Renal effects of glucose transporter 4 in Nω-nitro-L-arginine/ /high salt-induced hypertensive rats.

OBJECTIVES: The aim of study was to determine the renal effects of glucose transporter 4 (GLUT4) in a hypertensive nephropathy rat model. BACKGROUND: GLUT4 has been implicated in insulin resistance and hypertension in several animal models; however its role in hypertensive nephropathy still remains unclear. METHODS: Hypertensive nephropathy was induced by Nω-nitro-L-arginine (L-NNA), a nitric oxide (NO) synthase inhibitor, 100 mg/ml in drinking water and high salt (HS) diet (4 % NaCl), for 15 days in the presence of insulin, a GLUT 4 agonist (1 U/day) and indinavir, a GLUT4 inhibitor (80 mg/kg/day). RESULTS: Decreased basal renal medullary and cortical blood flow was enhanced in LNNA/HS/indinavir group (p < 0.01) but attenuated (p < 0.05) by insulin. Proteinuria was increased (p < 0.01) in LNNA/HS/indinavir group but attenuated (p < 0.01) by insulin. Insulin-treated rats decreased urine NO (p < 0.01) and urine Na2+ (p < 0.01) compared to other treated animals. In indinavir-treated animals, urine Na2+ was increased by benzamil, an epithelial sodium channel (ENaC) inhibitor (p < 0.01) and hydrochlorothiazide, a sodium/chloride co-transporter (NCC) inhibitor (p < 0.05). CONCLUSION: GLUT4 exerts a renoprotective role which may be related to increase NO production. The antinatriuretic effects of GLUT4 appear to be due to enhancement of ion transport activity of ENaC and NCC at the renal tubules (Fig. 9, Ref. 34).

Impaired endothelium-dependent and -independent relaxation of aorta from diabetic rats.

Vascular complication in diabetes has been reported to be due to the effects of chronic high blood glucose on the vascular system. Different relaxation mechanisms exist in the vasculature and effect of chronic high glucose on vascular relaxation mechanisms is not clearly understood. We assessed the effect of streptozotocin (STZ, 70 mg/kg, for 12 wks)-induced diabetes on vascular reactivity to isoproterenol (Isop, 10-9-10-5 M), a cAMP-dependent agent, acetylcholine (ACh, 10-9-10-5 M), a stimulant of NO (nitric oxide) synthase, sodium nitroprusside (SNP, 10-10-10-5 M), NO donor, or bradykinin (BK, 10-9-10-5 M) in the rat isolated aortic ring. Isop, ACh, SNP, or BK dose-dependently relaxed phenylephrine (PE, 10-7 M) pre-constricted ring producing a maximum relaxation of 82 % for Isop (10-5 M), 85 % for ACh (10-5 M), 100 % for SNP (10-6 M), and 30 % for BK (10-5 M) respectively. STZ attenuated Isop, ACh, and BK-induced relaxation by 45 % (n=7, pn (Fig. 5, Ref. 24).

Renal cytochrome P450 omega-hydroxylase and epoxygenase activity are differentially modified by nitric oxide and sodium chloride.

Renal function is perturbed by inhibition of nitric oxide synthase (NOS). To probe the basis of this effect, we characterized the effects of nitric oxide (NO), a known suppressor of cytochrome P450 (CYP) enzymes, on metabolism of arachidonic acid (AA), the expression of omega-hydroxylase, and the efflux of 20-hydroxyeicosatetraenoic acid (20-HETE) from the isolated kidney. The capacity to convert [(14)C]AA to HETEs and epoxides (EETs) was greater in cortical microsomes than in medullary microsomes. Sodium nitroprusside (10-100 microM), an NO donor, inhibited renal microsomal conversion of [(14)C]AA to HETEs and EETs in a dose-dependent manner. 8-bromo cGMP (100 microM), the cell-permeable analogue of cGMP, did not affect conversion of [(14)C]AA. Inhibition of NOS with N(omega)-nitro-L-arginine-methyl ester (L-NAME) significantly increased conversion of [(14)C]AA to HETE and greatly increased the expression of omega-hydroxylase protein, but this treatment had only a modest effect on epoxygenase activity. L-NAME induced a 4-fold increase in renal efflux of 20-HETE, as did L-nitroarginine. Oral treatment with 2% sodium chloride (NaCl) for 7 days increased renal epoxygenase activity, both in the cortex and the medulla. In contrast, cortical omega-hydroxylase activity was reduced by treatment with 2% NaCl. Coadministration of L-NAME and 2% NaCl decreased conversion of [(14)C]AA to HETEs without affecting epoxygenase activity. Thus, inhibition of NOS increased omega-hydroxylase activity, CYP4A expression, and renal efflux of 20-HETE, whereas 2% NaCl stimulated epoxygenase activity.

Adrenaline inhibits adenosine diphosphate induced intravascular aggregation of rat platelets through stimulation of alpha 2 adrenoceptors.

STUDY OBJECTIVE: The aim was to determine the receptors involved in the antiaggregatory effects of adrenaline in the rat. DESIGN: The 111indium oxine technique was used to evaluate ADP induced pulmonary accumulation of 111In labelled platelets in adrenalectomised rats (ie, no endogenous adrenaline) in the absence of anticoagulants. Adrenaline was infused (10, 20 and 40 micrograms.kg-1.h-1) and ADP aggregation measured. Adrenoceptor agonists, isoprenaline, methoxamine, and BHT 933, were given to evaluate whether they mimic the adrenaline effects. Adrenoceptor antagonists, yohimbine, propranolol, prazosin, and WY 26392, were given to assess whether they block the adrenaline effects. MEASUREMENTS AND MAIN RESULTS: In all cases, pulmonary accumulation of platelets was measured in response to ADP. Adrenaline dose dependently inhibited platelet aggregation. BHT 933 (1.5 micrograms.kg-1.min-1) mimicked, while phentolamine (1 mg.kg-1), yohimbine (2.5 mg.kg-1), and WY 26392 (0.1, 1.0, 5.0 mg.kg-1) blocked, the adrenaline effects. Methoxamine (3.3 micrograms.kg-1.min-1) produced a relatively weak non-specific inhibition of ADP aggregation. Isoprenaline (33 ng.kg-1.min-1) did not mimic the effects of adrenaline, neither did propranolol (1 mg.kg-1) affect the adrenaline inhibition of the aggregatory responses to ADP. Indomethacin (3 mg.kg-1) blocked the inhibitory effects of adrenaline. CONCLUSIONS: Adrenaline stimulates alpha receptors on platelets but inhibits platelet aggregation. There is no evidence to suggest that beta receptors participated in the effects produced by adrenaline. There is a role for cyclo-oxygenase products in the inhibitory effects of adrenaline on aggregation.

The influence of adrenaline on gender difference in adenosine diphosphate-induced aggregation of platelets in the rat.

The role of adrenaline on the inhibitory effects of physiological levels of oestradiol on ADP-induced intravascular aggregation has been studied. Platelets from pro-oestrous female rats aggregated less than those from dioestrous and male rats. Following adrenalectomy, there was no longer any difference(s) in the aggregability of the platelets to ADP in any of the rats. Adrenaline infusion (20 mg kg-1 hr-1) restored platelet aggregation to preadrenalectomy levels in pro-oestrous rate. Measurement of spontaneous fibrinolytic activity of the plasma showed highest value in pro-oestrous rats. Adrenalectomy reduced, while adrenaline infusion increased the fibrinolytic activity. The results suggest that the inhibitory effects of oestradiol on intravascular aggregation are dependent on endogenous adrenaline possibly working through the fibrinolytic pathway.

Functional response of the rat kidney to inhibition of nitric oxide synthesis: role of cytochrome p450-derived arachidonate metabolites.

1. We tested the hypothesis that nitric oxide (NO) exerts a tonic inhibitory influence on cytochrome P450 (CYP450)-dependent metabolism of arachidonic acid (AA). 2. N(omega)-nitro-L-Arginine methyl ester (L-NAME), an inhibitor of nitric oxide synthase (NOS), increased mean blood pressure (MBP), from 91+/-6 to 137+/-5 mmHg, renal vascular resistance (RVR), from 9.9+/-0.6 to 27.4+/-2.5 mmHg ml(-1) min(-1), and reduced renal blood flow (RBF), from 9.8+/-0.7 to 6.5+/-0.6 ml min(-1)) and GFR from 1.2+/-0.2 to 0.6+/-0.2 ml 100 g(-1) min(-1)) accompanied by diuresis (UV, 1.7+/-0.3 to 4.3+/-0.8 microl 100 g(-1) min (-1)), and natriuresis (U(Na)V, 0.36+/-0.04 to 1.25+/-0.032 micromol 100 g(-1) min(-1)). 3. 12, 12 dibromododec-enoic acid (DBDD), an inhibitor of omega hydroxylase, blunted L-NAME-induced changes in MBP, RVR, UV and U(Na)V by 63+/-8, 70+/-5, 45+/-8 and 42+/-9%, respectively, and fully reversed the reduction in GFR by L-NAME. Clotrimazole, an inhibitor of the epoxygenase pathway of CYP450-dependent AA metabolism, was without effect. 4. BMS182874 (5-dimethylamino)-N-(3,4-dimethyl-5-isoxazolyl)-1-naphthalenesulfo namide), an endothelin (ET)A receptor antagonist, also blunted the increases in MBP and RVR and the diuresis/natriuresis elicited by L-NAME without affecting GFR. 5. Indomethacin blunted L-NAME-induced increases in RVR, UV and U(Na)V. BMS180291 (1S-(1alpha,2alpha,3alpha,4alpha)]-2-[[3-[4-[(++ +pentylamino)carbonyl]-2-oxazolyl]-7-oxabicyclo[2.2.1]hept-2-yl ]methyl]benzenepropanoic acid), an endoperoxide receptor antagonist, attenuated the pressor and renal haemodynamic but not the renal tubular effects of L-NAME. 6. In conclusion, the renal functional effects of the CYP450-derived mediator(s) expressed after inhibition of NOS with L-NAME were prevented by inhibiting either CYP450 omega hydroxylase or cyclooxygenase or by antagonizing either ET(A) or endoperoxide receptors. 20-hydroxyeicosatetraenoic acid (20-HETE) fulfils the salient properties of this mediator.

The involvement of platelet activating factor in endotoxin-induced pulmonary platelet recruitment in the guinea-pig.

1 Exposure of conscious guinea-pigs to an aerosol of endotoxin (25-100 micrograms ml-1) resulted in a dose-related, progressive accumulation of platelets in the thoracic region. Accumulation of 111indium oxine labelled erythrocytes was not observed following exposure to an aerosol of endotoxin (50 micrograms ml-1). 2 Pretreatment of guinea-pigs with the selective platelet activating factor (Paf)-antagonists. CV-3988 or brotizolam resulted in a dose-related inhibition of endotoxin-induced pulmonary platelet recruitment. Pretreatment of guinea-pigs with the selective Paf-antagonist BN 52021 resulted in significant inhibition of endotoxin-induced pulmonary platelet recruitment, although the effects of BN 52021 were not dose-related. 3 Pretreatment of guinea-pigs with indomethacin at doses known to inhibit cyclo-oxygenase did not inhibit endotoxin-induced pulmonary platelet recruitment, whereas higher doses of indomethacin produced a reduction in platelet recruitment in the lung. 4 Pretreatment of guinea-pigs with the anticoagulant heparin and the prostacyclin analogue ZK 36374 inhibited endotoxin-induced platelet recruitment. 5 These observations suggest that endotoxin-induced pulmonary platelet recruitment in the guinea-pig is secondary to the release of platelet activating factor, but not to cyclo-oxygenase products of arachidonic acid and may also involve activation of the coagulation cascade.

The suppression by lipopolysaccharide of cytochrome P450-dependent renal vasodilation in the rat is mediated by nitric oxide.

The isolated perfused kidney of the rat was used to examine the hypothesis that lipopolysaccharide-induced nitric oxide (NO) production inhibits cytochrome P450-dependent vasodilation. The vasodilator responses to arachidonic acid and bradykinin were examined as the response to arachidonic acid is wholly dependent, and that to bradykinin partly dependent on cytochrome P450 metabolism. In endotoxin-treated rats, the vasodilator response to arachidonic acid was inhibited, and those to bradykinin and acetylcholine were enhanced. Following treatment with phenobarbitone, the inducer of certain isoforms of cytochrome P450 enzymes, the vasodilator effects of all three agonists, especially that of arachidonic acid, were amplified. Lipopolysaccharide inhibited the effect of phenobarbitone on the vasodilator effect of arachidonic acid and bradykinin but enhanced that of acetylcholine. The effect of lipopolysaccharide was antagonized by haemoglobin, a NO antagonist, and N omega-nitro-L-arginine, an inhibitor of NO synthase, suggesting that the inhibitory effect of lipopolysaccharide on arachidonic acid- and bradykinin-induced vasodilation was mediated by NO/NO synthase. N omega-Nitro-L-arginine enhanced vasodilation induced by arachidonic acid while that induced by bradykinin or acetylcholine was reduced, implying that endogenous NO inhibits vasodilator cytochrome P450 metabolites in the rat kidney. Pretreatment with dexamethasone, an inhibitor of inducible NO synthase, resulted in inhibition of the lipopolysaccharide modulation of arachidonic acid-induced vasodilation, suggesting that the inducible NO synthase is the target of the inhibitory effect of lipopolysaccharide. The inhibitory effect of lipopolysaccharide was mimicked by nitroprusside, the L-arginine-independent NO donor, and by L-arginine, the biosynthetic precursor of NO. The effect of L-arginine, but not of nitroprusside, was antagonized by N omega-nitro-L-arginine, suggesting a specific role for NO synthase in the inhibitory effect of lipopolysaccharide in the inhibition of cytochrome P450-dependent vasodilation in the rat kidney.

Cryptolepine-induced vasodilation in the isolated perfused kidney of the rat: role of G-proteins, K+ and Ca2+ channels.

The isolated perfused kidney of the rat was used to examine the contribution by guanosine triphosphate (GTP)-binding (G-) proteins, K+ and Ca2+ channels to the vasodilator actions of cryptolepine (5-methylquindoline). In normal Krebs-Henseleit buffer (4.7 mM KCl), cryptolepine elicited dose-dependent reductions in perfusion pressure of phenylephrine-preconstricted kidneys. The reductions in perfusion pressure by cryptolepine at bolus doses of 2.5, 5, and 10 micrograms were -18.0 +/- 3.4, -30.6 +/- 5.3, and -38.3 +/- 6.8 mm Hg, respectively (n = 19). In K(+)-free (0 mM KCl) Krebs-Henseleit solution, the vasodilator response to cryptolepine was reduced by 44.7 +/- 5.7% (n = 5; P < 0.01). The addition of ouabain (10(-4) M) further reduced cryptolepine-induced vasodilation to 63.0 +/- 7.2% (n = 11: P < 0.01) of the control. A combination of both conditions did not abolish the vasodilator responses to cryptolepine, suggesting the involvement of additional mechanisms. In 80, as opposed to 20 mM KCl, the reductions in perfusion pressure by cryptolepine, 2.5, 5, and 10 micrograms were markedly reduced to -0.8 +/- 0.8, -2.3 +/- 1.4, and -4.0 +/- 2.1 mm Hg, respectively (P < 0.01; n = 6). Responses to acetylcholine and diazoxide, an adenosine triphosphate (ATP)-dependent K+ channel activator, were also markedly reduced, suggesting the involvement of K+ channels for these agents. Furthermore, tetraethylammonium (5 and 10 mM), a non-specific K+ channel blocker, inhibited the vasodilator responses to cryptolepine (n = 5; P < 0.01) and to diazoxide and acetylcholine in a dose-related manner. However, glibenclamide (5 and 10 microM), an ATP-sensitive K+ channel blocker, inhibited the vasodilator responses to diazoxide and acetylcholine but was without effect on cryptolepine-induced vasodilation. This suggests that cryptolepine activates K+ channels which are tetraethyl ammonium- but not glibenclamide-sensitive. In pertussis toxin-treated rats, the vasodilator response to cryptolepine was not affected while that to acetylcholine and especially diazoxide was markedly inhibited. This suggests that, unlike diazoxide and acetylcholine, the K+ channels activated by cryptolepine are not coupled to pertussis toxin-sensitive G-proteins. In the presence of verapamil (5 microM) and cobalt chloride (1 mM), Ca2+ channel blockers, the vasodilator response to cryptolepine was inhibited (n = 5; P < 0.01), suggesting that Ca2+ flux across membranes is also involved in cryptolepine-induced vasodilation in the rat kidney.

Gender difference in vascular and platelet reactivity to thromboxane A(2)-mimetic U46619 and to endothelial dependent vasodilation in Zucker fatty (hypertensive, hyperinsulinemic) diabetic rats.

We examined the hypothesis that gender differences exist in platelet and vascular reactivity in type-2 diabetes mellitus, using Zucker fatty diabetic rats of both sexes and their lean littermates. Type-2 diabetes is characterized by excessive platelet production of TXA(2), which is thrombogenic. Testosterone up-regulates platelet TXA(2) receptors and the aggregation response to thromboxane mimetics. Conversely, estrogen increases vascular nitric oxide (NO) production and inhibits platelet aggregation. Hemodynamic studies were undertaken with the determination of dose-response curve for MAP and renal cortical blood flow (RCF) in response to U46619, angiotensin-II, phenylephrine and endothelin-1, as well as the systemic hemodynamic response to acetylcholine and L-NG nitro-arginine methylester (L-NAME). Platelet aggregation response was evaluated using whole blood impedance aggregometry. There were significant gender differences in the systemic blood pressure and RCF response to TXA(2)-mimetic U46619 and angiotensin-II (P<0.02, ANOVA) but not to phenylephrine or endothelin-1. Male rats exhibited a paradoxical hypotensive response to U46619 (-18+/-11 mmHg) compared with a peak pressor response of +6+/-1 mmHg in female rats (P<0.01, ANOVA). The male rats exhibited an attenuated systemic vasodilator response (P<0.001, ANOVA) to acetylcholine (fall in MAP in male diabetic rats being -24+/-8 mmHg, compared with a fall of -50+/-8 mmHg in females), but a greater rise in the renal cortical resistance in response to NO inhibition by L-NAME (P<0.03) compared with the female rats. Both the slope (46+/-2) and the peak magnitude of the U46619-induced whole blood platelet aggregation (13+/-1) ohms were significantly higher (P<0.01, ANOVA) in male (n=10) compared with female diabetic rats (n=8) (29+/-0.8 slope, 10.0+/-0.8 ohms, respectively). Thus, the male diabetic Zucker rats exhibited an impaired response to vasoconstrictors (U46619 and angiotensin-II) and to endothelial (NO)-mediated vasodilation. The male gender may therefore be associated with the greater prothrombotic activity and a worse impairment of endothelial reactivity in the type-2 diabetic state.

Alteration in endothelin receptor sub-type responsiveness and in the endothelin-TXA(2) mimetic U46619 interaction, in type-2 hypertensive diabetic Zucker rats.

BACKGROUND: Type-2 diabetes is characterized by endotheliopathy, which increases target organ damage and mortality. There is excessive endothelin-1 and TXA(2) production, and abnormal vascular reactivity to endothelin-1, manifested as a paradoxical hypotensive action in Zucker diabetic, but not lean rats. We examined the hypothesis that there is an alteration in the ET-A/ET-B receptor subtype sensitivity, and/or the interaction or cross-talk between ET-1 and TXA(2) in type-2 diabetes, using Zucker diabetic rats and their lean littermates. MATERIALS AND METHODS: Hemodynamic studies were performed in lean and Zucker fatty diabetic rats of both sexes. Laser doppler flowmetry was used to measure renal cortical (RCF) and medullary blood flow (MBF) responses. Dose response curves for mean arterial blood pressure (MAP), MBF and RCF in response to ET-1, U46619, acetylcholine, and L-NAME (25mg/kg) were constructed after pre-treatment of the rats with either BQ610 1mg/kg i.v. or BQ788 0.5mg/kg i.v. The effects of BQ610 and BQ788 on whole blood impedance aggregation were also assessed. RESULTS: BQ788, but not BQ610 abolished both the paradoxical hypotensive action of ET-1 in Zucker diabetic rats (n=7 each, P<0.001 ANOVA) as well as the dose-dependent rise in MBF (P<0.001 ANOVA). BQ788, but not BQ610 abolished the difference in response to ET-1 between lean and diabetic Zucker rats. U46619 caused a hypotensive action in male Zucker rats which was abolished by L-NAME 25mg/kg or indomethacin 10mg/kg i.v. The U46619 interaction with BQ788 on both MAP and MBF was significantly (P<0.03 ANOVA) different between lean and diabetic Zucker rats. BQ788, but not BQ610 attenuated both the MAP and MBF responses to acetylcholine or L-NAME P<0.02 ANOVA). However, BQ610 dose-dependently attenuated the slope of platelet aggregation in both lean and Zucker diabetic rats (P<0.02 ANOVA). CONCLUSION: ET-B receptor antagonism abolished the abnormal vascular reactivity and MBF responses to ET-1, and also normalized the vasoactive responses to the level seen in healthy lean Zucker rats. ET-1 receptor blockade influences the responses to TXA(2) receptor activation. In the systemic and renal circulation, this interaction appears to be mostly ET-B receptor mediated, whilst in platelets, ET-A receptor role may be predominant. The interaction or cross-talk between ET-1 and TXA(2) is altered in the type-2 diabetic state. Collectively, these pathophysiological changes may contribute to the vicious circle of diabetic endotheliopathy.

The energetics of the interaction of piroxicam with plasma albumin.

The thermodynamics of the binding of piroxicam to human and bovine plasma albumins revealed the reactions to be spontaneous and exothermic with bond strengths indicating the involvement of hydrogen and hydrophobic bonds. The association constants (K) decreased as temperature increased for both human serum albumin (HSA) and bovine serum albumin (BSA); and at all the temperatures in this study, K values obtained for BSA were higher (except at 36 degrees C) but not the bound fraction of piroxicam (beta) and the quantity of binding (V). Scatchard plots of the data indicated at least two classes of binding sites.

Effects of cryptolepine alone and in combination with dipyridamole on a mouse model of arterial thrombosis.

The effects of cryptolepine alone and in combination with other antiplatelet agents have been investigated using a mouse model of arterial thrombosis. Intraperitoneal premedication with crytolepine produced 25% maximal protection at 1 mg/kg while dipyridamole producedd a 20% maximal effect at 2 mg/kg. Higher doses of cryptolepine showed a reduced effect. In contrast, indomethacin and aspirin produced a dose-related and higher degree of protection. A combination of cryptolepine and dipyridamole was more effective than when the individual drugs were used alone. The use of 20% ethanol as a dosage vehicle enhanced the protective effects of all drugs tested and the ethanol vehicle alone provided 45% protection.

Endothelin-like action of Pausinystalia yohimbe aqueous extract on vascular and renal regional hemodynamics in Sprague Dawley rats.

The bark of the African tree Pausinystalia yohimbe has been used as a food additive with aphrodisiac and penile erection enhancing properties. The effect of an aqueous extract of P. yohimbe (CCD-X) on renal circulation was assessed in order to test the hypothesis that it possesses additional effects on nitric oxide production and/or endothelin-1 (ET-1)-like actions. In vivo studies with CCD-X in Sprague Dawley rats demonstrated a dose-dependent (1-1000 ng/kg) increase in mean blood pressure (p < 0.001) and an increase in medullary blood flow (MBF) (p < 0.001). Both the pressor action and renal medullary vasodilation were blocked by endothelinA (ETA) receptor antagonist BMS182874 and endothelinB (ETB) receptor antagonist BQ788 in combination. L-Nomega-nitro-l-arginine methyl ester (L-NAME; 10 mg/kg) also inhibited the increase in MBF induced by CCD-X. In vitro studies in isolated perfused kidney and in pressurized renal microvessels confirmed the dose-dependent vasoconstrictor action of this extract. ETA receptor antagonist BQ610 and ETB receptor antagonist BQ788 separately and significantly attenuated the renal vasoconstrictor actions of the extract (p < 0.001 ANOVA). These preliminary observations indicate that, in addition to the alpha-adrenergic antagonist actions that characterize yohimbine, CCD-X possesses endothelin-like actions and affects nitric oxide (NO) production in renal circulation. These findings suggest a strong possibility of post-receptor cross-talk between alpha2-adrenoceptors and endothelin, as well as a direct effect of alpha2-adrenoceptors on renal NO production.

Effects of fenofibrate, a PPAR-α ligand, on the haemodynamics of glycerol-induced renal failure in rats.

The modulating effect of peroxisome proliferator-activated receptor α ligand on haemodynamic effects of phenylepherine (PE), angiotensin II (AII), endothelin 1 (ET1), acetylcholine (Ach), sodium nitroprusside (SNP) and isoproterenol (ISO) were evaluated in glycerol-induced acute kidney injury in rats. The effect of PE on fenofibrate-treated animals was a dose-dependent increase in mean arterial blood pressure (MAP). For AII and ET1, MAP was also increased for the fenofibrate group but not in a dose-dependent fashion. On the medullary blood flow (MBF), while the lower doses of PE and AII increased the perfusion unit on the fenofibrate-treated group, the higher doses decreased the perfusion unit. The ET1 increased the perfusion unit on this group but not in dose-dependent fashion. The effects of PE and AII on the cortical blood flow (CBF) of fenofibrate-treated group is similar to that of MBF for the same group but not for ET1. The effect of Ach, SNP and ISO in all the groups was the decrease in MAP. ISO caused dose-dependent increase in MBF of fenofibrate-treated group. The effect of Ach, SNP and ISO on the CBF perfusion unit was that of the increase for the fenofibrate-treated group. The study showed that fenofibrate did not attenuate increased blood pressure induced by PE, AII and ET1 but caused enhanced vasodilation by Ach, SNP and ISO.

Antioxidant U74389G improves glycerol-induced acute renal failure without affecting PPARgamma gene.

Oxygen metabolites play an important role in the pathogenesis of myoglobinuric acute renal failure (ARF). Previously, we have reported a down regulation of peroxisome proliferator activated receptor gamma (PPARgamma) in glycerol-induced ARF, and the induction of PPARgamma has been shown to provide renal protection. In this study, we determined the protective influence of U74389G, a hydroxyl radical scavenger in myoglobinuric ARF, and its association with PPARgamma-mediated renal protection in the rat. Vascular responses to AII were determined in renal pre-glomerular vessels following the induction of ARF with glycerol (50%, v/v, i.m.). The extent of renal damage and function were assessed with or without pre-treatment with U74389G (10 mg/kg x 21 days). In ARF, AII vasoconstriction was enhanced (97%; p < 0.05), and AII production was doubled. U74389G reduced AII vasoconstriction and production by 42% (p < 0.05) and 40% (p < 0.05), respectively. U74389G reduced proteinuria (85%; p < 0.05), which was four times higher in ARF. Similarly, U74389G enhanced Na+ excretion twofold while reducing plasma creatinine (24%; p < 0.05) and BUN (31%; p < 0.05). U74389G attenuated free radical generation in ARF while nitrite excretion was unchanged. In renal pre-glomerular vessel, PPARgamma expression, activity, and mRNA were significantly lower in ARF rats; this was unchanged with U74389G treatment. On the other hand, U74389G significantly reduced NFkappaB protein expression, which was elevated in ARF by 25% (p < 0.05). We suggest that antioxidant U74389G blunted renal injury and improved renal function in glycerol-induced ARF through the reduction of free radical production and/or inhibition of NFkappaB without affecting PPARgamma.

Role of the endothelium and cyclic GMP in renal vasodilator responses to cryptolepine in rats.

Isolated perfused rat kidney was used to examine the possible mechanisms involved in the hypotensive/vasodilator actions of cryptolepine. In kidneys preconstricted by phenylephrine (PE 5-7.5 x 10(-7) M), cryptolepine at bolus doses of 2.5, 5, and 10 micrograms elicited dose-dependent reductions in perfusion pressure by 29.8 +/- 4.1, 43.3 +/- 3.9, and 54.3 +/- 4.9 mm Hg, respectively. In the presence of indomethacin, cryptolepine-induced reduction in perfusion pressure was not significantly changed, suggesting a lack of a cyclooxygenase-mediated component in its renal vasodilator response. Removal of the endothelium with p-bromophenacyl bromide (p-BPB 10 microM) inhibited the vasodilator response to cryptolepine 2.5, 5, and 10 micrograms to 10.2 +/- 1.8, 15.9 +/- 1.5, and 20.2 +/- 2.0 mm Hg, respectively (p < 0.01). The vasodilator response to acetylcholine (ACh 50 ng) was also reduced from a control value of 56.7 +/- 4.5 to 15.3 +/- 1.9 mm Hg (p < 0.01); responses to sodium nitroprusside (SNP 5 micrograms) and isoprenaline (1 microgram) were not affected. In kidneys treated with hydroquinone (10(-5) and 10(-4) M), a specific inhibitor of endothelium-dependent vasodilation, cryptolepine- and ACh-induced vasodilation were inhibited dose dependently (p < 0.01). N omega-nitro-L-arginine (L-NNA 10(-5)-10(-4) M), a specific inhibitor of the synthesis/release of endothelium-derived relaxing factor/nitric oxide (EDRF/NO), attenuated the vasodilator response to cryptolepine and ACh (50 ng) dose dependently. At 10(-4) M L-NNA, cryptolepine-induced vasodilation was reduced to 6.6 +/- 2.2 (2.5 micrograms), 10.9 +/- 2.2 (5 micrograms), and 13.3 +/- 1.4 mm Hg (10 micrograms). L-Arginine (10(-4) and 3 x 10(-4) M) but not D-arginine (10(-4) M) inhibited the effects of L-NNA, with vasodilatory effects of cryptolepine returning to control values, suggesting that the vasodilator material released by cryptolepine is EDRF, possibly NO. Methylene blue (MB 10(-4) M), the inhibitor of soluble guanylate cyclase which inhibited 50 ng ACh and 5 micrograms SNP-induced vasodilation also reduced the vasodilatory responses to cryptolepine to 0.8 +/- 0.8 (2.5 micrograms), 4.2 +/- 4.2 (5 micrograms), and 10.8 +/- 6.2 mm Hg (10 micrograms) suggesting that the effector pathway for cryptolepine-induced vasodilation is soluble guanylate cyclase-linked increase in cyclic GMP of vascular smooth muscle.

Role of the cytochrome P450 enzyme system as a humoral modulator of vasomotor responses in rat renal vasculature.

This study was conducted to examine regulation of vasomotor tone by cytochrome (cyt) P450 enzymes. Isolated perfused rat kidney was used to examine the vasoconstrictor responses to KCl, phenylephrine (PE), and 5-hydroxytryptamine (5-HT) in the presence of inhibitors of cytP450 enzymes. Vasoconstriction elicited by KCl 2.5-7.5 mg, PE 0.1-1.0 microgram, and 5-HT 10-50 ng was attenuated dose dependently after acute inhibition of cytP450 enzymes with alpha NF 2.5-10 microM and clotrimazole 0.1-3.0 microM. Similarly, depletion of cytP450 enzymes with CoCl2 significantly inhibited the vasoconstrictor responses to KCl and PE. These inhibitory effects were greater against KCl and PE, suggesting that release of endogenous arachidonic acid (AA) and its conversion to cytP450 vasoconstrictor products by these agonists may contribute to their vasoconstrictor activities. The renal microsomal oxidation of ethylene glycol to formaldehyde (cytP450IIE1 activity) was markedly inhibited by these inhibitors. In addition, conversion of radiolabeled AA ([14C]AA) by the indomethacin-treated kidney was reduced by CoCl2. Without indomethacin added, exogenous AA amplified vasoconstrictor responses whereas, with indomethacin added, AA attenuated vasoconstrictor responses. Clotrimazole inhibited both responses, suggesting involvement of a combination of cyclooxygenase-dependent and cyclooxygenase-independent cytP450 product(s). In Ca(2+)-free Krebs buffer containing 0.1 mM EGTA, vasoconstriction elicited by CaCl2 (2.5, 5, and 10 mg) was inhibited only moderately by clotrimazole 1 and 3 microM and alpha-naphthoflavone (alpha NF 2.5 and 5 microM), suggesting that the inhibitory effect of these agents may also proceed by an independent but less important mechanism involving interference with Ca2+ flux across membranes.(ABSTRACT TRUNCATED AT 250 WORDS)

There is no evidence of sexual dimorphism in platelet reactivity in the rat.

Changes in platelet reactivity (in vivo) to adenosine diphosphate (ADP) were evaluated in intact male and female rats, gonadectomized rats (with or without hormonal treatment with oestradiol or testosterone), feminized and androgenized rats (with or without hormonal treatment with oestradiol and testosterone). The 3',5'-cyclic adenosine monophosphate (cAMP) content of the respective platelet suspensions was also determined simultaneously. Changes recorded in platelet reactivity to ADP showed striking changes unreflective of endocrine status. No consistent concomitant changes were observed in the cAMP content of the respective platelet suspensions. The data obtained casts doubts on the presence of sexual dimorphism in platelet reactivity. A dependence of platelet reactivity on hormones per se as well as the second messenger role for cAMP in platelet reactivity also raises some doubts.

Cytochrome p450-dependent metabolites of arachidonic acid and renal function in the rat.

1. The present study examined whether renal cytochrome P450 (CYP450)-derived eicosanoids influence the pressure-natriuretic and haemodynamic responses to elevated renal perfusion pressure (RPP) in the rat. 2. Natriuresis and diuresis, as well as changes in renal blood flow (RBF) and glomerular filtration rate (GFR) following step-wise elevations in RPP from 75 to 125 mmHg were compared in control rats and in rats treated with 12,12-dibromodecenoic acid (DBDD; 2.5 mg/kg per h; n = 5), an inhibitor of omega/omega-1 hydroxylase, or miconazole (1.3 mg/kg per h; n = 7), an inhibitor of epoxygenase. 3. In control rats, sodium excretion (U(Na)V) and urine volume (UV) increased five-fold when RPP was increased from 75 to 125 mmHg, while RBF and GFR increased two-fold when RPP increased from 75 to 100 mmHg, with no further increase between 100 and 125 mmHg, the autoregulatory range. 4. Miconazole, but not DBDD, altered the pressure-natriuresis relationship, exaggerating the increases in U(Na)V and UV three- to four-fold when RPP was increased from 100 to 125 mmHg. 5. In contrast, DBDD eliminated the autoregulatory response because it abolished the plateau in RBF and GFR when RPP was increased from 100 to 125 mmHg, whereas miconazole was without effect. 6. These results suggest that CYP450-dependent omega/omega-1 hydroxylase metabolites of arachidonic acid contribute to vascular responses, while epoxygenase metabolites contribute to renal tubular responses to alterations in RPP in the rat.