Beta-adrenoceptor agonist mediated relaxation of rat isolated resistance arteries: a role for the endothelium and nitric oxide

Nitric oxide and beta-adrenergic agonist-induced bronchial arterial vasodilation

In anesthetized sheep, we measured bronchial blood flow (Qbr) by an ultrasonic flow probe to investigate the interaction between inhaled nitric oxide (NO; 100 parts/million) given for 5 min and 5 ml of aerosolized isoetharine (1.49 x 10(-2) M concentration). NO and isoetharine increased Qbr from 26.5 +/- 6.5 to 39.1 (SE) +/- 10.6 and 39.7 +/- 10.7 ml/min, respectively (n = 5). Administration of NO immediately after isoetharine further increased Qbr to 57.3 +/- 15.1 ml/min. NO synthase inhibitor N(omega)-nitro-L-arginine methyl ester hydrochloride (L-NAME; 30 mg/kg, in 20 ml saline given i.v.) decreased Qbr to 14.6 +/- 2.6 ml/min. NO given three times alternately with isoetharine progressively increased Qbr from 14.6 +/- 2.6 to 74.3 +/- 17.0 ml/min, suggesting that NO and isoetharine potentiate vasodilator effects of each other. In three other sheep, after L-NAME three sequential doses of isoetharine increased Qbr from 10.2 +/- 3.4 to 11.5 +/- 5.7, 11.7 +/- 4.7, and 13.3 +/- 5.7 ml/min, respectively, indicating that effects of isoetharine are predominantly mediated through synthesis of NO. When this was followed by three sequential administrations of NO, Qbr increased by 146, 172, and 185%, respectively. Thus in the bronchial circulation, there seems to be a close interaction between adenosine 3',5'-cyclic monophosphate- and guanosine 3',5'-cyclic monophosphate-mediated vasodilation.

Aminoguanidine--effects on endoneurial vasoactive nitric oxide and on motor nerve conduction velocity in control and streptozotocin-diabetic rats

1. The effects of aminoguanidine (AG) treatment on reductions in motor nerve conduction velocity (MNCV) and sciatic nerve blood flow, indexed by laser Doppler flux (LDF), were investigated in rats with experimental diabetes (streptozotocin-induced; 8-10 weeks duration). The contribution of endoneurial vasoactive nitric oxide to the LDF of these animals was also investigated by the direct micro-injection of NG-nitro-L-arginine methyl ester (L-NAME; 1 nmol in 1 microliter), followed by L-arginine (100 nmol in 1 microliter), into the sciatic nerve endoneurium. 2. The MNCV (m s-1, mean +/- 1 s.d.) of diabetic rats (38.2 +/- 1.5) was lower (P < 0.01) than that of age-matched controls (47.2 +/- 4.2). AG treatment (50 mg kg-1 day-1, i.p.) attenuated the diabetes-induced deficits in MNCV (43.4 +/- 5.9; P < 0.01), but had no effect in controls (48.8 +/- 3.8) or, if administered via drinking water (1 gl-1), diabetics (37.4 +/- 4.1). 3. L-NAME markedly reduced the resting LDF (arbitrary units; mean +/- s.e.mean) of controls (209 +/- 13 to 120 +/- 18; P < 0.005), an effect reversed by subsequent L-arginine (to 206 +/- 27). In diabetic rats the LDF reduction following L-NAME was much smaller (111 +/- 11 to 84 +/- 6; P < 0.05), but the change with L-arginine was significantly increased (to 145 +/- 12; P < 0.001). 4. AG treatment increased the resting LDF of control (265 +/- 34) and diabetic rats (133 +/- 14 for daily injection and 119 +/- 13 for drinking water). The responses to L-NAME and L-arginine were not changed markedly by AG treatment. However, L-arginine appeared to be less effective. 5. In conclusion, these data suggest that AG treatment may affect nitric oxide production in the vasa nervorum of peripheral nerves. However, the effects of AG-treatment are not consistent with the prevention of a diabetes-associated reduction in endoneurial nitric oxide production. The mechanisms by which AG attenuates nerve conduction slowing in streptozotocin-diabetic rats therefore remain unclear.

Adaptation of myocardial blood flow to increased metabolic demand is not dependent on endothelial vasodilators in the rat heart

OBJECTIVE

To investigate the role of endothelial vasodilating factors in adaptation of myocardial blood flow to increased metabolic demands.

DESIGN

Alterations in the effects of endothelium dependent (acetylcholine) and independent (sodium nitroprusside) vasodilators and the beta 1 receptor agonist dobutamine were studied after inhibition of endothelium derived relaxing factor (EDRF) with L-NG-nitro-arginine methyl ester (L-NAME), prostanoid synthesis with indomethacin, and ATP sensitive potassium channels with glibenclamide.

EXPERIMENTAL ANIMALS

Female Wistar rats, in situ perfused heart.

MAIN OUTCOME MEASURES

Myocardial blood flow (H2 clearance); systolic fractional thickening (pulsed Doppler); mean arterial blood pressure.

RESULTS

L-NAME reduced myocardial blood flow by 58 (12)% (mean (SD), P < 0.001) and systolic thickening fraction (FT) by 36 (9)% (P < 0.05). These effects were significantly reversed by administration of L-arginine but not D-arginine. Pretreatment with L-NAME inhibited the increase in myocardial blood flow caused by acetylcholine (control: +42 (9)%; L-NAME: -29 (7)%, P < 0.001) but did not affect the increase in myocardial blood flow caused by sodium nitroprusside (control: +44 (5)%; L-NAME: +34 (10)%, NS). Pretreatment with L-NAME did not change the effect of dobutamine on myocardial blood flow (+61 (3)%) and FT (+32 (8)%) compared with baseline values (P < 0.001). Neither pretreatment with indomethacin nor with glibenclamide reduced the dobutamine induced increase in myocardial blood flow.

CONCLUSIONS

Inhibition of EDRF, prostanoid synthesis, and ATP sensitive potassium channels did not reduce the vasodilator reserve during increased metabolic demands induced by beta 1 adrenergic stimulation. Therefore, adaptation of myocardial blood flow to increased metabolic demands is independent of endothelial relaxing factors in the rat heart.

Endothelium-mediated and N omega-nitro-L-arginine methyl ester-sensitive responses to cromakalim and diazoxide in the rat mesenteric bed

The effects of two 'K+ channel openers', (+/-)-6-cyano-3,4-dihydro-2,2-dimethyl-trans-4-(2-oxo-1-pyrrolidyl )-2 H-benzo[b]-pyran-3-ol (cromakalim) and 7-chloro-3-methyl-2 H-1,2,4-benzothiadiazine 1,1-dioxide (diazoxide), were studied on the rat isolated mesenteric bed. Differences in the perfusion pressure were measured as a parameter of vascular resistance. Cromakalim (0.1-700 microM) and diazoxide (1 microM-1 mM) reduced to 60% the contractions elicited by 10 microM noradrenaline and to 30% those evoked by 100 mM KCl. The relaxant effects of cromakalim and diazoxide on the noradrenaline-induced contractions were reduced by the K(+)-ATP channel blocker, 5-chloro-N-[2-[4-[[[(cyclohexylamino) carbonyl]amino]-sulfonyl]phenyl]ethyl]-2-methoxybenzamide (glibenclamide, 0.01-0.3 microM), endothelium removal with 0.1% saponin and pretreatment with the nitric oxide synthesis inhibitor, S(+/-)-N5-[imino(nitroamino)methyl]-L-ornithine methyl ester hydrochloride (L-NAME, 500 microM). Reductions in the relaxant responses after endothelium removal or L-NAME pretreatment were observed with 1-100 microM cromakalim and with 30 microM diazoxide but not with 100 and 300 microM diazoxide. Pretreatment with the inactive stereoisomer D-NAME as well as with the prostanoid synthesis inhibitor, 1-[p-chlorobenzoyl]-5-methoxy-2-methylindole-3-acetic acid (indomethacin, 10 microM), did not affect the reductions in contractile responses to noradrenaline caused by either cromakalim or diazoxide. It is concluded that the relaxant effects of cromakalim and diazoxide in the rat mesenteric bed are endothelium-mediated and L-NAME-sensitive and could at least partially involve the participation of nitric oxide.

Endothelium- and cytochrome P-450-dependent relaxation induced by isoproterenol in rat aortic rings

In rat aortic rings, the mechanism of endothelium-dependent relaxation induced by isoproterenol is examined. Pretreatment with (+/-)-1-[2,3]-(dihydro-7-methyl-1H-inden-4-yl)oxy]-3-[(1-methyleth yl)amino] -2-butanol (ICI-118,551), a beta 2-adrenoceptor antagonist, or atenolol, a beta 1-adrenoceptor antagonist, partly inhibited the relaxing response to isoproterenol. The relaxing response to isoproterenol in the presence of ICI-118,551 or atenolol was markedly inhibited by removal of endothelium. In the aorta pretreated with ICI-118,551 or atenolol, residual relaxing response to isoproterenol was also inhibited by 2-methyl-1,2-di-3-pyridyl-1-propanone (metyrapone), alpha-naphthoflavone or 8-methoxypsoralen, cytochrome P-450 monoxygenase inhibitors, and methylene blue, but not by indomethacin, a cyclooxygenase inhibitor, 2,3,5-trimethyl-6-(12-hydroxy-5,10-dodecadiynyl)-1, 4-benzoquinone (AA861), a 5-lipoxygenase inhibitor, NG-nitro-L-arginine (NOARG), a nitric oxide synthase inhibitor, Zn protoporphyrin IX, a heme oxygenase inhibitor, or yohimbine, a alpha 2-adrenoceptor antagonist. In the aorta denuded of endothelium, metyrapone did not affect the residual relaxing response to isoproterenol in the presence of atenolol. These results suggest that the cytochrome P-450 system may be involved in the endothelium-dependent relaxation induced by isoproterenol through beta 1- and beta 2-adrenoceptor activation.

Effects of short- and long-term sympathectomy on vasoconstrictor responses of the rat mesenteric arterial bed

1. The effects of short- and long-term sympathectomy were evaluated on vasoconstrictor function of constantly perfused mesenteric arterial beds isolated from rats: the effects of short-term sympathectomy were assessed at 3 and 8 days after 6-hydroxydopamine (6-OHDA) treatment of adult rats; the effects of long-term sympathectomy were assessed in adult rats treated at youth with guanethidine. 2. The relative degree of residual sympathetic innervation of the mesenteric arterial preparations was assessed by responses to electrical field stimulation (EFS; 16 Hz, 1 ms, 90 V, 30 s). Control responses were 95.6 +/- 3.9 mmHg (n = 35). Responses after sympathectomy were: 3 days after 6-OHDA, 2.9 +/- 0.9 mmHg (n = 15) < 8 days after 6-OHDA, 14.1 +/- 2.1 mmHg (n = 14) < guanethidine, 21.1 +/- 4.1 mmHg (n = 16). 3. Three days after 6-OHDA treatment there was an increase in the sensitivities of response to vasopressin and endothelin, producing leftward shifts of the dose-response curves of 0.66 +/- 0.11 and 0.88 +/- 0.13 log units respectively (n = 7-11), and a small increase in sensitivity of responses to noradrenaline (NA) and ATP. The maximal response to 5-hydroxytryptamine (5-HT) was increased. In contrast, there was a decrease in maximal constriction to NA and to the alpha 1-adrenoceptor agonist methoxamine. The alpha 2-adrenoceptor agonist clonidine did not elicit vasoconstriction at basal tone. There was no difference in vasodilator responses to the beta-adrenoceptor agonist isoprenaline in preparations with tone raised with prostaglandin F2 alpha (PGF2 alpha; 0.1-0.3 microM). 4. Eight days after 6-OHDA sympathectomy there was no significant difference in sensitivities or maximal responses to ATP, vasopressin and endothelin, but a small increase in the sensitivity of responses to 5-HT. Maximal responses to NA and methoxamine were significantly lower than the controls, but sensitivities were similar. There was no significant difference in vasodilator responses to isoprenaline in PGF2 alpha-raised tone preparations. 5. After long-term guanethidine sympathectomy maximal responses to 5-HT and NA were significantly reduced. Responses to ATP, vasopressin and endothelin were unchanged. 6. In mesenteric arterial preparations from untreated rats, ouabain (0.1 mM), a blocker of the Na+/K+ pump, significantly augmented the sensitivity and maximal responses to EFS, NA, methoxamine and 5-HT. Responses to ATP, vasopressin and endothelin were unaffected. 7. It is concluded that in the rat mesenteric arterial bed, short-term sympathectomy, where only 3% of the sympathetic nerve-mediated response remained, results in non-uniform changes in sensitivity and maximal responses to different vasoconstrictors, which cannot be entirely explained by changes in the Na+/K+ pump. Most of these changes disappeared at 8 days after 6-OHDA treatment, when nerve-mediated responses had partially returned. After long-term guanethidine sympathectomy, there was little change in responses to vasoconstrictors, and nerve-mediated responses were reduced to 22%. Although the variable factors are complex, it appears that in general, changes in responses of smooth muscle to vasoconstrictor substances after sympathetic denervation only occur if there is near-complete loss of nerve-mediated responses.

Effect of celiprolol therapy on arterial dilatation in experimental hypertension

1. It has recently been suggested that therapy with beta-adrenoceptor blockers reduces peripheral arterial resistance via enhanced vascular dilatation. Therefore, we studied the effects of celiprolol, which is a specific beta 1-antagonist that has a weak beta 2-agonist action, on arterial tone in spontaneously hypertensive rats (SHR) and Wistar-Kyoto (WKY) rats. 2. Two doses of celiprolol (5 and 50 mg kg-1 day-1) were administered to the SHR, while the WKY rats received only the higher dose of the drug. During the 12-week treatment period the higher dose attenuated the increase in blood pressure by approximately 20 mmHg in SHR, whereas the lower dose was without significant antihypertensive effect. Celiprolol therapy did not affect blood pressure in the normotensive WKY rats. 3. Responses of mesenteric arterial rings in vitro were examined at the end of the study. Interestingly, endothelium-mediated relaxations of noradrenaline (NA)-precontracted rings to acetylcholine (ACh) in the absence and presence of the cyclo-oxygenase inhibitor, diclofenac, were equally enhanced in both celiprolol-treated SHR groups. The nitric oxide synthase inhibitor NG-nitro-L-arginine methyl ester (L-NAME) practically abolished the relaxations to ACh in all SHR irrespective of whether they had received celiprolol, whereas in WKY rats L-NAME only attenuated the responses to ACh. However, no differences were found between the SHR groups in relaxations to ACh when hyperpolarization of smooth muscle was prevented by precontractions induced by 50 mM KCl. Vasorelaxation of NA-precontracted rings to the exogenous nitric oxide donor, nitroprusside, was also moderately augmented in both celiprolol-treated SHR groups, while the relaxation to beta-adrenoceptor agonist, isoprenaline, remained equally impaired in all SHR whether or not they had received celiprolol. No differences were observed between the two WKY groups in the responses to ACh, nitroprusside or isoprenaline. 4. Contractile sensitivity of mesenteric arterial rings to the receptor-mediated agonists, NA and 5-hydroxytryptamine, was comparable in all study groups. 5. In conclusion, SHR treatment with either the low or the higher dose of celiprolol was accompanied by enhancement of both endothelium-dependent and endothelium-independent nitric oxide-mediated arterial relaxation, possibly via a hyperpolarization mechanism. Interestingly, this effect appeared to be independent of the reduction in blood pressure.

The inhibitory effects of iberiotoxin and 4-aminopyridine on the relaxation induced by beta 1- and beta 2-adrenoceptor activation in rat aortic rings

1. In rat aortic rings contracted by phenylephrine, the relaxation induced by isoprenaline was partly inhibited by iberiotoxin, (ibTX), tetraethylammonium, 4-aminopyridine (4-AP) and 1,9-dideoxyforskolin, but not by glibenclamide. 2. In the presence of 4-AP, 1,9-dideoxyforskolin failed to inhibit further the relaxant response to isoprenaline. Cromakalim-induced relaxation was inhibited by glibenclamide. 3. In the absence of endothelium, ibTX and 4-AP still inhibited the relaxant response to isoprenaline. 4. The inhibitory effect of ibTX on the relaxant response to isoprenaline was eliminated by pretreatment with ICI-118,551, a beta 2-adrenoceptor antagonist, but not by atenolol, a beta 1-adrenoceptor antagonist. 5. The inhibitory effect of 4-AP on the relaxation induced by isoprenaline was abolished by atenolol, but not by ICI-118,551. 6. The inhibitory effect of ibTX on the isoprenaline-induced relaxation in the presence of atenolol was completely abolished by MDL 12,330A, an adenylate cyclase inhibitor. Further, the inhibitory effect of 4-AP on the isoprenaline-induced relaxation in the presence of ICI-118,551 was markedly reduced by MDL 12,330A. 7. The relaxation induced by dibutyryl cyclic AMP was partly inhibited by 4-AP but not by ibTX. However, in the presence of KT5720, an inhibitor of cyclic AMP-dependent protein kinase, ibTX failed to inhibit further the relaxation induced by isoprenaline. 8. These results suggest that, in rat aortic rings, KCa channels are involved in the relaxation induced by isoprenaline. In addition, KCa channels are mainly activated by beta 2-adrenoceptors through cyclic AMP-dependent pathways. Further, the inhibition of isoprenaline-relaxation by 4-AP may be related to the activation of beta 1-adrenoceptors and cyclic AMP formation.

Divergent effects of propranolol and nadolol in isolated mesenteric arteries from normal and portal hypertensive rats

Propranolol, a non-selective beta-blocker, is used for treatment of portal hypertension as it is believed to diminish splanchnic blood flow both by reducing cardiac output (beta(1)-blockade) and by increasing splanchnic arteriolar resistance (beta(2)-blockade). However, possible vasodilatory properties of propranolol at higher concentrations may counteract splanchnic vasoconstriction. Nadolol, another nonselective beta-blocker, has also been suggested for treatment of portal hypertension. The aim of the present study was to investigate the effects of various concentrations of propranolol and nadolol on vascular resistance in isolated perfused mesenteric arterial beds from normal and portal hypertensive rats. At concentrations of 10(-7) mol L-1 to 10(-6) mol L-1 neither propranolol nor nadolol changed pressor responses to noradrenaline in normal rats. However, nadolol 10(-5) mol L-1 significantly increased, whereas propranolol 10(-5) mol L-1 reduced, noradrenaline-induced vasoconstriction both in normal and in portal hypertensive rats. This unexpected vasodilatory effect of propranolol at high concentrations was present in preparations stimulated by both noradrenaline and methoxamine but not vasopressin and thus may be due to competitive alpha-receptor blockade. In contrast, nadolol lacked this effect and produced splanchnic arteriolar vasoconstriction at high concentrations also.

Deficient nitric oxide responsible for reduced nerve blood flow in diabetic rats: effects of L-NAME, L-arginine, sodium nitroprusside and evening primrose oil

1. This study examined the potential role of impaired nitric oxide production and response in the development of endoneurial ischaemia in experimental diabetes. Rats were anaesthetized (Na pentobarbitone 45 mg kg-1, diazepam 2 mg kg-1) for measurement of sciatic nerve laser Doppler flux and systemic arterial pressure. Drugs were administered into the sciatic endoneurium via a microinjector attached to a glass micropipette. 2. In two separate studies comparing diabetic rats (streptozotocin-induced; 8-10 wk duration) with controls, nerve Doppler flux in diabetic rats (Study 1, 116.6 +/- 40.4 and Study 2, 90.1 +/- 34.7 (s.d.) in arbitrary units) was about half that measured in controls (219.6 +/- 52.4 and 212.8 +/- 95.5 respectively; P < 0.005 for both). There were no significant differences between the two in systemic arterial pressure. 3. Inhibition of nitric oxide production by microinjection of 1 nmol L-NAME into the endoneurium halved flux in controls (to 126.3 +/- 41.3 in Study 1 and 102.1 +/- 38.9 in Study 2; both P < 0.001), with no significant effect in diabetic rats, indicating markedly diminished tonic nitric oxide production in the latter. D-NAME was without effect on nerve Doppler flux. 4. L-Arginine (100 nmol), injected after L-NAME, markedly increased flux in controls (by 65.8% (P < 0.03) and 97.8% (P < 0.01) in the two studies) and by proportionally similar amounts in diabetic rats [75.8% (P < 0.001) and 60.2% (P < 0.02)]. The nitro-donor, sodium nitroprusside (SNP; 10 nmol) had similar effects to L-arginine in both groups (increases of 66.0% in controls and 77.5% in diabetics; both P < 0.002). 5. A second diabetic group, treated with evening primrose oil performed exactly like control rats in respect of responses to L-NAME, L-arginine and SNP. 6. These findings implicate deficient nitric oxide in nerve ischaemia of diabetes and suggest correction thereof as a mechanism of action of evening primrose oil.

Myogenic and flow-mediated responses in isolated mesenteric small arteries from pregnant and nonpregnant rats

OBJECTIVES

Responses to pressure, agonist-induced constriction, endothelium-dependent vasodilators, and shear stress were investigated in resistance-sized mesenteric arteries in vitro from late-pregnant and nonpregnant rats.

STUDY DESIGN

Myogenic tone was determined in arteries mounted on a pressure myograph by evaluating the response to incremental increases in luminal pressure in resting arteries and arteries preconstricted with norepinephrine (10(-6) mol/L). Flow-mediated dilation was also investigated in the presence and absence of a nitric oxide synthase inhibitor, L-N(omega)-nitro-L-arginine methyl ester. Constrictor responses to norepinephrine (10(-9) to 10(-5) mol/L), were examined with a small vessel myograph. Responses of preconstricted arteries to acetylcholine (10(-9) to 10(-5) mol/L), bradykinin (10(-9) to 10(-5) mol/L), and sodium nitroprusside (10(-9) to 10(-5) mol/L) were also assessed.

RESULTS

Myogenic tone was only demonstrable in response to increasing pressure when arteries were preconstricted with norepinephrine (10(-6) mol/L) and was similar in arteries from both pregnant and nonpregnant rats. Flow-mediated dilation was greater in pregnant rats and was reduced by L-N(omega)-nitro-L-arginine methyl ester. Arteries from the pregnant rats demonstrated a reduced constrictor response to norepinephrine. Responses to acetylcholine were similar in both groups, but arteries from the pregnant rats showed enhanced relaxation to bradykinin.

CONCLUSIONS

The data substantiate previous studies indicating reduced constrictor responses in pregnancy but provide no evidence to suggest that blunted myogenic responses contribute to reduced vascular resistance in pregnancy. The results indicate that flow-mediated nitric oxide release may contribute to vasodilation in pregnant rats. Different responses to two endothelium-dependent vasodilators suggest that specific alterations in signal transduction pathways may influence nitric oxide synthesis in pregnancy.

Vasoconstrictor function of the rat isolated perfused mesenteric arterial bed seven days after hypophysectomy

The effect of removal of the pituitary on mesenteric arterial function was examined in adult male rats that had undergone hypophysectomy 7 days earlier. Sham-operated rats and weight-matched rats served as controls. The body weight of hypophysectomized rats decreased from 220.75 +/- 0.48 g to 188.03 +/- 2.53 g (n = 7). Sham-operated controls gained weight, from 223 +/- 1.47 to 275.85 +/- 3.45 g (n = 8). Frequency-dependent vasoconstriction to electrical field stimulation (2-32 Hz, 90 V, 1 ms, 30 s) was significantly augmented after hypophysectomy. The maximal constrictor response of hypophysectomized preparations, 215.5 +/- 14.9 mm Hg (n = 6), was approximately twice that of the sham-operated controls, 100 +/- 6.1 mm Hg (n = 7) and weight-matched controls 109.8 +/- 5.8 mm Hg (n = 8). Norepinephrine (NE) (0.05-1,500 nmol) elicited dose-dependent vasoconstriction; the maximal response was significantly augmented after hypophysectomy, 221.71 +/- 15.9 (n = 7) as compared with 148.0 +/- 16.0 mm Hg (n = 8) in sham-operated controls and 146.3 +/- 8.7 mm Hg (n = 7) in weight-matched controls. Dose-dependent vasoconstrictor responses to ATP, 5-hydroxytryptamine, vasopressin, and endothelin were similar between the groups. High-performance liquid chromatography analysis showed no difference in NE content of the superior mesenteric artery from hypophysectomized and sham-operated controls. Hypophysectomy of rats caused an increase in sympathetic constrictor function of the mesenteric arterial vasculature that appeared to involve postjunctional adrenoceptors rather than prejunctional mechanisms and was not due to arrested growth or the smaller size of the mesenteric preparations.

Effects of selected vasoconstrictor agonists on isolated omental artery from premenopausal nonpregnant women and from normal and preeclamptic pregnant women

OBJECTIVE

Our purpose was to compare the responsiveness of omental resistance arteries from nonpregnant women and from normotensive and preeclamptic pregnant women to selected contractile agonists.

STUDY DESIGN

Omental artery rings with intact endothelium from normotensive premenopausal nonpregnant women and from normal and preeclamptic pregnant women were mounted in Krebs-bicarbonate solution in organ baths for isometric tension recording. After the presence of endothelium was confirmed, cumulative concentrations of norepinephrine, serotonin, U46619, and endothelin-1 were added. Concentration-response curves were constructed and expressed as percentage of a reference 60 mmol/L potassium chloride contraction. Data analysis was by repeated-measures analysis of variance. Newman-Keuls test, and paired or unpaired Student t test, as appropriate. Statistical significance was by two-tailed p<0.05.

RESULTS

Endothelin-1 and U46619 increased tension similarly in all three groups. Norepinephrine increased tension in nonpregnant vessels to a greater extent than in either preeclamptic or pregnant vessels (nonpregnant 114.3 +/- 5.42% vs pregnant 65.2 +/- 10.5%, p<0.05). Nonpregnant omental artery developed significantly greater tension than did pregnant tissue at three concentrations of norepinephrine (10(-5) mol/L, 3 x 10(-5) mol/L, 10(-4) mol/L), and preeclamptic vessels developed more tension than that from normal pregnant vessels at 3 x 10(-6) mol/L (p=0.06) and 10(-5) mol/L (p<0.05). There was a negligible change in tension with increasing concentrations of serotonin in the vessels from nonpregnant women; serotonin-induced contraction in the omental arteries from normotensive pregnant women and preeclamptic patients was <6% of the potassium chloride reference contraction, but this was significantly (p<0.05) different from that of the nonpregnant women.

CONCLUSIONS

Omental artery segments from nonpregnant, normotensive pregnant and preeclamptic women contract similarly to endothelin-1 and U46619 but exhibit variable responses to norepinephrine and serotonin.

Mechanism of butyrate-induced vasorelaxation of rat mesenteric resistance artery

1. The vasorelaxant effect of the sodium salt of the short chain fatty acid, butyrate, on preconstricted rat small mesenteric arteries (mean inner diameter approximately 300 microns) was characterized. Isometric force development was measured with a myograph, and intracellular pH (pHi) was simultaneously monitored, in arteries loaded with the fluorescent dye BCECF in its acetomethoxy form. Sodium butyrate (substituted isosmotically for NaCl) was applied to arteries after noradrenaline (NA) or high K+ contractures were established. 2. Arteries preconstricted with a concentration of NA inducing an approximately half maximal contraction were relaxed by 91.5 +/- 6.3% by 50 mmol l-1 butyrate. This concentration of butyrate did not, however, cause a significant relaxation of contractures to a maximal (5 mumol l-1) NA concentration, and also failed to relax significantly contractures stimulated by high (45 and 90 mmol l-1) K+ solutions. Contractures elicited with a combination of NA (at a submaximal concentration) and 45 mmol l-1 K+ were, however, markedly relaxed by butyrate. 3. Investigation of the concentration-dependency of the butyrate-induced relaxation of the half maximal NA response revealed an EC50 for butyrate of approximately 22 mmol l-1. 4. Sodium butyrate (50 mmol l-1) caused pHi to decrease from 7.25 +/- 0.02 to 6.89 +/- 0.08 (n = 4, P < 0.001). However, the vasorelaxant effect of butyrate on the submaximal NA contracture was not significantly modified when this fall in intracellular pH was prevented by the simultaneous application of NH4Cl. 5. Butyrate-induced relaxation was also unaffected by endothelial denudation and inhibition of NO synthase with N omega-nitro-L-arginine methyl ester (100 mumol l-1). 6. The relaxation of the NA contracture by 50 mmol l-1 sodium butyrate was abolished in arteries pretreated with the cyclic AMP antagonist Rp-cAMPS (25 mumol l-1). 7. We conclude that the butyrate-induced relaxation of the NA contracture is independent of intracellular acidification. The ability of Rp-cAMPS to abolish the butyrate relaxation indicates that stimulation of the cyclic AMP second messenger system may play an important role in mediating this effect.

Role of nitric oxide in systemic hemodynamic responses to dobutamine, epinephrine, and amrinone

OBJECTIVE

This study was designed to investigate the extent to which the systemic vasodilator effects of dobutamine, epinephrine, and amrinone are modulated by the endothelium-derived relaxing factor, nitric oxide (NO).

DESIGN

This was a prospective study of low and high doses of the agonists before and after inhibition of NO synthesis.

SETTING

Experiments were performed in the basic research laboratories of the Center for Anesthesiology Research.

PARTICIPANTS

Pentobarbital-anesthetized, intact Sprague-Dawley rats were studied in seven separate groups of eight rats each.

INTERVENTIONS

The systemic vasodilator responses to the agonists were assessed before and after the administration of the NO synthase inhibitor, NG-nitro-L-arginine methyl ester.

MEASUREMENTS AND MAIN RESULTS

Decreases in systemic vascular resistance in response to dobutamine and epinephrine were not observed after inhibition of NO synthesis, whereas the decrease in systemic vascular resistance in response to amrinone was still apparent.

CONCLUSIONS

The results suggest that dobutamine and epinephrine produce systemic vasodilation through the release of NO, whereas amrinone produces vasodilation independent of NO release.

Exposure and characterization of the action of noradrenaline at dopamine receptors mediating endothelium-independent relaxation of rat isolated small mesenteric arteries

1. Previously, we reported that noradrenaline (NA), in addition to its alpha 1-adrenoceptor-mediated contractile effect, may relax the rat small mesenteric artery (SMA) in order to account for steep Schild plots obtained with compounds classified as alpha 1-adrenoceptor antagonists. In this study, a relaxant action of NA has been exposed in the rat isolated, endothelium-denuded SMA precontracted by the thromboxane A2-mimetic, U46619. 2. NA, but not the selective alpha 2-adrenoceptor agonist, UK14304, produced concentration-dependent contraction of the SMA (pEC50 = 5.7 +/- 0.1). After precontraction with 0.1 microM U46619, 10 nM-30 microM NA produced a further contraction (pEC50 = 6.1 +/- 0.2), while higher concentrations of NA produced small, but significant, relaxant responses. 3. In the presence of 1 microM prazosin, 0.1-30 microM NA produced concentration dependent relaxation (pIC50 = 5.9 +/- 0.1) after precontraction with 0.1 microM U46619. The NA relaxation concentration-effect curve was completely inhibited by 1 microM of the beta 1/beta 2-adrenoceptor antagonist, timolol. However, when the concentration of prazosin was increased by 10 fold (10 microM), NA once again produced concentration-dependent relaxation (pIC50 = 4.5 +/- 0.2). This relaxation concentration-effect curve was not blocked by a 10 fold higher concentration of timolol (10 microM), nor by the presence of idazoxan (10 microM), cyanopindolol (10 microM), NG-nitro-L-arginine methyl ester (L-NAME, 100 microM), indomethacin (10 microM) or sulpiride (1 microM). However, haloperidol (10 microM) and (+/-)-SCH-23390 (10 nM) produced significant inhibition of the relaxation, suggesting the involvement of dopamine D1 receptors. 4. Dopamine also produced concentration-dependent relaxation following U46619 precontraction (pIC50 = 5.4 +/- 0.1) which was significantly inhibited by haloperidol and (+)-SCH-23390. Pretreatment with 10 microM phenoxybenzamine for 60 min produced a significant inhibition of the dopamine and NA relaxation curves and application of the operational model of agonism yielded estimates of the affinity (pKA = 5.3 +/- 0.2 and 4.4 +/- 0.2) and efficacy (log gamma = 0.06 +/- 0.11 and 0.01 +/- 0.10) for dopamine and NA, respectively, at D1 receptors. 5. HV723 (0.1 and 1 microM), a ligand that yielded a Schild plot slope parameter of unity as an antagonist of NA in the contractile assay, produced concentration-dependent inhibition of the NA-mediated relaxation (pA2 approximately 8). 6. The results of this study indicate that NA can activate D1 receptors mediating relaxation in the rat SMA at concentrations which were encountered in our previous receptor classification experiments using competitive alpha 1-adrenoceptor antagonists.

The effect of norepinephrine and dobutamine on bladder epithelial oxygen tension

STUDY OBJECTIVES

To assess the effects of two contrasting vasoactive agents (dobutamine [DOB] and norepinephrine [NE]) on (1) global and regional cardiorespiratory variables, (2) acid base status, and (3) bladder epithelial oxygen tension (BEOT), a putative marker of organ perfusion.

DESIGN

Measurement of aortic blood flow (ABF) and renal blood flow (RBF), mean arterial blood pressure, arterial blood gases, and BEOT were made during infusion of placebo and varying doses of DOB and NE.

SETTING

Medical school laboratory.

SUBJECTS

Eighteen anesthetized, spontaneously breathing, male Sprague-Dawley rats divided into three groups.

INTERVENTIONS

Two groups were allocated to receive escalating doses of DOB (to 40 micrograms/kg/min) or NE (to achieve a 50% change in any hemodynamic variable). The drug therapy was then discontinued for 15 min and restarted at the previous maximum dose. A third group received 0.9% saline solution at the same infusion rate (16 mL/kg/h).

MEASUREMENTS AND RESULTS

There was a dose-related increase in mean blood pressure with NE and fall with DOB. Compared with control values, NE had no effect on ABF but decreased RBF significantly whereas DOB significantly increased ABF but had no effect on RBF. Base excess and BEOT decreased significantly and in parallel with both agents, more so with NE.

CONCLUSIONS

Despite their different macrocirculatory effects, DOB and NE both produced a significant but reversible fall in BEOT and a metabolic acidosis. BEOT shows potential as a monitor of the effectiveness of organ perfusion.

Dietary calcium and magnesium supplements in spontaneously hypertensive rats and isolated arterial reactivity

1. High calcium diet attenuates the development of hypertension but an associated undesirable effect is that Mg2+ loss to the urine is enhanced. Therefore, we studied the effects of high calcium diet alone and in combination with increased magnesium intake on blood pressure and arterial function. 2. Forty-eight young spontaneously hypertensive rats (SHR) were allocated into four groups, the dietary contents of Ca2+ and Mg2+ being: 1.1%, 0.2% (SHR); 2.5%, 0.2% (Ca-SHR); 2.5%, 0.8% (CaMg-SHR); and 1.1%, 0.8% (Mg-SHR), respectively. Development of hypertension was followed for 13 weeks, whereafter electrolyte balance, lymphocyte intracellular free calcium ([Ca2+]i), and mesenteric arterial responses in vitro were examined. Forty normotensive Wistar-Kyoto (WKY) rats were investigated in a similar manner. 3. Calcium supplementation comparably attenuated the development of Lypertension during normal and high magnesium intake in SHR, with an associated reduced lymphocyte [Ca2+]i and increased Mg2+ loss to the urine. 4. Endothelium-dependent arterial relaxation to acetylcholine was augmented in Ca-SHR and CaMg-SHR, while the relaxations to isoprenaline and the nitric oxide donor SIN-1 were similar in all SHR groups. Relaxation responses induced by the return of K+ to the organ bath upon precontractions in K(+)-free solution were used to evaluate the function of arterial Na+, K(+)-ATPase. The rate of potassium relaxation was similar in Ca-SHR and CaMg-SHR and faster than in untreated SHR. 5. Contractile responses to high concentrations of potassium and noradrenaline, and the ability of vascular smooth muscle to sequester Ca2+, which was evaluated by eliciting responses to caffeine or noradrenaline after loading periods in different Ca2+ concentrations, were comparable in all SHR groups. In SHR with increased magnesium intake, and in WKY rats with calcium or magnesium supplementation, no detectable effects on blood pressure and arterial function were observed.6. In conclusion, high calcium diet attenuated the development of hypertension in SHR, with an associated augmented endothelium-dependent relaxation, promoted recovery rate of ionic gradients across the cell membrane via Na+, K+-ATPase, and reduced basal [Ca2+ ]i. Dietary magnesium supplementation, whether combined with normal or high calcium intake, had no beneficial effects on blood pressure or arterial function.

Sympathetically mediated effects of mental stress on the cardiac microcirculation of patients with coronary artery disease

Mental stress often causes myocardial ischemia in patients with coronary artery disease (CAD). There is increasing evidence that the coronary microcirculation of patients with atherosclerosis may be dysfunctional, with the potential of contributing to myocardial ischemia. This study investigated sympathetically mediated coronary microcirculatory and regional noradrenergic effects of mental stress. We measured left anterior descending coronary artery blood flow and norepinephrine kinetics at rest and during a 10-minute video game in 10 CAD patients with nonsignificant atherosclerosis of this artery and in 5 patients with normal coronary angiograms (NCA). The 2 groups did not differ in their responses of systemic and cardiac norepinephrine spillovers, heart rate, and blood pressure during mental stress. Patients with NCA had microvascular dilation during mental stress (26 +/- 9% [mean +/- SD] decline in coronary vascular resistance from baseline, p < 0.01), whereas patients with CAD did not (9 +/- 20% decline, p = 0.11). Six patients with CAD then received intracoronary phentolamine (1.7 micrograms/kg/min for 5 minutes, followed by 0.17 micrograms/kg/min) and played the video game again. In contrast to nonsignificant changes in coronary resistance during the initial video game (6 +/- 15% decline, p = 0.20), coronary vascular resistance decreased significantly during the repeat video game (25 +/- 19% decline, p = 0.02). Vasomotor responses of epicardial coronary artery segments did not differ between the 2 video game studies. Five other patients (4 with CAD, 1 with NCA) repeated the video game during intracoronary administration of 5% dextrose, with systemic and coronary hemodynamic and noradrenergic responses unchanged from those during the initial video game.(ABSTRACT TRUNCATED AT 250 WORDS)

Nitric oxide and the control of renin secretion

Research during recent years has established nitric oxide as a unique signaling molecule that plays important roles in the regulation of the cardiovascular, nervous, renal, immune and other systems. Nitric oxide has also been implicated in the control of the secretion of hormones by the pancreas, hypothalamus, pituitary and other endocrine glands, and evidence is accumulating that it contributes to the regulation of the secretion of renin by the kidneys. The enzyme nitric oxide synthetase is present in vascular and tubular elements of the kidney, particularly in cells of the macula densa, a structure that plays an important role in the control of renin secretion. Guanylyl cyclase, a major target for nitric oxide, is also present in the kidney and is responsive to changes in nitric oxide levels. Drugs that inhibit nitric oxide synthesis generally suppress renin release in vivo and in vitro, suggesting a stimulatory role for the L-arginine-nitric oxide pathway in the control of renin secretion. Under some conditions, however, blockade of nitric oxide synthesis increases renin secretion. Recent studies indicate that nitric oxide not only contributes to the regulation of basal renin secretion, but also participates in the renin secretory responses to activation of the renal baroreceptor, macula densa and beta adrenoceptor mechanisms that regulate renin secretion. Future research should clarify the mechanisms by which nitric oxide regulates the secretion of renin and establish the physiological significance of this regulation.

Control of vascular resistance in the maternal and feto-placental arterial beds

This review aims to provide a comprehensive summary of the mechanisms involved in the physiological adaptation of the vasculature to pregnancy. Profound changes occur both systemically and in discrete circulations in the mother, but it is debatable which factors are responsible. Similarly, whilst the feto-placental circulation must be substantially controlled by humoral mechanisms, the exact role of each potential contributor is not known. In view of the hitherto unappreciated and very important role of the endothelium-derived vasodilator, nitric oxide, in the control of peripheral vascular resistance, considerable emphasis will be placed on the many recent investigations in this area.

Isoprenaline induces endothelium-independent relaxation and accumulation of cyclic nucleotides in the rat aorta

The role of endothelium in isoprenaline-induced relaxation was investigated in aortic rings brought to different levels of pre-contraction. Relaxation elicited by isoprenaline decreased with increasing pre-contraction. However, relaxation was identical in rings with and without endothelium brought to the same initial tension by adjusting the noradrenaline concentration. Furthermore, isoprenaline increased cAMP and cGMP contents to the same levels whether endothelium was present or not. These results do not support an obligatory role for the endothelium in isoprenaline-induced relaxation in rat aorta. They indicate that relaxation induced by isoprenaline can be enhanced by the endothelium as a consequence of its effect on the precontraction level of the aorta.

The effect of hyperglycaemia on function of rat isolated mesenteric resistance artery

1. Noradrenaline sensitivity and acetylcholine-induced relaxation were investigated in mesenteric resistance arteries from female Wistar rats (220-250 g) following exposure to isotonic supraphysiological glucose solutions (20 and 45 mM, in physiological buffer, 2 h incubation). 2. Arteries incubated in 20 mM glucose demonstrated enhanced noradrenaline sensitivity compared with those in physiological buffer. 3. Profoundly impaired endothelium-dependent relaxation to acetylcholine was observed in arteries incubated in 20 and 45 mM glucose. 4. Indomethacin (10 microM) normalized noradrenaline sensitivity in 20 mM glucose, but unmasked an enhanced maximum response in 20 and 45 mM glucose relative to controls. 5. Addition of L-arginine (0.1 mM) prevented the abnormality of acetylcholine-induced relaxation in the 20 mM glucose medium and significantly improved relaxation in 45 mM glucose. 6. The aldose reductase inhibitor, ponalrestat (10(-5) M, ZENECA Pharmaceuticals), prevented impaired acetylcholine-mediated relaxation in 20 mM glucose and significantly improved relaxation in 45 mM glucose. 7. Indomethacin (10 microM) improved maximum relaxation but did not alter impaired sensitivity to acetylcholine in the high glucose media (20 and 45 mM). 8. Superoxide dismutase (SOD, 150 u ml-1) also prevented impaired acetylcholine-induced relaxation in 20 mM glucose but not in 45 mM glucose. 9. Endothelium-independent relaxation to sodium nitroprusside (SNP, 10(-9)-10(-5) mM) was normal in 20 mM glucose but was slightly, although significantly impaired by 45 mM glucose. 10. Enhanced responsiveness of rat isolated mesenteric resistance arteries to noradrenaline caused by elevated glucose would appear to be mediated through abnormal cyclo-oxygenase activity and the reduced tonic release of nitric oxide. 11. Hyperglycaemia may lead to abnormal endothelium-dependent relaxation in these arteries through several mechanisms which include a role for increased free radical production, polyol pathway activation and altered L-arginine metabolism.

Nitric oxide mediated venodilator effects of nebivolol

1. Nebivolol, a selective beta 1-adrenoceptor antagonist with antihypertensive effects, has haemodynamic effects suggestive of a direct vasodilator action. 2. The dorsal hand vein technique was used to determine whether nebivolol has venodilator action in vivo in man. 3. Nebivolol and atenolol were infused into the phenylephrine preconstricted superficial hand veins of 11 healthy male volunteers. In separate studies L-NMMA (0.1 microgram min-1) was pre- and co-infused with nebivolol to determine whether nitric oxide (NO) mediated mechanisms were present. Further studies with prostaglandin F2 alpha (PGF2 alpha) preconstriction were performed to exclude an alpha-adrenergic antagonistic effect of nebivolol. Effects of L-NMMA infusion on nitroglycerin venodilation were also determined. 4. Nebivolol produced a dose dependent venodilation, (72 +/- 18% maximum), whereas atenolol produced no significant venodilation. At doses of nebivolol producing plasma concentrations comparable with plasma levels achieved after standard oral dosing (10(-13)-10(-12) mol min-1) small (14 +/- 6% and 23 +/- 8%) but significant (P < 0.05) venodilation was observed. 5. The venodilator response to nebivolol was significantly reduced by infusion of L-NMMA (maximum dilation 18% vs 72%, P < 0.01). Venodilator responses to nitroglycerin were unaffected by L-NMMA infusion. A venodilator effect to nebivolol was also seen following preconstriction with PgF2 alpha (40 +/- 20% maximum). 6. Nebivolol has nitric oxide mediated, venodilator effects in man.

Enhancement of arterial relaxation by long-term atenolol treatment in spontaneously hypertensive rats

1. The effects of long-term atenolol (25 mg kg-1 day-1) therapy on arterial function were studied in spontaneously hypertensive rats (SHR) and Wistar-Kyoto (WKY) rats. The 14-week treatment attenuated the increase in blood pressure by approximately 30 mmHg in SHR, but did not affect blood pressure in WKY rats. 2. Responses of mesenteric arterial rings in vitro were examined at the end of the study. The relaxation to acetylcholine was similar in WKY rats and atenolol-treated SHR and more pronounced than in untreated SHR, whereas the relaxation to the nitric oxide donor 3-morpholinosydnonimine (SIN-1) was comparable in all study groups. Moreover, after maximal relaxations to acetylcholine, marked recontractions developed in untreated SHR but not in the other groups. Vasorelaxation to isoprenaline was also attenuated in SHR and was moderately improved by the atenolol therapy. 3. Arterial relaxation induced by return of potassium to the organ bath upon precontractions elicited by potassium-free solution were used to evaluate vascular smooth muscle Na+, K+-ATPase. The rate of potassium relaxation was fastest in WKY rats and was also faster in atenolol-treated than in untreated SHR. 4. The ability of vascular smooth muscle to sequester calcium was evaluated by eliciting responses to caffeine or noradrenaline after loading periods in different organ bath calcium concentrations. The subsequent contractions were lower in untreated SHR than in WKY rats, and augmented in SHR by the atenolol treatment. 5. Smooth muscle contractions to noradrenaline were comparable in SHR and WKY rats, while atenolol treatment slightly increased the maximal response to this agonist in SHR. Responses to potassium chloride were not affected by atenolol and contractions following cumulative re-addition of calcium to the organ bath after precontraction with potassium chloride and noradrenaline in calcium free solution were comparable in all study groups.6. In conclusion, the moderate antihypertensive effect of atenolol in SHR was accompanied by enhancement of beta-adrenoceptor-mediated and normalization of endothelium-dependent arterial relaxation.Furthermore, ability to sequester calcium into cellular stores, and function of Na+,K+-ATPase were augmented in vascular smooth muscle. Therefore, the present results suggest that the long-term blood pressure-lowering action of atenolol in this type of genetic hypertension is accompanied by improved arterial relaxation and normalization of endothelial function.

Diuretic effect of NG-nitro-L-arginine methyl ester in the rat

Intravenous infusion of the nitric oxide synthase inhibitor NG-nitro-L-arginine methyl ester, L-NAME (10 micrograms kg-1 min-1), to anaesthetized rats produced a diuresis and natriuresis. By contrast, infusion of the same dose of NG-nitro-D-arginine methyl ester had no effect on either urine output or sodium excretion. The effects of L-NAME were first evident 120 min after the start of infusion and by 170 min a fivefold increase in urine volume and sodium excretion was recorded. L-NAME also produced a transient fall in inulin clearance and a persistent decline in renal blood flow. These renal effects of L-NAME were associated with a gradual elevation of mean arterial blood pressure, although this only attained statistical significance, in comparison with saline-infused animals, 170 min after the start of infusion. The findings indicate the diuresis and natriuresis evoked by L-NAME in the rat is a result of a direct tubular action together with a pressure diuresis.

Effects of cyclic AMP and analogues on neurogenic transmission in the rat tail artery

1 The effects of two 8-substituted analogues of adenosine 3':5'-cyclic monophosphate (cyclic AMP) were compared with those of forskolin and isoprenaline on [3H]-noradrenaline release and vasoconstriction induced by electrical field stimulation (24 pulses at 0.4 Hz, 200 mA, 0.3 ms duration) in the rat tail artery, in the absence and in the presence of protein kinase inhibitors. 2 8-Bromo-adenosine 3':5'-cyclic monophosphate (8-bromo-cyclic AMP, 10-300 microM), 8-(4-chlorophenyl-thio)-adenosine 3':5' cyclic monophosphate (8-pCPT-cyclic AMP, 3-300 microM), forskolin (0.3-10 microM) and isoprenaline (1 nM-1 microM) all concentration-dependently enhanced stimulation-induced [3H]-noradrenaline release. The effect of cyclic AMP analogues was larger (2.5 fold at 300 microM) than those of cyclic AMP elevating drugs (1.6 fold at 10 microM for forskolin and 1.5 fold at 30 nM for isoprenaline). 3 At concentrations active at the prejunctional level, the four drugs had differential effects on stimulation-induced vasoconstriction, which was enhanced by the two cyclic AMP analogues, decreased by forskolin and not significantly altered by isoprenaline. 4 The [3H]-noradrenaline release-enhancing effects of 8-bromo-cyclic AMP, forskolin and isoprenaline were significantly decreased by the cyclic AMP-dependent protein kinase (PKA) inhibitor (N-[2-((3-(4-bromophenyl)-2-propenyl)-amino)-ethyl]-5- isoquinolinesulphonamide, di-hydrochloride) (H-89; 100 nM). By contrast they were unaffected by the cyclic GMP-dependent protein kinase (PKG) inhibitor, 8-bromo-guanosine 3':5'-cyclic monophosphorothioate, Rp-isomer (Rp-8-bromo-cyclic GMPS; 10 microM). By contrast they were unaffected by the cyclic GMP-dependent protein kinase (PKG) inhibitor,8-bromo-guanosine 3':5'-cyclic monophosphorothioate, Rp-isomer (Rp-8-bromo-cyclic GMPS; 10 MicroM).At the same concentrations the PKA inhibitor attenuated only the nerve-induced vasoconstrictor responses obtained in the presence of 8-bromo-cyclic AMP, whereas the PKG inhibitor did not modify that obtained in the presence of 8-bromo-cycic AMP or forskolin.5. Exposure to the protein kinase C (PKC) activator, phorbol 12-myristate 13-acetate (1 MicroM) enhanced nerve-evoked [3H]-noradrenaline release, and this effect was decreased by the PKC inhibitor, 2-[1-(3-dimethylaminopropyl)-indol-3-yl]-3-(-indol-3-yl)-maleimide (GF 109203X; 100 nM). However, the latter drug did not modify the enhancing effect of 8-bromo-cyclic AMP on [3H]-noradrenaline release.6. It is concluded that activation of cyclic AMP-dependent protein kinase is involved in the enhancing effect of cyclic AMP-elevating compounds on prejunctional release of noradrenaline. In addition the results provide no clear-cut evidence for a vasodilator role of PKA.

Responses of cerebral arterioles to activation of beta-adrenergic receptors during diabetes mellitus

BACKGROUND AND PURPOSE

Diabetes mellitus impairs reactivity of large peripheral arteries and arterioles to activation of beta-adrenergic receptors. The goal of this study was to determine whether diabetes mellitus alters dilatation of cerebral arterioles to activation of beta-adrenergic receptors.

METHODS

In vivo diameter of pial arterioles was measured in nondiabetic and diabetic (streptozotocin 50 to 60 mg/kg IP) rats during superfusion with isoproterenol, forskolin, and nitroglycerin. In addition, we examined the contribution of nitric oxide or a nitric oxide-containing compound in dilatation of pial arterioles in response to the agonists.

RESULTS

Dilatation of pial arterioles in response to isoproterenol was significantly less in diabetic compared with nondiabetic rats (3 +/- 2% versus 14 +/- 1%, respectively, for 1.0 mumol/L isoproterenol). In contrast, dilatation of pial arterioles in response to nitroglycerin and forskolin was similar in nondiabetic and diabetic rats. Furthermore, dilatation of pial arterioles in nondiabetic rats in response to isoproterenol and forskolin was not related to the synthesis and release of nitric oxide or a nitric oxide-containing compound.

CONCLUSIONS

The findings of the present studies suggest that diabetes mellitus impairs dilatation of cerebral resistance arterioles in response to activation of beta-adrenergic receptors. Impairment of beta-adrenergic-mediated dilatation of cerebral arterioles during diabetes mellitus does not appear to be related to an alteration in cyclic adenosine monophosphate, since forskolin produced similar vasodilatation in nondiabetic and diabetic rats.

Endothelium-dependent noradrenaline-induced relaxation of rat isolated cerebral arteries: pharmacological characterization of receptor subtypes involved

1. The endothelium-dependence of catecholamine-induced relaxation of rat cerebral arteries was investigated in vitro. 2. In the basilar artery (BA), the maximal relaxant response was most pronounced with noradrenaline (NA), less with isoprenaline (Iso), and only very little with terbutaline. Methoxamine and the alpha 2-adrenoceptor selective agonists BHT 933 and clonidine, had no relaxant effect. 3. In BA, the relaxation by NA or Iso was markedly attenuated by N omega-nitro-L-arginine (L-NOARG) 10(-4) M. Short term perfusion of the vessels by Triton X 100 (1:1,000) suppressed the NA-induced relaxation. 4. The relaxation induced by NA or Iso was markedly reduced in presence of L-NOARG in the posterior, medial and anterior cerebral artery. 5. In BA, NA-induced relaxation was non-competitively inhibited by propranolol, atenolol, and the beta 1- and beta 2-adrenoceptor selective antagonists, CGP 20712 A and ICI 118551. 6. The relaxant NA-effect was not affected by prazosin but was non-competitively blocked by phentolamine. 7. The Iso-induced relaxation was competitively blocked by propranolol, whereas atenolol, CGP 20712 A and ICI 118551 caused a non-competitive inhibition. 8. The experiments indicate that the catecholamine-induced relaxation in rat isolated cerebral arteries depends upon the endothelium. They suggest that the NA-induced relaxation of BA is mediated by different alpha- and beta-adrenoceptors and that the Iso-induced relaxation is mediated by different beta-receptors. The findings would also be compatible with the idea of a receptor type which cannot be characterized by the pharmacological tools that we have used.