Tissue repair with a therapeutic transcription factor.

The healing of tissue involves a wide range of molecular, cellular, and physiological events that are coordinated in a temporally specific manner. The cellular transcription factor early growth response factor 1 (Egr-1) is expressed minutes after acute injury and serves to stimulate the production of a class of growth factors whose role is to promote tissue repair. We have studied the effects of Egr-1 expression at the site of dermal wounding in rodents. We find that Egr-1 promotes angiogenesis in vitro and in vivo, increases collagen production, and accelerates wound closure. These results show that Egr-1 gene therapy accelerates the normal healing process and raises the potential use of this therapeutic transcription factor for any aspect of tissue repair.

Effects of dopamine DA1-receptor blockade and angiotensin converting enzyme inhibition on the renal actions of fenoldopam in the anaesthetized dog.

Experiments were performed in anaesthetized dogs to characterize the renal effects of the selective dopamine DA1-receptor agonist, fenoldopam. Intrarenal artery infusion of fenoldopam (0.01-10 micrograms/kg per min) caused dose-related renal vasodilation. At low doses (0.01-0.3 micrograms/kg per min), renal vasodilation occurred without concomitant falls in blood pressure but was accompanied by increased urine output. This diuresis was most probably a result of reduced tubular reabsorption since glomerular filtration rate was not increased. Both fenoldopam-induced renal vasodilation and diuresis were blocked to a similar extent by the selective dopamine DA1-receptor antagonist, SCH 23390 (30 micrograms/kg, intravenously), suggesting that both effects were mediated by dopamine DA1-receptors. In the presence of the angiotensin converting enzyme inhibitor, captopril (1 mg/kg, intravenously, + 20 micrograms/kg per min, intrarenal artery), fenoldopam (0.01-0.3 micrograms/kg per min) significantly increased fractional excretion of sodium, despite reducing blood pressure; neither of these effects were observed in captopril-free dogs. These observations support the view that the inhibitory effect of fenoldopam on tubular function, and its vasodepressor activity, may be opposed by angiotensin II resulting from fenoldopam-induced renin release.

Pharmacological characterization of the presynaptic alpha-adrenoceptors regulating cholinergic activity in the guinea-pig ileum.

1 The presynaptic alpha-adrenoceptors located on the terminals of the cholinergic nerves of the guineapig myenteric plexus have been characterized according to their sensitivities to alpha-adrenoceptor agonists and antagonists.2 Electrical stimulation of the cholinergic nerves supplying the longitudinal muscle of the guinea-pig ileum caused a twitch response. Clonidine caused a concentration-dependent inhibition of the twitch response; the maximum inhibition obtained was 80 to 95% of the twitch response. Oxymetazoline and xylazine were qualitatively similar to clonidine but were about 5 times less potent. Phenylephrine and methoxamine also inhibited the twitch response but were at least 10,000 times less potent than clonidine.3 The twitch-inhibitory effects of clonidine, oxymetazoline and xylazine, but not those of phenylephrine or methoxamine, were reversed by piperoxan (0.3 to 1.0 mug/ml).4 Lysergic acid diethylamide (LSD) inhibited the twitch response, but also increased the basal tone of the ileum. Mepyramine prevented the increase in tone but did not affect the inhibitory action of LSD. Piperoxan or phentolamine only partially antagonized the inhibitory effect of LSD.5 Phentolamine, yohimbine, piperoxan and tolazoline were potent, competitive antagonists of the inhibitory effect of clonidine with pA(2) values of 8.51, 7.78, 7.64 and 6.57 respectively.6 Thymoxamine was a weak antagonist of clonidine; it also antagonized the twitch-inhibitory effect of morphine. Thus, its effect against clonidine is probably not mediated specifically at presynaptic alpha-adrenoceptors.7 Labetalol, itself, depressed the twitch response but did not antagonize the inhibitory effect of clonidine on the residual twitch.8 The results demonstrate that the presynaptic alpha-adrenoceptors in the guinea-pig ileum are of the same type as those located presynaptically in sympathetically innervated tissues. They are alpha(2)-adrenoceptors and are different from those located postsynaptically.

The effect of different calcium concentrations on the inhibitory effect of presynaptic alpha-adrenoceptors in the rat vas deferens.

The effects of different calcium concentrations on the twitch-inhibitory potency of clonidine and of guanethidine have been examined in the rat isolated vas deferens. Vasa deferentia did not respond to field stimulation at 0.3 Hz in Krebs solution containing 0.325 mmol/1 of calcium. Increasing the calcium concentration to 5.2 mmol/1 caused a concentration-dependent increase in size of the twitch response. The twitch inhibitory potency of clonidine was inversely proportional to the calcium concentration. The inhibitory effect of guanethidine was not influenced by changes in calcium concentration. The results show that the modulation of motor function by presynaptic alpha-adrenoceptors in the rat vas deferens is calcium-dependent.

Investigation of the inhibitory effect of N(G)-nitro-L-arginine methyl ester on the antihypertensive effect of the angiotensin AT1 receptor antagonist, GR138950.

1. The effect of systemic administration of the nitric oxide synthase inhibitor, N(G)-nitro-L-arginine methyl ester (L-NAME) on the antihypertensive effects of the angiotensin AT1 receptor antagonist, GR138950, the angiotensin-converting enzyme (ACE) inhibitor, enalapril, or hydralazine has been evaluated in unrestrained, conscious renal artery ligated hypertensive (RALH) rats. The effect of the phosphodiesterase type V inhibitor, zaprinast on the antihypertensive effect of GR138950 in RALH rats was also examined. The effect of GR138950 on blood pressure, and plasma and urine cyclic GMP levels was compared to that of zaprinast in conscious RALH rats. 2. GR138950, enalapril or hydralazine caused marked reductions in blood pressure associated with immediate tachycardia in conscious RALH rats. L-NAME pretreatment attenuated the antihypertensive effects of GR138950 or enalapril but not that of hydralazine in conscious RALH rats. The initial tachycardia caused by GR138950 or enalapril but not hydralazine was attenuated by L-NAME pretreatment. L-NAME alone caused a transient (20 min) pressor response and a prolonged (6 h) bradycardia in conscious RALH rats. 3. Pretreatment with indomethacin did not affect the cardiovascular effect of GR138950 in conscious RALH rats. Indomethacin alone did not significantly change basal blood pressure or heart rate in RALH rats. 4. Zaprinast pretreatment did not affect the antihypertensive effect of GR138950 in conscious RALH rats but potentiated the depressor response to sodium nitroprusside. Zaprinast alone caused a small reduction in basal blood pressure but did not change basal heart rate in RALH rats. 5. The antihypertensive effect of GR138950 was not associated with an increase in plasma or urine cyclic GMP levels in conscious RALH rats, whereas zaprinast caused a small fall in blood pressure associated with increases in plasma and urine cyclic GMP. 6. The ability of L-NAME to inhibit the antihypertensive action of GR138950 or enalapril suggests that these agents release nitric oxide (NO) and/or enhance the cardiovascular effects of NO as part of their mechanism of action. However, the inability of zaprinast to potentiate the antihypertensive effects of GR138950 and the finding that GR138950 did not increase urine and plasma cyclic GMP levels are not consistent with this view. Attenuation of the response to GR138950 or enalapril, but not hydralazine, suggests a selective interaction between L-NAME and inhibitors of the renin-angiotensin system, although the nature of this interaction is unknown.

Characterization of the coronary vascular -adrenoceptor in the pig.

The beta-adrenoceptor in pig coronary vascular smooth muscle has been characterized by the use of a selective agonist, salbutamol and a selective antagonist, practolol. In coronary artery strips contracted with KCI, salbutamol had only marginal relaxant activity and was a partial agonist compared with isoprenaline. Practolol had relatively high antagonist potency against isoprenaline (pA(2) 6.59). It is concluded that the pig coronary vascular,beta-adrenoceptor is of the beta(1)-type.

The effects of anticholinesterases on synaptic transmission through nicotinic and muscarinic receptors in rat sympathetic ganglia in vivo.

1 Stimulation of the entire spinal sympathetic outflow at supramaximal voltage and 25-100 Hz, in the chlorisondamine-treated, pithed, adrenalectomized rat produced a delayed pressor response (late pressor response; LPR).2 The LPR was abolished by phenoxybenzamine, bretylium or a small dose of atropine (25-50 mug/kg), suggesting the involvement of ganglionic muscarinic receptors.3 In the presence of atropine at a dose level (15 mug/kg) which did not influence the LPR, the anticholinesterases physostigmine, neostigmine and Ro 02-0683 but not BW 284C51 markedly enhanced and prolonged the LPR, whereas all of them reduced the pressor responses to AHR-602.4 After blockade of the ganglionic muscarinic receptors with a large dose of atropine (250 mug/kg) the four anticholinesterases did not influence responses to DMPP or noradrenaline and only slightly enhanced responses to preganglionic nerve stimulation at 6 Hz in the absence of chlorisondamine.5 It is concluded that inhibition of butyrylcholinesterase accounts for the enhancement and prolongation of the LPR by anticholinesterases.

Evidence for two distinct types of postsynaptic alpha-adrenoceptor in vascular smooth muscle in vivo.

1 The effects of the highly selective alpha(1)-adrenoceptor antagonist, prazosin, and the relatively selective alpha(2)-adrenoceptor antagonist, yohimbine, on the pressor responses to intravenous injections of phenylephrine and noradrenaline have been examined in anaesthetized cats and pithed rats in an attempt to determine whether alpha(1)- and alpha(2)-adrenoceptors are located postsynaptically on vascular smooth muscle.2 In anaesthetized cats prazosin caused a much greater reduction in the pressor responses to phenylephrine than to noradrenaline or splanchnic nerve stimulation (after adrenalectomy). Yohimbine was of similar potency in reducing the pressor responses to each stimulus.3 A differential blocking activity of prazosin against intra-arterial injections of phenylephrine and noradrenaline was also demonstrated in the blood-perfused cat hind limb. As in the whole animal, prazosin was more potent against phenylephrine than noradrenaline. A similar, though less marked, effect was seen in the mesenteric circulation, but not in the renal circulation, where prazosin was almost equipotent in reducing responses to phenylephrine and noradrenaline.4 In pithed rats prazosin was a potent, competitive antagonist of phenylephrine, but had little effect against noradrenaline; only the responses to high doses of noradrenaline were reduced by prazosin. Yohimbine was approximately equipotent as an antagonist of phenylephrine and noradrenaline. In the anococcygeus muscle, prazosin was as potent an antagonist of noradrenaline as it was of phenylephrine on vascular smooth muscle.5 The results suggest that there are two types of alpha-adrenoceptor in the vasculature of cats and rats. Phenylephrine produces pressor responses by stimulating one type of postsynaptic alpha-adrenoceptor that is blocked by prazosin and yohimbine; these are alpha(1)-adrenoceptors. Noradrenaline exerts some of its effect via these receptors but most of its effect appears to be exerted through prazosin-insensitive receptors. The latter receptors appear to differ from alpha(2)-adrenoceptors.

Prejunctional dopamine receptors modulate twitch responses to parasympathetic nerve stimulation in the rabbit isolated rectococcygeus muscle.

Field stimulation of the parasympathetic nerves supplying the rabbit isolated rectococcygeus muscle produced individual twitch responses that were inhibited by dopamine (1 x 10(-8)-1 x 10(-5)M). The twitch-inhibitory effect of dopamine was reversed by haloperidol or sulpiride (1 x 10(-8)-1 x 10(-5)M for either) but not by phentolamine or yohimbine (up to 1 x 10(-4)M). Haloperidol and sulpiride were potent, specific, competitive antagonists of the twitch-inhibitory effect of dopamine; their pA2 values were 8.39 and 7.75, respectively. In contrast, cis alpha-flupenthixol, fluphenazine, bulbocapnine and thioridazine were weak or inactive against dopamine. Concentrations of dopamine that inhibited the twitch response to parasympathetic nerve stimulation had little or no effect on contractions elicited by carbachol or by direct muscle stimulation after abolition of neuronal conduction by tetrodotoxin. Thus, the effects of dopamine on responses elicited by parasympathetic nerve stimulation seem to be exerted at a prejunctional level rather than directly on the smooth muscle. The twitch-inhibitory effect of dopamine was mimicked by epinine, N,N-diethyldopamine, N,N-di-n-propyldopamine, 5,6-ADTN, N,N-di-n-propyl 5,6-ADTN, 6,7-ADTN, apomorphine and Sandoz 27-403. Sulpiride reversed the effects of all these agonists. N,N-di-n-propyl-6,7-ADTN and SK & F 82526 also inhibited the twitch response but their effects were not reversed by sulpiride. SK & F 38393 and DPI had little effect on the twitch response. The pharmacological characteristics of the presynaptic dopamine receptors in the rabbit rectococcygeus muscle show that they resemble those in the cat heart and rabbit ear artery in some respects but there are differences that suggest that the presynaptic dopamine receptors in the rabbit rectococcygeus muscle constitute a specific subgroup of receptors.

The antihypertensive profile of the angiotensin AT1 receptor antagonist, GR138950, and the influence of potential homeostatic compensatory mechanisms in renal hypertensive rats.

The cardiovascular profile of the angiotensin AT1 receptor antagonist, GR138950, and the influence of potential compensatory homeostatic mechanisms on this profile, were investigated in renal artery ligated hypertensive (RALH) rats. GR138950 caused a marked reduction in blood pressure associated with immediate tachycardia in conscious RALH rats. The antihypertensive action of GR138950 appeared biphasic; an immediate fall in blood pressure, which plateaued within 1 h, and which was followed by a further slow decline that reached maximum between 5-7 h after administration. The tachycardia caused by GR138950 was attenuated by atenolol and was abolished by combined pretreatment with atenolol and atropine methyl nitrate. However, the antihypertensive profile of GR138950 was unchanged by these pretreatments. The resting blood pressure and the antihypertensive effect of GR138950, in RALH rats, were unaffected by the vasopressin V1 receptor antagonist, [beta-mercapto-beta,beta-cyclopentamethylene propionyl(1)-O-Me-Tyr2,Arg8]-vasopressin. Thus, vasopressinergic mechanisms are not involved in either maintaining blood pressure in RALH rats, or in compensating for the fall in blood pressure caused by GR138950. In anaesthetized RALH rats, GR138950 caused a marked fall in blood pressure that was accompanied by an increase in heart rate along with sustained increases in renal and splanchnic sympathetic nerve activity. In summary, the biphasic fall in blood pressure evoked by GR138950 in RALH rats can not be explained on the basis of changes in autonomic control of the heart, alteration of vasopressin-mediated vasoconstrictor mechanisms or overall suppression of central sympathetic outflow. Rather, increased vasoconstrictor tone might serve to oppose the initial fall in blood pressure.

Further investigations into the mechanism of the antihypertensive activity of the angiotensin AT1 receptor antagonist, GR138950.

1. The angiotensin AT1 receptor antagonist, GR138950, produces a long-lasting antihypertensive effect in conscious renal artery ligated hypertensive (RALH) rats but this effect does not correlate temporally with its antagonist profile against angiotensin II (AII). In the present experiments we have compared the inhibitory profiles of GR138950 and enalapril, against angiotensin I (AI), with their respective antihypertensive activities. 2. GR138950 (1 mg kg-1, i.a.) and enalapril (3 mg kg-1, i.a.) reduced blood pressure in RALH rats to a similar degree. Maximum reductions in blood pressure occurred approximately 5-24 h and 3-5 h after administration, respectively. The antihypertensive effect of GR138950 lasted for 24-48 h. However, the effect of enalapril lasted for only 5-24 h. 3. In conscious normotensive rats, inhibition of AI-induced pressor responses was maximal 1 h after systemic administration of GR138950 and enalapril. Dose-response curves to AI were displaced to the right, in a parallel manner, 1406 and 102 fold by GR138950 (1 mg kg-1, i.a.) and enalapril (3 mg kg-1 i.a.), respectively. The inhibitory effect of enalapril lasted for < 24 h whereas that of GR138950 lasted for up to 48 h. 4. Contractile responses to AI were extensively inhibited in aortae removed from either RALH rats or normotensive rats, 1 and 5 h after administration of GR138950 (1 mg kg-1, i.a.). Responses were still significantly reduced 24 h after administration but had returned to control levels after 48 h. Enalapril pretreatment (3 mg kg-1, i.a.) did not inhibit contractile responses to AI in aortae isolated from normotensive rats at any time point. 5. These experiments confirm that GR138950 is an effective and long-lasting antihypertensive agent. GR138950 was a more potent and longer lasting antagonist against AI than has previously been found against AII, and the duration of its antihypertensive activity coincides better with its blockade of responses to AI. Blockade of the effects of AII generated locally within the vascular wall might play an important role in the antihypertensive profile of GR138950.

Effect of labetalol on the uptake of [3H]-(-)-noradrenaline into the isolated vas deferens of the rat.

1 The effects of the combined alpha- and beta-adrenoceptor blocking drug, labetalol, on the uptake of [3H]-(-)-noradrenaline into the isolated vas deferens of the rat have been determined and compared with those of some other alpha-adrenoceptor blocking drugs and cocaine. 2 Labetalol, like cocaine, produced a simple competitive inhibition of [3H]-(-)-noradrenaline uptake and was about 4 times less potent than cocaine. It is concluded that labetalol is a potent inhibitor of uptake1. Phentolamine and thymoxamine also inhibited [3H]-(-)-noradrenaline uptake, and were respectively 8 and 14 times less potent than cocaine. Tolazoline, piperoxan and yohimbine were inactive in concentrations up to 30 microgram/ml. 3 The uptake1 blocking action of labetalol could explain, at least in part, the previously reported difference in its ability to block noradrenaline and phenylephrine vasopressor responses in the anaesthetized dog. 4 The possibility that uptake1 inhibitory concentrations of labetalol could be present in the blood of subjects receiving normal antihypertensive doses of the drug is discussed.

Presynaptic alpha-adrenoceptors: do exogenous and neuronally released noradrenaline act at different sites?

The effects of dopamine receptor and alpha-adrenoceptor agonists and antagonists on the stimulation-evoked overflow of radioactivity from strips of dog saphenous vein previously loaded with [3H]-noradrenaline have been examined alone and in combination. In the presence of neuronal and extraneuronal catecholamine uptake inhibitors, noradrenaline (0.1-1 X 10(-6)M) and dopamine (0.01-1 X 10(-6)M) both inhibited the stimulation-evoked overflow of radioactivity. Sulpiride (1 X 10(-6)M) was without effect and prazosin (1 X 10(-7)M) had little effect on stimulation-evoked overflow but yohimbine enhanced it approximately 2 fold; the effect of yohimbine was similar at concentrations of 1 X 10(-7) and 1 X 10(-6)M. Sulpiride abolished the inhibitory effect of dopamine on stimulation-evoked overflow, but was without effect against noradrenaline. When allowance was made for the effects of yohimbine, alone, on overflow, yohimbine (1 X 10(-7)M) had no effect against dopamine and minimal effects against noradrenaline. A similar result was obtained when the concentration of yohimbine was increased to 1 X 10(-6)M. Prazosin did not antagonize the effect of noradrenaline. In the absence of the uptake inhibitors, clonidine (0.01-1 X 10(-5)M) inhibited stimulation-evoked overflow of radioactivity. Yohimbine (1 X 10(-6)M) was without effect on its own and antagonized the effects of clonidine at a concentration of 0.1 X 10(-5)M, but not at 0.01 or 1.0 X 10(-5)M. These findings suggest that dopamine inhibits overflow by stimulating presynaptic dopamine receptors on the terminals of the noradrenergic nerves supplying the dog saphenous vein. The interaction between yohimbine and noradrenaline is discussed in terms of the current concepts of control of transmitter release mediated via presynaptic alpha 2-adrenoceptors.

Alpha 2-adrenoceptor blocking profile of SK&F 104078: further evidence for receptor subtypes.

1. The ability of the putative, selective post-junctional alpha 2-adrenoceptor antagonist, SK&F 104078 to antagonize the effects of structurally-diverse agonists at pre-junctional alpha 2-adrenoceptors in the guinea-pig ileum and rat vas deferens in vitro and in the rat heart in vivo, and at post-junctional alpha 2-adrenoceptors in the rabbit ear vein in vitro, was examined. Results obtained with SK&F 104078 were compared with those obtained with yohimbine. 2. Xylazine and B-HT933 each caused a concentration-dependent inhibition of the field-stimulation-evoked twitch responses of the guinea-pig ileum and rat vas deferens. SK&F 104078 did not antagonize either agonist in the guinea-pig ileum and exerted only minimal blocking activity against xylazine in the rat vas deferens. In contrast, SK&F 104078 competitively antagonized B-HT933 in the rat vas deferens (pA2 = 6.45). Yohimbine competitively antagonized both agonists in each tissue (pA2 values ranged between 7.46 and 7.88). 3. In the pithed rat xylazine and B-HT933, injected intravenously, caused a dose-dependent reduction in the tachycardia elicited by stimulation of the cardiac preganglionic sympathetic nerves. SK&F 104078 (10 mg kg-1, i.v.) caused a 20-30 fold rightward displacement of the dose-response curve to xylazine, but did not affect responses to B-HT933. Yohimbine (1 mg kg-1, i.v.) antagonized both agonists to a similar degree. 4. In the rabbit ear vein xylazine, B-HT933, noradrenaline and UK 14304 elicted vasoconstrictor responses. Prazosin was without effect, but in contrast, SK&F 104078 was a competitive antagonist of each of the agonists (pA2 values ranged between 6.63 and 6.72). Yohimbine also competitively antagonized each of the agonists in this preparation (pA2 values ranged between 7.81 and 8.07). 5. SK&F 104078 was also a competitive antagonist (pA2 = 6.20) against noradrenaline at post-junctional alpha 1-adrenoceptors in the rabbit aorta. 6. These data show that SK&F 104078 is a competitive antagonist at post-junctional alpha l- and alpha 2-adrenoceptors. Its antagonist potency at pre-junctional alpha 2-adrenoceptors is agonist- and tissuedependent. Yohimbine does not discriminate between pre- and post-junctional alpha 2-adrenoceptors. The findings are discussed in terms of the possible existence of subclasses of OC2-adrenoceptors.

Analysis of the depressant effect of the endothelium on contractions of rabbit isolated basilar artery to 5-hydroxytryptamine.

1. The effects of endothelium removal and of a number of pharmacological agents known to modify endothelial cell function on the contractile response of rabbit isolated basilar arteries to 5-hydroxytryptamine (5-HT) and other vasoconstrictors were studied. 2. Endothelium removal slightly reduced the contractile response to potassium chloride (40 mM) but markedly augmented and potentiated contractions to 5-HT (1 nM-10 microM). 3. L-NG-nitro-arginine (L-NOARG, 1-30 microM), an inhibitor of nitric oxide formation in vascular endothelial cells, evoked endothelium-dependent contraction, and augmented and potentiated contractions to 5-HT in endothelium-intact but not endothelium-denuded tissues. Prior incubation with L-arginine (1 mM), but not D-arginine (1 mM), abolished these effects of L-NOARG (1 microM). L-NOARG (30 microM) also augmented contractions of endothelium-intact tissues to noradrenaline, prostaglandin F2 alpha, and to a lesser degree endothelin-1. 4. Neither glibenclamide (3 microM) nor N-ethylmaleimide (1 microM), putative inhibitors of the effects of endothelium-derived hyperpolarizing factor (EDHF) and of agonist-stimulated endothelium-derived relaxing factor (EDRF) release respectively, had any effect on either resting tension or the contractile response to 5-HT. In some tissues indomethacin (3 microM), a cyclo-oxygenase inhibitor, produced a small contraction and augmented the contractile response to 5-HT, but in most cases indomethacin was without effect. 5. In endothelium-intact tissues precontracted with uridine 5'-triphosphate (UTP; 100 microM), 5-HT did not evoke relaxation but rather caused further contraction. Under the same conditions acetylcholine (0.01-10 microM) evoked endothelium-dependent relaxation.6. These data demonstrate that the endothelium profoundly depresses contractions of rabbit isolated basilar artery to 5-HT, and that this phenomenon can be fully accounted for by the release of an L-NOARG-sensitive relaxing factor. Neither glibenclamide-sensitive EDHF nor cyclo-oxygenase products plays a major role. As we could find no evidence that 5-HT stimulates the production of EDRF per se, and L-NOARG caused endothelium-dependent contraction and augmented contractions to other vasoconstrictor agents, it seems likely that a basal release of EDRF underlies this phenomenon.

Alpha 2-adrenoceptors mediate clonidine-induced sedation in the rat.

1 The central alpha-adrenoceptors responsible for mediating clonidine-induced sedation in rats have been characterized according to their sensitivity to alpha-adrenoceptor agonists and antagonists.2 Clonidine, injected intraperitoneally or intracerebroventricularly, caused dose-dependent sedation, both in terms of a reduction in the time that rats could remain on an accelerating rotarod and in terms of overt sedation assessed visually. Following intracerebroventricular injection, xylazine, naphazoline and methoxamine, but not phenylephrine, produced similar effects.3 The sedation caused by intraperitoneal injection of clonidine was antagonized by intracerebroventricularly injected phentolamine, yohimbine, piperoxan and tolazoline but not by labetalol, thymoxamine or prazosin.4 The relative potencies of the agonists in causing sedation and of the antagonists in inhibiting the sedative effect of clonidine clearly demonstrated that the central alpha-adrenoceptors mediating clonidine-induced sedation are the same as the peripheral presynaptic alpha(2)-adrenoceptors.5 All the alpha-adrenoceptor agonists caused hypothermia after intracerebroventricular injection, but their order of potency was different from that in producing sedation. The hypothermic effect of intraperitoneally injected clonidine was little affected by any of the antagonists administered intracerebroventricularly. No conclusions could be drawn concerning the type of receptor responsible for mediating hypothermia.

The alpha- and beta-adrenoceptor blocking potencies of labetalol and its individual stereoisomers in anaesthetized dogs and in isolated tissues.

1 The antagonist potencies of labetalol and each of its four stereoisomers have been compared at alpha 1-, beta 1- and beta 2-adrenoceptors in anaesthetized dogs and in isolated tissues. 2 The RR stereoisomer is a potent, non-selective antagonist at beta-adrenoceptors but has only weak alpha 1-adrenoceptor blocking activity. 3 The SR stereoisomer was the most potent antagonist at alpha 1-adrenoceptors, and it also had similar potency as an antagonist at beta-adrenoceptors. 4 The alpha- and beta-adrenoceptor blocking profile of the RS stereoisomer is intermediate between that of the RR and SR, but the SS stereoisomer is a relatively weak antagonist at both alpha- and beta-adrenoceptors. 5 It is concluded that, although most of the alpha 1-adrenoceptor blocking activity of labetalol is attributable to the SR stereoisomer and nearly all of its beta-adrenoceptor blocking activity resides in the RR stereoisomer, each of the stereoisomers contributes to the overall pharmacological profile of labetalol.

Role of angiotensin AT1 and AT2 receptors in mediating the renal effects of angiotensin II in the anaesthetized dog.

1. Experiments were performed using the selective AT1 receptor antagonist, GR117289, and the selective AT2 receptor antagonist, PD123177, to assess the relative importance of AT1 versus AT2 receptors in mediating the renal effects of angiotensin II (AII) in vivo, in salt-replete pentobarbitone-anaesthetized dogs. 2. The AT1 receptor antagonist, GR117289 (0.5 mg kg-1 + 1 microgram kg-1 min-1, i.v.), caused renal vasodilatation, characterized by a mean increase of 21 +/- 5% in renal blood flow, 45 min post-dose. GR117289 also caused a fall in mean blood pressure (12 +/- 4%), but despite this, sodium and urine excretion were not reduced. Indeed, there was a tendency for urine output and sodium excretion to increase, although the changes were not statistically significant. GR117289 caused a reduction in plasma aldosterone levels (-35 +/- 16%) 45 min post-dose, despite increasing plasma renin activity (+ 173 +/- 42%). In contrast to GR117289, the AT2 receptor antagonist, PD123177 (20 micrograms kg-1 min-1 intra-renal artery; i.r.a.) caused no significant change in blood pressure, renal blood flow, or sodium and urine excretion, indicating that the renal effects of endogenous AII in these salt-replete animals are mediated predominantly by AT1 receptors. 3. Intra-renal artery infusion of AII (1-300 ng kg-1 min-1) caused dose-related renal vasoconstriction, and decreases in urine output, sodium excretion, fractional excretion of sodium, and glomerular filtration rate (GFR). The AT1 receptor antagonist, GRI 17289 (0.5 mg kg-1 + 1 microg kg-1 min-1, i.v.)antagonized these renal effects of AII, causing 15-38 fold rightward displacements of mean dose response curves for these parameters. In contrast, PD123177 (20 microg kg-1 min-1, i.r.a.) failed to antagonize the renal haemodynamic and excretory effects of lower doses of All (1-10 ng kg-1 min-1,i.r.a.). However, at higher doses of AII (30-300 ng kg-l min-1, i.r.a.), while PD123177 still failed to antagonize the effects of the peptide on urine output, sodium excretion and GFR, it did cause a small,but significant, degree of inhibition of All-induced renal vasoconstriction. In addition, at a higher dose(50 microg kg-1 min-1, i.r.a.), PD123177 caused a greater degree of antagonism of AII-induced renal vasoconstriction, while renal excretory responses to AII remained unaffected.4. This study shows that the renal haemodynamic and excretory effects of AII in salt-replete anaesthetized dogs are mainly mediated by angiotensin AT1 receptors. However, the inhibitory effect of PD123177 on renal vasoconstrictor responses to high doses of AII, raises the possibility that functionally important AT2 receptors are present in the canine renal vasculature.

The effect of body temperature on myocardial protection conferred by ischaemic preconditioning or the selective adenosine A1 receptor agonist GR79236, in an anaesthetized rabbit model of myocardial ischaemia and reperfusion.

1 The cardioprotective effect of N-[(1S, trans)-2-hydroxycyclopentyl]adenosine (GR79236), an adenosine A1 receptor agonist, was compared with that produced by ischaemic preconditioning in an anaesthetized rabbit model of myocardial ischaemia and reperfusion. In addition, we examined the effect of different body core temperatures on GR79236- or ischaemic preconditioning-induced cardioprotection when administered prior to ischaemia, and on cardioprotection induced by GR79236 administered 10 min prior to the onset of reperfusion. 2 When rabbits were subjected to 30 min occlusion of the left coronary artery, followed by 2 h reperfusion, GR79236 (3 x 10(-8) mol kg-1 i.v. (10.5 microg kg-1 i.v.)) or ischaemic preconditioning (5 min ischaemia followed by 5 min reperfusion), administered or applied 10 min prior to the occlusion, significantly limited the development of infarction. The cardioprotective effect of ischaemic preconditioning was significantly greater than that seen after administration of GR79236. Pre-treatment with the selective adenosine A1 receptor antagonist 8-cyclopentyl-1,3-dipropylxanthine (DPCPX, 3.3 x 10(-6) mol kg-1 (1 mg kg-1 i.v.)), prevented the cardioprotective effect of GR79236, but not that of ischaemic preconditioning. 3 Maintaining body core temperature at 38.5 degrees C rather than at 37.0 degrees C did not influence infarct size in control groups of rabbits, but reduced the cardioprotective effect of GR79236 when administered 10 min prior to occlusion or 10 min prior to the onset of reperfusion. The cardioprotective effect of ischaemic preconditioning was not temperature-dependent. 4 In conclusion, myocardial protection conferred by GR79236 in anaesthetized rabbits is mediated via adenosine A1 receptors. Myocardial protection can be conferred when GR79236 is administered before the onset of ischaemia or reperfusion, and is reduced when body core temperature is maintained at 38.5 degrees C rather than at 37.0 degrees C. In contrast, myocardial protection conferred by ischaemic preconditioning is not reduced by adenosine A1 receptor blockade, or by maintaining body core temperature at 38.5 degrees C rather than at 37.0 degrees C. These findings point to distinct differences in the mechanisms of induction of myocardial protection by adenosine A1 receptor agonist and ischaemic preconditioning. They also highlight the need for careful control of body core temperature when investigating the phenomenon of cardioprotection.

Effects of prostaglandins and nitric oxide on the renal effects of angiotensin II in the anaesthetized rat.

1. The potential influences of nitric oxide (NO) and prostaglandins on the renal effects of angiotensin II (Ang II) have been investigated in the captopril-treated anaesthetized rat by examining the effect of indomethacin or the NO synthase inhibitor, N(omega)-nitro-L-arginine methyl ester (L-NAME), on the renal responses obtained during infusion of Ang II directly into the renal circulation. 2. Intrarenal artery (i.r.a.) infusion of Ang II (1-30 ng kg(-1) min(-1)) elicited a dose-dependent decrease in renal vascular conductance (RVC; -38+/-3% at 30 ng kg(-1) min(-1); P < 0.01) and increase in filtration fraction (FF; +49+/-8%; P < 0.05) in the absence of any change in carotid mean arterial blood pressure (MBP). Urine output (Uv), absolute (UNaV) and fractional sodium excretion (FENa), and glomerular filtration rate (GFR) were unchanged during infusion of Ang II 1-30 ng kg(-1) min(-1) (+6+/-17%, +11+/-17%, +22+/-23%, and -5+/-9%, respectively, at 30 ng kg(-1) min(-1)). At higher doses, Ang II (100 and 300 ng kg(-1) min(-1)) induced further decreases in RVC, but with associated increases in MBP, Uv and UNaV. 3. Pretreatment with indomethacin (10 mg kg(-1) i.v.) had no significant effect on basal renal function, or on the Ang II-induced reduction in RVC (-25+/-7% vs -38+/-3% at Ang II 30 ng kg(-1) min(-1)). In the presence of indomethacin, Ang II tended to cause a dose-dependent decrease in GFR (-38+/-10% at 30 ng kg(-1) min(-1)); however, this effect was not statistically significant (P=0.078) when evaluated over the dose range of 1-30 ng kg(-1) min(-1), and was not accompanied by any significant changes in Uv, UNaV or FENa (-21+/-12%, -18+/-16% and +36+/-38%, respectively). 4. Pretreatment with L-NAME (10 microg kg(-1) min(-1) i.v.) tended to reduce basal RVC (control -11.8+/-1.4, +L-NAME -7.9+/-1.8 ml min(-1) mmHg(-1) x 10(-2)), and significantly increased basal FF (control +15.9+/-0.8, +L-NAME +31.0+/-3.7%). In the presence of L-NAME, renal vasoconstrictor responses to Ang II were not significantly modified (-38+/-3% vs -35+/-13% at 30 ng kg(-1) min(-1)), but Ang II now induced dose-dependent decreases in GFR, Uv and UNaV (-51+/-11%, -41+/-14% and -31+/-17%, respectively, at an infusion rate of Ang II, 30 ng kg(-1) min(-1)). When evaluated over the range of 1-30 ng kg(-1) min(-1), the effect of Ang II on GFR and Uv were statistically significant (P < 0.05), but on UNaV did not quite achieve statistical significance (P=0.066). However, there was no associated change in FENa observed, suggesting a non-tubular site of interaction between Ang II and NO. 5. In contrast to its effects after pretreatment with L-NAME alone, Ang II (1-30 ng kg(-1) min(-1)) failed to reduce renal vascular conductance in rats pretreated with the combination of L-NAME and the selective angiotensin AT1 receptor antagonist, GR117289 (1 mg kg(-1) i.v.). This suggests that the renal vascular effects of Ang II are mediated through AT1 receptors. Over the same dose range, Ang II also failed to significantly reduce GFR or Uv. 6. In conclusion, the renal haemodynamic effects of Ang II in the rat kidney appear to be modulated by cyclooxygenase-derived prostaglandins and NO. The precise site(s) of such an interaction cannot be determined from the present data, but the data suggest complex interactions at the level of the glomerulus.