Angiotensin II type 1 receptor, but no type 2 receptor, interferes with the insulin-induced nitric oxide production in HUVECs.

OBJECTIVE: Two subtypes of angiotensin II (ATII) receptor have been defined on the basis of their differential pharmacological and biochemical properties: ATII-type1 receptors (AT(1)-R) and ATII-type2 receptors (AT(2)-R). It has been hypothesized that part of the protective effects on the cardiovascular system of AT(1)-R blockers is mediated by an ATII-mediated overstimulation of AT(2)-R. We hypothesized that the inhibition of AT(1)-R has a stronger impact on insulin-induced nitric oxide (NO) production than ATII-mediated overstimulation of AT(2)-R. Therefore we studied the effect of the inhibition of AT(1)-R and AT(2)-R on ATII-mediated actions in Human Umbilical Vein Endothelial Cells (HUVECs).

METHODS: We analyzed the phosphorylation state of IRS1 at Ser(616) and Ser(312) and on tyrosines after preincubation with PD123319, an inhibitor of AT(2)-R, alone and in combination with losartan, an inhibitor of AT(1)-R. In addition we measured eNOS and Akt activation through the evaluation of their phosphorylation at Ser(1177) and Ser(473) sites respectively.

RESULTS: ATII induces IRS-1 phosphorylation at Ser(312) and Ser(616) through the activation of JNK and ERK 1/2, resulting in the inhibition of the insulin-induced phosphorylation of IRS1 tyrosines, Akt and eNOS. Treatment of HUVECs with AT(1)-R inhibitor restored the insulin signaling leading to NO production, whereas AT(2)-R inhibitor did not have effects on NO production in presence of ATII.

CONCLUSION: Our results demonstrate that in presence of AT(1)-R antagonist, the AT(2)-R blockage does not modify the effect obtained with the AT(1)-R inhibition alone. Therefore, a possible positive role of an AT(2)-R overstimulation in condition of AT(1)-R antagonism seems to be irrelevant.