Antihyperalgesic Activities of Endocannabinoids in a Mouse Model of Antiretroviral-Induced Neuropathic Pain

Background: Nucleoside reverse transcriptase inhibitors (NRTIs) are the cornerstone of the antiretroviral therapy for human immunodeficiency virus/acquired immune deficiency syndrome (HIV/AIDS). However, their use is sometimes limited by the development of a painful sensory neuropathy, which does not respond well to drugs. Smoked cannabis has been reported in clinical trials to have efficacy in relieving painful HIV-associated sensory neuropathy. Objectives: The aim of this study was to evaluate whether the expression of endocannabinoid system molecules is altered during NRTI-induced painful neuropathy, and also whether endocannabinoids can attenuate NRTI-induced painful neuropathy. Methods: BALB/c mice were treated with 25 mg/kg of 2',3'-dideoxycytidine (ddC, zalcitabine), a NRTI, to induce thermal hyperalgesia. The expression of endocannabinoid system molecules was evaluated by real time polymerase chain reaction in the brain, spinal cord and paw skin at 6 days post ddC administration, a time point when mice had developed thermal hyperalgesia. The effects of the endocannabinoids, N-arachidonoyl ethanolamine (AEA) and 2-arachidonoyl glycerol (2-AG), the cannabinoid type 1 (CB1) receptor antagonist AM 251, CB2 receptor antagonist AM 630, and G protein-coupled receptor 55 (GPR55) antagonists ML193 and CID 16020046 on ddC-induced thermal hyperalgesia were evaluated using the hot plate test. Results: ddC treatment resulted in thermal hyperalgesia and increased transcripts of the synthesizing enzyme Plcβ1 and decreased Daglβ in the paw skins, but not Napepld, and Daglα compared to vehicle treatment. Transcripts of the inactivating enzymes Faah and Mgll were downregulated in the brain and/or paw skin but not in the spinal cord of ddC-treated mice. Both AEA and 2-AG had antihyperalgesic effects in mice with ddC-induced thermal hyperalgesia, but had no effect in ddC-naïve mice. The antihyperalgesic activity of AEA was antagonized by AM251 and AM630, whereas the activity of 2-AG was antagonized by AM251, ML193 and CID 16020046, but not by AM630. Conclusion: These data show that ddC induces thermal hyperalgesia, which is associated with dysregulation of the mRNA expression of some endocannabinoid system molecules. The endocannabinoids AEA and 2-AG have antihyperalgesic activity, which is dependent on cannabinoid receptor and GPR55 activation. Thus, agonists of cannabinoid receptors and GPR55 could be useful therapeutic agents for the management of NRTI-induced painful sensory neuropathy.

Molecular basis for the effects of zinc deficiency on spermatogenesis: An experimental study in the Sprague-dawley rat model

Introduction:

The objective of this study is to investigate the molecular mechanisms underlying the effects of zinc deficiency on spermatogenesis in the Sprague-Dawley (SD) rat.

Materials and Methods:

Three groups of eight adult male SD rats were maintained for 4 weeks on a normal diet as control, zinc deficient diet and zinc deficient diet with zinc supplementation of 28 mg zinc/kg body weight respectively. Using standard techniques, the following parameters were compared between the three groups of experimental animals at the end of 4 weeks: (a) Serum zinc, magnesium (Mg), copper (Cu), selenium (Se) and cadmium (Cd), (b) serum sex hormones, malondialdehyde (MDA), superoxide dismutase (SOD) and glutathione peroxidase (GPX), (c) interleukin-4 (IL-4), tumor necrosis factor-alpha (TNF-α), Bcl-2, Bax and caspase-3 expression in the testes, (d) assessment of apoptosis of testicular cells using electron microscopy and (e) testicular volume and histology using the orchidometer and Johnsen score, respectively.

Results:

The zinc deficient group showed a reduction of testicular volume, serum concentrations of Zn, Cu, Se, Mg, SOD, GPX, IL-4, Bcl-2 and testosterone (P < 0.05), as well as increased levels of serum Cd, MDA and tissue TNF-α, Bax, caspase-3 and apoptosis of the germ cells (P < 0.05) compared with control and zinc supplementation groups.

Conclusion:

Zinc deficiency is associated with impaired spermatogenesis because of reduced testosterone production, increased oxidative stress and apoptosis. These findings suggest that zinc has a role in male reproduction.

Perivascular adipose tissue, vascular reactivity and hypertension

Most blood vessels are surrounded by a variable amount of adventitial adipose tissue, perivascular adipose tissue (PVAT), which was originally thought to provide mechanical support for the vessel. It is now known that PVAT secretes a number of bioactive substances including vascular endothelial growth factor, tumor necrosis factor-alpha (TNF-α), leptin, adiponectin, insulin-like growth factor, interleukin-6, plasminogen activator substance, resistin and angiotensinogen. Several studies have shown that PVAT significantly modulated vascular smooth muscle contractions induced by a variety of agonists and electrical stimulation by releasing adipocyte-derived relaxing (ADRF) and contracting factors. The identity of ADRF is not yet known. However, several vasodilators have been suggested including adiponectin, angiotensin 1-7, hydrogen sulfide and methyl palmitate. The anticontractile effect of PVAT is mediated through the activation of potassium channels since it is abrogated by inhibiting potassium channels. Hypertension is characterized by a reduction in the size and amount of PVAT and this is associated with the attenuated anticontractile effect of PVAT in hypertension. However, since a reduction in size and amount of PVAT and the attenuated anticontractile effect of PVAT were already evident in prehypertensive rats with no evidence of impaired release of ADRF, there is the possibility that the anticontractile effect of PVAT was not directly related to an altered function of the adipocytes per se. Hypertension is characterized by low-grade inflammation and infiltration of macrophages. One of the adipokines secreted by macrophages is TNF-α. It has been shown that exogenously administered TNF-α enhanced agonist-induced contraction of a variety of vascular smooth muscle preparations and reduced endothelium-dependent relaxation. Other procontractile factors released by the PVAT include angiotensin II and superoxide. It is therefore possible that the loss could be due to an increased amount of these proinflammatory and procontractile factors. More studies are definitely required to confirm this.

Expression of alternatively spliced variants of Na-Ca-exchanger-1 in experimental colitis: role in reduced colonic contractility

Inflammation-induced colonic motility dysfunction is associated with a disturbance in Ca(2+) ion transporting mechanisms. The main objective of this study was to identify the types of Na-Ca-exchanger-1 (NCX-1) variants expressed in the rat colon, and how this was affected by colitis. In addition, the effect of colitis on the possible involvement of NCX-1 in the reduced carbachol-induced contraction of the rat colon was examined. Colitis was induced in male Sprague-Dawley rats by intra-rectal instillation of trinitrobenzenesulphonic acid (TNBS). Animals were killed on day 5. Colitis was characterized by estimating myeloperoxidase (MPO) activity, body weight, and histological scores. NCX-1 mRNA and protein variants were confirmed by RT-PCR coupled nucleotide sequencing and by Western blot analysis, respectively. Contractility of the colon segments was studied using standard procedure. There was a significant reduction in body weight of TNBS-treated rats. A significant increase in MPO activity and infiltration of inflammatory cells were observed in the inflamed rat colon. RT-PCR coupled nucleotide sequencing identified NCX-1.3 mRNA variant containing exons B and D. Western blot analysis confirmed 70 and 120 kDa molecular mass NCX-1 protein variants in rat colon. There was no significant difference (p > 0.05) in the level of NCX-1 protein variants in inflamed colon as compared to non-colitis controls. Functional experiments demonstrated that NCX in reverse mode played a role in carbachol-induced contraction of colon, and this was not affected by colitis. These findings demonstrated expression of a NCX-1.3 mRNA splice variant, and 70 and 118 kDa protein variants. Inhibition of the reverse mode of NCX-1 was not different in reduced carbachol-induced contraction between the groups. These findings are interpreted to suggest that NCX-1, though expressed did not play a role in reduced contractility in experimental colitis.

Hyperthyroidism enhances 5-HT-induced contraction of the rat pulmonary artery: role of calcium-activated chloride channel activation

Experimentally-induced hyperthyroidism in rodents is associated with signs and symptoms of pulmonary hypertension. The main objective of the present study was to investigate the effect of thyroxine-induced pulmonary hypertension on the contractile response of the pulmonary artery to 5-HT and the possible underlying signaling pathway. 5-HT concentration-dependently contracted artery segments from control and thyroxine-treated rats with pD(2) values of 5.04 ± 0.19 and 5.34 ± 0.14, respectively. The maximum response was significantly greater in artery segments from thyroxine-treated rats. Neither BW 723C86 (5-HT(2B)-receptor agonist) nor CP 93129 (5-HT(1B)-receptor agonist) contracted ring segments of the pulmonary artery from control and thyroxine-treated rats at concentrations up to 10(-4)M. There was no significant difference in the level of expression of 5-HT(2A)-receptor protein between the two groups. Ketanserin (3 × 10(-8)M) produced a rightward shift of the concentration-response curve to 5-HT in both groups with equal potency (-logK(B) values were 8.1 ± 0.2 and 7.9 ± 0.1 in control and thyroxine-treated rats, respectively). Nifedipine (10(-6)M) inhibited 5-HT-induced contractions in artery segments from control and thyroxine-treated rats and was more effective against 5-HT-induced contraction in artery segments for thyroxine-treated rats. The calcium-activated chloride channel blocker, niflumic acid (10(-4)M) also inhibited 5-HT-induced contractions in artery segments from control and thyroxine-treated rats and was more effective against 5-HT-induced contraction in artery segments for thyroxine-treated rats. It was concluded that hyperthyroidism enhanced 5-HT-induced contractions of the rat pulmonary artery by a mechanism involving increased activity of calcium-activated chloride channels.

Colonic inflammation increases the contribution of muscarinic M2 receptors to carbachol-induced contraction of the rat colon

OBJECTIVES

Carbachol-induced contraction of the rat colon is impaired in rats with trinitrobenzene sulfonic acid (TNBS)-induced colitis. The main objective of this study was to examine the effect of colitis on the expression and function of muscarinic (M) receptor subtypes in the rat colon.

MATERIALS AND METHODS

Rats (n = 80) were treated with TNBS and used 5 days later for measurement of contractility, myeloperoxidase activity, histology and expression of muscarinic receptor isoforms using Western blot analysis.

RESULTS

Carbachol produced concentration-dependent contractions of colonic segments from control (n = 40) and TNBS-treated (n = 40) rats with no significant difference in potency. However, the maximum response to carbachol was significantly reduced in colon segments of TNBS-treated rats. The selective muscarinic receptor antagonists 4-diphenylacetoxy-N-methyl piperidine (4-DAMP, M(3)), pirenzepine (M(1)) and methoctramine (M(2)) antagonized carbachol-induced contraction in control (9.1 ± 0.1, 6.7 ± 0.3 and 6.0 ± 0.1, respectively) and TNBS-treated rats (9.2 ± 0.2, 6.9 ± 0.2, 6.7 ± 0.2). The -logK(B) values in control rats are consistent with an action of carbachol on muscarinic M(3) receptors. There was no significant difference in -logK(B) values for 4-DAMP and pirenzepine in control and TNBS-treated rats, but methoctramine was fivefold more potent in TNBS-treated rats, possibly indicating an increased contribution of muscarinic M(2) receptors to carbachol-induced contraction in the inflamed colon. The expression of M(2) receptors was also significantly increased in colon segments from TNBS-treated rats, confirming the increased role of muscarinic M(2) receptors in the inflamed colon.

CONCLUSIONS

The data show that while only M(3) receptors appeared to mediate carbachol-induced contraction in control segments, expression of both M(2) and M(3) receptors was increased in the inflamed rat colon.

Lithium protects against toxic effects of cadmium in the rat testes

PURPOSE

To investigate the protective effect of Lithium against the toxic effect of Cadmium in the rat testes.

METHODS

Twenty four adult male Sprague-Dawley rats were treated with four different regimens: Cadmium only, Cadmium and lithium, lithium only and controls. Rats were sacrificed after 6 weeks and testicular levels of pro-inflammatory cytokine (IL-4), anti-inflammatory cytokine (TNF-α), Pro-apoptotic protein (Bax) and anti-apoptotic protein (Bcl-2) were measured by ELISA while serum levels of FSH, LH, Prolactin and Testosterone were measured using the Vidas parametric system. Antioxidant status (MDA, SOD) was also assessed in serum. Histopathological changes of testes were examined using light and electron microscopy. Immunohistochemical staining for Bax, Bcl-2 and Caspase 3 were performed.

RESULTS

Treatment with lithium was associated with significant reduction in the toxic effects of Cadmium as shown by reduced testicular levels of TNF-α, serum levels of Malondialdehyde and testicular level of Bax, and increased levels of IL-4, Zn-Cu SOD, Bcl-2 and Testosterone. Testicular histopathology showed that Cadmium produced an extensive germ cells apoptosis and the addition of lithium in Cadmium-treated rats significantly reduced cadmium-induced testicular damage.

CONCLUSION(S)

Lithium has a protective effect against cadmium-induced testicular apoptosis in the rat.

Curcumin reverses attenuated carbachol-induced contraction of the colon in a rat model of colitis

BACKGROUND

Curcumin ameliorates colitis whether it reverses colitis-induced reduction in colonic contractility remains to be investigated.

OBJECTIVES

To investigate the effect of curcumin on colitis-induced reduction of carbachol-induced contraction in colon segments from rats treated with trinitrobenzenesulphonic acid.

METHODS

Colitis was induced in rats by intra rectal administration of trinitrobenzenesulphonic acid and followed for 5 days. A group of animals which received trinitobenzene sulphonic acids was treated with curcumin (100 mg/Kg and 200 mg/kg body weight) 2 hrs prior to induction of colitis. The controls received phosphate buffered saline in a similar fashion. Markers of inflammation and contractility of colon were assayed using standard procedures.

RESULTS

Induction of colitis was associated with increased myeloperoxidase activity and malondialdehyde levels, gross histological changes characterized by infiltration of inflammatory cells. All these changes were prevented by treatment with curcumin (100 mg/kg). Treatment with curcumin also reduced the histological scores from 3.34+/-0.40 to 1.75+/-0.30 confirming an anti-inflammatory effect of curcumin in this experimental model of colitis. Colonic reactivity to carbachol was decreased in colitis affecting the maximum response but not sensitivity. Treatment with curcumin had no effect on sensitivity of the colon to carbachol in any of the preparations. Curcumin however reversed the decrease in carbachol-induced contraction associated with trinitrobenzenesulphonic acid treatment. The same dose of curcumin had no effect on either the potency of or the maximum response to carbachol in control rats. Tissue expression of NF-kB was increased in colon segments from trinitrobenzenesulphonic acid -treated rats and this was inhibited in rats treated with curcumin.

CONCLUSIONS

Based on these findings it is concluded that curcumin prevented the reduction in carbachol-induced contraction in trinitrobenzenesulphonic acid -treated rats by modulating NF-kB signaling pathway.

Curcumin attenuates inflammation through inhibition of TLR-4 receptor in experimental colitis

Curcumin, an active ingredient of Curcumin longa mediates its anti-inflammatory effects through inhibition of NFkB. Several pathways including toll-like receptors (TLR) induce NFkB leading to inflammation. In this study, we investigated the effects of curcumin on the expression of TLR-4 and MyD88, the upstream signaling pathway in experimental colitis induced in the Sprague-Dawley male rats by intra-rectal administration of trinitrobenzenesulfonic acid (TNBS). The animals which received TNBS were divided into two groups: Group 1, received aqueous suspension of curcumin (100 mg/Kg body weight) 2 h prior to inducing colitis, and the treatment was repeated every day for 5 days, and Group 2 and non-colitis (Group 3) animals received phosphate buffered saline (PBS) in a similar fashion. Non-colitis animals (Group 4) received curcumin and served as controls. Animals were sacrificed on day 5 post-TNBS by cervical dislocation, colon was taken out, and cleaned with PBS. Levels of TLR-4, MyD88, and NFkB proteins were measured using ECL Western blot analysis, and TLR-4 mRNA by a competitive RT-PCR method. Colitis was confirmed histologically by measuring myeloperoxidase (MPO) activity and malondialdehyde (MDA) levels in the colonic tissues. TNBS-induced increase in the level of MPO activity and MDA concentrations was reversed by curcumin treatment, whereas the same dose of curcumin did not affect their levels in the non-colitis animals. Increases in the levels of TLR-4, MyD88, and NFkB proteins in inflamed tissue were also suppressed significantly by curcumin treatment. The level of TLR-4 mRNA remained unchanged in the colitis animals. These findings demonstrate that signaling pathway of curcumin-induced inhibition of inflammation involves TLR-4 and MyD88, and therefore may serve as an important therapeutic target in IBD.

In vivo and in vitro assessment of human saphenous vein wall changes

Purpose:

To investigate if noradrenaline (NA) and 5-hydroxyptamine (5-HT) drugs induce responses of isolated control and varicose veins are altered by removal of the endothelium.

Subjects & Methods:

Specimens of the great saphenous vein (GSV) were obtained from 12 subjects with primary varicose veins and 12 subjects from donor vessels at cardiac surgery. A total of 10 normal healthy volunteers were selected for comparison. The diameter changes of GSV during the resting phase, at the end of 5 minutes occlusion, and then every 30 seconds post deflation for five minutes were measured using B-mode ultrasound. Post-surgery the vein sample was collected in a tube of Krebs-Henseleit solution.

Results:

The repeated measure ANOVA test for the diameter, percent, and difference changes of GSV diameter from maximum diameter at different time intervals showed significance difference within and between all groups. NA and 5-HT produced concentration-dependent contractions of control and varicose saphenous vein segments. There was no significant difference in the potency of NA and for 5-HT, but the maximum response, normalized for tissue weight, was less in varicose vein segments. Removal of the endothelium had no effect on the potency of NA or 5-HT but significantly (p<0.05) reduced the maximum response to NA and 5-HT in varicose vein segments but not to 5-HT in control veins.

Conclusion:

The venous endothelial damage may cause vascular smooth muscle contractions dysfunction that favours dilatation and secondary valvular insufficiency.

Indications of the mechanisms involved in improved sperm parameters by zinc therapy

OBJECTIVE

To determine possible indications of the mechanisms involved in improved sperm parameters by zinc therapy in asthenozoospermic men.

SUBJECTS AND METHODS

Forty-five men with asthenozoospermia (>or=40% immotile sperm) were randomized into four therapy groups: zinc only: n = 11; zinc + vitamin E: n = 12 and zinc + vitamins E + C: n = 14 for 3 months, and non-therapy control group: n = 8. Semen analysis was done according to WHO guidelines. Malone dialdehyde, tumour necrosis factor-alpha (TNF-alpha), total antioxidant capacity, superoxide dismutase (SOD) and glutathione peroxidase were determined in the semen and serum. Antisperm antibodies IgG, IgM and IgA were evaluated by immunobeads. Sperm chromatin integrity was determined by acid denaturation by acridine orange and sperm apoptosis by light and electron microscopy. The effect of zinc on in vitro induced sperm oxidative stress by NADH was evaluated.

RESULTS

Asthenozoospermia was significantly associated with oxidative stress with higher seminal malone dialdehyde (8.8 vs. 1.8 mmol/l, p < 0.001) and TNF-alpha (60 vs. 12 pg/l, p < 0.001), and low total antioxidant capacity (1.8 vs. 8.4, p < 0.01), SOD (0.8 vs. 3.1, p < 0.01) and glutathione peroxidase (1.6 vs. 4.2, p < 0.05), compared to normozoospermia. Zinc therapy alone, in combination with vitamin E or with vitamin E + C were associated with comparably improved sperm parameters with less oxidative stress, sperm apoptosis and sperm DNA fragmentation index (DFI). On the whole, there was no difference in the outcome measures between zinc only and zinc with vitamin E and combination of vitamins E + C. In the in vitro experiment zinc supplementation resulted in significantly lower DFI (14-29%, p < 0.05) compared to zinc deficiency.

CONCLUSION

Zinc therapy reduces asthenozoospermia through several mechanisms such as prevention of oxidative stress, apoptosis and sperm DNA fragmentation.

Mechanism of reduced colonic contractility in experimental colitis: role of sarcoplasmic reticulum pump isoform-2

Inflammatory bowel diseases (IBD) such as Crohn's disease and ulcerative colitis are inflammatory disorders associated with decreased colonic contractility. Here we show that, in experimental colitis in rat induced by trinitrobenzenesulfonic acid, there is a decrease in contraction in response to carbamoylcholine and the sarco/endoplasmic reticulum Ca(+2) (SERCA) pump inhibitor thapsigargin. However, the decrease in contractility may occur due to decrease in the SERCA pump levels or their inactivation. Therefore, we examined the protein and mRNA levels for SERCA2 isoform, which is predominant isoform in colonic smooth muscle. There was a decrease in the levels of SERCA2 protein and mRNA levels in inflamed colonic muscle. These findings suggest that decreased SERCA pump levels is responsible for a decrease in the Ca(+2) stores in the sarco/endoplasmic reticulum that causes a decrease in the contractility in colonic smooth muscle leading to poor bowel movements.

Mechanism underlying the reversal of contractility dysfunction in experimental colitis by cyclooxygenase-2 inhibition

Inflammatory bowel diseases are associated with reduced colonic contractility and induction of cyclooxygenase-2. In this study a possible role of cyclooxygenase-2 in and the underlying mechanism of the reduced contractility were investigated in experimental colitis. The effects of meloxicam, a cyclooxygenase-2 selective inhibitor were examined on colonic contractility and MAP kinase p38 and ERK(1/2) expression. Colitis was induced in Sprague-Dawley male rats by intra-colonic instillation of trinitrobenzenesulphonic acid (TNBS; 40 mg/rat in 50 ethanol). The animals were divided into three groups. Group 1 (n=9) received meloxicam (3 mg/kg-day) gavage 1 h before and 1 day (Group 2) after induction of colitis. Group 3 (n=9) received phosphate buffered saline (PBS) in a similar manner and served as colitic control. The non colitic control animals received meloxicam in a similar manner. The animals were sacrificed after 5 days of treatment, colon was cleaned with PBS and colonic smooth muscle was obtained which was used in this study. Meloxicam treatment given 1 h before or 1 day after administration of colitis restored the reduced colonic contractility without affecting the sensitivity to carbachol. The levels of colonic smooth muscle IL-1beta mRNA, PGE(2), ERK(1/2), p38, malondialdehyde, myeloperoxidase activity and colonic mass were increased, whereas the body weight was decreased due to TNBS. The changes except colonic muscle mass and p38 expression were reversed by meloxicam treatment. These findings indicate that restoration of reduced colonic contractility by meloxicam is mediated by ERK(1/2), and that ERK(1/2) may serve as an important anti inflammatory target for treatment of colitis.

Antihypertensive and vasodilator effects of methanolic and aqueous extracts of Tribulus terrestris in rats

The effects of methanolic and aqueous extracts of Tribulus terrestris on rat blood pressure (BP) and the perfused mesenteric vascular bed were investigated. The extracts dose-dependently reduced BP in spontaneously hypertensive rats (SHRs) with the aqueous fraction being more potent than the methanolic fraction at all doses tested. In vitro, the methanolic but not aqueous extract produced a dose-dependent increase in perfusion pressure of the mesenteric vascular bed. When perfusion pressure was raised with phenylephrine (10(-5) M), the aqueous extract produced a dose-dependent reduction in perfusion pressure at all doses. A low dose of the methanolic extract produced a vasoconstrictor effect while higher doses produced dose-dependent reduction in perfusion pressure. L-NAME (10(-4) M) significantly reduced but did not abolish vasodilation induced by the extracts. Vasodilator responses to aqueous and methanolic fractions were significantly reduced in preparations where perfusion pressure was raised with KCl (60 mM). A combination of KCl and L-NAME abolished the vasodilator responses induced by the extracts. It was concluded that methanolic and aqueous extracts of Tribulus terrestris possess significant antihypertensive activity in spontaneously hypertensive rats. The antihypertensive effects appeared to result from a direct arterial smooth muscle relaxation possibly involving nitric oxide release and membrane hyperpolarization.

Pregnancy-induced modulation of calcium mobilization and down-regulation of Rho-kinase expression contribute to attenuated vasopressin-induced contraction of the rat aorta

Normal pregnancy is characterized by attenuated vascular reactivity to a variety of contractile agonists and this, in part, has been attributed to increased circulating vasodilators and/or impaired Ca(2+)-influx through L-type Ca(2+)-channels. Our hypothesis in this study was that reduced Ca(2+)-dependent (influx) and Ca(2+)-independent (involving the RhoA/Rho-kinase pathway) mechanisms contributed to attenuated vasopressin-induced contraction of the pregnant rat aorta. AVP (10(-10) -3 x 10(-7) M) induced concentration-dependent contraction of aortic ring segments from nonpregnant and pregnant rats with no significant change in pD(2) values (8.53+/-0.11 and 8.33+/-0.18 in nonpregnant and pregnant rats, respectively). The maximum response was however significantly reduced in aorta segments from pregnant rats. Nifedipine (10(-6) M) significantly inhibited AVP-induced contraction in artery segments from nonpregnant but not pregnant rats indicating a reduced role for Ca(2+)-influx through L-type Ca(2+)-channels in AVP-induced contractions of the pregnant rat aorta. Western blot analysis revealed the expression of ROCK-1 and ROCK-II isoforms in aorta segments from both groups. There was a significant reduction in the expression of ROCK-1 and ROCK-II isoforms in aortic tissues from pregnant rats. This is consistent with the reduced potency of Y-27632 in inhibiting AVP (10(-7) M) induced contraction in aorta segments from pregnant rats. It was concluded that pregnancy-induced attenuated vascular response to AVP was due to decreased Ca(2+)-influx through L-type Ca(2+)-channels and decreased sensitization of the contractile myofilaments to Ca(2+).

Increased expression and activity of heme oxygenase-2 in pregnant rat aorta is not involved in attenuated vasopressin-induced contraction

Pregnancy is associated with attenuated vascular reactivity to a variety of contractile agonists. Heme oxygenases are expressed in the placenta, and it has been suggested that the heme oxygenase/carbon monoxide (HO/CO) pathway plays a significant role in regulating blood flow through the feto-placental unit. In this study we investigated the possible involvement of heme oxygenases in the reduced vascular reactivity associated with pregnancy. Arginine vasopressin (AVP) (10(-10)-3x10(-7) M) induced concentration-dependent contraction of aortic ring segments from non-pregnant and pregnant (16-19 days) rats. Pregnancy did not alter the sensitivity to AVP (pD2=8.5+/-0.1 and pD2=8.4+/-0.2 in non-pregnant and pregnant rats, respectively) but significantly reduced the maximum response (107.9+/-12.7% and 38.6+/-7.4%, respectively, relative to noradrenaline-induced contraction). Western blot analysis revealed the expression of HO-2 but not HO-1 isoform in both groups. There was a significant increase in the expression and activity of HO-2 protein in aortic tissues from pregnant rats compared with those from age-matched non-pregnant rats. In the presence of L-NAME to inhibit nitric oxide (NO) synthesis, tin protoporphyrin IX (SnPP-IX, 10(-5) M), an inhibitor of heme oxygenase, did not significantly affect AVP-induced contraction in aorta segments from pregnant and non-pregnant rats. It was concluded that, though pregnancy increased the expression and activity of HO-2 in the aorta, HO-2 was not involved in the attenuated response to AVP.

Attenuated Noradrenaline-Induced Contraction of Pulmonary Arteries from Rats Treated with Monocrotaline: Role of Rho Kinase

Noradrenaline-induced pulmonary artery contraction was reduced in monocrotaline-treated rats. The possibility that this could be due to alterations in the rho kinase pathway was examined in this study. A combination of nifedipine (10(-6) M) and thapsigargin (10(-6) M) attenuated noradrenaline-induced contraction significantly more in artery segments from monocrotaline-treated rats than in artery segments from control rats indicating a reduced role for calcium sensitization in artery segments from monocrotaline-treated rats. In artery segments permeabilized with ionomycin, CaCl(2) (1.25 mmol/l) produced significantly greater contraction in monocrotaline treated rats compared with control rats. Addition of noradrenaline (10(-5) M) to the bath produced further contractions in both groups. However, noradrenaline-induced contraction was less in monocrotaline-treated rats compared with controls. Y-27632 concentration dependently relaxed ring segments of pulmonary artery pre-contracted with noradrenaline (10(-5)M). The pIC(50) values were 6.46+/- 0.09 (n=5) 5.81+/- 0.06 (n=5) in control and pulmonary hypertensive rings, respectively. The maximum relaxation to Y-27632 was significantly higher in monocrotaline-treated rats. ROCK II was the predominant isoform of rho kinase expressed in the pulmonary artery. The level of expression was increased in rats treated with monocrotaline. These results would suggest that while basal rho kinase activity was elevated in monocrotaline-induced pulmonary hypertension, noradrenaline-induced contraction was attenuated, suggesting poor coupling of the receptor activation to rho kinase activation.

Effect of chronic exposure to cold on isoprenaline-induced cAMP accumulation and relaxation in the rat aorta

Rats chronically exposed to cold (5 degrees C for 5 weeks) develop hypertension. Isoprenaline-induced vascular smooth muscle relaxation is increased in these animals. Our main objective was to compare isoprenaline-induced relaxation of aortae isolated from control and cold-acclimated rats and attempt to relate the differences to changes in receptor parameters (affinity and reserve) and signaling mechanisms. Isoprenaline (10(-9)-10(-5) M)-induced relaxation was enhanced significantly (p < 0.05) in aorta segments from cold-acclimated rats. There was a significant (p < 0.05) increase in the potency of isoprenaline but with no change in affinity. Isoprenaline produced 50% of the maximum response while occupying about 50% and about 15% of the receptors in isolated rat aorta segments from control and cold-treated rats, respectively. Forskolin and db-cAMP also concentration-dependently relaxed aorta segments from control and cold-acclimated rats. There was no difference in potency or maximum response to forskolin (which directly activates adenylyl cyclase) and db-cAMP. cAMP concentrations in the presence of isoprenaline were significantly (p < 0.05) higher in aorta segments from rats chronically exposed to cold when compared with aorta segments from control rats. These findings suggested that altered mechanisms upstream of activation of adenylyl cyclase are involved in the increased beta-adrenoceptor-induced relaxation.

Cyclo-oxygenase-2, endothelium and aortic reactivity during deoxycorticosterone acetate salt-induced hypertension

OBJECTIVE

To test the hypothesis that the enhanced vascular responsiveness to norepinephrine that occurs during deoxycorticosterone acetate (DOCA)-salt induced hypertension is causally related to increased expression of cyclo-oxygenase (COX)-2 and oxidative stress, which diminishes the vasomodulatory influence of endothelium-derived nitric oxide.

METHODS

Four groups of age-matched, male Sprague-Dawley rats were studied: Sham (normotensive); DOCA-salt (hypertensive); DOCA-salt treated with manganese(III) tetra(4-benzoic acid) porphyrin chloride [MnTBAP, an antioxidant; 15 mg/kg intraperitoneally (i.p.) for 21 days]; DOCA-salt treated with {N-[2-(cyclohexyloxy)-4-nitrophenyl]-methane sulfonamide} (NS-398, a COX-2 selective blocker; 5 mg/kg i.p. for 7 days). Contraction and relaxation were measured with FT03 force transducers coupled to a Grass polygraph in aortic rings bathed with physiologic salt solution (37 degrees C) and bubbled with a 5%CO2/95%O2 gas mixture. Aortic sensitivities (pD2 values) to norepinephrine and serum isoprostanes (8-iso-prostaglandin F2alpha, a marker of oxidative stress) were measured for each experimental paradigm.

RESULTS

NS-398 significantly reduced maximal contractions in response to norepinephrine in aortic rings from Sham (44 +/- 3%) and DOCA-salt (96 +/- 2%) group rats. Expression of COX-2 protein increased significantly in vessels from DOCA-salt rats compared with those from Sham group rats. Treatment of DOCA-salt rats with either MnTBAP or NS-398 alleviated hypertension, normalized aortic pD2 values for norepinephrine and restored serum 8-isoprostane concentrations towards those observed in Sham group rats.

CONCLUSIONS

COX-2 expression increases during DOCA-salt hypertension, and mediates production of factors that enhance rat aortic contractility in response to norepinephrine. Our data also suggest a role for increased oxidative stress, which is at least in part dependent on enhanced COX-2 expression, in the mechanism(s) of enhanced aortic contractility in response to norepinephrine during DOCA-salt hypertension.

Evidence for the Presence of Beta-3-Adrenoceptors Mediating Relaxation in the Human Oviduct

Beta1- and beta2-adrenoceptors mediate relaxation in the oviductal smooth muscle. This study examines the existence and function of beta3-adrenoceptors in the human oviduct. Ring segments of the oviduct were set up for isometric tension recording. The effect of isoprenaline and BRL 37344 on smooth muscle tone was examined. The expression of beta3-adrenoceptors in the oviduct was also examined. Isoprenaline and BRL 37344 concentration-dependently relaxed circular muscles of the oviduct. BRL 37344 was less potent than isoprenaline and was a partial agonist. Propranolol shifted isoprenaline but not BRL 37344 concentration-response curve to the right without reducing the maximum response. Cyanopindolol (1 micromol/l), a beta3-adrenoceptor antagonist, shifted the isoprenaline concentration response curve to the right. The -log K(B) value of 7.8 indicates activation of beta3-adrenoceptors by isoprenaline. mRNA for beta3-adrenoceptors was expressed in the oviduct. These results suggest that beta3-adrenoceptors, mediating relaxation, are expressed in the human oviduct.

Amelioration of experimental colitis by Na-H exchanger-1 inhibitor amiloride is associated with reversal of IL-1ss and ERK mitogen-activated protein kinase

OBJECTIVE

Na-H exchanger-1 (NHE-1) is induced in experimental colitis. It has not yet been established whether its inhibition ameliorates colitis. The effects of amiloride, an inhibitor of NHE-1, on colitis were examined in this study. Levels of mitogen-activated protein (MAP) kinases ERK, p38 and interleukin 1ss which participate in intestinal inflammation were also examined in the colonic smooth muscle of rats with colitis.

MATERIAL AND METHODS

Colitis was induced in Sprague-Dawley male rats by intrarectal administration of trinitrobenzenesulphonic acid (TNBS) and treated daily with amiloride (3, 5, and 10 mg/kg b.w. (body-weight), orally) starting 1 h before induction of colitis. The animals were sacrificed on day 5 post-TNBS. Controls received phosphate buffered saline in a similar manner.

RESULTS

The highest dose of amiloride (10 mg/kg) was lethal. The lowest dose (3 mg/kg) was tolerated and was used in this study. Amiloride significantly reversed the colitis-reduced contractility and induction of MPO activity, NHE-1, IL-1ss and ERK, but not of p38 in inflamed colonic smooth muscle. Splenomegaly, increased colonic mass and decreased sodium pump activity were significantly reversed by amiloride treatment. There was no recovery of b.w. loss in the treated colitic animals. Urine output was increased, whereas food and water intake remained unchanged following amiloride treatment.

CONCLUSIONS

These findings suggest that the beneficial effects of NHE-1 inhibition in experimental colitis are mediated through IL-1ss and ERK MAP kinase.

Interaction of BKCa channel modulators with adrenergic agonists in the rat aorta is influenced by receptor reserve

Our main objective was to study the interaction of BKCa channel modulators with adrenergic agonists UK 14304 and noradrenaline (NA), acting on alpha1-adrenoceptors, in the rat aorta and how this is affected by receptor reserve. NA and UK 14304 evoked concentration-dependent contractions of the rat aorta. UK 14304 was a partial agonist relative to NA in this preparation. The BK(Ca) channel blocker tetraethylammonium (TEA, 1 mM) and opener NS 1619 (3 x 10(-5) M) modulated NA- and UK 14304-induced contractions, and were more effective on UK 14304-induced contractions. TEA (1 mM) increased the maximum response to NA and UK 14304 by about 13% and 300%, respectively, while NS 1619 (3 x 10(-5) M) reduced the maximum response to UK 14304 by about 81% compared to 31% for noradrenaline. The effect of TEA on the noradrenaline concentration-response curve was increased after treatment of the aorta with phenoxybenzamine (PBZ), an irreversible alpha1-adrenoceptor antagonist, to reduce receptor reserve. We concluded that the interaction of BKCa channel modulators with alpha1-adrenergic agonists in the rat aorta was influenced by receptor reserve.

Chloride channels and α1-adrenoceptor-mediated pulmonary artery smooth muscle contraction: effect of pulmonary hypertension

Noradrenaline induced concentration-dependent contractions of pulmonary artery segments from control and monocrotaline-treated rats. There was a significant decrease in the maximum response but not sensitivity in artery segments from monocrotaline-treated rats. At a concentration (10(-6) M) that abolished KCl-induced contraction, nifedipine attenuated but did not abolish, noradrenaline-induced contraction in both groups. However, noradrenaline-induced contraction in artery segments from pulmonary hypertensive rats was more susceptible to inhibition by nifedipine. Bumetanide (10(-4) M), a chloride transport inhibitor and niflumic acid, a chloride channel inhibitor, reduced noradrenaline-induced contraction of the pulmonary artery in control and pulmonary hypertensive groups. These compounds were more effective in ring segments from pulmonary hypertensive rats. It was concluded that activation of chloride channels was involved in noradrenaline-induced contraction and that the contribution of chloride channels was enhanced in pulmonary hypertensive rats.

Ex vivo reactivity of the ovarian vascular bed to noradrenaline and carbachol during ovarian hyperstimulation syndrome

OBJECTIVE

To study reactivity of the ovarian vascular bed to noradrenaline and carbachol during an experimentally induced ovarian hyperstimulation syndrome (OHSS) in rabbits.

MATERIALS AND METHODS

Rabbits were treated with human menopausal gonadotropin (75 IU) daily for 6 days, followed by human chorionic gonadotropin (2,500 IU) to induce OHSS. The ovarian vascular bed was isolated and perfused with physiological solution and its reactivity to injected noradrenaline and acetylcholine was examined.

RESULTS

The mean weight of the hyperstimulated ovary was 2.85 +/- 0.5 g compared to 0.25 +/- 0.1 g for the control rabbits. There was no significant difference in (a) the basal perfusion pressure of the ovarian vascular bed ex vivo; (b) the potency of, or maximum response to, noradrenaline, and (c) agonist dissociation constant or receptor density. Carbachol induced significantly greater vasodilation in ovarian vascular beds from hormone-treated rabbits, indicating a greater role for nitric oxide in this syndrome, as further supported by the observation that NW-nitro-L-arginine methyl ester hydrochloride (L-NAME) was more effective against carbachol-induced response in hormone-treated rabbits.

CONCLUSION

In the rabbit model of OHSS, carbachol produced an increased ex vivo vascular response but noradrenaline did not.

α1-adrenoceptor subtypes mediating noradrenaline-induced contraction of pulmonary artery from pulmonary hypertensive rats

The effect of monocrotaline-induced pulmonary hypertension on alpha(1)-adrenoceptor-mediated contractions of pulmonary artery segments was studied. In control and monocrotaline-treated rats, noradrenaline evoked concentration-dependent contractions of the pulmonary artery. There was no change in the potency and affinity of noradrenaline but the maximum response and receptor reserve were significantly reduced. Noradrenaline-induced contractions were competitively antagonized by prazosin, 2-(2-6dimethoxyphenoxyethyl)aminomethyl-1,4-benzodioxane hydrochloride (WB 4101) and 8-[2-[4-(2methoxyphenyl)-1-piperazinyl]ethyl]-8-azaspiro[4,5]decane-7,9 dione dihydrochloride (BMY 7378) with pA(2) values of 9.64+/-0.16, 9.45+/-0.10 and 8.30+/-0.14, respectively. These antagonists also competitively antagonized noradrenaline-induced contractions of pulmonary artery segments isolated from rats with monocrotaline-induced pulmonary hypertension. The pA(2) values were 9.66+/-0.11 (prazosin), 9.62+/-0.09 (WB 4101) and 8.47+/-0.15 (BMY 7378). Chloroethylclonidine (CEC) shifted noradrenaline concentration-response curve to the right and depressed the maximum response. There was no difference between the effects of CEC in both groups. It was therefore concluded that pulmonary hypertension significantly reduced noradrenaline-induced contractions of the rat pulmonary artery without affecting the sensitivity. Studies with receptor-selective antagonists confirmed that alpha(1)D-adrenoceptor subtype is the predominant receptor subtype in the pulmonary artery and this was maintained in this disease state.

Noradrenaline-induced vasoconstriction in the uterine vascular bed of pregnant rats chronically treated with L-NAME: role of prostanoids

Vascular reactivity to vasoconstrictors has been observed in preeclamptic vessels. In this investigation, the possible role of endothelin-1 and endoperoxide/thromboxane receptor activation in the exaggerated response of the uterine vascular bed from rats with experimentally induced preeclampsia-like syndrome to noradrenaline was studied. The mean blood pressure in non-pregnant rats was 126.0 +/- 8.7 mm Hg (n = 5) while in pregnant rats, the mean blood pressure was 110.0 +/- 4.7 mm Hg (n = 5). Corresponding values in l-NAME-treated non-pregnant and pregnant rats were 167.5 +/- 6.9 mm Hg (n = 6) and 167.5 +/- 6.9 mm Hg (n = 6). These values were not significantly (P > 0.05) different from each other but were significantly (P < 0.05) different from corresponding values in control rats (not treated with l-NAME). Noradrenaline (10-10-10-6 mol) produced potent and reproducible vasoconstriction in isolated perfused rat uterine vascular bed from l-NAME-treated and untreated pregnant and non-pregnant rats. There was no significant difference in the potency of noradrenaline. However, there was an increase in the absolute maximum response to noradrenaline in uterine vascular bed from l-NAME-treated pregnant rats when compared with the other groups. Noradrenaline-induced vasoconstriction was not significantly affected by AT1-receptor antagonist, ZD 7155 or SB 209670, a potent ETA/ETB receptor antagonist. Vasoconstrictor responses to noradrenaline were however significantly reduced by indomethacin and SQ 29548 in l-NAME-treated pregnant rats. These observations would suggest that in pregnant rats treated with l-NAME, cyclooxygenase products play a significant role in noradrenaline-induced vasoconstriction of this preparation.

Histamine-induced vasodilatation in the perfused mesenteric arterial bed of diabetic rats

In this study, we have examined the contribution of endothelium-derived nitric oxide (EDNO) and endothelium-derived hyperpolarizing factor (EDHF) to histamine-induced endothelium-dependent relaxation in the perfused mesenteric arterial bed of rats treated with streptozotocin (STZ) to induce diabetes. Histamine (10(-10) to 5 x 10(-6) mol) produced dose-dependent vasodilator response in the perfused mesenteric arterial bed of both control and diabetic animals. In order to isolate the EDHF component of histamine-induced vasodilator response, NG-nitro-L-arginine-methyl ester hydrochloride (L-NAME) (10(-4) M) and indomethacin (10(-6) M) were added to the Krebs solution throughout the experiment. Histamine induced vasodilatation in the perfused mesenteric bed in preparations from both control and diabetic rats. The vasodilator response to histamine was slightly potentiated in the diabetic rat preparations. Sodium nitroprusside (SNP)-induced relaxation was similar in diabetic and control rats. The role of EDNO in histamine-induced vasodilatation was also examined. Vascular preparations were perfused with 20 mM K(+)-Krebs solution to inhibit the EDHF contribution to histamine-induced vasodilatation. Under this condition, histamine induced a vasodilator response in preparations from both control and diabetic rats. However, relative to nondiabetic control animals, histamine-induced maximal response was significantly reduced in preparations from diabetic animals. Pretreatment with L-NAME (10(-4) M) attenuated histamine-induced vasodilatation in both preparations, indicating an NO-mediated vasodilator response. There was a significant attenuation in histamine-induced vasodilatation in the vascular preparations from diabetic rats. The vasodilator effect of calcium ionophore A23187 was investigated in preparations from control and diabetic rats to investigate receptor dysfunction associated with diabetes. A23187 (10(-11) to 10(-7) mol)-induced vasodilator response was not significantly different in the preparations from control and diabetic animals. In conclusion, our results indicated that histamine-induced vasodilation in the perfused mesenteric arterial bed of the STZ-induced diabetic rats is mediated by two vasodilator components, namely EDHF and EDNO. Under diabetic conditions, the EDHF component was potentiated, while histamine-induced vasodilation mediated by the EDNO component was attenuated.

BRL 37344 inhibited adrenergic transmission in the rat portal vein via atypical beta-adrenoceptors

The effect of BRL 37344, a beta(3)-adrenergic agonist on adrenergic transmission in isolated segments of the rat portal vein was examined in this study. BRL 37344 (10(-9) - 10(-5)M) produced concentration-dependent inhibition of electrically induced contractions. This inhibitory effect of BRL 37344 was not antagonized by propranolol ( 10(-6)M). Isoprenaline ( 10(-9) - 10(-4)M) also produced a concentration-dependent inhibition of electrically induced contractions in the portal vein. Propranolol (10(-6)M) antagonized isoprenaline responses with a -logK(B) value of 8.14 +/- 0.32. BRL 37344-induced inhibition of electrically induced contractions was also unaffected by cyanopindolol (10(-6)M). Isoprenaline but not BRL 37344 significantly reduced noradrenaline-induced contractions of the rat portal vein. CGP12177A produced propranolol-resistant inhibition of electrically induced contractions of the rat portal vein. It was therefore concluded that BRL 37344 inhibited adrenergic transmission in the rat portal vein via atypical beta -adrenoceptors located prejunctionally.

Endothelium-dependent relaxation in isolated renal arteries of diabetic rabbits

1 In this study, we have investigated the vasodilator response to acetylcholine under diabetes conditions in isolated renal arteries of rabbits. We have also examined the contribution of endothelium-derived nitric oxide (EDNO) and endothelium-derived hyperpolarizing factor (EDHF) to the endothelium-dependent relaxation caused by acetylcholine in the renal arteries of alloxan-induced diabetic rabbits. 2 Acetylcholine (10(-10) - 10(-4) M) produced cumulative concentration-response curve in the renal arteries of both control and diabetic rabbits. The EC50 values and maximal responses to acetylcholine were not significantly different relative to diabetic conditions. In order to isolate the EDHF component of acetylcholine-induced vasodilator response, L-nitro-methyl arginine ester (L-NAME, 10(-4) M) and indomethacin (10(-6) M) were added to the Krebs' solution throughout the experiment. Under these conditions, acetylcholine induced vasodilatation in the isolated renal arteries from both control and diabetic rabbits. The vasodilator response to acetylcholine was not affected under diabetic conditions. 3 Sodium nitroprusside (SNP)-induced relaxation was increased in the diabetic rabbits compared with the control animals. 4 Tetrabutyl ammonium (TBA, 0.5 mM) produced a significant reduction in acetylcholine-induced vasodilatation in both preparations from control and diabetic animals, consistent with involvement of K+ channels in mediating this response. Glibenclamide (1 microM) attenuated acetylcholine-induced vasodilatation in preparations from control animals only, while iberiotoxin (0.05 microM) significantly reduced the vasodilator response to acetylcholine in preparations from both control and diabetic animals. 5 The role of EDNO in mediating acetylcholine-induced vasodilatation was examined. The vascular preparations were incubated with 20 mM K(+)-Krebs' solution to inhibit the EDHF contribution to acetylcholine-induced vasodilatation. Under this condition, acetylcholine induced a vasodilator response in both preparations from control and diabetic rats. Pretreatment with L-NAME (10(-4) M) attenuated acetylcholine-induced vasodilatation in both preparations, indicating an nitric oxide-mediated vasodilator response. 6 Our results indicated that acetylcholine-induced vasodilatation in the isolated renal arteries of alloxan-induced diabetic rabbits was not affected under diabetic conditions. Acetylcholine-induced vasodilatation is mediated by two vasodilator components; namely, EDHF and EDNO. The contribution of EDHF and EDNO to acetylcholine-induced vasodilatation was not affected under diabetic conditions and there was no indication of endothelial dysfunction associated with diabetes. EDHF component was found to act mainly through high conductance Ca(2+)-activated K+ channels under normal and diabetic conditions, while the adenosine triphosphate-dependent K+ channels were involved in mediating acetylcholine vasodilator response in the control preparations only.

Acetylcholine-induced vasodilation in the uterine vascular bed of pregnant rats with adriamycin-induced nephrosis

OBJECTIVE

This project was designed to study endothelium-dependent vasodilation in the uterine vascular bed during experimentally induced preeclampsia in rats.

METHODS

Uterine vascular beds were isolated from non-pregnant and pregnant rats with or without treatment with adriamycin (ADR) and perfused with physiological solution. Thereafter, vasodilator responses to acetylcholine were recorded. RECORDS: Pregnant ADR-treated rats displayed symptoms of preeclampsia including hypertension and proteinuria. Blood pressure was 110.0 +/- 4.7 mm Hg (n = 5) in control pregnant rats and 136.0 +/- 5.3 mm Hg (n = 5) in ADR-treated pregnant rats, and urinary protein concentrations were 0.35 mg/ml (n = 5) and 13.2 +/- 3.6 mg/ml (n = 9), respectively. Both blood pressure and proteinuria values were significantly (p < 0.05) different between controls and ADR-treated rats. However, acetylcholine-induced dose-dependent vasodilator responses in the vascular beds were not significantly different between the pregnant and nonpregnant rats. Although acetylcholine-induced vasodilation was significantly reduced by N omega-nitro-L-arginine methyl ester hydrochloride (L-NAME) in both groups, the residual response to acetylcholine was not affected by indomethacin, suggesting that prostanoids were not involved in this response. The L-NAME-resistant component, endothelium-derived hyperpolarizing factor (EDHF), was greater in ADR-treated uterine beds than in those of the controls, indicating a significant contribution from EDHF in these vessels. In the presence of an elevated external potassium ion concentration, acetylcholine produced similar vasodilator responses, indicating that the release of nitric oxide was not impaired.

CONCLUSION

These results indicate that endothelium-dependent vasodilation was not impaired in this model of preeclampsia.

Antihypertensive effect of an aqueous extract of Zygophyllum coccineum L. in rats

The effects of an aqueous extract of Zygophyllum coccineum L. on rat blood pressure (BP) and on the mesenteric vascular bed were investigated. The extract dose-dependently reduced BP and heart rate in normotensive and spontaneously hypertensive rats (SHRs). It also reduced BP in pithed SHRs. In vitro, the extract had no effect on basal perfusion pressure of the mesenteric vascular bed. When the perfusion pressure was raised with noradrenaline or potassium chloride, the extract produced a dose-dependent reduction in perfusion pressure. However, in preparations in which the perfusion pressure was raised with KCl, the depressor response to lower doses of the extract was abolished while higher doses produced responses that were reduced in magnitude when compared with similar responses in preparations in which the perfusion pressure was raised with noradrenaline. It was concluded that extracts of Z. coccineum possess significant antihypertensive activity that may involve some membrane hyperpolarization.

Effect of extracellular Mg concentration on electrically induced contractions of rat vas deferens in vitro

Contraction of smooth muscles of the vas deferens plays an important role in the propulsion of sperm into the pelvic urethra. This study examined the influence of external Mg2+ concentration on reactivity of the rat vas deferens to electrical stimulation in vitro. Vasa deferentia isolated from adult male rats were set up in tissue baths containing physiological salt solution at 37 degrees C and were stimulated electrically. Thereafter, increasing concentrations of Mg2+ were added to the bath and their effects on electrically evoked contractions were recorded. The effect of external Mg2+ depletion on evoked contractions was also examined. External Mg2+ depletion enhanced the contractile response to electrical stimulation while increasing external Mg2+ concentration inhibited the contractions. The inhibitory effect of Mg2+ was partially reversed by increasing extracellular Ca2+ concentration and was not additive with nifedipine. The results indicate that reactivity of the vas deferens to electrical stimulation is modulated by extracellular Mg2+ concentration. The possible relevance of these data to sperm transport through the vas deferens is discussed.

Magnesium in human semen: possible role in premature ejaculation

Although magnesium is involved in many biological process and it is found higher levels in semen than serum, its role in human semen has not been elucidated. This investigation was conducted to evaluate the relationship between premature ejaculation and the levels of seminal magnesium. The levels of magnesium, zinc, copper, and selenium were evaluated with an atomic absorption spectrophotometer in serum and seminal plasma in 3 groups of men: (a) normal sperm parameters (15) (b) oligoasthenozoospermia (15), and genuine premature ejaculation (9). There were normal serum and semen levels of all the elements in the three groups, but significantly lower seminal plasma magnesium levels in men with premature ejaculation. The hormonal profile, body mass index (BMI) had no association with premature ejaculation. Decreased levels of magnesium gives rise to vasoconstriction from increased thromboxane level, increased endothelial intracellular Ca2+, and decreased nitric oxide. This may lead to premature emission and ejaculation processes. Magnesium is probably involved in semen transport. More research into the role of magnesium in the male physiology of reproductive tract, especially its association with premature ejaculation, is advocated.

Buspirone, a 5-HT1A receptor agonist, dilates the perfused rat uterine vascular bed through α1-adrenoceptor blockade

In the perfused rat uterine vascular bed, 5-hydroxytryptamine (5-HT) produced dose-dependent vasoconstrictor responses. Buspirone, a selective 5-HT(1A) receptor agonist, was not effective at low doses but produced a response at high doses. When perfusion pressure was raised with phenylephrine, responses to 5-HT were enhanced while buspirone produced dose-dependent vasodilator responses. Buspirone did not produce vasodilation when perfusion pressure was raised with vasopressin or U46619. Buspirone-induced vasodilator responses were not affected by selective 5-HT(1A) receptor antagonists, 8-[2-[4-(2-methoxyphenyl)-1-piperazinyl]ethyl]-8-azaspiro[4,5]-decane-7,9-dione (BMY 7378) and N-tert-butyl-3-(4-[2-methoxyphenyl]piperazin-1-yl)-2-phenylpropanamide (WAY 100478), indicating that specific 5-HT(1A) receptors might not be involved in buspirone-induced vasodilation. Buspirone (3 x 10 (-5) M) and prazosin (3 x 10(-9) M) antagonized noradrenaline-induced constriction with dose ratios of 19.1+/-2.9 and 11.7+/-2.1, respectively. The dose ratio of these antagonists in combination was 46.6+/-8.1. Since the combination ratio is closer to the sum of their individual dose ratios less 2 (i.e. DR(p)+DR(b)-2) than it is to the product of their individual dose ratios, our data suggest an interaction of buspirone with alpha(1)-adrenoceptors. Buspirone also protected adrenoceptors against inactivation by phenoxybenzamine confirming that buspirone interacted with alpha(1)-adrenoceptors. We concluded that buspirone-induced vasodilation of the perfused rat uterine vascular bed is mediated through blockade of alpha(1)-adrenoceptors rather than through 5-HT(1A) receptors.

Inhibitory effect of capsaicin on cholinergic transmission in ovine airways: evidence for non-cholinergic contractions

Electrical stimulation of ovine trachealis smooth muscle and bronchial ring segments induced neurogenic and monophasic atropine-sensitive contractions. Pretreatment of the tissues with capsaicin (100 microM) significantly reduced these contractions indicating a possible contribution of a peptidergic neurotransmitter to the contractions. The effect of capsaicin on electrically induced contractions was significantly inhibited by capsazepin indicating an action on vanilloid receptors. In both preparations, electrically induced contractions were not modified by tachykinin NK(1)- and NK(2)-receptor antagonists singly and in combination. It was therefore concluded that a component of the atropine-sensitive electrically induced contractions of ovine airways smooth muscles involved the release of a peptide neurotransmitter which is probably not a tachykinin. However, an action of capsaicin on prejunctional vanilloid receptors located on cholinergic nerves cannot be ruled out.

Inhibitory effects of cannabinoid receptor ligands on electrically-evoked responses in rat isolated tracheal ring segments

We have examined the possible existence of cannabinoid receptors in the isolated rat tracheal ring segments by studying the effects of some cannabinoid receptor ligands on electrically-induced contractions. Anandamide (10(-8)-3 x 10(-5)m), an endogenous ligand for cannabinoid receptors, and WIN 55,212-2 (10(-9)-3 x 10(-5)m), a moderately selective CB(2)agonist, inhibited electrically evoked contractions of the rat tracheal ring segments in a concentration-related manner. Addition of phentolamine (10(-6)m) to Krebs Henseleit solution to block alpha(2)-adrenoceptors did not affect anandamide-induced inhibition of the electrically evoked contractions. The EC(25)(-log m) values were 5.25+/-0.2 and 5.8+/-0. 4 for anandamide and WIN 55,212-2, respectively. The maximal inhibition produced by the highest concentration of the agonists used was 51.4+/-5.8% for anandamide and 35.1+/-19.5% for WIN 55, 212-2. WIN 55,212-3 also produced a concentration-dependent inhibition of the electrically evoked contractions. The maximal inhibition produced by WIN 55,212-3 was 15.8+/-2.4. The inhibitory effects of anandamide and WIN 55,212-2 were not attenuated by SR141716A (10(-6)m), a selective CB(1)receptor antagonist. Anandamide (10(-8)-3 x 10(-5)m) did not relax rat tracheal ring segments pre-contracted with carbachol (10(-6)m). These results suggest that anandamide and WIN 55,212-2 produce pre-junctional inhibitory effects in the rat trachea and that these effects were likely mediated through cannabinoid CB(2)receptors. These effects were probably non-cannabinoid receptor-mediated considering the high concentrations of the agents required to produce inhibitory responses and the effectiveness of WIN 55,212-3.

Alpha1-adrenoceptor antagonist effect of (+/-)-dobutamine in rat isolated gastric artery preparation

(+/-)-Dobutamine at concentrations < or =10(-5) M did not evoke contractions of rat gastric artery segments. However, when the tissues were contracted with methoxamine, (+/-)-dobutamine evoked concentration-dependent relaxation. The relaxant responses were not significantly affected by propranolol. In the same preparation, propranolol competitively antagonized isoprenaline-induced relaxation with a -log K(B) value of 7.90+/-0.26. (+/-)-Dobutamine did not relax arterial ring segments precontracted with vasopressin (10(-7) M). (+/-)-Dobutamine antagonized noradrenaline-induced contractions of the gastric artery segments. The pA2 value was 6.93+/-0.20, and the slope of the Schild regression line was 1.22+/-0.14. This value (slope) was not significantly different from 1, indicating competitive antagonism. Pretreatment of gastric artery segments with dobutamine before phenoxybenzamine (PBZ) protected against inactivation of alpha1-adrenoceptors by PBZ. The dose ratio of prazosin (3x10(-9) M) and (+/-)-dobutamine (10(-5) M) in combination was close to the expected sum of their individual dose ratios minus 1, indicating interaction with a common site. It was therefore concluded that (+/-)-dobutamine evoked relaxation of rat gastric artery segments by an action not involving beta-adrenoceptor activation but by blocking alpha1-adrenoceptors.

Beta1- and beta3-adrenoceptors mediate relaxation in ovine trachealis smooth muscle

Isoprenaline (non-selective) and noradrenaline (beta1-selective) concentration-dependently relaxed ovine tracheal strips precontracted with carbachol. The pD2 values were 7.07 +/- 0.08 and 6.13 +/- 0.10 for isoprenaline and noradrenaline, respectively. In the same preparation, salbutamol either produced weak relaxation or in some cases, contractile responses indicating the presence of very little or no beta2-adrenoceptors in this preparation. Isoprenaline-and noradrenaline-induced relaxations were antagonized by propranolol and atenolol with pA2 values in the range reported in the literature for an action on beta1-adrenoceptors. ICI 118551 also antagonized isoprenaline- and noradrenaline-induced relaxation but at concentrations much higher than are required to block beta2-adrenoceptors, confirming that beta2-adrenoceptors do not contribute significantly to these responses. The selective beta3-adrenoceptor agonist, BRL 37344A produced concentration-dependent relaxation of tracheal strips. BRL 37344A was a full agonist producing 100% relaxation of carbachol-induced tone. BRL 37344A-induced relaxation was weakly antagonized by propranolol confirming an action, mainly, on beta3-adrenoceptors. Cyanopindolol antagonized isoprenaline-induced relaxation (in the presence of propranolol, 10(-7) M) with a pA2 value of 8.06 +/- 0.24. It was therefore concluded that beta1- and beta3-adrenoceptors mediated agonist-induced relaxation in sheep tracheal strips.

Endothelial modulation of vasoconstrictor responses in the perfused rabbit ovarian vascular bed

The purpose of this study was to investigate the effects of endothelial denudation, inhibitors of nitric oxide (NO) and prostanoid synthesis on vasoconstrictor responses in the perfused rabbit ovarian vascular. The experiments were conducted using an in vitro perfusion system, where the ovarian vascular bed (en bloc) was perfused with Krebs' solution delivered at a constant flow rate using a peristaltic pump. Changes in perfusion pressure, which reflected peripheral resistance, were measured. Results showed that noradrenaline (NA) (10(-9) to 10(-6) mol) induced reproducible dose-dependent vasoconstrictor responses. Vasoconstrictor effects of low doses of noradrenaline were not affected by perfusion of the vascular bed with CHAPS (4.7 mg/ml for 30 s) to remove the endothelium. The same treatment however, significantly reduced responses induced by the higher doses of noradrenaline, thus depressing the maximum response. KCl-induced vasoconstriction was not affected by CHAPS. L-N(G)-nitroarginine (L-NOARG) (10(-5) mol/l) enhanced NA-induced vasoconstriction. D-NOARG, the inactive isomer of L-NOARG and aminoguanidine, an inhibitor of inducible nitric oxide synthase reduced rather than enhanced noradrenaline-induced responses. Methylene blue (3 x 10(-5) mol/l) and LY 83583 (10(-5) mol/l) produced a potentiation of NA-induced vasoconstrictor responses. Indomethacin (3 x 10(-6) mol/l) did not significantly enhance NA-induced vasoconstriction. The nonselective endothelin antagonist, SB 209670 (10(-7) and 10(-6) mol/l) did not inhibit the vasoconstriction to NA. In conclusion, results are interpreted to suggest that NA-induced vasoconstriction in the perfused rabbit ovarian vascular bed is accompanied by a release of NO and possibly endothelium-derived contracting factor. There was no evidence for a modulation of vasoconstrictor responses by products of arachidonic acid metabolism or endothelins released from the endothelium.

Functional characterization of beta-adrenoceptors mediating relaxation in sheep gallbladder

The purpose of this study was to characterize beta-adrenoceptor subtype(s) mediating relaxation in smooth muscle strips of the sheep gallbladder. Experiments were performed on isolated smooth muscle strips suspended in tissue baths containing Krebs' solution. Isoprenaline (10(-8) M-10(-5) M) and salbutamol (10(-7) M-10(-4) M) produced concentration-dependent relaxation of carbachol (10(-7) M-3 x 10(-7) M) contracted smooth muscles of the sheep gall bladder. Isoprenaline-induced relaxation was significantly antagonized by propranolol with -logKB values of 7.81 +/- 0.11 (n = 7) and 7.73 +/- 0.12 (n = 6) in the fundic and ductal strips respectively. Atenolol (10(-5) M), a selective beta 1-adrenoceptor antagonist, also significantly antagonized isoprenaline-induced relaxation with -logKB values of 5.82 +/- 0.11 and 6.09 +/- 0.09 in the fundic and ductal strips respectively. However, ICI 118551, a selective beta 2-adrenoceptor antagonist, at concentrations up to 10(-6) M had little or no effect on isoprenaline-induced relaxation in either of these preparations. BRL 37344A, a selective beta 3-adrenoceptor agonist produced concentration-dependent relaxation of carbachol-precontracted fundic and ductal strips. BRL 37344 was approximately 9-fold more potent in the ductal than fundic strips. In both preparations, BRL 37344-induced relaxation was not significantly (p > 0.05) antagonized by propranolol (3 x 10(-7) M). This would confirm that the response was mediated via beta 3-adrenoceptors. It was concluded that beta 1- and beta 3-adrenoceptors coexist in the sheep gallbladder and mediate smooth muscle relaxation.

Source(s) of activator calcium for noradrenaline-induced vasoconstriction in the perfused rabbit isolated ovarian vascular bed: a role for tyrosine kinase

The effects of Ca2+ withdrawal and agents affecting Ca2+ translocation on alpha1-adrenoceptor-mediated vasoconstrictor responses in the perfused rabbit ovarian vascular bed were studied. Noradrenaline-induced vasoconstriction was lost in a Ca(2+)-free Krebs' solution, and the rate of loss of the response was accelerated by EGTA (2 mM). Noradrenaline-induced vasoconstriction and SDZ NVI 085-induced vasoconstriction were concentration-dependently inhibited by verapamil and nifedipine. These agents were, however, more effective against KCl-induced responses. Cyclopiazonic acid, an intracellular Ca(2+) depletor, concentration-dependently inhibited noradrenaline-induced responses and abolished the response in Ca(2+)-free Krebs' solution. GF 109203X and polymyxin B, inhibitors of protein kinase C (PKC), had no significant effect on noradrenaline-induced responses. Tyrosine kinase inhibitors, genistein and erbstatin, inhibited noradrenaline-induced vasoconstriction in the perfused rabbit ovarian vascular bed. The results would suggest that both extracellular Ca2+ and intracellular Ca2+ participate in noradrenaline-induced vasoconstrictor responses in the perfused rabbit ovarian vascular bed. The results would also suggest that tyrosine kinase and not protein kinase C activation has a role in such effects.

Biphasic relaxant response of ovine trachealis muscle to electrical field stimulation: influence of cooling

Electrical field stimulation of ovine trachealis muscle produced neurogenic atropine-sensitive contractions under resting conditions. However, when the tissues were precontracted with 5-hydroxytryptamine in the presence of atropine, electrical field stimulation induced a frequency-dependent tetrodotoxin-sensitive relaxation. The relaxation was biphasic, consisting of fast and slow phases. The fast component was attenuated by propranolol, indicating an action on beta-adrenoceptors. The slow phase was attenuated by capsaicin and, therefore, involved release of a peptide. These results showed that excitatory responses in ovine trachealis muscles are cholinergically mediated, while both adrenergic and peptidergic components mediate electrically induced relaxation in the trachea. We also examined the influence of lowering bath temperature to 20 degrees C on electrically evoked responses. These were significantly reduced by cooling. At 20 degrees C, under resting conditions, the time-to-peak tension was lengthened, and the amplitude of the contractile responses was significantly (p < 0.05) reduced. In the same preparation, carbachol-induced contractions were not reduced by cooling, indicating that the reduction in electrically induced contractions was probably due to a reduction in transmitter release. Cooling also abolished the fast inhibitory phase (adrenergic in nature) without significantly inhibiting the slow (non-adrenergic, non-cholinergic) component. Propranolol (1 micromol/l) and capsaicin (100 micromol/l) did not affect significantly the slow relaxation observed during cooling. It was concluded that cooling inhibited cholinergically mediated, electrically induced contractions and selectively abolished the adrenergic component of electrically induced relaxant responses.

Sodium nitroprusside-induced cGMP-independent vasodilator responses in the perfused rabbit ovarian vascular bed

Sodium nitroprusside (SNP) (10(-9)-10(-6) mol) and carbachol (10(-9)-10(-6) mol) induced dose-dependent vasodilatation in the perfused rabbit isolated ovarian vascular bed. Carbachol, but not SNP-induced vasodilatation was abolished by treatment with CHAPS (4. 7 mg ml-1, 30 s) to remove the endothelium. Carbachol-induced responses were also significantly attenuated by LY 83583 (10(-5) M) and methylene blue (3x10(-5) M). L-NOARG (10(-5) M) reduced carbachol-induced vasodilatation. None of these compounds affected SNP-induced vasodilator responses. Both SNP- and carbachol-induced vasodilatation were attenuated by raising the [K+] in the Krebs' solution to 40 mM. The responses were also reduced by TEA (20 mM) but not by glibenclamide. It was therefore concluded that SNP induced cGMP-independent vasodilator responses in the perfused rabbit ovarian vascular bed. This vasodilator response involved membrane hyperpolarisation since it was lost in high [K+] Krebs' solution. (c) 1998 The Italian Pharmacological Society.

Functional characterization of alpha1-adrenoceptor subtypes in the rabbit spleen

Phenylephrine and (+/-)N-[5-(4,5-dihydro-1-H-imidazol-2yl)-2-hydroxy-5,6,7,8-tetr ahydronaphthalen-1-yl] methanesulphonamide hydrobromide (A 61603) evoked concentration-dependent contractions of the rabbit spleen. These contractions were antagonized by prazosin (10(-8)-10(-7) M) with pA2 values of 8.34+/-0.11 and 8.15+/-0.10 against phenylephrine and A 61603, respectively. In both cases, the slopes of the Schild plots were not significantly (P>0.05) different from 1.0, indicating competitive antagonism. The effects of subtype-selective antagonists WB 4101 [2-(2-6-dimethoxyphenoxyethyl)aminomethyl-1,4-benzodioxane hydrochloride] and 5-methylurapidil on agonist-induced contractions were also examined. WB 4101 competitively antagonized agonist-induced contractions; pA2 values were 8.13+/-0.10 and 8.10+/-0.03 against phenylephrine and A 61603, respectively. Corresponding values for 5-methylurapidil were 8.28+/-0.17 and 7.93+/-0.02 against phenylephrine and A 61603, respectively. Tamsulosin and Rec 15/2739 [(8-3-[4-(2-methoxyphenyl)-1-piperazinyl]-propylcarbamoyl)-3-methy l-4-oxo-2-phenyl-4H-1-benzopyran dihydrochloride] also antagonized phenylephrine- and A 61603-induced contractions with pA2 values of 9.38+/-0.13 and 9.18+/-0.06 (tamsulosin) and 8.41+/-0.12 and 8.34+/-0.11 (Rec 15/2739) against phenylephrine and A 61603, respectively. HV 723 (alpha-ethyl-3,4,5-trimethoxy-alpha-(3-((2-(2-methoxyphenoxyethyl) -amino)-propyl)benzene-aceto-nitrile) fumarate) competitively antagonized phenylephrine-induced contractions with a pA2 value of 8.57+/-0.06. Chloroethylclonidine (CEC; 10(-4) M) shifted phenylephrine and A 61603 concentration-response curves to the right, reducing their potencies approximately two- to threefold, while the maximum response was reduced by 8% in both cases. It was therefore concluded that contractions of the rabbit spleen induced by alpha1-adrenergic agonists were mediated predominantly by a relatively CEC-insensitive alpha1-adrenoceptor subtype, possibly the alpha1L-subtype.

Neurogenic control of the ovine gallbladder: ultrastructural and functional study

The purpose of this study was to investigate the ultrastructure of the local nerve supply of ovine gallbladders as well as the functional characteristics of inhibitory nerves. We used electron microscopy of thin sections of ovine gallbladders and in vitro isometric tension recording using gallbladder strips. Specifically, we measured contractile and inhibitory responses induced by transmural electrical field stimulation (EFS). We found a ganglionated plexus with intramural nerve cells and interconnecting axons. Clear and large dense-core vesicles colocalized in axons close to smooth muscle cells. EFS elicited gallbladder contractions which were converted to relaxation after atropine. EFS-induced relaxation was reduced by the nitric oxide (NO) synthase inhibitor, L-NOARG and blocked by propranolol and/or tetrodotoxin. In conclusion, enteric ganglia and neurones with synaptic vesicles (clear and dense core) were detected close to smooth muscle bundles. Neural inhibition of gallbladder contraction was mediated by beta-adrenoceptors coupled to NO generation.

Histamine receptor subtypes mediating hyperpolarization in the isolated, perfused rat mesenteric pre-arteriolar bed

Histamine is a general dilator of rat blood vessels. We investigated the relative contribution of receptor subtypes to the rat mesenteric dilator responses initiated by histamine and related agonists. Histamine initiated dose, and endothelium-dependent, dilation of constricted mesenteric beds with an ED50 of 0.4 +/- 0.1 nmol. The ED50 was increased 10-fold by 0.1 microM chlorpheniramine (a histamine H1-receptor selective antagonist). Histamine H2 receptor blockade with tiotidine (0.1 microM) slightly decreased, while thioperamide (1 microM), a selective histamine H3 receptor antagonist, did not block histamine-induced dilation. Mesenteric bed dilation initiated by histamine H2 receptor selective agonists, amthamine and dimaprit, were antagonized markedly by tiotidine. However, the dilation initiated by the putative histamine H3 receptor selective agonists, R(-)- or S(+)-alpha-methylhistamine and imetit were not affected by thioperamide (1 microM). Histamine H2- and H3-receptor mediated dilator effects were endothelium-independent and were blocked by either excess (80 mM) extracellular K+, or 1 mM tetrabutylammonium (a non-selective K+ channel blocker), as well as by 1 microM dequalinium, a non-peptide blocker of the small conductance Ca2+-activated (SKCa) K+ channels. We conclude that (i) histamine H1 receptor subtype predominantly mediates endothelium-dependent dilator effect of histamine, and (ii) vascular hyperpolarization through opening of K+ channels (SKCa) mediate the dilator responses to histamine H2 receptor (amthamine and dimaprit) and the putative histamine H3 receptor (R(-)-alpha-methylhistamine and imetit) agonists.

Heterogeneity of alpha 1-adrenoceptor subtypes mediating noradrenaline-induced contractions of the rat superior mesenteric artery

The effects of subtype-selective alpha 1-adrenoceptor antagonists on noradrenaline-induced contractions of ring segments of rat superior mesenteric artery were investigated to determine the subtype(s) of alpha 1-adrenoceptors mediating contractions in this preparation. Noradrenaline-induced contractions of rat mesenteric artery ring segments were potently and surmountably antagonized by prazosin, WB 4101 and BMY 7378. Judging from the slopes of the Schild regression lines, which were significantly different from 1, WB 4101 and BMY 7378 behaved as noncompetitive antagonists. Spiperone and 5-methylurapidil were only effective at high concentrations. Chloroethylclonidine (CEC, 100 mumol/l) displaced the noradrenaline concentration-response curve to the right reducing its potency approximately 100-fold. Noradrenaline-induced contractions post-CEC were also antagonized by prazosin. However, prazosin was less potent against these contractions. A 61,603, a selective alpha 1A-adrenoceptor agonist, contracted ring segments of the mesenteric artery. These contractions were antagonized by prazosin, however with a low affinity, indicating interaction with a low-affinity receptor subtype. It was therefore concluded that alpha 1D- and, possibly, alpha 1L-adrenoceptor subtypes mediated noradrenaline- induced contractions of the rat superior mesenteric artery.

Atypical beta-adrenoceptors mediate isoprenaline induced vasodilatation in the rabbit uterine vascular bed

beta-Adrenoceptor subtype(s) mediating isoprenaline-induced vasodilator responses in the perfused rabbit uterine vascular bed was characterized. Isoprenaline induced dose-dependent reduction in perfusion pressure with -logED50 value of 5.8 +/- 0.1. Propranolol (10(-6) M) had little or no effect on isoprenaline-induced vasodilatation. Similarly, cyanopindolol (10(-6) M) did not antagonize the vasodilator response. CGP 12177, an agonist on beta 3- or beta 2- adrenoceptor mediated responses. The results would indicate that isoproterenol-induced vasodilation in the perfused rabbit (oestrus or pregnant) uterine vascular bed was mediated by atypical beta-adrenoceptors which may not be identical with those in adipose tissues or gastro-intestinal tract. In addition, the fact that pregnancy did not enhance isoprenaline-induced vasodilation would suggest that these receptors may not be involved in the hyperaemia of pregnancy.

Neural inhibition in the rat lower esophageal sphincter: role of beta 3-adrenoceptor activation

1. Electrical field stimulation (EFS) of the rat lower esophageal sphincter produced tetrodotoxin-sensitive relaxant responses. 2. The relaxant responses were not significantly affected by propranolol but were attenuated by 6-hydroxydopamine and cyanopindolol, indicating beta 3-adrenoceptor activation. 3. The relaxant responses were significantly reduced in tissues previously exposed to BRL 37344, a beta 3-adrenoceptor agonist. 4. It was concluded that EFS-induced relaxation was adrenergic in origin and was mediated by beta 3-adrenoceptors.