Case and reanalysis

In this paper we discuss an asymmetry in the Case system of German and its implications for human sentence processing: the asymmetry between nominative/accusative and dative case. Starting from the assumption that dative case has a distinct grammatical representation--dative DPs are embedded into an extra structural layer KP--the results of two experiments will be presented, which show that dative assignment during reanalysis is accompanied by additional processing operations that are not needed when accusative or nominative are assigned. In particular, we show that dative assignment during reanalysis triggers reaccess to the mental lexicon, giving rise to greater processing difficulty. We conclude with a discussion of empirical and theoretical consequences of our findings.

Functional, biochemical, and molecular investigations of renal kallikrein-kinin system in diabetic rats

A reduction of renal kallikrein has been found in non-insulin-treated diabetic individuals, suggesting that an impaired renal kallikrein-kinin system (KKS) contributes to the development of diabetic nephropathy. We analyzed relevant components of the renal KKS in non-insulin-treated streptozotocin (STZ)-induced diabetic rats. Twelve weeks after a single injection of STZ, rats were normotensive and displayed hyperglycemia, polyuria, proteinuria, and reduced glomerular filtration rate. Blood bradykinin (BK) levels and prekallikrein activity were significantly increased compared with controls. Renal kallikrein activity was reduced by 70%, whereas urinary BK levels were increased up to threefold. Renal kininases were decreased as indicated by a 3-fold reduction in renal angiotensin-converting enzyme activity and a 1.8-fold reduction in renal expression of neutral endopeptidase 24.11. Renal cortical expression of kininogen and B2 receptors was enhanced to 1.4 and 1. 8-fold, respectively. Our data suggest that increased urinary BK levels found in severely hyperglycemic STZ-diabetic rats are related to increased filtration of components of the plasma KKS and/or renal kininogen synthesis in combination with decreased renal kinin-degrading activity. Thus, despite reduced renal kallikrein synthesis, renal KKS is activated in the advanced stage of diabetic nephropathy.

[The detection of transgenic animals using a polymerase chain reaction in situ]

The technique for detecting both foreign and host specific DNA sequences inside nuclei and chromosomes of single cells of transgenic mice with the help of polymerase chain reaction (PCR) in situ is described. The mouse preimplantation and postimplantation embryonic and adult cells were studied. The methodology is described in detail with particular attention to the optimization of composition of reaction mixture, kind of fixation and preliminary denaturation of target DNA. The reaction takes only several hours and needs no sophisticated equipment.

The heterotrimeric Gi(3) protein acts in slow but not in fast exocytosis of rat melanotrophs

Besides having a role in signal transduction some trimeric G-proteins may be involved in a late stage of exocytosis. Using immunocytochemistry and confocal microscopy we found that Gi(3)-protein resides mainly in the plasma membrane, whereas Gi(1/2-)protein is preferentially associated with secretory granules. To study the function of trimeric Gi(3)- and Gi(1/2)-proteins, secretory responses in single rat melanotrophs were monitored by patch-clamp membrane capacitance measurements. We report here that mastoparan, an activator of trimeric G-proteins, enhances calcium-induced secretory activity in rat melanotrophs. The introduction of synthetic peptides corresponding to the C-terminal domain of the (α)-subunit of Gi(3)- and Gi(1/2)-proteins indicated that Gi(3)peptide specifically blocked the mastoparan-stimulated secretory activity, which indicates an involvement of a trimeric Gi(3)-protein in mastoparan-stimulated secretory activity. Flash photolysis of caged Ca(2+)-elicited biphasic capacitance increases consisting of a fast and a slower component. Injection of anti-Gi(3) antibodies selectively inhibited the slow but not the fast component of secretory activity in rat melanotrophs. We propose that the plasma membrane-bound Gi(3)-protein may be involved in regulated secretion by specifically controlling the slower kinetic component of exocytosis.

Biomonitoring of manganese in blood, urine and axillary hair following low-dose exposure during the manufacture of dry cell batteries

OBJECTIVES

A cross-sectional study was carried out on 100 workers from three different workplace areas in a dry cell battery manufacturing plant and on 17 currently nonexposed referents, to examine the relationship between the external exposure to manganese dioxide (MnO(2)) and the body burden of manganese in blood, urine and hair.

METHODS

Inhalable dust was measured gravimetrically after stationary active sampling. Manganese was analyzed in dust samples, blood, urine and axillary hair by atomic absorption spectro- metry.

RESULTS

The average air concentrations of manganese in the three workplace areas were 4 microg/m(3) (range: 1-12 microg/m(3)), 40 microg/m(3) (12-64 microg/m(3)) and 400 microg/m(3) (137-794 microg/m(3)). Manganese in blood and axillary hair correlated with airborne manganese in group-based calculations but not on an individual level. The manganese concentrations varied between 3.2 microg/l and 25.8 microg/l in the blood (mean: 12.2 +/- 4.8 microg/l) and between 0.4 microg/g and 49.6 microg/g in hair (mean: 6.2 +/- 6.2 microg/g in the proximal sequence), respectively. The results for the nonexposed referents were 7.5 +/- 2.7 microg/l (mean) in the blood (range: 2.6-15.1 microg/l) and 2.2 +/- 1.8 microg/g (mean) in axillary hair (range: 0.4-6.2 microg/g). In these matrices, manganese differed significantly between the highly exposed workers and both the reference and the low-exposure group. Manganese in blood revealed the lowest background variance. No differences for manganese in urine were observed between workers (mean: 0.36 +/- 0.42 microg/l, range: 0.1-2.2 microg/l) and referents (mean: 0.46 +/- 0.47 microg/l, range: 0.1-1.7 microg/l).

CONCLUSIONS

Manganese in blood is a specific and suitable parameter for the biomonitoring of MnO(2) exposure, although its validity is limited to group-based calculations. Urinary manganese failed to allow a differentiation between exposed workers and referents. The suitability of manganese analysis in hair for biomonitoring purposes suffers from a relatively great background variation as well as from analytical problems.

Myocardial expression of rat bradykinin receptors and two tissue kallikrein genes in experimental diabetes

To characterize the role of the kallikrein-kinin system in diabetic cardiopathy, we studied the effect of streptozotocin (STZ) on the regulation of the myocardial bradykinin (BK) receptors, the B1 and B2 type, and two tissue kallikrein genes, rat kallikrein 1 (rKLK1) and rKLK7, in severely hyperglycemic rats. Experiments were performed in STZ-induced diabetic male Wistar rats (n = 7) and compared to controls (n = 7). After extraction of myocardial total RNA, specific oligonucleotides were used to generate reverse transcription PCR (RT-PCR) products from myocardial rKLK1 and rKLK7 mRNA. Southern blot analyses of these RT-PCR products were hybridized with appropriate gene-specific oligonucleotide probes. Myocardial B1 and B2 receptor expression were analyzed by RNase protection assays using specific probes from the coding region of the receptor genes. Twelve weeks after diabetes induction, the rats were normotensive and hyperglycemic and polyuric. We observed an impairment of the main myocardial kinin-forming enzymes, indicated by a reduction of the expression of both, rKLK1 and rKLK7. At this time the myocardial expression of the B1 receptor was not detectable in either group. Thus, the B1 receptor does not play a regulatory role in either the healthy or in STZ-diabetic heart. In contrast, the B2-receptor expression was detectable but did not differ significantly in either group. The reduced synthesis of myocardial tissue KLK implies a reduced capacity to generate BK in diabetic rats. This reduction is not compensated by elevated BK receptor levels. We suggest that alterations of the KKS may contribute to myocardial dysfunction in diabetes mellitus.

Upregulation of the cardiac bradykinin B2 receptors after myocardial infarction

An increase in myocardial bradykinin (BK) might be a mechanism to protect the heart during acute myocardial infarction (MI). To characterize the regulation of the myocardial B2 receptor during MI, we studied the expression of this BK receptor in the right ventricle (RV), left ventricle (LV) and myocardial septum (S) 24 h after left coronary ligation. Experiments were performed in male Wistar Kyoto rats (n = 10) and compared with sham operated animals (n = 6). After total RNA extraction, the myocardial B2-receptor expression was analyzed by a RNase protection assay (n = 6), using a specific probe from the coding region of the receptor gene. After 24 h, rats with MI were normotensive and showed an impaired left ventricular function. The B2-receptor expression of the LV of these rats was significantly elevated (2.3-fold) compared to sham operated rats. Furthermore, we found a dramatic upregulation of the B2 receptor in the RV (7.8-fold) and a dramatic expression of B2 receptor mRNA in S of infarcted hearts, whereas in the S of sham operated rats no B2 receptor expression could be detected. Our data show clearly that the described increase in BK during myocardial ischemia is accompanied by an elevated B2-receptor expression in the infarcted and non-infarcted parts of cardiac ventricles.

Larger anastomoses in angiotensinogen-knockout mice attenuate early metabolic disturbances after middle cerebral artery occlusion

Abnormalities in the homeostasis of the renin-angiotensin system have been implicated in the pathogenesis of vascular disorders, including stroke. The authors investigated whether angiotensinogen (AGN) knockout mice exhibit differences in brain susceptibility to focal ischemia, and whether such differences can be related to special features of the collateral circulation. Wild-type and AGN-knockout mice were submitted to permanent suture occlusion of the middle cerebral artery (MCA). The collateral vascular system was visualized by systemic latex infusion, and the ischemic lesions were identified by cresyl-violet staining. The core and penumbra of the evolving infarct were differentiated by bioluminescence and autoradiographic imaging of ATP and protein biosynthesis, respectively. In wild-type mice, mean arterial blood pressure was 95.0 +/- 8.6 mm Hg, and the diameter of fully relaxed anastomotic vessels between the peripheral branches of the anterior and middle cerebral arteries 26.6 +/- 4.0 microm. In AGN knockouts, mean arterial blood pressure was significantly lower, 71.5 +/- 8.5 mm Hg (P < .01), and the anastomotic vessels were significantly larger, 29.4 +/- 4.6 microm (P < .01). One hour after MCA occlusion, AGN-knockout mice exhibited a smaller ischemic core (defined as the region of ATP depletion) but a larger penumbra (the area of disturbed protein synthesis with preserved ATP). At 24 hours after MCA occlusion, this difference disappeared, and histologically visible lesions were of similar size in both strains. The observations show that in AGN-knockout mice the more efficient collateral blood supply delays ischemic injury despite the lower blood pressure. Pharmacologic suppression of angiotensin formation may prolong the therapeutic window for treatment of infarcts.

Oxidative protein folding is driven by the electron transport system

Disulfide bond formation is catalyzed in vivo by DsbA and DsbB. Here we reconstitute this oxidative folding system using purified components. We have found the sources of oxidative power for protein folding and show how disulfide bond formation is linked to cellular metabolism. We find that disulfide bond formation and the electron transport chain are directly coupled. DsbB uses quinones as electron acceptors, allowing various choices for electron transport to support disulfide bond formation. Electrons flow via cytochrome bo oxidase to oxygen under aerobic conditions or via cytochrome bd oxidase under partially anaerobic conditions. Under truly anaerobic conditions, menaquinone shuttles electrons to alternate final electron acceptors such as fumarate. This flexibility reflects the vital nature of the disulfide catalytic system.

Returning perchlorate-contaminated fume hood systems to service. Part II. Disassembly, decontamination, disposal, and analytical procedures

Part I presented work leading up to and including a pilot study for remediation of laboratory fume hood systems contaminated with residues from processes that used fuming perchloric acid. Since publication of Part I, three incidents involving explosions and fires related to perchlorates have come to the attention of the authors. Experience has been gained through decontamination/remediation of 41 additional systems. This article expands on previous one and includes (1) administrative details that need to be addressed before and during the execution of the decontamination itself, (2) a seven-step procedure for decontamination-remediation/disposal, (3) some precautions associated with the use of methylene blue as a diagnostic tool for perchlorates, and-specific electrode to augment or replace the methylene blue test.

Serotonin synthesis in murine embryonic stem cells

Serotonin (5-HT) is a monoaminergic neurotransmitter involved in various processes in the mammalian nervous system with tryptophan hydroxylase (TPH) as the rate-limiting enzyme in its biosynthesis. Interestingly, there is accumulating evidence that neurotransmitters including 5-HT are directly involved in cleavage divisions and morphogenetic movements during early embryogenesis, even before neurons appear. Clonal cell models will be indispensable for investigating these pre-neuronal actions of neurotransmitter systems. Totipotent embryonic stem (ES) cells represent early embryonic stages, are amenable to genetic manipulations and can be easily induced to differentiate into cells with neuronal and glial properties enabling the recapacitation of neurulation. In this study, we used high-pressure liquid chromatography with fluorometric detection (HPLC-FD) to demonstrate the presence of 5-HT in ES cells. In addition, RNase protection assays and immunohistochemical methods detected TPH mRNA and protein, respectively, confirming the endogeneous production of 5-HT in these cells. Furthermore, TPH protein was detected in mouse zygotes after fertilization. These results indicate that ES cells may be useful for the investigation of neurotransmitters in pre-nervous embryos and their actions during ontogeny.

Learning and anxiety in angiotensin-deficient mice

Angiotensin II in the brain was shown to be involved in mechanisms influencing cardiovascular and electrolyte homeostasis, anxiety and learning. Here, we report behavioural studies in mice lacking angiotensinogen. We analysed learning and anxiety related behaviour using the Morris water maze task and the elevated plus maze task, respectively. In both tests no differences were found between control mice and angiotensin-deficient mice. This implicates that angiotensin does not influence learning and anxiety-related behaviour in mice under normal conditions.

Blood pressure reduction and diabetes insipidus in transgenic rats deficient in brain angiotensinogen

Angiotensin produced systemically or locally in tissues such as the brain plays an important role in the regulation of blood pressure and in the development of hypertension. We have established transgenic rats [TGR(ASrAOGEN)] expressing an antisense RNA against angiotensinogen mRNA specifically in the brain. In these animals, the brain angiotensinogen level is reduced by more than 90% and the drinking response to intracerebroventricular renin infusions is decreased markedly compared with control rats. Blood pressure of transgenic rats is lowered by 8 mmHg (1 mmHg = 133 Pa) compared with control rats. Crossbreeding of TGR(ASrAOGEN) with a hypertensive transgenic rat strain exhibiting elevated angiotensin II levels in tissues results in a marked attenuation of the hypertensive phenotype. Moreover, TGR(ASrAOGEN) exhibit a diabetes insipidus-like syndrome producing an increased amount of urine with decreased osmolarity. The observed reduction in plasma vasopressin by 35% may mediate these phenotypes of TGR(ASrAOGEN). This new animal model presenting long-term and tissue-specific down-regulation of angiotensinogen corroborates the functional significance of local angiotensin production in the brain for the central regulation of blood pressure and for the pathogenesis of hypertension.

Transcriptional regulation of the rat renin gene by regulatory elements in intron I

Renin catalyzes the rate-limiting step in the enzymatic cascade leading to the vasoactive peptide angiotensin II. Therefore, the activity of the renin-angiotensin system in a tissue is regulated significantly at the level of transcription of the renin gene. Besides transcription factor binding sites in the promoter region, the renin genes of human and rat contain regulatory elements also in intron I. Inclusion of intron I in reporter gene constructs with the renin promoter leads to a marked down-regulation of gene expression in nonrenin expressing 293 human embryonic kidney cells but has hardly any effect in renin-expressing L8 rat skeletal myoblasts. In combination with the cytomegalovirus immediate early gene promoter, the silencing occurs in both cell lines but is less pronounced in L8 cells. By partially deleting intron I in these constructs, we describe 5 negative (I-NRE) and 2 positive (I-PRE) regulatory elements responsible for these effects. Using gel-retardation and methylation-interference assays with 293-nuclear extracts, we detected a pseudo-palindromic protein-binding sequence between position +159 and +171 relative to the transcriptional start site. Binding of transcription factors to this sequence may be important for the tissue-specific silencing of the renin gene outside the juxtaglomerular cells of the kidney.

Heat stress-induced B1 receptor synthesis in the rat: an ex vivo study

1. This ex vivo study was performed to characterize B1 receptor induction in rats submitted to heat stress. Changes in aortic isometric tension were recorded after a 90 min in vitro incubation with [des-Arg9]-bradykinin. B1 receptor mRNA were detected in aorta and heart using RT-PCR technique. 2. Aortic rings from sham rats did not respond to [des-Arg9]-bradykinin. In contrast, this agonist induced a concentration-dependent relaxation of aortic rings from rats submitted to lipopolysaccharide (LPS) treatment or to heat stress 24 h earlier. 3. The concentration-dependent relaxation induced by [des-Arg9]-bradykinin on aortic rings from heat-stressed rats was abolished by [des-Arg10]-HOE 140, a selective B1 receptor antagonist. 4. In endothelium denuded aortic rings from heat-stress rats, [des-Arg9]-bradykinin induced a concentration-dependent constriction. 5. Pretreatment of intact aortic rings from heat-stress rats with the cyclo-oxygenase inhibitor, diclofenac (1 microM) did not prevent the concentration-dependent relaxation in response to [des-Arg9]-bradykinin. In contrast. NO synthase inhibition with N(omega)-nitro-L-arginine methyl ester (30 microM) totally prevented the vasorelaxant response. 6. B1 receptor mRNA were not detected in aorta and heart from sham animals but were present in tissue from heat-stressed and LPS-treated rats. 7. In conclusion, our results suggest that heat stress induces a transcriptional activation of the B1 receptor gene. The induction of B1 receptors leads to an endothelium- and NO-dependent vasorelaxant response to [des-Arg9]-bradykinin.

Transgenic animal models for the functional analysis of vasoactive peptides

The interplay of vasoactive peptide systems is an essential determinant of blood pressure regulation in mammals. While the endothelin and the renin-angiotensin systems raise blood pressure by inducing vasoconstriction and sodium retention, the kallikrein-kinin and the natriuretic-peptide systems reduce arterial pressure by eliciting vasodilatation and natriuresis. Transgenic technology has proven to be very useful for the functional analysis of vasoactive peptide systems. As an outstanding example, transgenic rats overexpressing the mouse Ren-2 renin gene in several tissues become extremely hypertensive. Several other transgenic rat and mouse strains with genetic modifications of components of the renin-angiotensin system have been developed in the past decade. Moreover, in recent years gene-targeting technology was employed to produce mouse strains lacking these proteins. The established animal models as well as the main insights gained by their analysis are summarized in this review.

Molecular biology of the kallikrein-kinin system: from structure to function

The participation of the kallikrein-kinin system, comprising the serine proteases kallikreins, the protein substrates kininogens and the effective peptides kinins, in some pathological processes like hypertension and cardiovascular diseases is still a matter of controversy. The use of different experimental set-ups in concert with the development of potent and specific inhibitors and antagonists for the system has highlighted its importance but the results still lack conclusivity. Over the last few years, transgenic and gene-targeting technologies associated with molecular biology tools have provided specific information about the elusive role of the kallikrein-kinin system in the control of blood pressure and electrolyte homeostasis. cDNA and genomic sequences for kinin receptors B2 and B1 from different species were isolated and shown to encode G-protein-coupled receptors and the structure and pharmacology of the receptors were characterized. Transgenic animals expressing an overactive kallikrein-kinin system were established to study the cardiovascular effects of these alterations and the results of these investigations further corroborate the importance of this system in the maintenance of normal blood pressure. Knockout animals for B2 and B1 receptors are available and their analysis also points to the role of these receptors in cardiovascular regulation and inflammatory processes. In this paper the most recent and relevant genetic animal models developed for the study of the kallikrein-kinin system are reviewed, and the advances they brought to the understanding of the biological role of this system are discussed.

Alternative splicing of the mRNA coding for the human endothelial angiotensin-converting enzyme: a new mechanism for solubilization

Angiotensin converting enzyme (ACE) is a zinc metalloprotease anchored in the plasma membrane with a carboxy-terminal hydrophobic domain. In addition, the existence of a soluble form of ACE lacking the transmembrane domain has been reported. We show evidence for the existence of an mRNA specific for this isoform produced by alternative splicing. In human umbilical vein endothelial cells, two ACE mRNAs of different length (4.3 and 3.5 kb) were detected by Northern blot. Ribonuclease protection assays and the sequence of a PCR-amplified cDNA fragment show that the shortened ACE mRNA lacks the exons coding for the transmembrane domain of the protein. As this mRNA could be the source of soluble ACE, plasma ACE activity may be regulated on the level of mRNA processing.

Analysis of nitroaromatic compounds in urine by gas chromatography-mass spectrometry for the biological monitoring of explosives

Organic nitrocompounds are the most frequently used constituents of explosives and some of them have been evaluated to be highly toxic or even carcinogenic. Human contact with explosives may originate from a variety of sources, including occupational exposure during the production of ammunition as well as environmental exposure due to the contamination of soil and ground water reservoirs on former military production sites and training areas. This paper describes two gas chromatography-mass spectrometry-selected ion monitoring methods for the determination of twelve nitroaromatic compounds in urine (nitrobenzene, 1,2-dinitrobenzene, 1,3-dinitrobenzene, 1,3,5-trinitrobenzene, 2-nitrotoluene, 3-nitrotoluene, 4-nitrotoluene, 2,4-dinitrotoluene, 2,6-dinitrotoluene, 2,4,6-trinitrotoluene, 2-amino-4,6-dinitrotoluene, 4-amino-2,6-dinitrotoluene). The analytes are detectable in the lowest microg/l range, with imprecisions of 3-22% within series and 5-29% between series, depending on the compound of interest. Both procedures are rapid and relatively easy to perform and, therefore, are advantageous for the screening of occupationally or environmentally exposed persons. We analysed urine samples obtained from nine workers from an ammunition dismantling workshop and from twelve control persons. 2,4,6-Trinitrotoluene was detected in six samples at concentrations between 4 and 43 microg/l. The main metabolites of 2,4,6-trinitrotoluene, 4-amino-2,6-dinitrotoluene and 2-amino-4,6-dinitrotoluene, were found in a concentration range from 143 to 16,832 microg/l and from 24 to 5787 microg/l, respectively. Nonconjugated aminodinitrotoluenes were present as varying percentages of the total amount. 2,4-Dinitrotoluene and 2,6-dinitrotoluene were found in two samples (2-9 microg/l). Nitroaromatics were not detectable in urine specimens from control persons.

Sustained long term potentiation and anxiety in mice lacking the Mas protooncogene

The Mas protooncogene is a maternally imprinted gene encoding an orphan G protein-coupled receptor expressed mainly in forebrain and testis. Here, we provide evidence for a function of Mas in the central nervous system. Targeted disruption of the Mas protooncogene leads to an increased durability of long term potentiation in the dentate gyrus, without affecting hippocampal morphology, basal synaptic transmission, and presynaptic function. In addition, Mas-/- mice show alterations in the onset of depotentiation. The permissive influence of Mas ablation on hippocampal synaptic plasticity is paralleled by behavioral changes. While spatial learning in the Morris water maze is not significantly influenced, Mas-deficient animals display an increased anxiety as assessed in the elevated-plus maze. Thus, Mas is an important modulating factor in the electrophysiology of the hippocampus and is involved in behavioral pathways in the adult brain.

Reconstitution of a protein disulfide catalytic system

Disulfide bonds are important for the structure and stability of many proteins. In prokaryotes their formation is catalyzed by the Dsb proteins. The DsbA protein acts as a direct donor of disulfides to newly synthesized periplasmic proteins. Genetic evidence suggests that a second protein called DsbB acts to specifically reoxidize DsbA. Here we demonstrate the direct reoxidation of DsbA by DsbB. We have developed a fluorescence assay that allows us to directly follow the reoxidation of DsbA. We show that membranes containing catalytic amounts of DsbB can rapidly reoxidize DsbA to completion. The reaction strongly depends on the presence of oxygen, implying that oxygen serves as the final electron acceptor for this disulfide bond formation reaction. Membranes from a dsbB null mutant display no DsbA reoxidation activity. The ability of DsbB to reoxidize DsbA fits Michaelis-Menten behavior with DsbA acting as a high affinity substrate for DsbB with a Km = 10 microM. The in vitro reconstitution described here is the first biochemical analysis of DsbB and allows us to study the major pathway of disulfide bond formation in Escherichia coli.

Cortical and medullary hemodynamics in deoxycorticosterone acetate-salt hypertensive mice

The effect of acutely increasing renal perfusion pressure or extracellular fluid volume on renal medullary and cortical blood flow was examined in the low-renin deoxycorticosterone acetate (DOCA)-salt hypertension model in mice. A 50-mg DOCA tablet was implanted, and 1% saline was given as drinking water for 3 wk. Medullary and cortical blood flow were determined with laser-Doppler flowmetry, and whole-kidney blood flow was measured with a transit-time ultrasound flowprobe around the renal artery. In control mice, total renal blood flow ranged from 6.3 and 7.6 ml/min per g kidney weight and in DOCA-salt mice from 4.3 and 4.7 ml/min per g kidney weight, respectively, and was minimally affected as renal perfusion pressure was increased. Renal vascular resistance increased correspondingly. During stepwise increases in renal artery pressure from 90 to 140 mmHg, medullary blood flow progressively increased in control mice to 125% of baseline values, whereas cortical blood flow did not change. In DOCA-salt mice, increasing BP from 100 to 154 mmHg had no effect on either cortical or medullary blood flow. Urine flow and sodium excretion were lower in DOCA-salt mice than in controls and increased nearly to the same extent in both groups after volume expansion with isotonic saline. Total renal blood flow increased after saline loading, more in controls than in DOCA-salt mice. Increases in medullary blood flow after saline loading were up to 122% of baseline values in controls and demonstrated a significantly steeper slope than the 110% of baseline increases in DOCA-salt mice. Cortical blood flow, however, was not different between the groups. Thus, medullary blood flow is not as tightly autoregulated as cortical blood flow in normal mice. Natriuresis with acute volume loading is facilitated by increased medullary blood flow. In DOCA-salt mice, the medullary blood flow reaction to renal perfusion pressure increases is abolished, whereas flow increases with extracellular volume expansion are diminished. These results suggest that diminished pressure-natriuresis responses in DOCA-salt mice are related to perturbed medullary blood flow.