Structurally based changes of renal vascular reactivity in spontaneously hypertensive and two-kidney, one-clip renal hypertensive rats, as compared with kidneys from uninephrectomized and intact normotensive rats.

Renal vascular beds from spontaneously hypertensive rats (SHR) at different stages of hypertension, from two-kidney, one-clip renal hypertensive rats (RHR) and from uninephrectomized rats (UNR) were in constant-flow, paired perfusions compared with kidneys from normotensive control rats (NCR) concerning vascular smooth muscle sensitivity to noradrenaline (NA) and resistance vessel reactivity, as reflected by the position, respectively the shape, of the dose-resistance response curves. None of these kidney variants differed significantly from controls concerning smooth muscle sensitivity to NA during in vitro perfusion. However, both the steepness and maximal pressor responses of the renal resistance curves increased progressively with age in SHR, to become ultimately much enhanced when related to age-matched controls. It suggests a well preserved smooth muscle contractility and a progressive elevation of the average wall/lumen ratio in the SHR renal resistance vessels. Also the untouched, "high-pressure" RHR kidneys showed increased vascular reactivity, while it was somewhat reduced in the clipped, "low-pressure" RHR kidneys and unchanged in the hypertrophied but normotensive UNR kidneys. These results, when combined with other findings concerning renal vascular design (Göthberg & Folkow 1982a), illustrate how the renal resistance vessels readily adapt structurally to hypertension, hypotension, kidney hypertrophy and also with age, and in directions which tend to chronically "autoregulate" glomerular blood supply and filtration.