Effect of nitric oxide and renal nerves on renomedullary haemodynamics in SHR and Wistar rats, studied with laser Doppler technique

Abstract

The threshold for activation of the humoral renal antihypertensive system, presumably residing in the renomedullary interstitial cells (RIC), is substantially reset upwards in the spontaneously hypertensive rat (SHR). Depressor reactions, normally elicited by an increased renal perfusion pressure, can be inhibited either by high frequency renal nerve stimulation or blockade of nitric oxide synthesis, i.e. manoeuvres decreasing renal blood flow at this high perfusion pressure. The present study was designed to explore the effects on regional renal haemodynamics of blocking NO synthesis with N-omega-nitro-L-arginine (L-NNA) in chloralose anaesthetized SHR and Wistar rats. Mean arterial blood pressure (MAP), heart rate (HR), renal blood flow (RBF), cortical blood perfusion (CBP) and papillary blood perfusion (PBP) were measured in renally innervated and denervated SHR (Si n = 8, Sd n = 8) and in Wistar rats (Wi n = 10, Wd n = 10). An innervated non-treated Wistar group served as control (Ci n = 12). The laser Doppler technique was used to record CBP and PBP. MAP increased in all groups receiving L-NNA while HR, RBF and CBP simultaneously decreased. The relative decreases in RBF were more marked into the two SHR groups than in the corresponding Wistar groups. After L-NNA PBP also decreased in all four groups despite the increased MAP and more so in the Si group; Wi -19 +/- 8 (P < 0.05), Wd -17 +/- 6 (P = 0.07), Si -50 +/- 9 (P < 0.01) and Sd -25 +/- 9% (P < 0.05). We conclude that NO is important for maintaining PBP especially in SHR. The more marked decrease in PBP in the innervated SHR suggests a NO/renal nerve interaction in the control of renomedullary blood flow in SHR. This finding may be of importance for the regulation of the humoral renal depressor mechanism.

Mechanisms underlying the antihypertensive functions of the renal medulla

“…2000). These observations in the rabbit extracorporeal circuit model were consistent with previous observations in the rat cross‐circulation model, showing that manoeuvres that reduce MBF such as blockade of NO synthase (Bergström et al. 1996, Cowley et al.…”

The role of nitric oxide in the spatial heterogeneity of basal microvascular blood flow in the rat diaphragm

“…However, after normalization of Q LDF to 100% at baseline, the LDF at a fixed probe position seems a very promising technique for measuring the acute effects of pathophysiological and pharmacological stimuli [6,18,19]. Similarly, local pharmacological studies using LDF have also been performed in rat kidney, human skin, and human nasal mucosa [16,[20][21][22].…”

Changes in mean arterial pressure predict degranulation of renomedullary interstitial cells

“…Studies using extracorporeal circuits have suggested that increases in renal perfusion pressure (RPP) concomitant with increases in renal medullary blood flow (MBF) promote identical antihypertensive responses as observed following the infusion of fragments of RMIC 10–12 . These studies suggest that the trigger for the release of RMIC depressor substances is an increase in RPP and MBF.…”

“…Thus far, however, no study has examined directly the changes in RPP and MBF on RMIC granule content. Furthermore, the medullary depressor activity can be prevented by blockade of angiotensin (Ang) II (via converting‐enzyme inhibition) 3,10 . These studies suggest that alterations in the activity of agents controlling systemic blood pressure also affect the antihypertensive property of the renal medulla.…”