Blockade of Na+/H+ exchanger contracts the portal vein of spontaneously hypertensive and Wistar Kyoto rats.

ABSTRACT

It has been claimed that the activity of Na+/H+ exchanger (NHE) is altered in spontaneously hypertensive rats (SHR) suggesting a possible role for it in the pathophysiology of hypertension. The purpose of this study has been to investigate the effect of blockade of NHE on the noradrenaline (NA) and 26K+ induced tone and on the recovery of tone from acid induced contractions in the portan vein of spontaneously hypertensive rats (SHR) as compared to their controls of Wistar Kyoto rats (WKY). Blockade of NHE by 10(-4) dimethylamiloride (DMA) raised the tone of NA and 26K+ activated preparation of both strains, the contractions being higher with NA activation. Total blockade of NHE by replacement of Na in solution with N-methy-D-Glucamine (NMDG) raised the tone of the NA activated preparations by 45+/-10%, n=8, P<0.01 and 33+/-4%, n=12, P < 0.01 in SHR and WKY respectively. The time for 50% relaxation from NH4Cl washout contraction was significantly prolonged by 10(-5) and 10(-4) M DMA in both strains under NA or 26K+ activation. DMA effect was greater on NA than on 26K+ activated preparations, and was not significantly different when comparing SHR to WKY results. In conclusion the results reported in this study indicate that NHE has similar activity in WKY and SHR portal veins and that its blockade contracts both preparations. Therefore, it is unlikely that increased NHE activity, acting directly on vascular smooth muscle tone, could be a primary cause for hypertension.