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.

Abstract-This study exammed the effect of intravenous mfuslon of subpressor doses of anglotensm (Ang II) on renal medullary blood flow (MBF), medullary partial oxygen pressure (PoJ, and mtnc oxide (NO) concentration under normal condltlons and during reduction of the medullary nitric oxide synthase (NOS) activity m anesthetized rats With laser Doppler flowmetry and polarographlc measurement of PO, with mlcroelectrodes, Ang II (5 rig/kg per mmute) did not alter renal cortical and medullary blood flows or medullary PO, iV,-mtro-L-argmme methyl ester (L-NAME) was infused mto the renal medullary mterstltlal space at a dose of 1 4 pg/kg per minute, a dose that did not slgmficantly alter basal levels of MBF or PO, Intravenous mfuslon of Ang II at the same dose m the presence of L-NAME decreased MBF by 23% and medullary PO, by 28%, but it had no effect on cortical blood flow or arterial blood pressure An m vlvo rmcrodlalysls-oxyhemoglobm NO trappmg technique was used m other rats to determine tissue NO concentrations using the $ame protocol Ang II infusion mcreased tissue NO concentrations by 85% m the renal cortex and 150% m the renal medulla Renal medullary mterstltlal mfuclon of L-NAME(1 4 Fg/kg per mmute) reduced medullary NO concentrations and substantially blocked Ang II-induced increases m NO concentrations m the renal medulla, but not m the renal cortex Tissue slices of the renal cortex and medulla were studled to determine the effects of Ang II and L-NAME on the mtnte/mtrate production Ang II stimulated the rntrlte/mtrate production predominately m the renal medulla, which was slgmficantly attenuated by L-NAME We conclude that small elevations of clrculatmg Ang II levels increase medullary NO production and concentrations, which plays an important role m buffering the vasoconstrlctor effects of this peptlde and m mamtammg a constancy of MBF (Hypertension.1997;31[part 2]:271-276.)Key Words: nitric oxide n anglotensm II n renal hemodynamlcs n renal medulla n laser Doppler flowmetry T here have been many stumes defining the role of Ang II m the regulation of total renal blood flow, glomemlar filtration, and tubular transport The role of Ang II m the regulation of blood flow to the renal medulla, however, remains poorly understood It has been demonstrated that the vasa recta bundles exhibit a high density of Ang II receptors' and that Ang II can produce a remarkable vasoconstncaon of the Isolated perfused vasa recta * These observations have suggested that Ang II could pamclpate m the control of MBF as m the renal cortex However, m vlvo stu&es using laser Doppler flowmetry and vldeormcroscopy techmques have demonstrated that intravenous mfuslon of Ang II has mmlmal effects on MBF and can even increase papillary blood 5ow at high doses 3-6 This suggested that the vasoconstnctlve effects of Ang II on the medullary vessels could be modulated by stlmulatlon of a local counterregulatory mechamstn Gwen the importance of Ml3F m the long-term control of blood pressure,'" this counterregulatory mechanism may play an import...

New cancer rates exhibited a consistent-with-linear dependence on time beginning after initial cancer-free intervals ranging between 88 and 95 days. Epidermal hyperplasia was elevated by arsenite alone and UVR alone and was greater than additive for the combined exposures as were growth rates of the cancers. These results demonstrate the usefulness of a new animal model for studying the carcinogenic action of dietary arsenite on skin exposed to UVR and should contribute to understanding how to make use of animal data for assessment of human cancer risks in tissues exposed to mixtures of carcinogens and cancer-enhancing agents.

Abstract-Previous studies have shown that chronic salt loading increased renal interstitial adenosine concentrations and desensitized renal effects of adenosine, a phenomenon that could facilitate sodium excretion. However, the mechanisms responsible for the increased adenosine production and decreased adenosine response are poorly understood. This study examined the effects of the dietary high salt intake on adenosine metabolism and receptor expression in the renal cortex and medulla in Sprague Dawley rats. Fluorescent high-performance liquid chromatography analyses were performed to determine adenosine levels in snap-frozen kidney tissues. Comparing rats fed a normal (1% NaCl) versus high salt (4% NaCl) diet, renal adenosine concentrations in rats fed a high salt diet were significantly higher Key Words: adenosine Ⅲ 5Ј-nucleotidase Ⅲ adenosine deaminase Ⅲ salt intake Ⅲ kidney Ⅲ isoelectric focusing Ⅲ gel electrophoresis T he role of adenosine in the regulation of renal vascular tone and tubular function has been studied extensively. Adenosine produces a prompt, transient fall in renal blood flow and a decrease in glomerular filtration rate (GFR) when infused into the renal artery. It has been reported that the adenosine-induced decrease in GFR is associated with a fall in glomerular hydrostatic pressure resulting from preglomerular vasoconstriction and postglomerular vasodilation. 1,2 Adenosine A 1 receptor mediates preglomerular vasoconstriction, and A 2 receptor mediates postglomerular vasodilation. [1][2][3][4] Infusion of adenosine into the renal artery also produces diuresis and natriuresis in rats. 5 Micropuncture studies have indicated that adenosine inhibits sodium reabsorption in the loop of Henle. 6 With the use of isolated, perfused tubules and cultured tubular cell lines, adenosine has been reported to alter ion transport in the collecting duct 7,8 or the thick ascending limb, 9 indicating that adenosine may have a direct effect on tubules. Moreover, adenosine increases medullary blood flow, which also plays an important role in mediating the diuresis and natriuresis. 10

Abstract-Experiments were performed to quantify nitric oxide synthase (NOS) activity and identify the NOS isoforms present in the Sprague-Dawley rat renal vasculature. NOS enzymatic activity was measured by adding [ 3 H]arginine to microdissected renal blood vessels and quantifying the conversion to [ 3 H]citrulline by reverse-phase high-performance liquid chromatography. Total NOS activity was greatest in microdissected vasa recta (123Ϯ41 pmol ⅐ mg Ϫ1 ⅐ h Ϫ1 , nϭ5) and significantly less in glomeruli (46Ϯ9 pmol ⅐ mg Ϫ1 ⅐ h Ϫ1 , nϭ6) and afferent arterioles (42Ϯ10 pmol ⅐ mg Ϫ1 ⅐ h Ϫ1 , nϭ6) and averaged Ͻ5 pmol ⅐ mg Ϫ1 ⅐ h Ϫ1 in arcuate (nϭ8) and interlobular (nϭ9) arteries. Addition of 1.0 mmol/L EDTA to the reaction decreased NOS activity to Ͻ5 pmol ⅐ mg Ϫ1 ⅐ h Ϫ1 in afferent arterioles, glomeruli, and vasa recta (nϭ5 each), indicating that the NOS enzymatic activity in these segments is primarily a result of constitutive NOS. Both neuronal and endothelial NOS mRNA were identified in each vascular segment by reverse transcription-polymerase chain reaction, but inducible NOS mRNA was detected only in microdissected arcuate arteries. The present experiments indicate that the vasa recta, glomeruli, and afferent arterioles contain large amounts of calcium-dependent NOS enzymatic activity and that neuronal NOS and endothelial NOS mRNA are present in these segments. Key Words: rats, Sprague-Dawley Ⅲ kidney Ⅲ nitric oxide synthase Ⅲ RNA N itric oxide (NO) has potent effects on the renal vasculature. The inhibition of NO synthase (NOS) leads to increased renal vascular resistance, 1-5 whereas stimulation of endogenous NOS after L-arginine administration leads to decreased vascular resistance. 6 A number of studies have demonstrated that inhibition or stimulation of NOS can influence the diameter of large preglomerular vessels, 7,8 the afferent and efferent arterioles, 7-10 and vasa recta. 11 Therefore, NO is an important modulator of vascular tone throughout the renal vasculature.Many biochemical and molecular studies have been performed to identify both mRNA and immunoreactive protein of neuronal NOS (nNOS), endothelial NOS (eNOS), and inducible NOS (iNOS) in renal vessels. The mRNA for nNOS has been localized in glomeruli and vasa recta 12 ; nNOS protein has been identified in efferent arterioles 13 ; eNOS mRNA has been identified in glomeruli, arcuate arteries, interlobular arteries, and afferent arterioles 14 ; and eNOS protein has been identified in the endothelium of preglomerular and postglomerular vessels by immunohistochemical techniques. 13 The mRNA encoding iNOS has also been found in arcuate and interlobular arteries and glomeruli by in situ hybridization and reverse transcription (RT)-polymerase chain reaction (PCR) of microdissected segments. 15 Despite these types of studies, however, there is little information available regarding NOS enzymatic activity in the individual segments of the renal vasculature. The present study was designed to examine total and calcium-independent NOS enzymatic activity in ...