Normal and sinoaortic baroreceptor-denervated dogs were monitored continuously (24 hours a day) to quantify the role of the baroreceptors in determining the average level and the variability of arterial blood pressure, heart rate, cardiac output, and total peripheral resistance. The frequency of occurrence over 24-hour periods was obtained for each variable using a fiber optic curve-scanning system to read the variables from continuously recorded charts and a digital computer system to plot curves. The results indicate that the degree of hypertension previously reported for this preparation has been highly exaggerated, presumably due to the methods of study. The average 24-hour mean arterial blood pressure was 101.6 mm Hg in normal dogs and only 112.7 mm Hg in baroreceptor-denervated dogs. The normal dogs exhibited narrowly distributed 24-hour frequency distribution curves for blood pressure; in contrast the denervated dogs exhibited curves with twice the 24-hour standard deviation. Similar analysis indicated that the baroreceptors exerted less influence on the daily stabilization of heart rate than they did on arterial blood pressure and that they had very little if any influence on the daily stabilization of cardiac output and total peripheral resistance. Hemodynamic variables during postural changes were studied along with diurnal rhythms. We concluded that the primary function of the baroreceptor reflex is not to set the chronic level of arterial blood pressure but, instead, to minimize variations in systemic arterial blood pressure, whether these variations are caused by postural changes of the animal, excitement, diurnal rhythm, or even spontaneous fluctuations of unknown origin.

Abstract-The present study characterized the biochemical pathways responsible for superoxide (O 2 Ϫ· ) production in different regions of the rat kidney and determined the role of O 2 Ϫ· in the control of renal medullary blood flow (MBF) and renal function. By use of dihydroethidium/DNA fluorescence spectrometry with microtiter plates, the production of O 2 Ϫ· was monitored when tissue homogenate from different kidney regions was incubated with substrates for the major O 2 Ϫ· -producing enzymes, such as NADH/NADPH oxidase, xanthine oxidase, and mitochondrial respiratory chain enzymes. The production of O 2 Ϫ· via NADH oxidase was greater (PϽ0.05) in the renal cortex and outer medulla (OM) than in the papilla. The mitochondrial enzyme activity for O 2 Ϫ· production was higher (PϽ0.05) in the OM than in the cortex and papilla. Compared with NADH oxidase and mitochondrial enzymes, xanthine oxidase and NADPH oxidase produced much less O 2 Ϫ· in the kidney under this condition. Overall, the renal OM exhibited the greatest enzyme activities for O 2 Ϫ· production. In anesthetized rats, renal medullary interstitial infusion of a superoxide dismutase inhibitor, diethyldithiocarbamate, markedly decreased renal MBF and sodium excretion. Diethyldithiocarbamate (5 mg/kg per minute by renal medullary interstitial infusion [RI]) reduced the renal medullary laser-Doppler flow signal from 0.6Ϯ0.04 to 0.4Ϯ0.03 V, a reduction of 33%, and both urine flow and sodium excretion decreased by 49%. In contrast, a membrane-permeable superoxide dismutase mimetic, 4-hydroxytetramethyl-piperidine-1-oxyl (TEMPOL, 30 mol/kg per minute RI) increased MBF and sodium excretion by 34% and 69%, respectively. These effects of TEMPOL on renal MBF and sodium excretion were not altered by pretreatment with N G -nitro-L-arginine methyl ester (10 g/kg per minute RI). We conclude that (1) Key Words: free radicals Ⅲ oxygen Ⅲ hemodynamics, renal Ⅲ kidney I n contrast to the conventional idea that reactive oxygen species (ROS) are of only pathological consequence, recent studies have indicated that under physiological conditions, low concentrations of ROS play an important role in the normal regulation of cell and organ function. 1-4 Redoxmediated signaling is emerging as a fundamental regulatory mechanism in cell biology and physiology. 2,4 In this regard, ROS have been reported to participate in the control of vascular tone, and the interaction of superoxide (O 2 Ϫ· ) and NO has been considered as one of the important mechanisms regulating cardiovascular function. 1,2,4,5 It has been demonstrated that O 2 Ϫ· inactivates the endothelium-dependent relaxing factor, thereby reducing the arteriolar dilation to acetylcholine or other endothelium-dependent vasodilators 6 and that endothelial superoxide dismutase (SOD) activity significantly increased the half-life of the endothelium-dependent relaxing factor produced by acetylcholine. 5 Recent studies have provided direct evidence that inactivation of SOD activity with diethyldithiocarbamate (DETC) selectively in...

The original fascination with the medullary circulation of the kidney was driven by the unique structure of vasa recta capillary circulation, which Berliner and colleagues (Berliner, R. W., N. G. Levinsky, D. G. Davidson, and M. Eden. Am. J. Med. 24: 730-744, 1958) demonstrated could provide the economy of countercurrent exchange to concentrate large volumes of blood filtrate and produce small volumes of concentrated urine. We now believe we have found another equally important function of the renal medullary circulation. The data show that it is indeed the forces defined by Starling 100 years ago that are responsible for the pressure-natriuresis mechanisms through the transmission of changes of renal perfusion pressure to the vasa recta circulation. Despite receiving only 5-10% of the total renal blood flow, increases of blood flow to this region of the kidney cause a washout of the medullary urea gradient and a rise of the renal interstitial fluid pressure. These forces reduce tubular reabsorption of sodium and water, leading to a natriuresis and diuresis. Many of Starling's intrinsic chemicals, which he named "hormones," importantly modulate this pressure-natriuresis response by altering both the sensitivity and range of arterial pressure around which these responses occur. The vasculature of the renal medulla is uniquely sensitive to many of these vasoactive agents. Finally, we have found that the renal medullary circulation can play an important role in determining the level of arterial pressure required to achieve long-term fluid and electrolyte homeostasis by establishing the slope and set point of the pressure-natriuresis relationship. Measurable decreases of blood flow to the renal medulla with imperceptible changes of total renal blood flow can lead to the development of hypertension. Many questions remain, and it is now evident that this is a very complex regulatory system. It appears, however, that the medullary blood flow is a potent determinant of both sodium and water excretion and signals changes in blood volume and arterial pressure to the tubules via the physical forces that Professor Starling so clearly defined 100 years ago.

Abstract-Dahl salt-sensitive (SS) rats exhibit increased renal medullary oxidative stress and blood pressure salt-sensitivity compared with consomic, salt-resistant SS-13 BN rats, despite highly similar genetic backgrounds. The present study examined potential sources of renal medullary superoxide in prehypertensive SS rats fed a 0.4% NaCl diet by assessing activity and protein levels of superoxide producing and scavenging enzymes. Superoxide production was nearly doubled in SS rats compared with SS-13 BN rats as determined by urinary 8-isoprostane excretion and renal medullary oxy-ethidium microdialysate levels. Medullary superoxide production in tissue homogenates was greater in SS rats, and the NADPH oxidase inhibitor diphenylene iodonium preferentially reduced SS levels to those found in SS-13 BN rats. Dinitrophenol, a mitochondrial uncoupler, eliminated the remaining superoxide production in both strains, whereas inhibition of xanthine oxidase, NO synthase, and cycloxygenase had no effect. L-arginine, NO synthase, superoxide dismutase, catalase, and glutathione peroxidase activities between SS and SS-13 BN rats did not differ. Chronic blood pressure responses to a 4% NaCl diet were then determined in the presence or absence of the NADPH oxidase inhibitor apocynin (3.5 g/kg per minute), chronically delivered directly into the renal medulla. Apocynin infusion reduced renal medullary interstitial superoxide from 1059Ϯ130 to 422Ϯ80 (oxyethidium fluorescence units) and mean arterial pressure from 175Ϯ4 to 157Ϯ6 mm Hg in SS rats, whereas no effects on either were observed in the SS-13 BN . We conclude that excess renal medullary superoxide production in SS rats contributes to salt-induced hypertension, and NADPH oxidase is the major source of the excess superoxide.

ANG II contributes importantly to the regulation of renal vascular resistance, glomerular filtration, and tubular epithelial transport, yet there remains a paucity of information regarding the localization of the ANG II type 1 and 2 (AT1 and AT2) receptors within the rat kidney particularly within the vasculature. The present study was designed to localize the transcriptional and translational site(s) of AT1 and AT2 receptor (AT1R and AT2R, respectively) expression within the rat kidney. Using immunohistochemistry, we detected the AT1R translational sites throughout the kidney, with the strongest labeling found in the vasculature of the renal cortex and the proximal tubules of the outer medulla. The AT2R protein expression was found throughout the rat kidney, although there was little to no expression found in the glomerulus and medullary thick ascending limbs of Henle (TAL). Gene-specific primers were then designed to distinguish between the receptor subtypes within microdissected renal tubular and vascular segments using RT-PCR. AT1AR, AT1BR, and AT2R mRNA were found within the renal vasculature (afferent arterioles, arcuate artery, and outer medullary descending vasa recta). The mRNA for both the AT1R isoforms was also detected in the glomeruli and the renal tubules (proximal tubules, TAL, and collecting ducts); however, no AT2R mRNA was detected within the glomerulus and was inconsistently found within the medullary TAL (MTAL). Taken together, these data show that mRNA for the AT1R subtypes was located in all of the renal tubular and vascular segments. Evidence for AT2R mRNA was also found in all but two of the vascular and tubular segments, the MTAL, and the glomeruli. These results are consistent with the whole tissue immunohistochemically localized receptors.

Abstract-Consomic rats (SS.BN13), in which chromosome 13 from normotensive inbred Brown Norway rats from a colony maintained at the Medical College of Wisconsin (BN/Mcw) was introgressed into the background of Dahl salt-sensitive (SS/Mcw) rats, also maintained in a colony at the Medical College of Wisconsin, were bred. The present studies determined the mean arterial pressure (MAP) responses to salt and renal and peripheral vascular responses to norepinephrine and angiotensin II; 24-hour protein excretion and histological analyses were used to assess renal pathology in rats that received a high salt (4% NaCl) diet for 4 weeks. MAP of rats measured daily during the fourth week averaged 170Ϯ3. Key Words: hypertension, sodium dependent Ⅲ rats Ⅲ sodium Ⅲ chromosome 13 Ⅲ blood pressure Ⅲ consomic D ahl salt-sensitive (SS) rats exhibit many of the abnormalities that occur with hypertension in African Americans, 1,2 including blood pressure salt sensitivity, 3,4 insulin resistance, 5 and hyperlipidemia. 6 They have a low renin form of hypertension 3 that is refractory to treatment with converting enzyme inhibitors 7,8 and is effectively treated with diuretics. 7,9 Moreover, these rats rapidly develop severe progressive hypertensive glomerulosclerosis that leads to end-stage renal disease, as is commonly also seen in African Americans with hypertension. 9,10 For these reasons, insights and findings of the studies in SS rats may provide valuable clues to the genetic basis of hypertension and related traits in African Americans.The explosion of genomic resources in the rat has led to remarkable advances in identifying the regions of the rat genome that contain blood pressure quantitative trait loci (QTLs), as reviewed by Hamet et al, 11 Zicha and Kunes,12 and Rapp. 13 We have recently completed a linkage analysis based on an intercross of SS and Brown Norway (BN) salt-insensitive rats in which total genome scans using 238 polymorphic markers, evenly distributed throughout the genome, were scored. All F2 rats (113 males and 99 females) were extensively phenotyped for 239 measured or derived traits. This linkage analysis indicated the existence of a broad range of traits related to pathways of functional importance in hypertension that mapped to 19 chromosomes. 14,15 The development of congenic strains has been used by a number of laboratories, including our own, to confirm and narrow QTL regions of interest. 16,17 Despite the usefulness of congenic rat models in the deconstruction of complex traits and the identification of candidate genes, this work has been hampered by the time and expense involved in producing these informative recombinant rats. Even with the use of markerassisted selection to identify the rats best suited for backcrossing in generations, 18 we have found that the process of developing an inbred congenic strain requires nearly 2 years and 5 to 7 generations of backcrosses to achieve rats that are sufficiently isogenic to make meaningful comparisons.To overcome these limitations, we have been developing ...

QTL mapping in humans and rats has identified hundreds of blood-pressure-related phenotypes and genomic regions; the next daunting task is gene identification and validation. The development of novel rat model systems that mimic many elements of the human disease, coupled with advances in the genomic and informatic infrastructure for rats, promise to revolutionize the hunt for genes that determine susceptibility to hypertension. Furthermore, methods are evolving that should enable the identification of candidate genes in human populations. Together with the computational reconstruction of regulatory networks, these methods provide opportunities to significantly advance our understanding of the underlying aetiology of hypertension.

This study was designed to quantify nitric oxide synthase (NOS) activity in microdissected glomeruli (Glm), pars convoluta, pars recta, cortical collecting duct, cortical thick ascending limb, outer medullary collecting duct, medullary thick ascending limb and thin limb, inner medullary collecting duct (IMCD) and thin limb, and vasa recta (VR). Total protein from microdissected segments was incubated withl-[3H]arginine and appropriate cofactors, and thel-arginine and convertedl-citrulline were separated by reverse-phase HPLC and radiochemically quantitated. NOS activity was found to be greatest in IMCD (11.5 ± 1.0 fmol citrulline ⋅ mm−1 ⋅ h−1) and moderate in Glm (1.9 ± 0.3 fmol ⋅ glomerulus−1 ⋅ h−1) and VR (3.2 ± 0.8 fmol ⋅ mm−1 ⋅ h−1). All other renal structures studied exhibited significantly less NOS activity. The mRNA for NOS isoforms in the NOS activity-positive segments was then identified by RT-PCR. The IMCD contained mRNA for neuronal (nNOS), endothelial (eNOS), and inducible NOS (iNOS), but Glm and VR only expressed the mRNA for nNOS and eNOS. These experiments demonstrate that the greatest enzymatic activity for NO production in the kidney is in the IMCD, three- to sixfold less activity is present in the Glm and VR, and minimal NOS activity is found in other segments studied.