Advances in Clinical and Experimental Medicine

Title abbreviation: Adv Clin Exp Med
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Advances in Clinical and Experimental Medicine

2011, vol. 20, nr 1, January-February, p. 47–55

Publication type: original article

Language: English

Influence of High Dietary Sodium Intake on Functional Contribution of Renal α1a-Adrenoceptor of SHR

Wpływ dużej podaży sodu w diecie na czynnościowy wkład α1a-adrenoceptora u szczurów z samoistnym nadciśnieniem tętniczym

Raisa N. Kazi1,, Munavvar A. Sattar1,, Nor A. Abdullah2,, Hassaan A. Rathore1,, Anand S. Kolla1,, Nurjannah M. Hussain1,, Mohammed H. Abdulla1,, Ibrahim M. Salman1,, Abdul H. Khan3,, Edward J. Johns4,

1 School of Pharmaceutical Sciences, University Sains Malaysia, 11800, Penang, Malaysia

2 Department of Pharmacology, Faculty of Medicine, University of Malaya, 50603 Kuala Lumpur, Malaysia

3 Department of Pharmacology and Toxicology, Medical College of Wisconsin, Wisconsin, USA

4 Department of Physiology, Western Gateway Building, University College Cork, College Road, Cork, Ireland

Abstract

Background. Elevated dietary sodium intake exacerbates the elevation of blood pressure in spontaneously hypertensive rats (SHR) which is associated with increased renal vascular resistance and fluid reabsorption. The renal sympathetic nerves exert their action via α1-adrenoceptors (α1-AR) with α1A as the major subtype in regulating renal hemodynamics and excretory function.
Objectives. This study investigated whether the contribution of α1A-AR in regulating renal vasoconstriction and excretory function was enhanced in SHR receiving high sodium intake.
Material and Methods. SHR received either water (SHRNNa) or normal saline (SHRHNa) for six weeks. Metabolic cage studies followed by acute experiments were carried out on these SHR to examine renal vasoconstrictor and excretory responses to catecholamine viz. noradrenaline (NA), phenylephrine (PE) and methoxamine (ME) in the presence and absence of a α1A-AR blocker, 5-methylurapidil (5-MeU).
Results. Daily water intake and urine output were increased in SHRHNa (P < 0.05 vs. SHRNNa). Renal cortical vascular responses to NA, PE and ME were enhanced in SHRHNa (P < 0.05 vs. SHRNNa) and the greatest effect was seen with ME. Intra-renal infusion of PE caused antidiuresis and antinatriuresis. Irrespective of the sodium intake, 5-MeU markedly blunted adrenergically induced renal cortical vasoconstrictions in SHR, while the antinatriuretic and antidiuretic responses to PE were inhibited by 5-MeU in SHRHNA only (P < 0.05).
Conclusion. The data suggest that, irrespective of the level of dietary sodium intake, α1A-ARs are the functional subtypes in SHR. However, there also appears to be a role for α1A-AR in mediating enhanced renal cortical vascular resistance, augmented tubular Na+ and water reabsorption in SHRHNa rats.

Streszczenie

Wprowadzenie. Zwiększone spożycie sodu nasila wzrost ciśnienia krwi u szczurów z samoistnym nadciśnieniem tętniczym (SHR), które jest związane z nasileniem oporu naczyniowego nerek i wchłanianiem zwrotnym płynu. Nerwy współczulne nerek wywierają swoje działanie przez α1-adrenoreceptory (α1-AR), a α1A jest głównym podtypem w regulacji hemodynamiki nerek i czynności wydalniczych.
Cel pracy. Zbadanie, czy wkład α1A-AR do regulacji zwężenia naczyń nerek i czynności wydalniczych został zwiększony u szczurów z samoistnym nadciśnieniem tętniczym spożywających dużo sodu.
Materiał i metody. Szczury otrzymywały albo wodę (SHRNNa), albo sól fizjologiczną (SHRHNa) przez sześć tygodni. Badanie w klatkach metabolicznych przeprowadzono po doświadczeniu ostrym w celu zbadania odpowiedzi zwężającej naczynia i wydalniczej nerek na katecholaminy, a mianowicie noradrenalinę (NA), fenylefrynę (PE) i metoksaminę (ME) w obecności i braku leku blokującego α1A-AR i 5-methylurapidilu (5-Meu).
Wyniki. Dzienne spożycie wody i wydalanie moczu było większe w grupie SHRHNa (p < 0,05 vs SHRNNa). Odpowiedź korowa naczyń nerek na NA, PE i ME była większa w grupie SHRHNa (p < 0,05 vs SHRNNa), a największy rezultat zaobserwowano pod wpływem ME. Śródnerkowy wlew PE wywołał antydiurezę i antynatriurezę. Niezależnie od spożycia sodu, 5-Meu wyraźnie ograniczył zwężenie naczyń krwionośnych wywołane adrenergicznie u szczurów z samoistnym nadciśnieniem tętniczym, a antynatriuretyczne i antydiuretyczne odpowiedzi na PE były hamowane przez 5-Meu tylko w grupie SHRHNA (P < 0,05).
Wnioski. Dane wskazują, że niezależnie od poziomu spożycia sodu, α1A-AR są czynnościowym podtypem u szczurów z samoistnym nadciśnieniem tętniczym. Wydaje się też, że swoją rolę spełnia α1A-AR w mediacji zwiększenia oporu naczyń nerkowych warstwy korowej, wzbogacania cewkowego Na+ i reabsorpcji wody u szczurów SHRHNa.

Key words

high salt, α1A-adrenoceptors, kidney, SHR

Słowa kluczowe

duże stężenie soli, α1A-adrenoreceptory, nerka, szczury z samoistnym nadciśnieniem tętniczym

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