Characterization of the angiotensin II AT1 receptor subtype involved in DNA synthesis in cultured vascular smooth muscle cells.

1. This study was undertaken in cultured vascular smooth muscle cells to characterize the angiotensin II (AII) AT1 receptor subtype involved in DNA synthesis because (i) the AII receptor involved in vascular proliferation has previously been characterized in vitro in rat aortic cells and identified as an AT1 subtype and (ii) molecular cloning and biochemical studies have provided evidence for the existence of different AT1 receptor subtypes. 2. In cultured rat aortic vascular smooth muscle (VSMC), exposure to AII (0.1 to 100 nM) resulted in a concentration-dependent increase in [3H]-thymidine incorporation with an EC50 of 1.41 +/- 0.51 nM. Maximal stimulation was observed in the presence of 100 nM AII and corresponded to 271 +/- 40% of basal [3H]-thymidine incorporation. 3. To characterize the AII AT1 receptor subtype involved in this effect, cells were exposed to AII (3 nM) in the absence or presence of increasing concentrations of various AII receptor antagonists. The stimulatory effect of AII (3 nM) on [3H]-thymidine incorporation in VSMC was antagonized by the non-selective AT1/AT2 receptor antagonist, [Sar1, Ile8]-AII (IC50 = 5.6 nM), by the AT1A/AT1B receptor antagonist, losartan (IC50 = 10.5 nM) and the AT1 receptor antagonist, L-158809 (IC50 = 0.20 nM). The selective AT2 receptor ligand, CGP 42112A, antagonized AII-induced [3H]-thymidine incorporation with an IC50 of 6.3 +/- 1.3 microM while the AT2/AT1B receptor antagonist, PD 123319, was found to be almost inactive (IC50 > 10 microM).(ABSTRACT TRUNCATED AT 250 WORDS)     

Regulation of NO-dependent cyclic GMP formation by inflammatory agents in neural cells

In the CNS, NO is an important physiological messenger involved in the modulation of brain development, synaptic plasticity, neuroendocrine secretion, sensory processing, and cerebral blood flow [Annu. Rev. Physiol. 57 (1995) 683]. These NO actions are largely mediated by cyclic GMP (cGMP) formed by stimulation of soluble guanylyl cyclase (sGC). NO has also been recognized as a neuropathological agent in conditions such as epilepsy, stroke and neurodegenerative disorders. In these conditions, NO may contribute to excitotoxic cell death and neuroinflammatory cell damage [Brain Res. Bull. 41 (1996) 131; Glia 29 (2000) 1]. NO can be formed in every type of CNS parenchymal cell, however, cGMP appears to be formed mainly in neurons and astroglia [Annu. Rev. Physiol. 57 (1995) 683]. There is a large body of information about the regulation of NO formation in brain cells under both normal and pathological conditions but much less is known about the control of cGMP generation, in particular during neuroinflammation when there is a high NO output. Here we briefly review our present knowledge on the regulation of NO-dependent cGMP formation in brain cells under inflammatory conditions.     

Lithium ions have a potent and selective inhibitory effect on cyclic GMP formation stimulated by neurotensin, angiotensin II and bradykinin

The effect of lithium ion (Li+) on receptor-mediated synthesis of cyclic GMP, a putative second messenger, was examined using intact murine neuroblastoma cells (clone N1E-115). Lithium chloride potently inhibited cyclic GMP formation stimulated by the neuropeptides, neurotensin, angiotensin II and bradykinin in an identical concentration-dependent (IC50 s of around 12 mM), saturable and reversible manner. In the presence of veratridine, an alkaloid which by stimulating sodium channels can increase Li+ entry into the cells, Li+ inhibited neurotensin-stimulated cyclic GMP formation more potently (IC50 = 7 mM). No effect of Li+ was observed on phosphodiesterase (EC 3.1.4.17) activity. These results suggest that Li+ may interfere with the function of these receptors through its inhibitory effect at a common site in the pathway of receptor-mediated cyclic GMP formation.     

Effects of angiotensin II on the renal interstitial concentrations of NO2/NO3 and cyclic GMP in anesthetized rats

The present study was conducted to determine whether exogenous angiotensin II (Ang II) may increase the renal interstitial fluid concentrations of NO2/NO3 (NOx) and cyclic guanosine monophosphate (cGMP) concomitantly and which Ang II receptor subtypes may induce these changes in anesthetized rats, using a microdialysis method. Ang II (50 ng/kg per min, i.v.) significantly increased mean blood pressure (MBP), extraction rates of renal interstitial NOx from 23.9+/-1.0 to 31.2+/-1.9 pmol/min, and cGMP from 4.1+/-0.3 to 6.4+/-0.5 fmol/min, and decreased renal blood flow (RBF). The AT1-receptor antagonist CV11974 alone significantly increased RBF, but did not alter MBP, renal interstitial concentrations of NOx and cGMP. A superimposition of Ang II on CV11974 did not affect MBP and RBF, but significantly increased renal interstitial concentrations of NOx and cGMP. The AT2-receptor antagonist PD123319 alone did not change any of the parameters. However, superimposition of Ang II on PD123319 increased MBP and decreased RBF without any effects on renal interstitial concentrations of NOx and cGMP. These results suggest that Ang II stimulates NO production via the AT2-receptor in the kidney.     

Role of angiotensin II receptor subtype activation in cognitive function and ischaemic brain damage

Recent clinical studies have demonstrated that angiotensin II type 1 (AT(1) ) receptor blockers (ARBs) reduce the onset of stroke, stroke severity and the incidence and progression of Alzheimer's disease and dementia. We can expect that ARBs exert these effects by both AT(1) receptor blockade and angiotensin II type 2 (AT(2) ) receptor stimulation. Moreover, recent experimental results support the notion that AT(2) receptor stimulation with AT(1) receptor blockade could contribute to protection against ischaemic brain damage at least partly due to an increase in cerebral blood flow and decrease in oxidative stress, and prevent cognitive decline. Cellular therapy has been focused on as a new therapeutic approach to restore injured neurons. In this context, it has been reported that AT(2) receptor stimulation enhances neurite outgrowth and decreases neural damage, thereby enhancing neurogenesis. Moreover, additional beneficial effects of ARBs with an AT(1) receptor blocking action with a partial peroxisome proliferator-activated receptor (PPAR)-γ agonistic effect have been reported, and interaction of AT(2) receptor activation and PPAR-γ might be involved in these ARBs' effects. This article reviews the effects of regulation of activation of angiotensin II receptor subtypes on ischaemic brain damage and cognitive function, focusing on the effects of AT(2) receptor stimulation.     

Cross-talk between angiotensin II and glucagon receptor signaling mediates phosphorylation of mitogen-activated protein kinases ERK 1/2 in rat glomerular mesangial cells

We have recently shown that the pancreatic hormone glucagon-induced phosphorylation of mitogen-activated protein (MAP) kinase ERK 1/2 as well as growth and proliferation of rat glomerular mesangial cells (MCs) via activation of cAMP-dependent protein kinase A (PKA)- and phospholipase C (PLC)/Ca2+-mediated signaling pathways. Since circulating glucagon and tissue angiotensin II (Ang II) levels are inappropriately elevated in type 2 diabetes, we tested the hypothesis that glucagon induces phosphorylation of ERK 1/2 in MCs by interacting with Ang II receptor signaling. Stimulation of MCs by glucagon (10 nM) induced a marked increase in intracellular [Ca2+]i that was abolished by [Des-His1, Glu9]-glucagon (1 microM), a selective glucagon receptor antagonist. Both glucagon and Ang II-induced ERK 1/2 phosphorylation (glucagon: 214+/-14%; Ang II: 174+/-16%; p<0.001 versus control), and these responses were inhibited by the AT1 receptor blocker losartan (glucagon + losartan: 77+/-14%; Ang II + losartan: 84+/-18%; p<0.01 versus glucagon or Ang II) and the AT2 receptor blocker PD 123319 (glucagon + PD: 78+/-7%; Ang II + PD: 87+/-7%; p<0.01 versus glucagon or Ang II). Inhibition of cAMP-dependent PKA with H89 (1 microM) or PLC with U73122 (1 microM) also markedly attenuated the phosphorylation of ERK 1/2 induced by glucagon (glucagon + U73122: 109+/-15%; glucagon + H89: 113+/-16%; p<0.01 versus glucagon) or Ang II (Ang II + U73122: 111+/-13%; Ang II + H89: 86+/-10%; p<0.01 versus Ang II). Wortmannin (1 microM), a selective PI 3-kinase inhibitor, also blocked glucagon- or Ang II-induced ERK 1/2 phosphorylation. These results suggest that AT1 receptor-activated cAMP-dependent PKA, PLC and PI 3-kinase signaling is involved in glucagon-induced MAP kinase ERK 1/2 phosphorylation in MCs. The inhibitory effect of PD 123319 on glucagon-induced ERK 1/2 phosphorylation further suggests that AT2 receptors also play a similar role in this response.     

The subtype 2 of angiotensin II receptors and pressure-natriuresis in adult rat kidneys

The present work examined the effects of the subtype 2 of angiotensin II (AT2) receptors on the pressure-natriuresis using a new peptide agonist, and the possible involvement of cyclic guanosine 3', 5' monophosphate (cyclic GMP) in these effects. In adult anaesthetized rats (Inactin, 100 mg kg(-1), i.p.) deprived of endogenous angiotensin II by angiotensin converting enzyme inhibition (quinapril, 10 mg kg(-1), i.v.), T2-(Ang II 4-8)2 (TA), a highly specific AT2 receptor agonist (5, 10 and 30 microg kg(-1) min(-1), i.v.) or its solvent was infused in four groups. Renal functions were studied at renal perfusion pressures (RPP) of 90, 110 and 130 mmHg and urinary cyclic GMP excretion when RPP was at 130 mmHg. The effects of TA (10 microg kg(-1) min(-1)) were reassessed in animals pretreated with PD 123319 (PD, 50 microg kg(-1) min(-1), i.v.), an AT2 receptor antagonist and the action of the same dose of PD alone was also determined. Increases in RPP from 90 to 130 mmHg did not change renal blood flow (RBF) but induced 8 and 15 fold increases in urinary flow and sodium excretion respectively. The 5 microg kg(-1) min(-1) dose of TA was devoid of action. The 10 and 30 microg kg(-1) min(-1) doses did not alter total RBF and glomerular filtration rate, but blunted pressure-diuresis and natriuresis relationships. These effects were abolished by PD. TA decreased urinary cyclic GMP excretion. After pretreatment with PD, this decrease was reversed to an increase which was also observed in animals receiving PD alone. In conclusion, renal AT2 receptors oppose the sodium and water excretion induced by acute increases in blood pressure and this action cannot be directly explained by changes in cyclic GMP.     

Inhibition of inositol 1,4,5-trisphosphate formation by cyclic GMP in cultured aortic endothelial cells of the pig.

1. In cultured endothelial cells of the pig the endothelium-derived relaxing factor (EDRF) releasing agent thrombin (2 u ml-1) caused a significant increase in basal levels of both guanosine 3':5'-cyclic monophosphate (cyclic GMP) and inositol 1,4,5-trisphosphate (IP3). This increase was time dependent, with peak levels occurring at 2 min and returning towards basal values after 5 min. 2. Pretreatment of the cells with the EDRF inhibitors haemoglobin (1 microM) or L-NG-nitro arginine (50 microM) significantly reduced the cyclic GMP response to thrombin. Both agents also resulted in significant elevations in basal levels of IP3. The IP3 response to thrombin was significantly enhanced at all time points by haemoglobin and at 5 min for L-NG-nitro arginine, when compared with the response to thrombin alone. 3. Pretreatment of the cells with either sodium nitroprusside (10 microM) or atrial natriuretic peptide (1 microM) caused a significant elevation of basal cyclic GMP levels. Although subsequent exposure to thrombin caused a further increase in cyclic GMP, which together with the rise induced by the previous two agents was significantly greater than the increase caused by thrombin alone, the incremental increase induced by thrombin was markedly less in the presence of nitroprusside or atrial natriuretic peptide. Both these agents, as well as 8-bromo cyclic GMP, resulted in a significant suppression of the IP3 response to thrombin. 4. These findings show that one mechanism for the inhibitory effect of cyclic GMP on EDRF release from endothelium may be through the inhibition of IP3 formation in response to EDRF releasing agents.     

Evidence for the AT1 subtype of the angiotensin II receptor in the rat submandibular gland

We have characterized angiotensin II (Ang II) receptor subtypes on rat submandibular gland membranes using a radioligand binding assay. [3H]Ang II binding to the membrane fractions exhibited both high (Kd =0.08 nm, Bmax =2.19 fmol/mg protein) and low (Kd =4.19 nm, Bmax = 13.7 fmol/mg protein) affinity. Ang 11, Ang III and saralasin completely displaced the [3H]Ang II binding, whereas CV-11974, an AT1 receptor antagonist and PD123319, an AT2 receptor antagonist maximally displaced up to approximately 87 and 13% of the total binding, respectively. [3H]DuP753 binding to the membrane fractions exhibited a single population of binding site with a Kd of 4.22 nM and Bmax of 3.77 pmol/mg protein. Ang II, Ang III and CV-11974 completely displaced the [3H]DuP753 binding with slope factors near unity, but PD123319 did not. These findings suggest that rat submandibular gland membranes contain predominantly the AT1 receptor subtype.     

The receptor subtype mediating the action of angiotensin II on intracellular sodium in rat proximal tubules

1. An investigation was undertaken to explore the subtype of receptor involved in mediating the actions of angiotensin II on intracellular sodium content in suspensions of isolated proximal tubules of the rat.
2. Intracellular sodium content of the proximal tubules was measured with ²³Na n.m.r. spectroscopy and under these conditions basal sodium content of the tubular cells was 69.04±1.73 nmol mg⁻¹ dry weight and the ATP levels, at 8.3±0.9 nmol ATP mg⁻¹ protein, were consistent with active respiration by the tissue.
3. In the presence of 10⁻⁴ M PD123319, a selective non-peptide AT₂ receptor antagonist, intracellular sodium levels rose from steady state by 30% (P<0.01; n=7) within 10 min of exposure to angiotensin II 10⁻¹¹ M. Over the subsequent 30 min steady state levels were re-established. Administration of angiotensin II 10⁻¹¹ M, in the presence of the selective AT₁ receptor antagonist, losartan at either 10⁻⁶ M (n=5) or 10⁻⁴ M (n=6), was without effect on intracellular sodium levels, which were significantly different (P<0.001) from those observed when PD 123319 was present.
4. Angiotensin II 10⁻⁵ M, administered to the tubular suspension in the presence of 10⁻⁴ M PD123319, decreased (P<0.01, n=6) intracellular sodium content by 16% in the first 5 min, but in the following 25 min returned to steady state levels. However, in the presence of losartan 10⁻⁴ M, angiotensin II 10⁻⁵ M had no effect on intracellular sodium content which was markedly different (P<0.001) from that obtained in the presence of PD123319.
5. These findings show that at both the high and low concentrations of angiotensin II, its modulation of intracellular sodium levels within the proximal tubule cells is mediated via the activation of AT₁ receptors. The intracellular mechanism underlying this effect remain to be investigated.

     

The stimulation of human neutrophil migration by angiotensin II: its dependence on Ca2+ and the involvement of cyclic GMP

1. Angiotensin II had a bimodal effect on human neutrophil migration. Low concentrations of angiotensin II stimulated random migration. At a concentration of 10⁻¹⁰ M it caused a maximal increase of migration; migration increased from 47.2±2.1 μm in the absence of angiotensin II, to 73.1±2.2 μm with 10⁻¹⁰ M angiotensin II present in the lower compartment of the Boyden chamber (n=5, P<0.001). Stimulation of migration by angiotensin II was partly chemotactic and partly chemokinetic. Angiotensin II concentrations of 10⁻⁸ M and higher inhibited chemotactic peptide-stimulated chemotaxis.
2. The stimulant effect of angiotensin II on migration was completely dependent on extracellular Ca²⁺. In the presence of 1 mM Ca²⁺, angiotensin II stimulated migration to 76.1±1.7 μm, while migration in the absence of Ca²⁺ was 42.2±1.9 μm (n=4, P<0.001). Different types of calcium channel blockers either moderately or strongly inhibited angiotensin II-activated migration. Stimulation of migration by angiotensin II in intact cells required higher concentrations of Ca²⁺ than in electroporated cells. This supports the view that there is an influx of Ca²⁺ through the plasma membrane, and a requirement of calcium for an intracellular target.
3. Angiotensin II-stimulated migration was inhibited by pertussis toxin; from 71.6±2.0 μm in the absence, to 43.6±1.5 μm in the presence of pertussis toxin (n=4, P<0.001). Migration of electroporated neutrophils stimulated by angiotensin II was synergistically enhanced by GTPγS. This suggests that one or more G-proteins are involved in the activating effect of angiotensin II.
4. Inhibitors of soluble guanylate cyclase and antagonists of cyclic GMP-dependent kinase strongly inhibited the activating effect of angiotensin II. The results suggest that the activating effect of angiotensin II is mediated by cyclic GMP and by cyclic GMP-dependent kinase.

     

Endothelium-derived relaxing factor and atriopeptin II elevate cyclic GMP levels in pig aortic endothelial cells

1. Two directly-acting stimulants of soluble guanylate cyclase, glyceryl trinitrate (0.1 microM) and sodium azide (10 microM), and a receptor-mediated stimulant of particulate guanylate cyclase, atriopeptin II (10 nM), each elevated the cyclic GMP content of primary cultures of pig aortic endothelial cells without affecting the cyclic AMP content. 2. Two receptor-mediated stimulants of adenylate cyclase, glucagon (1 microM) and isoprenaline (10 microM), had no effect on the cyclic AMP or cyclic GMP content of these cells, but the directly acting stimulant, forskolin (30 microM), induced a small increase in cyclic AMP content. 3. Three agents that release endothelium-derived relaxing factor (EDRF); bradykinin (0.1 microM), ATP (10 microM) and ionophore A23187 (0.1 microM), each markedly elevated the cyclic GMP content of pig aortic endothelial cells, but acetylcholine (1 microM) had no effect. None of these agents had any effect on cyclic AMP content. 4. Two agents that potentiate the actions of EDRF; M & B 22948 (100 microM) and superoxide dismutase (30 units ml-1), each elevated the cyclic GMP content of pig aortic endothelial cells without affecting the cyclic AMP content. Pretreating cells with catalase (100 units ml-1) did not affect the rise in cyclic GMP content induced by superoxide dismutase (30 units ml-1). 5. Pretreatment of pig aortic endothelial cells with haemoglobin (10 microM) reduced the resting content of cyclic GMP and blocked the increase in cyclic GMP content induced by glyceryl trinitrate (0.1 microM), sodium azide (10 microM), bradykinin (0.1 microM), ATP (10 microM), ionophore A23187 (0.1 microM), M & B 22948 (100 microM) and superoxide dismutase (30 units ml-1), but not that induced by atriopeptin II (10 nM). 6. Pretreatment of pig aortic endothelial cells with an inhibitor of soluble guanylate cyclase, methylene blue (20 microM), had no effect on the resting content of cyclic GMP. Methylene blue (20 microM) blocked the increase in cyclic GMP content induced by glyceryl trinitrate (0.1 microM), M & B22948 (100 microM) and bradykinin (0.1 microM), but not that induced by atriopeptin II (10 nM). 7. The data show that soluble guanylate cyclase, particulate guanylate cyclase and adenylate cyclase are present in pig aortic endothelial cells. They further suggest that EDRF, produced spontaneously or in response to vasoactive agents, elevates endothelial cyclic GMP content by stimulating soluble guanylate cyclase. It is possible that this may serve as a feedback loop by which the endothelial cell modulates EDRF production.     

Effect of endotoxin on the angiotensin II receptor in cultured vascular smooth muscle cells.

1. In some tissues, a decrease in the number of cell surface receptors and alterations of the receptor coupling have been proposed as possible mechanisms mediating the deleterious effects of bacterial endotoxin in septic shock. 2. The effects of bacterial lipopolysaccharide (Escherichia coli 0111-B4; LPS) on vascular angiotensin II and vasopressin receptors have been examined in cultured aortic smooth muscle cells (SMC) of the rat by use of radioligand binding techniques. 3. In vascular SMC exposed to 1 micrograms ml-1 endotoxin for 24 h, a significant increase in angiotensin II binding was found. The change in [125I]-angiotensin II binding corresponded to an increase in the number of receptors whereas the affinity of the receptors was not affected by LPS. In contrast, no change in [3H]-vasopressin binding was observed. 4. The pharmacological characterization of angiotensin II binding sites in control and LPS-exposed cells demonstrated that LPS induced an increase in the AT1 subtype of the angiotensin II receptors. Receptor coupling as evaluated by measuring total inositol phosphates was not impaired by LPS. 5. The effect of LPS on the angiotensin II receptor was dose-, time- and protein-synthesis dependent and was associated with an increased expression of the receptor gene. 6. The ability of LPS to increase angiotensin II binding in cultured vascular SMC was independent of the endotoxin induction of NO-synthase. 7. These results suggest that, besides inducing factors such as cytokines and NO-synthase, endotoxin may enhance the expression of cell surface receptors. The surprising increase in angiotensin II binding in LPS exposed VSM cells may represent an attempt by the cells to compensate for the decreased vascular responsiveness. It may also result from a non-specific LPS-related induction of genes.     

Age-associated decrease in histamine-induced vasodilation may be due to reduction of cyclic GMP formation.

1. The effects of aging on histamine-induced vasodilatation and cyclic GMP production in rat thoracic aorta were investigated. 2. This histamine-induced dilatation of the aorta was mediated by H1-receptors and was dependent on the endothelium. 3. Histamine induced the greatest dilatation of arteries of 3-4 week old rats, progressively less of those of rats of 8 to 56 weeks old, and scarcely detectable dilatation of those of 100 week old rats. 4. Histamine induced cyclic GMP production in aorta from rats of 4 weeks old, with no change in the cyclic AMP level. This increase in the cyclic GMP level induced by histamine also decreased with age, being about 70% as great at 8 weeks, 50% as great at 50-60 weeks, and 10% as great at 130 weeks of age. 5. Removal of the endothelium completely abolished the histamine-induced increase in cyclic GMP. 6. The dilator effect of nitroprusside, which enhances cyclic GMP production by stimulating guanylate cyclase directly (not indirectly via the endothelium derived relaxing factor, EDRF), also showed age-related attenuation. 7. The dilator effect of 8-bromo cyclic GMP, which stimulates cyclic GMP-dependent protein kinase, also decreased during aging. 8. These results suggest that aging reduces the ability of the endothelium to produce EDRF, which stimulates guanylate cyclase, and so decreases cyclic GMP production. Thus the decreased dilator response of the arteries to histamine during aging is probably due to both loss of endothelial function and reduction of guanylate cyclase activity. Alteration of cyclic GMP-dependent protein kinase activity may also participate in the age-related changes.     

Imbalance between the endothelial cell-derived contracting factors prostacyclin and angiotensin II and nitric oxide/cyclic GMP in human primary varicosis

1. The role of the endothelium in the vasomotor control of human veins in the lower extremity is little understood. We tested the hypothesis that the production of relaxing and contracting factors is altered in endothelial cells from varicose saphenous veins which may predispose to the decreased vessel tone observed in primary varicosis.
2. We determined the intracellular accumulation of guanosine 3′:5′-cyclic monophosphate cyclic GMP; a measure of nitric oxide production) and the release of endothelin and prostacyclin (measured as its stable metabolite 6-keto-prostaglandin F_1α) from cultured cells derived from the long saphenous veins of patients with primary varicosis (Varicose saphena group, n=27) or from patients undergoing coronary artery bypass surgery (Healthy saphena group, n=22). In addition, levels of endothelin, angiotensin II, bradykinin, cyclic GMP and cyclic AMP in plasma from patients with primary varicosis and healthy volunteers (n=8–11 in each group) were determined.
3. Although basal cyclic GMP levels were similar, more cyclic GMP accumulated in response to histamine (1–100 μmol l⁻¹) in cells from varicose saphenous veins (0.75±0.1 pmol per well) than in cells from veins without varicosis (0.27±0.05 pmol per well). Furthermore, the relaxant potency of nitroprusside (1 nmol l⁻¹–300 μmol l⁻¹) in vitro was higher for varicose veins (mean EC₅₀=5.9 μmol l⁻¹; n=8) than healthy veins (mean EC₅₀=20.0 μmol l⁻¹; n=7).
4. The production of prostacyclin was significantly less in cells from varicose than healthy saphenous veins (66±8.7 and 121±20.1 nmol g⁻¹ protein), but the production of endothelin was similar in both groups. Prostacyclin (3 nmol l⁻¹–30 μmol l⁻¹) consistently contracted rings of varicose saphenous vein in vitro with a mean EC₅₀ value of 10–20 μmol l⁻¹ (n=7); the maximum tension generated was ∼50% of that of a completely depolarizing solution of K⁺ (120 mmol l⁻¹).
5. In plasma from patients with varicose veins, levels of cyclic GMP were higher than in healthy controls (9.2±0.03 and 7.2±0.02 nmol l⁻¹), levels of angiotensin II were lower (81±11.5 and 147±21.7 pmol l⁻¹), and levels of endothelin, cyclic AMP, and bradykinin were not different.
6. It is concluded that endothelial cells from diseased saphenous veins secrete less constrictor mediators than cells from healthy veins and that in diseased veins the nitric oxide/cyclic GMP system is up-regulated which may shift the balance of vasoactive factors towards vasodilatation and contribute to the development of primary varicosis.

     

Evidence that an alpha 2A-adrenoceptor subtype mediates antinociception in mice.

In the hot-plate test in mice, the antinociceptive action of the alpha 2-adrenoceptor agonist, UK 14,304, was abolished by the alpha 2-adrenoceptor antagonist, idazoxan, the potent alpha 2A-adrenoceptor antagonist, RX 821002 and the preferential alpha 2A-adrenoceptor antagonist, BRL 44408. In contrast, the preferential alpha 2B- (and alpha 2C)-adrenoceptor ligands ('antagonists'), ARC-239, BRL 41992 and prazosin were inactive. The preferential alpha 2A-adrenoceptor partial agonist, guanfacine, partially inhibited UK 14,304-induced antinociception. Further, guanfacine BRL 44408 reversibly elicited submaximal antinociception. It is concluded that alpha 2A-adrenoceptors mediate antinociception in mice.     

Synthesis and structure-activity relationships of a novel series of non-peptide angiotensin II receptor binding inhibitors specific for the AT2 subtype

Structure-activity relationships are reported for a novel class of 4,5,6,7-tetrahydro-1H-imidazo[4,5-c]pyridine-6-carboxylic acid derivatives that displace 125I-labeled angiotensin II from a specific subset of angiotensin II (Ang II) binding sites in rat adrenal preparations. This binding site is not the Ang II receptor mediating vascular contraction or aldosterone release, but, rather, is one whose function has not yet been fully elucidated. It has been identified in a number of tissues and has a similar affinity for Ang II and its peptide analogues as does the vascular receptor. The non-peptide compounds reported here are uniquely specific in displacing Ang II at this binding site and are inactive in antagonizing Ang II at the vascular receptor or in pharmacological assays measuring vascular effects. PD 123,319 (79), one of the most potent compounds, has an IC50 of 34 nM. Certain of these compounds may have utility in the definition and study of Ang II receptor subtypes.     

Down-regulation of atrial natriuretic peptide receptor and cyclic GMP response in cultured rat vascular smooth muscle cells

Treatment of cultured rat vascular smooth muscle cells with human atrial natriuretic peptide (hANP) or Met(O)12hANP caused a similar and marked reduction (approximately 80%) of ANP receptor number (down-regulation). A second challenge with hANP stimulated the accumulation of intracellular cGMP in the down-regulated cells to the same extent as in control cells. These data suggest that ANP receptor sites are functionally heterogenous, the more abundant site being uncoupled from guanylate cyclase but susceptible to down-regulation.