We examined the role of Rho/Rho-kinase in renal afferent and efferent arteriolar tone induced by angiotensin (Ang) II, KCl and elevated renal arterial pressure (from 80 to 180 mm Hg), using isolated perfused rat hydronephrotic kidney. In the condition with no vasoconstrictor stimuli, Y-27632, a Rho-kinase inhibitor, dilated only afferent (from 11.6 ± 0.4 to 14.1 ± 0.5 µm) but not efferent arterioles (from 11.6 ± 0.2 to 12.6 ± 0.7 µm) at 10^–5 mol/l. During renal vasoconstriction by Ang II, Y-27632 restored the afferent arteriolar constriction (141 ± 10% reversal at 10^–5 mol/l), whereas the ability of Y-27632 to inhibit the Ang II-induced efferent arteriolar constriction was diminished (73 ± 7% reversal). A similar action was observed with fasudil, another Rho-kinase inhibitor. Furthermore, Y-27632 impaired myogenic afferent arteriolar constriction, with 117 ± 17% inhibition at 10^–5 mol/l. The inhibition by Y-27632 of the myogenic vasoconstriction was almost the same as that of the Ang II-induced tone of this vessel type. However, Y-27632 had a modest effect on KCl-induced vasoconstriction of afferent arterioles. In conclusion, the present study demonstrates a predominant role of Rho/Rho-kinase in mediating the basal and Ang II-induced tone of afferent, but not efferent, arterioles. Furthermore, the role of Rho/Rho-kinase in afferent arteriolar constriction differs, with a substantial contribution to Ang II-induced and myogenic constriction but a minimal role in depolarization-induced constriction. Since Ang II-induced, KCl-induced and myogenic constriction of afferent arterioles require calcium entry through voltage-dependent calcium channels, the interaction between Rho/Rho-kinase and the calcium entry pathway may determine the afferent arteriolar tone induced by these stimuli.

To assess cellular mechanisms mediating afferent (AA) and efferent arteriolar (EA) constriction by angiotensin II (AngII), experiments were performed using isolated perfused hydronephrotic kidneys. In the first series of studies, AngII (0.3 nM) constricted AAs and EAs by 29 Ϯ 3 ( n ϭ 8, P Ͻ 0.01) and 27 Ϯ 3% ( n ϭ 8, P Ͻ 0.01), respectively. Subsequent addition of nifedipine restored AA but not EA diameter. Manganese (8 mM) reversed EA constriction by 65 Ϯ 9% ( P Ͻ 0.01). In the second group, the addition of N -ethylmaleimide (10 M), a Gi/Go protein antagonist, abolished AngIIinduced EA ( n ϭ 6) but not AA constriction ( n ϭ 6). In the third series of experiments, treatment with 2-nitro-4-carboxyphenyl-N , N -diphenyl-carbamate (200 M), a phospholipase C inhibitor, blocked both AA and EA constriction by AngII ( n ϭ 6 for each). In the fourth group, thapsigargin (1 M) prevented AngII-induced AA constriction ( n ϭ 8) and attenuated EA constriction (8 Ϯ 2% decrease in EA diameter at 0.3 nM AngII, n ϭ 8, P Ͻ 0.05). Subsequent addition of manganese (8 mM) reversed EA constriction. Our data provide evidence that in AAs, AngII stimulates phospholipase C with subsequent calcium mobilization that is required to activate voltage-dependent calcium channels. Our results suggest that AngII constricts EAs by activating phospholipase C via the Gi protein family, thereby eliciting both calcium mobilization and calcium entry. ( J.

Abstract-It has not been examined whether the pressure-natriuresis response is altered in the insulin-resistant condition.Furthermore, despite an important role of nitric oxide (NO) in modulating pressure-natriuresis, no investigations have been conducted assessing the renal interstitial NO production in insulin resistance. The present study examined whether pressure-natriuresis was altered in insulin-resistant obese Zucker rats (OZ) and assessed the cortical and medullary nitrate/nitrite (NOx) levels with the use of the renal microdialysis technique. In OZ, serum insulin/glucose ratio (23.0Ϯ4.0ϫ10 Ϫ8 , nϭ9) and blood pressure (119Ϯ3 mm Hg) were greater than those in lean Zucker rats (LZ; 7.0Ϯ1.9ϫ10Ϫ8 and 103Ϯ4 mm Hg, nϭ9). The pressure-natriuresis curve in OZ was shifted to higher renal perfusion pressure (RPP), and the slope was blunted compared with that in LZ (0.073Ϯ0.015 vs 0.217Ϯ0.047 Eq/min kidney weight/mm Hg, PϽ0.05). The basal renal NOx level was reduced in OZ (cortex, 4.032Ϯ0.331 mol/L; medulla, 4.329Ϯ0.515 mol/L) compared with that in LZ (cortex, 7.315Ϯ1.102 mol/L; medulla: 7.698Ϯ0.964 mol/L). Furthermore, elevating RPP increased the medullary NOx in LZ, but this pressure-induced response was lost in OZ. Four-week treatment with troglitazone, an insulin-sensitizing agent, improved hyperinsulinemia, systemic hypertension, and basal renal NOx levels (cortex, 5.639Ϯ0.286 mol/L; medulla, 5.978Ϯ0.284 mol/L), and partially ameliorated the pressure-natriuresis curves; the slope of pressure-natriuresis curves and elevated RPP-induced NOx, however, were not corrected. In conclusion, our study suggests that insulin resistance is closely associated with abnormal pressurenatriuresis and hypertension. These deranged renal responses to insulin resistance are most likely attributed to impaired medullary NO production within the medulla. (Hypertension. 1999;33:1470-1475.) Key Words: natriuresis Ⅲ nitric oxide Ⅲ insulin resistance Ⅲ hypertension Ⅲ troglitazone Ⅲ microdialysis Ⅲ obesity A growing body of evidence has been accumulated demonstrating that insulin resistance is an important risk factor to the development of cardiovascular diseases, including hypertension. 1-3 Although the pathophysiology of hypertension in insulin resistance remains fully undetermined, several investigations suggest that the kidney plays an important role in the development of hypertension. 4 Thus renal sodium homeostatic mechanisms are reported to be impaired in obesity, in which insulin resistance conceivably develops. 5 Furthermore, we have recently demonstrated that the pressure-natriuresis relation is impaired in Wistar fatty rats, manifesting obesity, hyperinsulinemia, and hyperglycemia. 6 Thus balanced sodium homeostasis is attained only at a higher renal perfusion pressure (RPP) in these obese rats than in normal littermates. The altered relation between RPP and renal sodium excretion is characteristic of several models of experimental hypertension, including spontaneously hypertensive rats and Dahl salt-sensitive rats 7,8 and is ...

Experiments were performed to evaluate the hypothesis that opening of Ca(2+)-activated K(+) channels (BK(Ca) channels) promotes juxtamedullary arteriolar dilation and curtails constrictor responses to depolarizing agonists. Under baseline conditions, afferent and efferent arteriolar lumen diameters averaged 23.4 +/- 0.9 (n = 36) and 22.8 +/- 1.1 (n = 13) microm, respectively. The synthetic BK(Ca) channel opener NS-1619 evoked concentration-dependent afferent arteriolar dilation. BK(Ca) channel blockade (1 mM tetraethylammonium; TEA) decreased afferent diameter by 15 +/- 3% and prevented the dilator response to 30 microM NS-1619. ANG II (10 nM) decreased afferent arteriolar diameter by 44 +/- 4%, a response that was reduced by 30% during NS-1619 treatment; however, TEA failed to alter afferent constrictor responses to either ANG II or arginine vasopressin. Neither NS-1619 nor TEA altered agonist-induced constriction of the efferent arteriole. Thus, although the BK(Ca) channel agonist was able to curtail afferent (but not efferent) arteriolar constrictor responses to ANG II, BK(Ca) channel blockade did not allow exaggerated agonist-induced arteriolar constriction. These observations suggest that the BK(Ca) channels evident in afferent arteriolar smooth muscle do not provide a prominent physiological brake on agonist-induced constriction under our experimental conditions.

Abstract-Although calcium antagonists exert preferential vasodilation of renal afferent arterioles, we have recently demonstrated that nilvadipine and efonidipine, possessing both L-type and T-type calcium channel blocking action, reverse the angiotensin (Ang) II-induced afferent and efferent arteriolar constriction. In the present study, we investigated the role of T-type calcium channels in mediating the Ang II-induced efferent arteriolar tone using the selective T-type calcium channel blocker mibefradil. Isolated perfused hydronephrotic rat kidneys were used for direct visualization of renal microcirculation. Administration of Ang II (0.3 nmol/L) caused marked constriction of afferent (from 13.5Ϯ0.6 to 9.2Ϯ0.6 m, PϽ0.01, nϭ6) and efferent (from 11.5Ϯ1.0 to 7.4Ϯ0.7 m, PϽ0.01, nϭ5) arterioles. Mibefradil (1 mol/L) dilated both vessels, with 82Ϯ11% and 72Ϯ7% reversal of afferent and efferent arterioles, respectively. Similarly, nickel chloride (100 mol/L) caused dilation of both arterioles, similar in magnitude in afferent (68Ϯ10%, nϭ7) and efferent (80Ϯ7%, nϭ7) arterioles. To eliminate the possibility that the mibefradil-induced dilation was mediated by L-type channel blockade, mibefradil was administered in the presence of nifedipine (1 mol/L). Thus, nifedipine caused modest efferent arteriolar dilation (30Ϯ6% reversal, nϭ9), and subsequent addition of mibefradil elicited further dilation of this vessel (80Ϯ4%, PϽ0.01 versus nifedipine). Furthermore, mibefradil reversed the Ang II-induced efferent arteriolar constriction even in the presence of nifedipine and phentolamine. These findings demonstrate that T-type calcium antagonists markedly dilate the Ang II-induced efferent arteriolar constriction, but the action is not mediated by inhibition of catecholamine release. This potent activity would contribute to the efferent arteriolar response to nilvadipine and efonidipine and may offer benefit in light of glomerular hemodynamics. Key Words: mibefradil Ⅲ afferent arteriole Ⅲ efferent arteriole Ⅲ T-type calcium channel Ⅲ calcium antagonists Ⅲ renal microcirculation A growing body of evidence has accrued that the calcium antagonist, a blocker of L-type voltage-dependent calcium channels, exerts potent renal vasodilatory action in the face of systemic hypotension. 1 This unique action is frequently accompanied by an elevation in glomerular filtration rate and filtration fraction. 2,3 To elucidate the mechanism for calcium antagonist-induced alterations in renal hemodynamics, several lines of recent investigations indicate that the calcium antagonist elicits predominant dilation of the afferent arteriole but modest action on the efferent arteriole. 4 -6 These observations are endorsed by the fact that L-type voltagedependent calcium channels prevail functionally in the afferent arteriole but are silent in the efferent arteriole. 7,8 Such a preferential role of voltage-dependent calcium channels in the afferent arteriole thus favors the elevation in glomerular filtration rate by the calcium antagonist. 2,3 In contra...