Proximal Renal Tubular Pressure-Natriuresis-Relation in Essential Hypertensives Following Acute Vasodilatation

Abstract

Blood pressure (BP) and excretory function including lithium clearance were investigated during waterloading and constant infusion of ¹³¹I-hippuran and ¹²⁵I-iothalamate for measurement of renal haemodynamics in 8 untreated essential hypertensives (mean BP ± SD: 169 ± 14/107 ± 6 mmHg) before and after vasodilatation with an i.v. bolus of the potassium-channel opener, pinacidil, 0.01 mg/kg. Systolic BP (-7 ± 4%; p <0.05) and diastolic BP (-13 ± 8%;p < 0.01) decreased significantly and heart rate increased (11 ± 8%; p<0.01). Clearance (C) of lithium, sodium, urinary flow rate, potassium and absolute distal reabsorption of sodium all fell significantly. The changes of these variables were significantly correlated with the fall in BP (CLi:r = 0.92, CNa: r = 0.85, V: r = 0.81, CK:r = 0.84), despite no significant changes in renal haemodynamic parameters: glomerular filtration rate, renal plasma flow and renal vascular resistance. A proximal tubular effect was also indicated by a fall in Curic acid and fractional Curic acid. In conclusion, vasodilatation in essential hypertensives following administration of the potassium channel opener, pinacidil, induces a fall in blood pressure with a corresponding fall in fractional proximal tubular excretion of sodium and output of sodium and water from proximal to distal tubular segments, proposing an acute proximal tubular pressure-natriuresis relation.

Key Words:

• hypertension
• pinacidil
• potassium channel opener
• antinatriuresis
• antidiuresis
• lithium clearance
• renal function
• vasodilatation
• uric acid
• renal tubular function