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Afolabi JM, Michael OS, Falayi OO, Kanthakumar P, Mankuzhy PD, Soni H, Adebiyi A. Activation of renal vascular smooth muscle TRPV4 channels by 5-hydroxytryptamine impairs kidney function in neonatal pigs. Microvasc Res 2023; 148:104516. [PMID: 36889668 PMCID: PMC10258165 DOI: 10.1016/j.mvr.2023.104516] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/17/2023] [Revised: 02/10/2023] [Accepted: 03/01/2023] [Indexed: 03/08/2023]
Abstract
Control of microvascular reactivity by 5-hydroxytryptamine (5-HT; serotonin) is complex and may depend on vascular bed type and 5-HT receptors. 5-HT receptors consist of seven families (5-HT1-5-HT7), with 5-HT2 predominantly mediating renal vasoconstriction. Cyclooxygenase (COX) and smooth muscle intracellular Ca2+ levels ([Ca2+]i) have been implicated in 5-HT-induced vascular reactivity. Although 5-HT receptor expression and circulating 5-HT levels are known to be dependent on postnatal age, control of neonatal renal microvascular function by 5-HT is unclear. In the present study, we demonstrate that 5-HT stimulated human TRPV4 transiently expressed in Chinese hamster ovary cells. 5-HT2A is the predominant 5-HT2 receptor subtype in freshly isolated neonatal pig renal microvascular smooth muscle cells (SMCs). HC-067047 (HC), a selective TRPV4 blocker, attenuated cation currents induced by 5-HT in the SMCs. HC also inhibited the 5-HT-induced increase in renal microvascular [Ca2+]i and constriction. Intrarenal artery infusion of 5-HT had minimal effects on systemic hemodynamics but reduced renal blood flow (RBF) and increased renal vascular resistance (RVR) in the pigs. Transdermal measurement of glomerular filtration rate (GFR) indicated that kidney infusion of 5-HT reduced GFR. HC and 5-HT2 receptor antagonist ritanserin attenuated 5-HT effects on RBF, RVR, and GFR. Moreover, the serum and urinary COX-1 and COX-2 levels in 5-HT-treated piglets were unchanged compared with the control. These data suggest that activation of renal microvascular SMC TRPV4 channels by 5-HT impairs kidney function in neonatal pigs independently of COX production.
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Affiliation(s)
- Jeremiah M Afolabi
- Department of Physiology, College of Medicine, University of Tennessee Health Science Center, Memphis, TN, USA
| | - Olugbenga S Michael
- Department of Physiology, College of Medicine, University of Tennessee Health Science Center, Memphis, TN, USA
| | - Olufunke O Falayi
- Department of Physiology, College of Medicine, University of Tennessee Health Science Center, Memphis, TN, USA
| | - Praghalathan Kanthakumar
- Department of Physiology, College of Medicine, University of Tennessee Health Science Center, Memphis, TN, USA
| | - Pratheesh D Mankuzhy
- Department of Physiology, College of Medicine, University of Tennessee Health Science Center, Memphis, TN, USA
| | - Hitesh Soni
- Department of Physiology, College of Medicine, University of Tennessee Health Science Center, Memphis, TN, USA
| | - Adebowale Adebiyi
- Department of Physiology, College of Medicine, University of Tennessee Health Science Center, Memphis, TN, USA.
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Beierwaltes WH, Harrison-Bernard LM, Sullivan JC, Mattson DL. Assessment of renal function; clearance, the renal microcirculation, renal blood flow, and metabolic balance. Compr Physiol 2013; 3:165-200. [PMID: 23720284 DOI: 10.1002/cphy.c120008] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
Historically, tools to assess renal function have been developed to investigate the physiology of the kidney in an experimental setting, and certain of these techniques have utility in evaluating renal function in the clinical setting. The following work will survey a spectrum of these tools, their applications and limitations in four general sections. The first is clearance, including evaluation of exogenous and endogenous markers for determining glomerular filtration rate, the adaptation of estimated glomerular filtration rate in the clinical arena, and additional clearance techniques to assess various other parameters of renal function. The second section deals with in vivo and in vitro approaches to the study of the renal microvasculature. This section surveys a number of experimental techniques including corticotomy, the hydronephrotic kidney, vascular casting, intravital charge coupled device videomicroscopy, multiphoton fluorescent microscopy, synchrotron-based angiography, laser speckle contrast imaging, isolated renal microvessels, and the perfused juxtamedullary nephron microvasculature. The third section addresses in vivo and in vitro approaches to the study of renal blood flow. These include ultrasonic flowmetry, laser-Doppler flowmetry, magnetic resonance imaging (MRI), phase contrast MRI, cine phase contrast MRI, dynamic contrast-enhanced MRI, blood oxygen level dependent MRI, arterial spin labeling MRI, x-ray computed tomography, and positron emission tomography. The final section addresses the methodologies of metabolic balance studies. These are described for humans, large experimental animals as well as for rodents. Overall, the various in vitro and in vivo topics and applications to evaluate renal function should provide a guide for the investigator or physician to understand and to implement the techniques in the laboratory or clinic setting.
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Affiliation(s)
- William H Beierwaltes
- Hypertension and Vascular Research Division, Department of Internal Medicine, Henry Ford Hospital, and Department of Physiology, Wayne State University School of Medicine, Detroit, Michigan, USA.
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Badzyńska B, Sadowski J. Differential action of bradykinin on intrarenal regional perfusion in the rat: waning effect in the cortex and major impact in the medulla. J Physiol 2009; 587:3943-53. [PMID: 19528250 DOI: 10.1113/jphysiol.2009.172007] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
The renal kallikrein-kinin system is involved in the control of the intrarenal circulation and arterial pressure but bradykinin (Bk) effects on perfusion of individual kidney zones have not been examined in detail. Effects of Bk infused into renal artery, renal cortex or medulla on perfusion of whole kidney (RBF, renal artery probe) and of the cortex, outer- and inner medulla (CBF, OMBF, IMBF: laser-Doppler fluxes), were examined in anaesthetized rats. Renal artery infusion of Bk, 0.3-0.6 mg kg(-1) h(-1), induced no sustained increase in RBF or CBF. OMBF and IMBF increased initially 6 or 16%, respectively; only the IMBF increase (+10%) was sustained. Pre-treatment with L-NAME, 2.4 mg kg(-1) I.V., prevented the sustained but not initial transient elevation of medullary perfusion. Intracortical Bk infusion, 0.75-1.5 mg kg(-1) h(-1), did not alter RBF or CBF but caused a sustained 33% increase in IMBF. Intramedullary Bk, 0.3 mg kg(-1) h(-1), did not alter RBF or CBF but caused sustained increases in OMBF (+10%) and IMBF (+23%). These responses were not altered by pre-treatment with 1-aminobenzotriazole, 10 mg kg(-1)i.v., a cytochrome P-450 (CYP450) inhibitor, but were prevented or significantly attenuated by L-NAME or intramedullary clotrimazole, 3.9 mg kg(-1) h(-1), an inhibitor of CYP450 epoxygenase and of calcium-dependent K(+) channels (K(Ca)). Thus, cortical vasodilatation induced by Bk is only transient so that the agent is unlikely to control perfusion of the cortex. Bk selectively increases perfusion of the medulla, especially of its inner layer, via activation of the NO system and of K(Ca) channels.
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Affiliation(s)
- Bozena Badzyńska
- Laboratory of Renal and Body Fluid Physiology, Medical Research Centre of the Polish Academy of Sciences, Pawiskiego 5, 02-106 Warsaw, Poland
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Badzynska B, Sadowski J. Opposed effects of prostaglandin E2 on perfusion of rat renal cortex and medulla: interactions with the renin-angiotensin system. Exp Physiol 2008; 93:1292-302. [PMID: 18586855 DOI: 10.1113/expphysiol.2008.043604] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
While prostaglandin E(2) (PGE(2)) is an established renal vasodilator, studies of prostaglandin EP receptors suggest that it also has vasoconstrictor potential. Prostaglandin E(2) is much more abundant in the medulla than in the cortex, yet likely differences in effects between zones have not been defined. This study is focused on different vascular effects in the cortex and medulla and interaction with the renin-angiotensin system (RAS). In anaesthetized rats, the effects of cyclo-oxygenase blockade and of PGE(2) infused into the renal artery or renal interstitium were examined. Total renal blood flow was measured by ultrasonic renal artery probe, and local perfusion, separately, of the superficial cortex, outer- and inner medulla, as laser-Doppler fluxes. Indomethacin (5 mg kg(-1) i.v.) increased cortical perfusion (by approximately 10%) and decreased medullary perfusion (by approximately 20%). Renal artery infusion of PGE(2) (15-30 microg kg(-1) h(-1)) increased cortical and medullary perfusion only transiently. Previous inactivation of the RAS using losartan or captopril, and background infusion of exogenous angiotensin II, prevented the transient increase and enhanced the subsequent stable decrease in perfusion. Prostaglandin E(2) infused into the medullary interstitium (7-22 microg kg(-1) h(-1)) increased medullary perfusion by 13%, while cortical perfusion decreased by 6%. Misoprostol, an agonist of constrictor EP(3) receptors, decreased perfusion of the cortex and medulla, with both renal artery and medullary interstitial infusion. In conclusion, in rat renal cortex the dominating stable PGE(2) effect is vasoconstriction, most probably mediated by EP(3) receptors and unrelated to activation of the RAS. Prostaglandin E(2) applied to the cortical or medullary interstitium, a natural route for paracrine agents, induces medullary vasodilatation.
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Affiliation(s)
- Bozena Badzynska
- Laboratory of Renal and Body Fluid Physiology, Medical Research Centre of the Polish Academy of Sciences, Pawińskiego 5, 02-106 Warsaw, Poland
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Eppel GA, Ventura S, Evans RG. Regional vascular responses to ATP and ATP analogues in the rabbit kidney in vivo: roles for adenosine receptors and prostanoids. Br J Pharmacol 2006; 149:523-31. [PMID: 16981003 PMCID: PMC2014670 DOI: 10.1038/sj.bjp.0706901] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
BACKGROUND AND PURPOSE Our knowledge of the effects of P2-receptor activation on renal vascular tone comes mostly from in vitro models. We aimed to characterise the pharmacology of ATP in the renal circulation in vivo. EXPERIMENTAL APPROACH In pentobarbitone anaesthetized rabbits, we examined total renal and medullary vascular responses to ATP (0.2 and 0.8 mg kg(-1)), beta, gamma-methylene ATP (beta, gamma-mATP, 7 and 170 microg kg(-1)), alpha, beta-mATP (0.2 and 2 microg kg(-1)) and adenosine (2 and 6 microg kg(-1)) using transit-time ultrasound and laser Doppler flowmetry, respectively. We also determined whether adenosine receptors, NO or prostanoids contribute to the actions of the purinoceptor agonists. KEY RESULTS Renal arterial boluses of ATP, beta,gamma-mATP, and adenosine produced biphasic changes; ischaemia followed by hyperaemia, in total renal and medullary blood flow. alpha,beta-mATP induced only ischaemia. The adenosine receptor antagonist 8-(p-sulphophenyl)theophylline reduced the responses to adenosine and the hyperaemic responses to ATP and beta,gamma-mATP only. NO synthase inhibition (Nomega-nitro-L-arginine) did not significantly alter responses to the P2 receptor agonists. Subsequent cyclooxygenase inhibition (ibuprofen) reduced the ATP- and beta, gamma-mATP-induced increases in renal blood flow. All other responses remained unchanged. CONCLUSIONS AND IMPLICATIONS In the rabbit kidney in vivo, alpha, beta-mATP sensitive receptors mediate vasoconstriction. beta,gamma-mATP and ATP induce vasodilation at least partly through adenosine receptors. ATP induced renal vasodilatation is independent of NO and partly dependent on prostanoids in the bulk of the kidney, but not in the vasculature controlling medullary blood flow.
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Affiliation(s)
- G A Eppel
- Department of Physiology, Monash University, Melbourne, Victoria, Australia.
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Badzyńska B, Sadowski J. Renal hemodynamic responses to intrarenal infusion of acetylcholine: Comparison with effects of PGE2 and NO donor. Kidney Int 2006; 69:1774-9. [PMID: 16572111 DOI: 10.1038/sj.ki.5000338] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
Acetylcholine (Ach) could serve as a selective renal medullary vasodilator in studies of the mechanism of arterial pressure regulation; however, effects of intramedullary Ach infusion were disparate. In anesthetized rats, the total renal blood flow (RBF) was measured by renal artery probe, and local perfusion of the cortex (CBF), outer medulla (OMBF) and inner medulla (IMBF) as laser-Doppler (l-D) flux. Renal artery infusion of Ach (60-150 microg/kg/h) significantly increased RBF by 17% and l-D parameters by 7-14%, without affecting arterial blood pressure (BP); the responses were prevented by inhibition of nitric oxide (NO) synthesis with N(omega)-nitro-L-arginine methyl ester (L-NAME). Intramedullary Ach (180 microg/kg/h) significantly increased OMBF by 9% and IMBF by 7% but also RBF and CBF (both 9%). Carbamylcholine (Cch, 15 or 30-60 microg/kg/h), a stable Ach analog, increased CBF, OMBF, and IMBF by 5-8%; there was no dose dependency and, as with Ach, no preferential effect on medullary perfusion. Intramedullary infusion of prostaglandin E(2) (PGE2) (15 microg/kg/h), and S-nitroso-N-acetyl-D,L penicillamine (SNAP), an NO donor (15-30 mg/kg/h), significantly and substantially increased OMBF and IMBF only. Ach increased perfusion of all kidney zones by an NO-dependent mechanism. Infusion of Ach or Cch into the renal medullary interstitium failed to affect preferentially the medullary perfusion, in contrast to the well-demonstrable selective effects of PGE2 and SNAP. The reason was probably the Ach's dual opposed action, vasoconstrictor and vasorelaxant, on the intrarenal vasculature.
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Affiliation(s)
- B Badzyńska
- Laboratory of Renal and Body Fluid Physiology, M Mossakowski Medical Research Centre of the Polish Academy of Sciences, Warsaw
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Eppel GA, Ventura S, Denton KM, Evans RG. Lack of contribution of P2X receptors to neurally mediated vasoconstriction in the rabbit kidney in vivo. Acta Physiol (Oxf) 2006; 186:197-207. [PMID: 16497199 DOI: 10.1111/j.1748-1716.2006.01526.x] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
AIM The contribution of adenosine triphosphate (ATP) to the neural control of regional renal perfusion in vivo remains unknown. We therefore examined whether P2X receptors mediate renal vascular responses to electrical stimulation of the renal nerves (RNS) in pentobarbitone anaesthetized rabbits. METHODS Responses to RNS were tested before and during renal arterial infusion of alpha,beta-methylene ATP (alpha,beta-mATP, 7-56 microg kg(-1) min(-1)) to desensitize P2X1 receptors. RNS consisted of 3 min trains at graded frequencies and short trains of RNS (4-32 pulses). RESULTS Three-minute trains of RNS reduced renal blood flow (RBF), cortical laser Doppler flux (CLDF), and medullary LDF (MLDF) by -90 +/- 3%, -89 +/- 3% and -31 +/- 11%, respectively, at 4 Hz. MLDF was reduced less than CLDF or RBF. During short train RNS, RBF, CLDF and MLDF were reduced by -22 +/- 2%, -15 +/- 2% and -12 +/- 2%, respectively, for 32 s at 1 Hz. CLDF and MLDF were reduced to a similar extent. Infusion of alpha,beta-mATP induced transient reductions in RBF, CLDF and MLDF, but within 5 min these variables had recovered to control levels. Vascular responses to RNS were not significantly altered by alpha,beta-mATP treatment. CONCLUSIONS In the rabbit kidney in vivo, alpha,beta-mATP-sensitive receptors mediate vasoconstriction and reduce perfusion in both cortical and medullary vascular beds. However, these receptors do not mediate neurally induced reductions in renal perfusion.
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Affiliation(s)
- G A Eppel
- Department of Physiology, Monash University, Melbourne, Vic., Australia.
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Eppel GA, Luff SE, Denton KM, Evans RG. Type 1 neuropeptide Y receptors and alpha1-adrenoceptors in the neural control of regional renal perfusion. Am J Physiol Regul Integr Comp Physiol 2005; 290:R331-40. [PMID: 16195497 DOI: 10.1152/ajpregu.00317.2005] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The aim of this study was to determine the contribution of neuropeptide Y (NPY) Y1 receptors in neurally mediated reductions in renal medullary perfusion. In pentobarbital sodium-anesthetized rabbits, electrical stimulation of the renal nerves (RNS, 0.5-16 Hz) decreased renal perfusion in a frequency-dependent manner. Under control conditions, 4 Hz reduced cortical and medullary perfusion by -85 +/- 3% and -43 +/- 7%, whereas 8 Hz reduced them by -93 +/- 2% and -73 +/- 4%, respectively. After Y1 receptor antagonism with BIBO3304TF (0.1 mg/kg plus 0.2 mg x kg x (-1) x h(-1)), RNS reduced perfusion less (by -65 +/- 9% and -12 +/- 8% at 4 Hz) x alpha1-Adrenoceptor antagonism with prazosin (0.2 mg/kg plus 0.2 mg kg(-1)h(-1)) also inhibited RNS-induced reductions in renal perfusion (-80 +/- 4% and -37 +/- 10% reductions in the cortex and medulla, respectively, at 8 Hz). When given after BIBO3304TF treatment, prazosin inhibited RNS-induced reductions in cortical and medullary perfusion more profoundly (-57 +/- 12% and -25 +/- 9% reductions, respectively, at 8 Hz) x Y1 receptor- and alpha1-adrenoceptor-blockade were confirmed by testing vascular responses to renal arterial NPY and phenylephrine boluses. NPY-positive immunolabeling was observed around interlobular arteries, afferent and efferent arterioles, and in the outer medulla. In conclusion, Y1 receptors and alpha1-adrenoceptors contribute to RNS-induced vasoconstriction in the vessels that control both cortical and medullary perfusion. Consistent with this, NPY immunostaining was associated with blood vessels that control perfusion in both regions. There also seems to be an interaction between Y1 receptors and alpha1-adrenoceptor-mediated neurotransmission in the control of renal perfusion.
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Bergström G, Evans RG. Mechanisms underlying the antihypertensive functions of the renal medulla. ACTA ACUST UNITED AC 2004; 181:475-86. [PMID: 15283761 DOI: 10.1111/j.1365-201x.2004.01321.x] [Citation(s) in RCA: 37] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Abstract
There is good evidence that the renal medulla plays a pivotal role in long-term regulation of blood pressure. 'Renal medullary' blood pressure regulating systems have been postulated to involve both exocrine (pressure natriuresis/diuresis) and endocrine [renal medullary depressor hormone (RMDH)] functions. However, recent studies indicate that pressure diuresis/natriuresis dominates the antihypertensive renal response to increased renal perfusion pressure, suggesting little physiological role for a putative RMDH in compensatory responses to acutely increased blood pressure. The medullary circulation appears to play a key role in mediating pressure diuresis, although the precise mechanisms involved remain controversial. Counter-regulatory vasodilator mechanisms (e.g. nitric oxide), at least partly mediated through cross-talk between the vasculature and the tubular epithelium, protect the medullary circulation from the vasoconstrictor effects of hormonal factors such as angiotensin II. These mechanisms also appear to contribute to compensatory responses to increased salt intake in salt-resistant individuals. Failure of these mechanisms predisposes the organism towards the development of hypertension, appears to underlie the development of some forms of experimental hypertension, and may even contribute to the pathogenesis of essential hypertension.
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Affiliation(s)
- G Bergström
- Department of Clinical Physiology, Cardiovascular Institute, Göteborg University, Göteborg, Sweden
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Eppel GA, Lee LL, Evans RG. α-Adrenoceptor subtypes mediating regional kidney blood flow responses to renal nerve stimulation. Auton Neurosci 2004; 112:15-24. [PMID: 15233926 DOI: 10.1016/j.autneu.2004.03.001] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/02/2003] [Revised: 02/13/2004] [Accepted: 03/01/2004] [Indexed: 11/25/2022]
Abstract
The mechanisms underlying the relative insensitivity of the renal medullary circulation to renal sympathetic nerve stimulation (RNS) remain unknown. Therefore, we tested the effects of systemic alpha(1)- and alpha(2)-adrenoceptor blockade on responses to electrical RNS in pentobarbitone anaesthetized rabbits. Renal blood flow (RBF), cortical laser Doppler flux (CLDF), and to a lesser extent medullary LDF (MLDF) were reduced by RNS in a frequency-dependent manner. Prazosin decreased responses of RBF and CLDF, but not MLDF, to RNS. For example, during the control period 4 Hz stimulation reduced RBF, CLDF and MLDF by 85+/-3%, 89+/-2%, and 20+/-12%, respectively, but after prazosin, corresponding responses were 39+/-3%, 42+/-5% and 28+/-7%, respectively. Prazosin markedly blunted pressor and renal vasoconstrictor responses to intravenous phenylephrine, without altering pressor responses to intravenous xylazine. Rauwolscine enhanced renal vasoconstrictor responses to RNS, although this was statistically significant for RBF and CLDF but not MLDF. For example, during the control period 2 Hz stimulation reduced RBF, CLDF and MLDF by 63+/-7%, 58+/-7%, and 29+/-17%, respectively, and after rauwolscine, corresponding responses were 83+/-4%, 87+/-1%, and 53+/-12%, respectively. Rauwolscine markedly blunted renal vasoconstrictor responses to renal arterial guanabenz, but not phenylephrine. These data suggest that alpha(1)-adrenoceptors contribute to RNS-induced vasoconstriction in the renal cortex, but contribute less in vascular elements controlling medullary perfusion. Activation of alpha(2)-adrenoceptors appears to blunt RNS-induced renal vasoconstriction, but this mechanism does not underlie the relative insensitivity of medullary perfusion to RNS.
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Affiliation(s)
- Gabriela A Eppel
- Department of Physiology, Monash University, P.O. Box 13F, Melbourne, Victoria 3800, Australia.
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Dobrowolski L, Sadowski J. Renal medullary infusion of indomethacin and adenosine. Effects on local blood flow, tissue ion content and renal excretion. Kidney Blood Press Res 2003; 27:29-34. [PMID: 14679312 DOI: 10.1159/000075620] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 07/18/2003] [Indexed: 11/19/2022] Open
Abstract
Perfusion of the renal medulla and osmotic hypertonicity of its interstitium are the two important features of this zone which can influence body fluid homeostasis, especially arterial blood pressure. Separate manipulation of the two variables is best obtained with the intramedullary infusion of active agents. In this study, a set-up combining the possibility of infusion into the medulla with measurement of local blood flow (MBF, laser-Doppler flux) and extracellular ion concentration (tissue electrical admittance, Y) was used to determine effects of intramedullary indomethacin (Indo) and adenosine (Ado) in anaesthetized rats. Intramedullary Indo, 1 mg kg(-1 )h(-1), significantly increased tissue Y, by 12 +/- 3%, and significantly decreased MBF by 20 +/- 3%. There was also an unexplained increase of sodium excretion (U(Na)V) by 169 +/- 24% and of urine flow (V) by 62 +/- 6% (n = 10, both p < 0.03). Intramedullary Ado, 5 microg kg(-1) h(-1), did not alter Y, MBF or U(Na)V, whereas V increased 45 +/- 6% and urine osmolality decreased 25 +/- 4% (both changes significant). Elevation of medullary interstitial Ado to a level that did not alter MBF or U(Na)V induced a moderate defect of urine concentration that was not due to a decrease in ionic medullary hypertonicity.
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Affiliation(s)
- Leszek Dobrowolski
- Laboratory of Renal and Body Fluid Physiology, M. Mossakowski Medical Research Centre, Polish Academy of Sciences, Warsaw, Poland.
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