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Kidney, Sodium, Renin-Angiotensin System Renovascular Hypertension. Andreas Pittaras MD. Anatomy and Physiology. The juxtaglomerular apparatus. 5' flanking region of the renin gene. Pathway of active renin in the juxtaglomerular cell. Renin mRNA accumulation in the juxtaglomerular cells.
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Kidney, Sodium, Renin-Angiotensin System Renovascular Hypertension Andreas Pittaras MD
Renin protein in the juxtaglomerular cells of the afferent arteriole
Major mechanisms governing renin release • Individual nephron signals • Low macula densa sodium chloride (stimulates) • Decreased afferent arteriolar pressure (stimulates) • Whole kidney modulating signals • Angiotensin II negative feedback (inhibits) • β-1 receptor stimulation (stimulates) • Other humoral factors Vasopressin (inhibits) • Atrial natriuretic peptide (inhibits) • Dopamine DA-1 receptor (stimulates) • Local effectors • Prostaglandins (stimulate) • Nitric oxide (inhibits) • Adenosine (inhibits) • Kinins (stimulate)
Physiologic stimulation of renin release PHYSIOLOGYPHARMACOLOGY Blood pressureAntihypertensive agents Fluid volumeStimulators Sodium intakeRenin-angiotensin blockade HydrationDiuretics DiureticsVasodilators Menstrual cycleSuppressors Diurnal changesβ-Adrenergic blockers PostureCentral α2-adrenergic agonists Potassium intakeNeutral Protein intakeCalcium antagonists
Half-life of renin and angiotensin Metabolism of the renin-angiotensin system COMPONENTHALF-LIFE IN CIRCULATIONDEGRADING ENZYME(S) Renin15 -20 min - Angiotensinogen4 -16 HRenin Angiotensin I1 -2 minAngiotensin-converting enzyme Angiotensin IISecondsAminopeptidase A, Εndopeptidase, Ρrolylcarboxypeptidase
Angiotensin peptides and receptor subtypes that interact with each peptide RECEPTORANGIOTENSIN NoneAngiotensinogen Asp-Arg-Val-Tyr-Ile-His-Pro-Phe-His-Leu-Val-Ile-His-Asn-Glu Renin NoneAngiotensin I NH2-Asp-Arg-Val-Tyr-Ile-His-Pro-Phe-His-Leu-COOH Angiotensin-converting enzyme AT1, AT2Angiotensin II Asp-Arg-Val-Tyr-Ile-His-Pro-Phe Angiotensinases AT1, AT2Angiotensin III Arg-Val-Tyr-Ile-His-Pro-Phe Angiotensinases UnknownAngiotensin (1-7) Asp-Arg-Val-Tyr-Ile-His-Pro Angiotensinases AT4Angiotensin (3-7) Val-Tyr-Ile-His-Pro
Heterogeneity in the angiotensin II receptor population Classification criteria of angiotensin receptor subtypes AT1AT2 Potency orderAngiotensin II > angiotensin IIIAngiotensin II =angiotensin III Selective antagonistsILosartanPD 123177 (Parke-Davis, NJ) PD 123319 (Parke-Davis) ValsartanCGP 42112A (Novartis) Eprosartan Zorsartan Irbesartan Candesartan Telmisartan Tasosartan Effector pathwaysPhospholipase CGuanylate cyclase Phospholipase D Adenylate cyclase Sensitivity to dithiothreitol (sulfhydryl-reducing agents)BindingBinding AffinityNo change Effect of GppNHpHill coefficient to no Change ~1
Renal effects of angiotensin subtype-2 receptor • Release of bradykinin, nitric oxide, and cGMP • Cell differentiation • Antiproliferation • Apoptosis • Vasodilation
Renal effects of angiotensin II • Decreased renal blood flow • Proportionately increased efferent arteriolar resistanceincreased glomerular capillary hydrostatic pressure increased filtration • Glomerular mesangial cell contraction decreased glomerular capillary surface area available for filtration decreased filtration (offsets above effect) • Decreased medullary blood flow • Increased tubular sodium reabsorption sodium retention
Causes of renal artery stenosis • Clinical clues suggesting renovascular hypertension • Systolic/diastolic epigastric, subcostal, or flank bruit • Accelerated or malignant hypertension (HTN) • Unilateral small kidney discovered by any clinical study • Severe HTN in child or young adult, or after age 50 y • Sudden development or worsening of HTN at any age • HTN and unexplained impairment of renal function • Sudden worsening of renal function in hypertensive patient • Hypertension refractory to appropriate three-drug regimen • Impairment in renal function in response to ACE inhibitor • Extensive occlusive disease in coronary, cerebral, and peripheral circulation
Diagnostic indicators for renovascular hypertension Diagnostic studies for renovascular hypertension • SENSITIVITY, %SPECIFICITY, % • Rapid sequence IVP7486 • Isotope renography 9395 • with ACE inhibitiontest • Peripheral vein PRA with 7489 • ACE inhibition test (captopril test) • Renal vein ratio of PRA test • (stenotic/contralateral): • >1.38540 • >1.97860 • Peripheral vein PRA9296 • Intravenous digital 8889 • subtraction angiography • Doppler ultrasonography8693 • MRI9795 • Renal artery angiography100100
The captopril test • Criteria for renovascular hypertension • Stimulated PRA of 12 ng/mL/h • Absolute increase in PRA of 10 ng/mL/h • Increase in plasma renin activity PRA of 150% or 400% if baseline PRA is <3 ng/mL/h
Objectives in the management of renovascular hypertension Outcome after angioplasty or surgery for renal artery stenosis ETIOLOGYATHEROMAFIBROMUSCULAR DYSPLASIA TreatmentAngioplastySurgeryAngioplastySurgery Patients3911310175486 BP response Cured19455064 ( 56- 81) Improved52294223 ( 5 -40) Failed3024911 ( 0 -25)
Selective renal arteriogram of a 43-year-old nonsmoking male