Rhokinase Mediates Increased Vascular Reactivity in Hypertensive Rat Lungs

To test if Rho-kinase activity also plays a role in increased vasoconstrictor reactivity in chronically hypoxic hypertensive lungs, we measured pressor responses to KCl (a receptor-independent and voltage-gated influx-mediated vasoconstrictor) in normotensive and chronically hypoxic hypertensive physiological salt solution (PSS)-perfused lungs with and without Y-27632 pretreatment (37). The vasoconstrictor response to KCl was augmented in hypertensive lungs, and the augmentation was eliminated by Y-27632 (Fig. 4A). In contrast, the Rho-kinase inhibitor caused minimal blunting of the smaller KCl vasoconstriction in normotensive lungs, indicating that Y-27632 had little, if any, effects on membrane depolarization and voltage-gated Ca2+ influx, which is consistent with the effects of Y-27632 in isolated rat pulmonary arteries (50). KCl vasoconstriction in both groups of lungs was blocked by 1 ^M nifedipine (not shown). Collectively, these results suggest that Rho/Rho-kinase signaling increases pulmonary vascular Ca2+ sensitivity and potentiates vasoconstriction to voltage-gated Ca2+ influx in HPH.

ET-1 and both ETA and ETB receptors are upregulated in chronically hypoxic rat lungs (6). To test if increased endogenous ET-1 activity contributes to the augmented vasoconstrictor response to KCl, we examined effects of pretreatment with the ETa receptor blocker BQ-123 (Fig. 4A) and the dual ETWB blocker J-104132 on KCl vasoconstriction (42). The augmented KCl response in hypertensive lungs was reduced equally by ETa and ETA/B receptor blockade. This suggested that activation of ETA but not ETB receptors played a role in the increased vasoreactivity to KCl; a finding in keeping with evidence that acute ET-1 -induced Ca2+ sensitization of rat normotensive pulmonary artery involves ETA but not ETb receptor stimulation (14). ETA receptor blockade was not as effective as inhibition of Rho-kinase in reducing the exaggerated response to KC1 (Fig. 4), and further attenuation by the combination of BQ-123 plus the 5-HT1B/1D receptor antagonist GR-127935 (42) suggests that 5-HT, and possibly other endogenous vasoconstrictors, are also involved in stimulating the Rho-kinase-mediated sensitization.

Veh Y-27 BQ

fell Y-27 BQ

Figure 4. A: The Rho-kinase inhibitor Y-27632 (Y-27,10 nM) markedly inhibits augmented KC1 (40 mM) vasoconstriction in hypoxic hypertensive rat lungs (HL). In contrast, Y-27632 has little effect on the smaller KC1 response in normotensive lungs (NL). The ETA receptor blocker BQ-123 (BQ, 5 fiM) also causes some inhibition of KC1 vasoconstriction in hypertensive lungs, but has no effect in normotensive lungs. *P<0.05 vs. respective vehicle (Veh) control value (n=4-8/group). B: While nifedipine (Nif, 10 nM) has little effect, Y-27632 (10 ^M) almost completely reverses the vasoconstriction elicited by inhibiting NOS (200 yM nitro-L-arginine, NLA) in hypoxic hypertensive rat lungs. In comparison, the MLCK inhibitor ML-9 (100 |iM) causes only partial reversal of the NLA vasoconstriction (* P<0.05; n=3/group). These observations suggest that increased vasoconstrictor reactivity of hypoxia-induced hypertensive rat lungs is due largely to Rho-kinase-mediated Ca2+ sensitization, and that the apparent activation of Rho/Rho-kinase signaling is mediated partly by endogenous ET-1-induced activation of ETA receptors and

We have previously observed that normoxia-ventilated hypertensive lungs from chronically hypoxic rats produce increased amounts of NO (53), and that acute inhibition of NO synthesis by nitro-L-arginine (NLA) elicits a marked sustained vasoconstriction that is mediated partly by endogenous ET-1 (41, 46, 48). We investigated if this NLA-induced vasoconstriction also involves Rho-kinase-mediated Ca2+ sensitization by comparing the vasodilator effects of nifedipine and Y-27632 (37). The Rho-kinase inhibitor, but not nifedipine, caused complete reversal of the NLA vasoconstriction (Fig. 4B). Similar experiments showed that the MLCK inhibitor ML-9 elicited only partial reversal of the NLA vasoconstriction (Fig. 4B). Thus, Rho-kinase-mediated Ca2+ sensitization rather than solely Ca27calmodulin-induced activation of MLCK, is apparently essential for the marked NLA-induced vasoconstriction in the hypertensive lungs (41). Because we have previously found that Ca2+-free perfusion of hypertensive lungs prevents the NLA vasoconstriction, increased cytosolic [Ca2+] and activation of MLCK may be required for the onset of the response (46, 48).

Figure 5. A: Treatment of rats with the Rho-kinase inhibitor Y-27632 (40 mg/kg/day, sq) during 2 weeks of exposure to chronic hypoxia reduces development of pulmonary hypertension as reflected in decreased mean pulmonary artery pressure (PAP) and RV hypertrophy (RV/LV+S). N are normoxic controls and H and H+Y are hypoxic rats treated, respectively, with either vehicle or Y-27632 (*P<0.05 vs. respective H value; n=3/group). B: Western blot of eNOS in lungs of vehicle- and Y-27632-treated chronically hypoxic mice. It appears that treatment with Y-27632 augments the upregulation of eNOS expression in hypoxic lungs. These observations indicate that Rho/Rho-kinase signaling plays a role in the pathogenesis of HPH, and that this might involve

Figure 5. A: Treatment of rats with the Rho-kinase inhibitor Y-27632 (40 mg/kg/day, sq) during 2 weeks of exposure to chronic hypoxia reduces development of pulmonary hypertension as reflected in decreased mean pulmonary artery pressure (PAP) and RV hypertrophy (RV/LV+S). N are normoxic controls and H and H+Y are hypoxic rats treated, respectively, with either vehicle or Y-27632 (*P<0.05 vs. respective H value; n=3/group). B: Western blot of eNOS in lungs of vehicle- and Y-27632-treated chronically hypoxic mice. It appears that treatment with Y-27632 augments the upregulation of eNOS expression in hypoxic lungs. These observations indicate that Rho/Rho-kinase signaling plays a role in the pathogenesis of HPH, and that this might involve

Was this article helpful?

0 0
Reducing Blood Pressure Naturally

Reducing Blood Pressure Naturally

Do You Suffer From High Blood Pressure? Do You Feel Like This Silent Killer Might Be Stalking You? Have you been diagnosed or pre-hypertension and hypertension? Then JOIN THE CROWD Nearly 1 in 3 adults in the United States suffer from High Blood Pressure and only 1 in 3 adults are actually aware that they have it.

Get My Free Ebook


Post a comment