Nitric oxide (NO) induces vasodilatatory, antiaggregatory, and antiproliferative effects in vitro. To delineate potential beneficial effects of NO in preventing vascular disease in vivo, we generated transgenic mice overexpressing human erythropoietin. These animals induce polyglobulia known to be associated with a high incidence of vascular disease. Despite hematocrit levels of 80%, adult transgenic mice did not develop hypertension or thromboembolism. Endothelial NO synthase levels, NO-mediated endothelium-dependent relaxation and circulating and vascular tissue NO levels were markedly increased. Administration of the NO synthase inhibitor N G -nitro-L-arginine methyl ester (L-NAME) led to vasoconstriction of peripheral resistance vessels, hypertension, and death of transgenic mice, whereas wild-type siblings developed hypertension but did not show increased mortality. L-NAMEtreated polyglobulic mice revealed acute left ventricular dilatation and vascular engorgement associated with pulmonary congestion and hemorrhage. In conclusion, we here unequivocally demonstrate that endothelial NO maintains normotension, prevents cardiovascular dysfunction, and critically determines survival in vivo under conditions of increased hematocrit.

Connexins have been hypothesized to play an important role in intercellular communication within the vascular wall and may provide a mechanistic explanation for conduction of vasomotor responses. To test this hypothesis, we studied the transmission of vasomotor responses in the intact skeletal muscle microcirculation of connexin40-deficient mice (Cx40(-/-)). Arterioles were locally stimulated with hyperpolarizing dilators (acetylcholine [ACh] as well as bradykinin [Bk]) or depolarizing K(+) solution, and the resulting changes in diameter were measured using a videomicroscopy technique at the site of application and up to 1.32 mm upstream. Arterial pressure was elevated 25% in Cx40(-/-) mice (94+/-5 versus 75+/-4 mm Hg). Vessels selected for study had equivalent basal diameter and vasomotor tone in both genotypes of mice. Vasomotion was present in small arterioles of both genotypes, but its intensity was exaggerated in Cx40(-/-) mice. ACh and Bk induced dilation (33% and 53%, respectively, of maximal response) at the site of application that was of similar magnitude in both genotypes. These dilations were observed to spread upstream within <1 second without significant attenuation in Cx40(+/+) mice. However, spreading was severely attenuated in Cx40(-/-) animals (11+/-4% versus 35+/-7% with ACh and 38+/-5% versus 60+/-7% with Bk in Cx40(-/-) and Cx40(+/+), respectively; P<0.05). In contrast, conducted vasoconstrictions, induced by K(+) solution decreased equally with distance in both genotypes. These results support a significant role for Cx40 in vascular intercellular communication. Our observations indicate that Cx40 is required for normal transmission of endothelium-dependent vasodilator responses and may underlie altered vasomotion patterns.

Abstract-Renin secretion and synthesis in renal juxtaglomerular cells are controlled by short feed back loops involving angiotensin II and the intrarenal blood pressure. The operating mechanisms of these negative feed back regulators are widely unknown, except for the fact that both require calcium to exert their inhibitory action. We here show that in the absence of connexin40 (Cx40), which form gap junctions between juxtaglomerular and endothelial cells, the negative control of renin secretion and synthesis by angiotensin II and by intravasal pressure is abrogated, while the regulation by salt intake and ␤-adrenergic stimulation is maintained. Renin secretion from Cx40-deficient kidneys or wild-type kidneys treated with the nonselective gap junction blocker 18␣-glycyrrhetinic acid (10 mol/L) resembles the situation in wild-type kidneys in the absence of extracellular calcium. This disturbed regulation is reflected by an enhanced plasma renin concentration despite an elevated blood pressure in Cx40-deficient mice. These findings indicate that Cx40 connexins and likely intercellular communication via Cx40-dependent gap junctions mediate the calcium-dependent inhibitor effects of angiotensin II and of intrarenal pressure on renin secretion and synthesis. Because Cx40 gap junctions are also formed between renin producing cells and endothelial cells our finding could provide additional information to suggest that the endothelium may be strongly involved in the control of the renin system. (Circ Res. 2007;100:556-563.)