Mechanisms involved in the vasorelaxing influence of histamine on isolated human subcutaneous resistance arteries

Simulate SubQ: The Methods and the Media

For decades, there has been a growing interest in injectable subcutaneous formulations to improve the absorption of drugs into the systemic circulation and to prolong their release over a longer period. However, fluctuations in the blood plasma levels together with bioavailability issues often limit their clinical success. This warrants a closer look at the performance of long-acting depots, for example, and their dependence on the complex interplay between the dosage form and the physiological microenvironment. For this, biopredictive performance testing is used for a thorough understanding of the biophysical processes affecting the absorption of compounds from the injection site in vivo and their simulation in vitro. In the present work, we discuss in vitro methodologies including methods and media developed for the subcutaneous route of administration on the background of the most relevant absorption mechanisms. Also, we highlight some important knowledge gaps and shortcomings of the existing methodologies to provide the reader with a better understanding of the scientific evidence underlying these models.

Histamine-dependent prolongation by aldosterone of vasoconstriction in isolated small mesenteric arteries of the mouse

In arterioles, aldosterone counteracts the rapid dilatation (recovery) following depolarization-induced contraction. The hypothesis was tested that this effect of aldosterone depends on cyclooxygenase (COX)-derived products and/or nitric oxide (NO) synthase (NOS) inhibition. Recovery of the response to high K+ was observed in mesenteric arteries of wild-type and COX-2−/− mice but it was significantly diminished in preparations from endothelial NOS (eNOS)−/− mice. Aldosterone pretreatment inhibited recovery from wild-type and COX-2−/− mice. The NO donor sodium nitroprusside (SNP) restored recovery in arteries from eNOS−/− mice, and this was inhibited by aldosterone. Actinomycin-D abolished the effect of aldosterone, indicating a genomic effect. The effect was blocked by indomethacin and by the COX-1 inhibitor valeryl salicylate but not by NS-398 (10−6 mol/l) or the TP-receptor antagonist S18886 (10−7 mol/l). The effect of aldosterone on recovery in arteries from wild-type mice and the SNP-mediated dilatation in arteries from eNOS−/− mice was inhibited by the histamine H2 receptor antagonist cimetidine. RT-PCR showed expression of mast cell markers in mouse mesenteric arteries. The adventitia displayed granular cells positive for toluidine blue vital stain. Confocal microscopy of live mast cells showed loss of quinacrine fluorescence and swelling after aldosterone treatment, indicating degranulation. RT-PCR showed expression of mineralocorticoid receptors in mesenteric arteries and in isolated mast cells. These findings suggest that aldosterone inhibits recovery by stimulation of histamine release from mast cells along mesenteric arteries. The resulting activation of H2 receptors decreases the sensitivity to NO of vascular smooth muscle cells. Aldosterone may chronically affect vascular function through paracrine release of histamine.

Microvascular responsiveness in obesity: implications for therapeutic intervention

Obesity has detrimental effects on the microcirculation. Functional changes in microvascular responsiveness may increase the risk of developing cardiovascular complications in obese patients. Emerging evidence indicates that selective therapeutic targeting of the microvessels may prevent life-threatening obesity-related vascular complications, such as ischaemic heart disease, heart failure and hypertension. It is also plausible that alterations in adipose tissue microcirculation contribute to the development of obesity. Therefore, targeting adipose tissue arterioles could represent a novel approach to reducing obesity. This review aims to examine recent studies that have been focused on vasomotor dysfunction of resistance arteries in obese humans and animal models of obesity. Particularly, findings in coronary resistance arteries are contrasted to those obtained in other vascular beds. We provide examples of therapeutic attempts, such as use of statins, ACE inhibitors and insulin sensitizers to prevent obesity-related microvascular complications. We further identify some of the important challenges and opportunities going forward.

LINKED ARTICLES

This article is part of a themed section on Fat and Vascular Responsiveness. To view the other articles in this section visit http://dx.doi.org/10.1111/bph.2012.165.issue-3.

Histamine-induced contraction and relaxation of placental chorionic plate arteries

Studies of the human placental vasculature suggest a low resistance circulation. Using wire myography, endothelial-dependent relaxation of human chorionic plate arteries has been difficult to demonstrate with any consistency. However, histamine has been suggested to relax placental vessels in the perfused organ in vitro. Here we aimed to demonstrate endothelial-dependent relaxation to histamine under physiological conditions of stretch and oxygenation. Histamine administration to pre-contracted arteries induced a triphasic response; an initial contraction followed by a dilatation which stabilized to a significant relaxation compared to time control arteries. Relaxation was partially inhibited by blockers of endothelial-dependent relaxation pathways. The initial contraction was abolished by H(1)-receptor blockade with mepyramine. The relaxation was significantly reduced by H(2)-receptor blockade with famotidine but only abolished in the presence of both H(1)- and H(2)-receptor antagonists. In conclusion, histamine induced contraction and relaxation of human chorionic plate arteries. Our data suggest that contraction is mediated by activation of H(1)-receptors. Relaxation occurs directly, via activation of H(2)-receptors on vascular smooth muscle cells, and indirectly via H(1)-receptor stimulation of endothelial-dependent relaxation.

Maximum skin hyperaemia induced by local heating: possible mechanisms

BACKGROUND

Maximum skin hyperaemia (MH) induced by heating skin to > or = 42 degrees C is impaired in individuals at risk of diabetes and cardiovascular disease. Interpretation of these findings is hampered by the lack of clarity of the mechanisms involved in the attainment of MH.

METHODS

MH was achieved by local heating of skin to 42-43 degrees C for 30 min, and assessed by laser Doppler fluximetry. Using double-blind, randomized, placebo-controlled crossover study designs, the roles of prostaglandins were investigated by inhibiting their production with aspirin and histamine, with the H1 receptor antagonist cetirizine. The nitric oxide (NO) pathway was blocked by the NO synthase inhibitor, NG-nitro-L-arginine methyl esther (L-NAME), and enhanced by sildenafil (prevents breakdown of cGMP).

RESULTS

MH was not altered by aspirin, cetirizine or sildenafil, but was reduced by L-NAME: median placebo 4.48 V (25th, 75th centiles: 3.71, 4.70) versus L-NAME 3.25 V (3.10, 3.80) (p = 0.008, Wilcoxon signed rank test). Inhibition of NO production (L-NAME) resulted in a more rapid reduction in hyperaemia after heating (p = 0.011), whereas hyperaemia was prolonged in the presence of sildenafil (p = 0.003). The increase in skin blood flow was largely confined to the directly heated area, suggesting that the role of heat-induced activation of the axon reflex was small.

CONCLUSION

NO, but not prostaglandins, histamine or an axon reflex, contributes to the increase in blood flow on heating and NO is also a component of the resolution of MH after heating.

Histamine-induced vasodilation and vasoconstriction in the mesenteric resistance artery of the rat

The present study was designed to examine the vascular response to histamine in rat perfused mesenteric vascular beds with active tone. In preparations with intact endothelium, perfusion of histamine (1 nM-100 microM) produced a concentration-dependent vasodilation. Histamine-induced vasodilation was attenuated by L-NAME (nitric oxide (NO) synthase inhibitor, 100 microM) and olopatadine (histamine H(1) receptor antagonist, 1 microM) but not by lafutidine (histamine H(2) receptor antagonist, 1 microM). Cold-storage denervation (4 degrees C for 72 h) of the preparation with intact endothelium attenuated the histamine-induced vasodilation. In preparations without endothelium, histamine at low concentrations (1-100 nM) produced only a small and rapid vasodilation, whereas histamine at concentrations higher than 1 muM produced triphasic vascular responses: initial sharp vasodilation followed by transient vasoconstriction and subsequent gradual vasodilation. Lafutidine abolished only the histamine-induced initial vasodilation. Olopatadine abolished the histamine-induced second vasoconstriction and third vasodilation. Cold-storage denervation of the denuded preparation abolished the histamine-induced second vasoconstriction and third vasodilation. These findings suggest that histamine induced endothelium-dependent vasodilation via endothelium histamine H(1) receptors and endothelium-independent vasodilation via smooth muscle histamine H(2) receptors. It is also suggested that the histamine-induced endothelium-independent vasoconstriction and vasodilation are mediated by histamine H(1) receptors and perivascular nerves.

Abolition of arteriolar dilation but not constriction to histamine in cremaster muscle of eNOS-/- mice

Histamine increases the permeability of capillaries and venules but little is known of its precapillary actions on the control of tissue perfusion. Using gene ablation and pharmacological interventions, we tested whether histamine could increase muscle blood flow through stimulating nitric oxide (NO) release from microvascular endothelium. Vasomotor responses to topical histamine were investigated in second-order arterioles in the superfused cremaster muscle of anesthetized C57BL6 mice and null platelet endothelial cell adhesion molecule-1 (PECAM-1-/-) and null endothelial NO synthase (eNOS-/-) mice aged 8-12 wk. Neither resting (17 +/- 1 microm) nor maximum diameters (36 +/- 2 microm) were different between groups, nor was the constrictor response (approximately 5 +/- 1 microm) to elevating superfusate oxygen from 0 to 21%. For arterioles of C57BL6 and PECAM-1-/- mice, cumulative addition of histamine to the superfusate produced vasodilation (1 nM-1 microM; peak response, 9 +/- 1 microm) and then vasoconstriction (10-100 microM; peak response, 12 +/- 2 microm). In eNOS-/- mice, histamine produced only vasoconstriction. In C57BL6 and PECAM-1-/- mice, vasodilation was abolished with Nomega-nitro-l-arginine (30 microM); in all mice, vasoconstriction was abolished with nifedipine (1 microM). Vasomotor responses were eliminated with pyrilamine (1 microM; H1 receptor antagonist) yet remained intact with cimetidine (1 microM; H2 receptor antagonist). These findings illustrate that the biphasic vasomotor response of mouse cremaster arterioles to histamine is mediated through H1 receptors on endothelium (NO-dependent vasodilation) as well as smooth muscle (Ca2+ entry and constriction). Thus histamine can increase as well as decrease muscle blood flow, according to local concentration. However, when NO production is compromised, only vasoconstriction and flow reduction occur.

An in vitro study of histamine on the pulmonary artery of the Wistar-Kyoto and spontaneously hypertensive rats

The vascular response to most neurotransmitters of different vascular beds is altered under hypertensive condition. The modulatory effect of genetic pulmonary arterial hypertension on histamine responses is not known. The present study was undertaken to evaluate the modulatory effect of enzymatic degradation (via histamine N-methyl-transferase and diamine oxidase) on the vascular response of histamine, and the subtype(s) of histamine receptor present in the pulmonary artery (first branch, O.D. approximately 800 microm) of the normotensive Wistar-Kyoto (WKY) and spontaneously hypertensive rats (SHR) (male, 22-26 weeks old). In phenylephrine (1 microM) pre-contracted preparations, histamine and 6-[2-(4-imidazolyl)ethylamino]-N-(4-trifluoromethylphenyl) heptanecarboxamide (HTMT, a histamine H(1) receptor agonist) elicited a concentration-dependent relaxation, with a smaller magnitude recorded in SHR. Application of 10 microM S-[4-(N,N-dimethylamino)-butyl]isothiourea (SKF 91488, a selective histamine N-methyl-transferase inhibitor), but not aminoguanidine (100 microM, a diamine oxidase inhibitor), significantly attenuated histamine-induced relaxation. Clobenpropit (1 nM, a potent histamine H(3) receptor antagonist) "antagonised" the suppressive effect of SKF 91488 and histamine-evoked relaxation was restored. Endothelial denudation reduced histamine- and abolished HTMT-elicited relaxation. Dimaprit (a histamine H(2) receptor agonist) caused an endothelium-independent, cis-N-(2-phenylcyclopentyl)azacyclotridec-1-en-2-amine (MDL 12330A, 10 microM, an adenylate cyclase inhibitor)-sensitive, concentration-dependent relaxation, with a similar magnitude in both strains of rat. Histamine-evoked relaxation was reversed into a further contraction (clobenpropit (10 nM)-sensitive) (with a greater magnitude occurred in the WKY rat) after blocking the histamine H(1) and H(2) receptors with diphenhydramine plus cimetidine (30 microM each). A similar further contraction (clobenpropit-sensitive) was observed with imetit (a histamine H(3)/H(4) receptor agonist) (> or =3 microM). Under resting tension, imetit (> or =0.3 microM) caused a clobenpropit (10 nM)- and prazosin (1 microM)-sensitive, concentration-dependent contraction, with a greater contraction in the WKY rats. Our results suggest that inhibition of histamine catabolism using SKF 91488 (histamine N-methyl-transferase inhibitor) resulted in a reduction of histamine-mediated relaxation that was due to the activation of the clobenpropit-sensitive, histamine H(3)/H(4) receptor and the release of catecholamine. In addition, activation of histamine H(1) and H(2) receptors resulted in relaxation whereas histamine H(3)/H(4) receptor activation by imetit yielded a prazosin-sensitive contraction of the pulmonary artery.

Nitric oxide, interleukin and prostaglandin interactions affecting the magnocellular system

Magnocellular neurons are innervated by an excitatory histaminergic pathway. They also express neuronal NO synthase, interleukin-1beta (IL-1beta) and cyclo-oxygenase (COX). In normally hydrated rats when NO synthase activity is inhibited with N(G)-nitro-L-arginine methyl ester (L-NAME), administered intracerebroventricularly (i.c.v.), OT concentration in plasma increases. In the present study, the increase in hormone after L-NAME is attenuated by indomethacin, an inhibitor of COX, as well as by antagonists of histamine receptors at H1 (pyrilamine) and H2 (cimetidine) subtypes injected i.c.v. Moreover, enhanced OT secretion induced by centrally administered IL-1beta, but not naloxone (opiate receptor antagonist), is prevented by indomethacin. PGE2 and PGD2 (i.c.v.) stimulate OT release, but only PGD2 affects circulating vasopressin levels. Thus, NO inhibits release of OT stimulated by: (1) a COX-dependent mechanism, i.e. NO-->-(COX-->+PG-->+OT release); (2) histamine, i.e. NO-->-(histamine-->H1 and H2 receptors-->+OT release); and possibly (3) IL-1beta, i.e. NO-->-(IL-1beta-->+COX-->+PG-->+OT release). These interactions of NO, cytokine and histamine may be important for management of stress-induced activation of neuroendocrine systems.

L-arginine partially reverses established adrenocorticotrophin-induced hypertension and nitric oxide deficiency in the rat

BACKGROUND

L-arginine treatment prevents adrenocorticotrophin (ACTH) induced hypertension in the rat. This study examined whether L-arginine treatment could reverse established ACTH hypertension and its effects on markers of decreased NO activity.

METHODS

Sixty-four male Sprague-Dawley rats were randomly divided into 6 groups given 12 days of treatment: (1) sham (0.9% NaCl, 0.5 ml/kg, subcutaneously, sc, n = 16); (2) ACTH (0.5 mg/kg/day, sc, n = 16); (3) sham + L-arginine (0.6% in food, from treatment day 8 onwards, n = 10); (4) ACTH + L-arginine (n = 10); (5) sham + D-arginine (0.6% in food, from T 8 onwards) (n = 6); and (6) ACTH + D-arginine (n = 6). Systolic blood pressure, water intake, urine volume, and body weight were measured every second day. At the end of the experiments, plasma and urinary nitrate/nitrite (NOx), plasma amino acid concentrations (in groups 1-4), and urinary cyclic guanosine monophosphate (cGMP) concentrations were measured.

RESULTS

Sham, sham + L-arginine, and sham + D-arginine treatments did not affect blood pressure. ACTH increased systolic blood pressure (from 121 +/- 1 to 147 +/- 2 mmHg, p < 0.001, pooled control vs treatment day 12, mean +/- sem), and this was partially reversed by L-arginine (group 4: from 141 +/- 2 on day 8 to 133 +/- 1 mmHg on day 12, n = 10, p < 0.001). In contrast, D-arginine did not affect blood pressure in ACTH-treated rats (group 6). ACTH increased water intake and urine volume and decreased body weight, and L-arginine administration did not alter these parameters. ACTH decreased plasma citrulline (group 1 vs 2: 115 +/- 7 vs 67 +/- 6 micro M/L, n = 16, p < 0.001) and NOx concentrations (group 1 vs 2: 8.3 +/- 0.8 vs 4.5 +/- 0.6 microM/L, n= 10, p < 0.001) and these decreases were reversed by L-arginine treatment (group 4: citrulline 98 +/- 9 micro M/L, NOx 9.1 +/- 1.6 micro M/L, group 2 vs 4, both p < 0.05). ACTH produced marked increases in urinary cGMP excretion (group 1 vs 2: 0.5 +/- 0.1 vs 1.9 +/- 0.4 nmol/24 h, p < 0.01).

CONCLUSION

Supplementation with L-arginine partly reversed established ACTH-induced hypertension and restored plasma NOx and citrulline concentrations to levels seen in sham-treated rats. These data are consistent with previous studies suggesting that functional NO deficiency has a role in ACTH-induced hypertension in rats.

Modified histamine-induced NO-mediated relaxation in resistance arteries in pre-eclampsia

We investigated the characteristic changes in histamine-induced, endothelium-derived nitric oxide (NO)-mediated relaxation in human omental resistance arteries seen in pre-eclampsia. Isometric contraction was provoked by a stable analogue of thromboxane A(2) in endothelium-intact strips from both pre-eclamptic and normotensive pregnant women. Histamine (0.3 nM-10 microM) produced a concentration-dependent relaxation of this contraction in both groups. The magnitude of the relaxation induced by histamine (1 microM) was significantly smaller in pre-eclampsia both in the presence and absence of famotidine (H(2)-receptor blocker). In the presence of famotidine, L-N(G)-nitroarginine significantly attenuated the histamine-induced relaxation in strips from normotensive pregnant women but not in those from pre-eclamptic women. The relaxation induced by human atrial natriuretic peptide (0. 1 nM-1 microM) was also significantly smaller in the pre-eclamptic group. It is concluded that the histamine-induced, endothelium-derived NO-mediated relaxation (mediated via H(1)-receptors) is down-regulated in resistance arteries in pre-eclampsia and we suggest that this is due, at least in part, to an attenuation of the action of cyclic GMP in smooth muscle cells.

Biphasic response to histamine in rabbit penile dorsal artery

The effects of specific histamine agonists and antagonists on isolated rabbit penile dorsal artery segments were explored using in vitro isometric techniques. Histamine caused the constriction of both precontracted and resting segments. In precontracted arterial rings treated with the H1 receptor antagonist mepyramine, histamine evoked a vasodilatation, followed by contraction at higher concentrations. The vasoconstrictor effect of histamine and the H1 receptor agonist, 2-pyridylethylamine (PEA) on preparations under conditions of basal tone, was competitively antagonized by mepyramine (10(-9)-10(-8) M). The relaxant effect of histamine, unmasked by mepyramine, was abolished by cimetidine. Dimaprit, the H2 receptor agonist, provoked a relaxation of precontracted segments that was also competitively inhibited by cimetidine (10(-6)-10(-5) M). Selective H3 receptor activation with the agonist (R)alpha-methylhistamine (10(-10)-10(-4) M) produced no effect in penile dorsal artery. The biphasic response to histamine was unaffected by endothelium removal or the nitric oxide inhibitor NG-nitro-L-arginine methyl ester (L-NAME) (3 x 10(-4) M) and its precursor, L-arginine (3 x 10(-4) M). Similarly, the cyclooxygenase inhibitor, indomethacin (3 x 10(-6) M) and a combination of Ca2+-activated K+ channel blockers apamin (5 x 10(-7) M) and charybdotoxin (10(-7) M) showed no effect on the histamine-induced relaxation or contraction. In conclusion, contraction, the predominant effect of histamine, is mediated by the activation of H1 receptors that mask the relaxant effect brought about by H2 receptors. Both these effects appear to be mediated by direct action on the smooth muscle, with no participation of nitric oxide or cyclooxygenase products or Ca2+-activated K+ channels.

Characterization of changes in mechanical responses to histamine in omental resistance arteries in pre-eclampsia

Changes in the effect of histamine on the smooth muscle of resistance arteries in pre-eclampsia were investigated by measuring isometric contractions in endothelium-denuded strips of omental resistance arteries from pre-eclamptic and normotensive pregnant women (pregnancy-term matched). Histamine (0.03 -1 microM) caused concentration-dependent relaxation of the contraction induced by 9, 11-epithio-11,12-methano-thromboxane A(2) (STA(2)) in strips from both groups. Sensitivity (for pre-eclampsia: pD(2)=6.66+/-0.04, n=5 and for normotensive pregnant women: pD(2)=7.07+/-0.03, n=10, P<0.001) was lower and the maximum response (90.6+/-0.6% vs 95.5+/-1.1%, P<0.05) was smaller in strips from pre-eclamptic women. Although 8-bromoadenosine-3', 5'-cyclic monophosphorothioate (Sp-isomer: Sp-8-Br-cAMPS, 0.1 - 0.3 mM), a phosphodiesterase (PDE)-resistant activator of adenosine-3',5'-cyclic monophosphate (cyclic AMP)-dependent protein kinase, concentration-dependently attenuated the contraction induced by STA(2) in strips from both groups, the sensitivity (for pre-eclampsia: pD(2)=3.68+/-0.04, n=5 and for normotensive pregnant women: 3.94+/-0.09, n=7, P:=0.02) was lower and the maximum response (64.2+/-2.4% vs 74.9+/-4.4%, P:<0.05) was smaller in pre-eclampsia. In beta-escin-skinned strips, the pD(2) value for the contraction-inducing effect of Ca(2+) did not differ significantly between the two groups (for pre-eclampsia, n=6; for normotensive pregnant women, n=6). Thus, omental resistance arteries from human subjects with pre-eclampsia showed (i) a weaker H(2)-receptor-mediated relaxation to histamine and (ii) a weaker cyclic AMP-analogue-induced relaxation, suggesting that the reduced action of histamine may be partly due to a decreased effect of cyclic AMP.

Endothelium-independent relaxation induced by histamine in human dorsal penile artery

1. In vitro preparations of human dorsal penile arteries were used to evaluate the effect of histamine and to characterize the histamine receptors involved in the response. 2. Cumulative administration of histamine induced a concentration-dependent relaxation in precontracted arteries. The H1 receptor agonist 2-pyridylethylamine induced a biphasic response: contraction followed by dilation. The H2 receptor agonist dimaprit produced a marked relaxation. Mepyramine, a histamine H1 receptor antagonist, led to a slight but statistically significant change in the pD2 value corresponding to the relaxant phase of the H1 receptor agonist and the histamine curve. The H2 receptor antagonist cimetidine induced a marked shift in the dimaprit concentration-response curve without affecting the maximum response. Incubation with cimetidine led to a considerable loss in the sensitivity of the arteries to histamine and in the maximum relaxation. Combined treatment with histamine H1 and H2 receptor antagonists resulted in an additional displacement compared with the effect of each antagonist alone on the histamine response. The effects observed using a histamine H3 receptor agonist and antagonist suggest that the involvement of this receptor is unlikely. 3. Removal of the endothelium was unable to reverse the histamine response. Pretreatment with NG-nitro-L-arginine methyl ester, L-arginine and indomethacin had no effect on the histamine control curve. 4. In conclusion, the vasodilation of human dorsal penile artery induced by histamine seems to be mainly mediated by muscular histamine H2 receptors, without the intervention of key intracellular mediators, such nitric oxide or relaxant prostanoids. A minor population of relaxant histamine H1 receptors cannot be excluded.

Mepyramine but not cimetidine or clobenpropit blocks pertussis toxin-induced histamine sensitization in rats

The effects of pertussis toxin (PT) and the role of histaminergic H(1), H(2) and H(3) receptor blockade on the actions of histamine on blood pressure, heart rate, blood gas values, and mortality were studied in anaesthetized rats. Four days after treatment with PT, histamine dose-dependently decreased mean arterial blood pressure (MAP) and PT enhanced the histamine-induced decrease in MAP. In the PT but not in the inactivated PT (IPT) or saline treated group three out of six animals died after the highest dose of histamine (300 mg kg(-1), i.v.) In order to determine the type of histamine receptor that mediates HS, 4 days after PT the selective antagonists mepyramine (H(1)), cimetidine (H(2)) and clobenpropit (H(3)) were administered 20 min before the challenge with histamine. Mepyramine completely inhibited both the enhanced histamine-induced decrease in MAP and mortality brought about by PT. Cimetidine and clobenpropit had no protective effects, but rather enhanced the histamine-induced mortality elicited by PT. The present study shows that PT caused HS in rats which is primarily mediated via H(1) and secondarily via H(2) and H(3) receptors. These results are considered to be a first step in the elucidation of the mechanism(s) of the HS test used in the quality control of acellular pertussis vaccine.