of de-endothelialized rat aortic rings. These contractions were poorly inhibited by the histamine H1-receptor antagonist, mepyramine (1 and 10 microM) and insensitive to the histamine H2-receptor antagonist, cimetidine (10 microM), and to the cyclooxygenase inhibitor, indomethacin (5 microM). In contrast, the alpha-adrenoceptor antagonists, prasozin and pentholamine, antagonized these contractions in a concentration-dependent manner (respective apparent pKB values 9.7 and 7.9) and nifedipine (3 microM) reduced them by about 75%. Pretreatment of de-endothelialized rings with 8-bromo-cyclic GMP and of intact rings with methylene blue resulted in respective inhibition and enhancement of histamine-induced contractions, quite similarly to the effects in the presence and in the absence of endothelium, respectively. Histamine elicited endothelium-dependent relaxation of aortic rings precontracted by prostaglandin F2 alpha. This relaxation was abolished in the presence of mepyramine (1 microM). However, mepyramine failed to mimic the enhancing effect of endothelium removal on histamine-induced contractions of resting aortic rings. It is concluded that, in rat aorta, (1) contractions induced by high concentrations of histamine (greater than 10 microM) are probably mediated by alpha 1-adrenoceptors; and (2) spontaneous, but not histamine-stimulated, release of endothelium-derived relaxing factor is mainly involved in the modulation of histamine-induced contractions.

Histamine receptors in the smooth muscle of human internal mammary artery and saphenous vein

The effects of histamine were characterized and compared in the vascular smooth muscle of two human isolated blood vessels, the human internal mammary artery (HIMA) and the human saphenous vein (HSV). Segments of these vessels were obtained during aortocoronary bypass surgery and their intimal surface was rubbed in order to eliminate any possible influence of the endothelium. Histamine contracted both types of vessels in a concentration-dependent manner and this effect was antagonized by the H1 receptor antagonists mepyramine and cicletanine. In the case of HIMA only this antagonism was found to be competitive (pA2 values of 9.3 and 7.7 for mepyramine and cicletanine, respectively). Histamine-induced contractions were not significantly affected by phentolamine (0.3 microM). In HSV, but not HIMA, indomethacin (5 microM) significantly depressed histamine-induced contractions (by about 30%). In the presence of the H2 receptor antagonist cimetidine (10 microM), concentration-response curves of histamine-induced contractions were significantly shifted to the left in both HIMA and HSV, suggesting the presence of H2 receptors mediating relaxation. HIMA and HSV precontracted by noradrenaline could be partially and concentration dependently relaxed by histamine, only in the presence of a H1 receptor antagonist. This relaxation was inhibited by cimetidine. The results show that in de-endothelialized HIMA and HSV histamine induced mainly contraction which is sensitive to the H1 receptor antagonists. Only in HIMA, nevertheless, was competitive antagonism established. In addition, histamine-induced relaxation, antagonized by cimetidine, could be demonstrated in both precontracted vessels, indicating the presence of H2 receptors.

Studies on the mechanism of ethanol-induced gastric damage in rats

Concentrated ethanol causes gastric lesions by a mechanism that is poorly understood. We have investigated this mechanism in the rat stomach via gross morphologic, videomicroscopic, histochemical, and pharmacologic approaches. Within 1 min of contact, ethanol caused diffuse mucosal hyperemia. By 5 min, hyperemia greatly intensified at some mucosal sites. Beneath sites where mucosal hyperemia developed, intramural venules strongly constricted at 3-13 s postethanol, whereas submucosal arterioles dilated more than two times in diameter by 25 s. Submucosal venular constriction began sooner than arteriolar dilation (9 vs. 16 s, p less than 0.05). One-third of the gastric mucosal mast cells degranulated by 15 s postethanol; 50% discharged by 30 s. Ethanol-induced hyperemia was markedly reduced by lipoxygenase-selective inhibitors BW755C or nordihydroguaiaretic acid, or by the H1-antihistamine pyrilamine, but not by indomethacin, cimetidine, phentolamine, or methysergide. Based on these results, a model for the pathogenesis of ethanol-induced gastric lesions is proposed.

Histamine responses mediated via H1- and H2-receptors in the isolated portal vein of the dog

The effects of histamine were studied on the isolated circular muscle strip and longitudinal muscle strip of the dog portal vein. Histamine-induced contractions of the circular muscle were inhibited by H1-receptor antagonist pyrilamine but increased by H2-receptor antagonist ranitidine. When the tissues were contracted with PGF2 alpha in the presence of pyrilamine, histamine produced the relaxation of the circular muscle but not longitudinal muscle. The relaxation of the circular muscle was inhibited by ranitidine in a concentration dependent manner, the pA2 value for ranitidine being 6.97 (6.55-7.39). It is concluded that the response of the circular muscle to histamine is the sum of two components, H1-receptor mediated contraction and H2-receptor mediated relaxation.

Glomerular immune injury in the rat: effect of antagonists of histamine activity

The participation of histamine via H1 and H2 receptors, in the alteration of glomerular ultrafiltration consequent to acute glomerular immune injury was evaluated in three groups of Munich-Wistar rats, before and after the administration of large doses of antiglomerular basement membrane antibody (AGBM). Group 1 was the control and was untreated; group 2, rats continuously infused with H1 receptor antagonist diphenhydramine; and group 3, rats receiving continuous infusion of the H2 receptor antagonist cimetidine. In group 1, nephron filtration rate (SNGFR) decreased within 60 min after AGBM from 58 +/- 2 to 32 +/- 5 nl . min-1 . g kidney wt-1 (P less than 0.0005) due to decreases in both nephron plasma flow (RPF) (291 +/- 35 to 119 +/- 23 nl . min-1 . g kidney wt-1) (P less than 0.0005) and the glomerular permeability coefficient (LpA) (0.13 +/- 0.02 to 0.06 +/- 0.01 nl . sec-1 . g kidney wt-1 . mm Hg-1) (P less than 0.01). In group 2, SNGFR decreased similarly with AGBM (59 +/- 2 to 23 +/- 10 nl . mm-1 . g kidney wt-1) (P less than 0.0005) due again to major reductions in RPF and LpA, suggesting no protective effect of H1 receptor blockade. In group 3, control, pre-AGBM values for SNGFR and RPF were lower than they were in groups 1 and 2 due to cimetidine infusion. SNGFR and RPF decreased but to a lesser extent in group 3 (48 +/- 3 to 41 nl . min-1 . g kidney wt-1) (P less than 0.0005). Renal vascular resistance did not change after AGBM in this group but interpretation of this finding is complicated because blood pressure decreased after the antibody administration. LpA decreased in group 3 as in group 1, therefore neither H1 nor H2 receptor antagonist prevented reductions in LpA. The absence of vasoconstriction after AGBM during H2 receptor blockade may have been a nonspecific effect of cimetidine. Histamine plays no major role in AGBM-induced immune injury in the rat and does not prevent a reduction in nephron filtration rate.

Effect of subarachnoid hemorrhage on contractile responses and noradrenaline release evoked in cat cerebral arteries by histamine

This study analyzes the changes induced by subarachnoid hemorrhage (SAH) on the contractile responses and the noradrenaline release evoked in cat cerebral arteries by histamine. The dose-dependent vasoconstriction induced by histamine on the cerebral arteries of normal cats was significantly reduced by diphenhydramine and phentolamine. When SAH was produced 3 and 7 days before the experiment, the histamine-induced vasoconstriction also decreased. Thereafter, a tendency to normalization in the contractile vascular responses was observed such that in 15 days after the hemorrhage it was not significantly different from that found in controls animals. The decrease in the contractile responses to histamine provoked by SAH was similar to that seen after pretreatment with intracisternal injections of 6-hydroxydopamine. The amount of radioactivity released by histamine following preincubation with 3H-noradrenaline from the cerebral arteries of cats exposed to SAH 3, 7, and 15 days before the experiment was significantly reduced when compared with controls. Moreover, the basal level of tritium release and the radioactivity retained at the end of the experiment were also decreased after SAH. These decreases were less marked 15 days after SAH. Intracisternal injections of 6-hydroxydopamine 3, 7, and 15 days prior to the assay, and the removal of both superior cervical ganglia 15 days before the experiment, also markedly reduced these three parameters. These results indicate that histamine releases noradrenaline from cat cerebral arteries, and SAH produces a transient denervation of the perivascular adrenergic nerve endings. The inhibition of the histamine-induced vasoconstriction observed after SAH might be explained by the impairment of the indirect adrenergic mechanism involved in the overall contractile response elicited by this amine in cerebral arteries. According to the present findings, histamine does not seem to play a significant role in the production of the cerebral vasospasm occurring after SAH.

The effect of histamine on the smooth muscle cells of the ear artery of the rabbit

Histamine activates both H1- and H2-receptors in the ear artery of the rabbit. The specific action of these receptor activations on the membrane potential and the force development has been investigated by using the H1-blocking agent mepyramine and the H2-blocking agent cimetidine. H1-activation depolarizes and increases force development, while H2-activation hyperpolarizes and reduces force development. These effects on the force development can occur independently of the changes of the membrane potential. By determining the effect of histamine on tissues which were denervated with 6-hydroxydopamine it was shown that histamine exerts its effect directly on the smooth muscle cells. Na-deficiency depolarizes the smooth muscle cells, but it also reduces the changes of the membrane potential and the force development induced by H1-stimulation. K-free medium prevents the hyperpolarizing effect of H2-activation. As far as the ion fluxes are concerned an H1-activation is found to induce an increased efflux of K while a simultaneous H2-activation only reduces the increase of flux induced by H1-activation. H1-activation induces a release of Ca from the intracellular Ca stores, while H2-activation inhibits this release.