The Interaction Of Renin Angiotensin And Sympathetic Nervous Systems On Renal Haemodynamics In Hypertension
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Date
2005-09
Authors
Wong, Kuan Yau
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Abstract
The renin angiotensin (RAS) and sympathetic nervous system (SNS) are
closely interrelated and are involved in the maintenance of blood pressure and
body fluid homeostasis. This study examined the role of the RAS and SNS at
the peripheral levels in normo and hypertension in the control of renal
haemodynamics and to assess any alterations in renal haemodynamics after
chemical sympathectomy. For this purpose, WKY rats, SHR, 2K1C Goldblatt
and DOCA-salt hypertensive rats were utilised. Chemical sympathectomy was
carried out by the administration of 6-0HDA intraperitoneally to animals at a
dose of 50mg/kg on day 1, 100 mg/kg on day 2 and 50mg/kg on days 5 and 8.
Perindopril was given orally at a dose of 0.2 mg/kg for 7 days. In
haemodynamics study, the animal was anaesthetized (60 mg/kg IP, sodium
pentobarbitone), followed by cannulation of carotid artery & jugular vein and
isolation of renal artery. Renal blood flow (RBF) was measured using
electromagnetic flow probe. Arterial blood pressure was measured using
pressure transducer. All data were recorded in computerized data acquisition
system. Data was expressed as mean ± S.E.M and compared by 2 way ANOVA
followed by Bonferroni post hoc with the significance level of 5%. A substantial
change was observed in the sympathectomized rats in terms of
haemodynamics. There was a marked reduction of blood pressure in
sympathectomized hypertensive rats. However, there was no significant change
in renal blood flow after sympathectomy. Without ACE inhibition, noradrenaline
and phenylephrine were found to exert a significant difference (p<0.05) in
peripheral and renal haemodynamics of both of normo- and hypertensive rats
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except in DOCA-salt models when administered peripherally and intrarenally.
However, a significant change (p<O.05) was observed in blood pressure to
peripheral methoxamine in both normo- and hypertensive rats. Moreover, when
administered intrarenally it caused a significant reduction in RBF only, in both
normo-and hypertensive rats. Angiotensin II, peripherally and intrarenally
caused significant change (p<O.05) in peripheral and renal haemodynamics in
normotensive rats only. Angiotensin II caused a significant change in RBF only
in sympathectomized SHR and DOCA-salt hypertensive rats when administered
intrarenally. With ACE inhibition, NA was found to exert a significant difference
(p<O.05) in peripheral arid renal haemodynamics in 2K1C Goldblatt and DOCAsalt
.h ype-rtensive animal when-administered intrarenally. PE did not cause any .
significant change in pressor and renal vasoconstrictor responses in both normo
and hypertensive animals except renal vasoconstrictor responses to intrarenal
PE in 2K1C Goldblatt and DOCA salt. A meaningful change (p<O.05) was
observed in RBF to MTX when administered peripherally and intrarenally in
sympathectomized SHR. Ang II peripherally and intrarenally did not cause major
changes in pressor responses in both sympathectomized WKY and SHR.
However there was attenuation in renal vasoconstrictor responses to peripheral
and intrarenal Ang II in sympathectomized DOCA-salt hyperten~ive animals.
These results suggested that, u1-adrenoceptors and RAS are involved in
mediating the pressor responses in both the peripheral and renal resistance
vessels, thus indicating a complex interaction of SNS and RAS in hypertension.
Description
Keywords
The renin angiotensin (RAS) and sympathetic nervous system (SNS) are , involved in the maintenance of blood pressure and body fluid homeostasis.