Enhanced myogenic responsiveness of renal interlobular arteries in spontaneously hypertensive rats.

Abstract

We recently demonstrated that the interlobular artery (ILA) constricts in response to elevating renal arterial pressure (RAP), suggesting that the ILA contributes to renal autoregulation. In the present study, we examined the segmental myogenic responsiveness of the ILA in kidneys from Wistar-Kyoto (WKY) rats and spontaneously hypertensive rats (SHR). The tapered nature of the ILA allowed us to characterize the regional responsiveness, using the basal diameter to define segments as either proximal (greater than 60 fim), intermediate ( 2 We have previously demonstrated that myogenic afferent arteriolar vasoconstriction is reset to higher renal arterial pressure (RAP) levels in spontaneously hypertensive rats (SHR).3 Although the afferent arteriole is primarily responsible for both acute 4 -5 and chronic 6 ' 7 adaptations to elevated RAP, the interlobular artery (ILA) may also contribute to renal autoregulation. 8 ' 9 The involvement of the ILA in chronic adaptations of the renal vasculature to hypertension has not been previously examined.

Biophysical Signals Underlying Myogenic Responses in Rat Interlobular Artery

“…10 In accordance, recent investigations using various approaches demonstrated that increasing RAP elicited ILA constriction. 5,8,18,22 However, the mechanisms mediating autoregulatory responses of ILAs were not fully characterized. Furthermore, differing mechanisms may underlie myogenic responses in distinct segments of ILAs.…”

“…17 Three separate segments, Ϸ10 to 50 m in length, were chosen from an ILA. As described previously, 18 the segments of ILAs were divided into 3 groups according to their basal diameters at 80 mm Hg: proximal(Ͼ60 m), intermediate (40 to 60 m), and distal (Ͻ40 m) ILAs.…”

Arterial Myogenic Properties of the Spontaneously Hypertensive Rat

“…The myogenic responses of SHR and WKY afferent arterioles were similar in amplitude but myogenic behaviour was shifted to higher pressures in the SHR. The same group (Hayashi et al 1992) also demonstrated that myogenic responsiveness is enhanced in the intermediate segment of the interlobular artery of SHR kidneys mediated by enhanced calcium channel activity; the increased myogenic activity of the SHR renal vessels might act to prevent or attenuate elevated glomerular pressure. As described by Guyton (1987) renal vascular resistance must increase to permit the development of hypertension otherwise a natriuretic response will rapidly normalise blood pressure.…”

Endothelial dysfunction augments myogenic arteriolar constriction in hypertension.

“…Interestingly, whereas in renal arteries of SHR myogenic tone was enhanced, 34 in Dahl (salt-sensitive) hypertensive rats renal microvessels showed impaired myogenic responses, 33 indicating that different mechanisms are present in different forms of hypertension.…”