Ag. Correia et al., Effects of renal medullary and intravenous norepinephrine on renal antihypertensive function, HYPERTENSIO, 35(4), 2000, pp. 965-970
Citations number
15
Categorie Soggetti
Cardiovascular & Respiratory Systems","Cardiovascular & Hematology Research
Increasing renal arterial pressure activates at least 3 antihypertensive me
chanisms: reduced renin release, pressure natriuresis, and release of a put
ative renal medullary depressor hormone. To examine the role of renal medul
lary perfusion in these mechanisms, we tested the effects of the infusion o
f norepinephrine, either infusion into the renal medullary interstitium or
intravenous infusion, on responses to increased renal arterial pressure in
pentobarbital-anesthetized rabbits. We used an extracorporeal circuit, whic
h allows renal arterial pressure to be set to any level above or below syst
emic arterial pressure. With renal arterial pressure initially set at 65 mm
Hg, intravenous and medullary interstitial norepinephrine (300 ng.kg(-1).m
in(-1)) similarly increased mean arterial pressure (by 12% to 17% of baseli
ne) and reduced total renal blood flow (by 16% to 17%) and cortical perfusi
on (by 13% to 19%), but only medullary norepinephrine reduced medullary per
fusion (by 28%). When renal arterial pressure was increased to approximate
to 160 mm Hg, in steps of approximate to 65 mm Hg, urine output and sodium
excretion increased exponentially, and plasma renin activity and mean arter
ial pressure fell. Medullary interstitial but not intravenous norepinephrin
e attenuated the increased diuresis and natriuresis and the depressor respo
nse to increased renal arterial pressure. This suggests that norepinephrine
can act within the renal medulla to inhibit these renal antihypertensive m
echanisms, perhaps by reducing medullary perfusion. These observations supp
ort the concept that medullary perfusion plays a critical role in the long-
term control of arterial pressure by its influence on pressure diuresis/nat
riuresis mechanisms and also by affecting the release of the putative renal
medullary depressor hormone.