Hemodynamic effects of chronic infusion of rANP in renal hypertensive rats

Natriuretic peptides buffer renin-dependent hypertension

The renin-angiotensin-aldosterone system and cardiac natriuretic peptides [atrial natriuretic peptide (ANP) and B-type natriuretic peptide (BNP)] are opposing control mechanisms for arterial blood pressure. Accordingly, an inverse relationship between plasma renin concentration (PRC) and ANP exists in most circumstances. However, PRC and ANP levels are both elevated in renovascular hypertension. Because ANP can directly suppress renin release, we used ANP knockout (ANP−/−) mice to investigate whether high ANP levels attenuate the increase in PRC in response to renal hypoperfusion, thus buffering renovascular hypertension. ANP−/− mice were hypertensive and had reduced PRC compared with that in wild-type ANP+/+ mice under control conditions. Unilateral renal artery stenosis (2-kidney, 1-clip) for 1 wk induced similar increases in blood pressure and PRC in both genotypes. Unexpectedly, plasma BNP concentrations in ANP−/− mice significantly increased in response to two-kidney, one-clip treatment, potentially compensating for the lack of ANP. In fact, in mice lacking guanylyl cyclase A (GC-A−/− mice), which is the common receptor for both ANP and BNP, renovascular hypertension was markedly augmented compared with that in wild-type GC-A+/+ mice. However, the higher blood pressure in GC-A−/− mice was not caused by disinhibition of the renin system because PRC and renal renin synthesis were significantly lower in GC-A−/− mice than in GC-A+/+ mice. Thus, natriuretic peptides buffer renal vascular hypertension via renin-independent effects, such as vasorelaxation. The latter possibility is supported by experiments in isolated perfused mouse kidneys, in which physiological concentrations of ANP and BNP elicited renal vasodilatation and attenuated renal vasoconstriction in response to angiotensin II.

Effects of glibenclamide on systemic and splanchnic haemodynamics in conscious rats

1. The effects of the sulphonylurea, glibenclamide (20 mg kg-1, i.v.), at a dose that blocks vascular potassium channels, on systemic and splanchnic haemodynamics (radioactive microspheres) were studied in conscious rats. 2. Glibenclamide significantly decreased cardiac index and hepatic artery blood flow while it significantly increased vascular resistance in systemic, portal and hepatic arterial territories. 3. In rats with suppressed cardiovascular reflexes, glibenclamide induced vasoconstriction in systemic, portal and hepatic arterial territories. 4. Intracerebroventricular administration of glibenclamide did not alter systemic or regional vascular tone. 5. Glibenclamide blunted the vasodilator effect of the potassium channel opener, diazoxide but not that of the L-type calcium channel blocker, nicardipine. 6. Another sulphonylurea, glipizide (20 mg kg-1, i.v.), induced significant systemic and splanchnic vasoconstriction. 7. Thus, the glibenclamide-induced blockade of vascular potassium channels caused a vasoconstriction in the systemic and splanchnic vascular beds. In these territories, therefore, the opening of glibenclamide-sensitive potassium channels might be responsible for a basal vasodilator tone.