Endothelial nitric oxide synthase protein is reduced in the renal medulla of two-kidney, one-clip hypertensive rats

Objective We studied endothelial nitric oxide synthase (eNOS) expression in the kidneys of two-kidney, one-clip renal hypertensive rats (2K1C) before and after removal of the clip (unclipping, UC). We hypothesised that the ha emodynamic changes induced by 2K1C and UC would change eNOS expression in t he two kidneys. Methods Six weeks after inducing 2K1C, mean arterial pressure (MAP) was mea sured in conscious rats and hypertension reversed by UC. Left and right kid ney eNOS protein in cortex and outer medulla was semi-quantified using immu noblotting. Groups were; normotensive (n = 10), 2K1C (n = 10), 3 h (n = 10) , 48 h (n = 7) and 4 weeks (n = 7) after UC. The effect of 7 days of aldost erone or angiotensin II (Ang II) infusion on medullary eNOS protein was tes ted as well as the effect Of L-NAME (nitric oxide (NO) synthase inhibitor) on medullary blood flow (MBF) in anaesthetized 2K1C. Results UC reduced MAP from 178 +/- 5 to 134 +/- 3 mmHg after 3 h and norma lized MAP at 48 h and 4 weeks. The medulla from 2K1C kidneys contained abou t 33% less eNOS protein compared with normotensive kidneys (P < 0.05). This difference was still evident at 3 h (P < 0.05), but completely reversed at 48 h and 4 weeks after UC. Similar levels of eNOS expression were seen in the left and right kidney at all time points. Cortical eNOS was increased i n kidneys from 2K1C. Neither Ang I I nor aldosterone affected eNOS expressi on in the medulla. MBF was under similar influence of NO in 2K1C compared w ith normotensive kidneys. Conclusions 2K1C is associated with reduced levels of eNOS protein in the r enal medulla of both clipped and contralateral kidney. eNOS expression in r ight and left kidney was not changed despite expected large changes in haem odynamics of the two kidneys. The reduced level of eNOS may be associated w ith a reduction in MBF and thus be of patho-physiological importance in ren ovascular hypertension. (C) 2001 Lippincott Williams & Wilkins.