Increase In Cortical Blood Flow Research Articles

Unraveling a Novel Mechanism of Altered Glomerular Hemodynamics in Pre-diabetic Obesity

Background: In pre-diabetic obesity, disrupted glomerular autoregulation leads to increased glomerular capillary pressure and renal blood flow, causing potential barotrauma-induced glomerular damage. A decrease in Afferent arteriole ( Af-Art) resistance causes higher glomerular capillary pressure but the underlying mechanism behind this, specifically in pre-diabetic obesity, remains unclear. Hyperinsulinemia is common in pre-diabetic obesity, but its role in reducing Af-Art resistance in the kidneys is unknown. Kidney blood flow is auto-regulated by vasoconstriction via tubuloglomerular feedback (TGF) and vasodilation through the Distal convoluted tubule-2/connecting tubule (DCT-2/CNT) mechanism. Our earlier studies indicate increased Af-Art dilation in pre-diabetic obese rats through the DCT-2/CNT mechanism without affecting TGF. This DCT-2/CNT induced Af-Art dilation requires initiation from epithelial sodium channels (ENaC) present at this tubular segment and interestingly insulin is a known ENaC activator. Hypothesis: We hypothesize that in the context of pre-diabetic obesity, hyperinsulinemia contributes to an increase in renal cortical blood flow (CBF) by increasing DCT-2/CNT-induced Af-Art dilation, subsequently leading to glomerular injury. Methods: We assessed the effects of insulin on Af-Art dilation by perfusing juxtaposed DCT-2/CNT segments with insulin in normal rabbits. Contribution of DCT-2/CNT induced Af-Art dilation was measured by co-administration of the ENaC blocker benzamil. To study hyperinsulinemia's role in an in-vivo setting without altering blood glucose levels, we used a hyperinsulinemic-euglycemic (HI-EUG) clamp in obese rats with intravenous (IV) glucose and insulin infusions. Renal CBF and blood pressure were monitored using a laser Doppler probe and femoral artery catheter, respectively, both with and without benzamil administration (400 μg/kg, IV). To evaluate insulin's potential role in causation of renal damage, we infused insulin directly into one kidney of lean rats for 6 weeks via a renal sub-capsular catheter, with the contralateral kidney serving as control. Glomerular basement membrane (GBM) thickness, a marker of renal damage, was measured via electron microscopy. Untargeted lipidomic analysis of the renal cortex was performed to identify potential renal damage pathways in insulin infused kidneys. Results: Insulin perfusion in rabbits' DCT-2/CNT potentiated the dilation of adherent Af-Art compared to control infusions with artificial tubular fluid. ENaC inhibition reversed the insulin-induced Af-Art dilation, confirming that insulin increases Af-Art dilation through the ENaC-initiated DCT-2/CNT mechanism. In obese rats, insulin delivery using a HI-EUG clamp resulted in a significant 20.8±4.9% increase in CBF, which was negated by the administration of the ENaC blocker benzamil, indicating the potential involvement of DCT-2/CNT-mediated vasodilation. Neither the HI-EUG clamp nor benzamil infusion affected blood pressure. Additionally, continuous direct insulin infusion into the kidneys of lean rats led to an increase in glomerular basement membrane (GBM) thickness and ceramide accumulation in the renal cortex, both indicative of renal damage. Conclusion: Our study demonstrates that insulin directly augments DCT-2/CNT-mediated Af-Art dilation and increases renal cortical blood flow in obese rats. Chronic renal insulin infusion led to structural changes and damage markers in the kidney, independent of blood glucose and blood pressure levels. Henry Ford Health System Internal Funding. Pilot and Feasibility grant from southeast center for integrated metabolomics. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Effects of Fumarate on Blood Pressure and Renal Hemodynamics in Normotensive Rats: Possible Contribution of Sodium Potassium Co‐transporter (NKCC)

The tricarboxylic acid cycle product, fumarate, and its related products, have been implicated in the etiology of genetic and non‐genetic models of hypertension. Fumarate showed a mechanistic link to nitric oxide (NO) production and thus impacted blood pressure and renal hemodynamics in both models. This study evaluated the possibility of a role of fumarate in regulation of blood pressure and renal hemodynamics in normotensive rats and elucidate possible mechanisms involved. Animals were anaesthetized with Thiobutabarbital (100 mg/kg, ip). The carotid artery was cannulated for mean arterial blood pressure (MABP) measurement and the left kidney was exposed to measure cortical blood flow (CBF) and medullary blood flow (MBF). Blood and urine were collected to determine glomerular filtration rate (GFR), urine volume (Uv) and sodium excretion (UNaV). The fumarase inhibitor, pyromellitic acid (PMA) (0.1 mg/kg/h), or fumarate (0.1 mg/kg/h) were infused in these animals. To determine renal sodium excretory mechanisms involved with fumarate, fumarate (1 mg/kg, po) was administered to normotensive rats treated with hydrochlorothiazide (HCTZ) (10 mg/kg, po) or furosemide (10 mg/kg, po), urine was collected hourly for five (5) hours and assayed for sodium. Fumarate elicited a hypotensive effect, with peak effect at the 45th minute (126 ± 6.2 vs 93 ±2.6 mmHg, p<0.05). Similarly, inhibition of fumarase caused a time‐dependent decrease in MABP (p<0.05). There was a consistent drop in CBF in fumarate‐infused rats and although PMA caused an initial rise in CBF at 15 mins, there was a 10‐fold increase in CBF at 60 min when compared to fumarate‐infused rats (p<0.05). MBF also decreased in a time‐dependent fashion in rats infused with fumarate. Consistent with the drop in MABP and CBF, GFR reduced (0.89 ± 0.26 vs 0.39 ± 0.11 mL/min, p<0.05) at 30 mins before to returning to baseline levels at 60 mins in fumarate‐infused rats. Uv was unchanged in rats infused with fumarate but there was a 1‐fold reduction in UNaV at 30 mins (p<0.05). Also, PMA, tended to increase UNaV at 30 mins, compared to baseline. However, there was an exacerbation in UNaV in PMA‐infused rats (24.2 ± 3.8 µmol/L) compared to fumarate‐infused rats at 30 mins (4.56 ±1.4 µmol/L, p<0.05). Fumarate increased UNaV compared to control (p<0.05), however, there was no significant difference in UNaV between furosemide‐treated and furosemide‐treated fumarate rats. These data indicate that fumarate and its products elicited vasodilatory effects that reduced blood pressure and exerted vascular and tubular effects on renal hemodynamics. Also, the tubular effects, possibly involves inhibition of sodium potassium co‐transporter (NKCC).

Abstract P025: Hyperinsulinemia Causes Renal Hyperperfusion And Increases Glomerular Basement Membrane Thickness Independent Of Renal Perfusion Pressure And Glycemic Status: Potential Role Of Connecting Tubule Glomerular Feedback?

Obesity is often associated with hyperinsulinemia (HI) and renal damage. However, the role of HI in Obesity related Renal Damage (ORD) is unclear. Renal hyperperfusion/hyperfiltration plays a major role in ORD. Normally, the kidneys autoregulate blood flow by two feedback mechanisms: 1.) Tubuloglomerular feedback (TGF), a vasoconstrictor mechanism and 2.) Connecting Tubule Glomerular Feedback (CTGF), a vasodilator mechanism. Previously, we found that Zucker obese rats had higher CTGF (TGF was unchanged) and were hyperinsulinemic before the development of ORD. Epithelial sodium channel (ENaC) initiates CTGF and Insulin is a known ENaC activator. Hypothesis: HI increases renal cortical blood flow (CBF) by increasing CTGF and causes renal damage. To isolate the effect of HI from the blood glucose (BG) level, HI-euglycemic clamp was created in normal anesthetized Sprague Dawley (SD) rats by simultaneous intravenous (IV) infusion of 10% glucose and insulin. Average baseline BG in non-fasted anesthetized SD rats was 199.0±31.6 mmol/L. Insulin infusion increased CBF significantly by 12.2 ± 1.3% (n=3, p<0.05) from the baseline even before the BG level starts decreasing. Insulin was further infused to attain normoglycemic condition (96.0±2.3 mmol/L) and this was associated with additional increase in CBF by 19.2 ± 4.5% (p<0.05) from the baseline. Subsequent ENaC inhibition by benzamil (BZ) (400 μg/kg, IV) completely reversed the insulin-induced increase in CBF. Neither Insulin nor BZ treatment altered the renal perfusion pressure (RPP) suggesting insulin-induced increase in CBF was independent of RPP. In a separate group of SD rats, renal-HI (1.8 IU/kg/day) was created in only one of the two kidneys for 6 weeks using renal subcapsular catheter to measure glomerular basement membrane (GBM) thickness (a marker of renal damage). GBM was significantly thickened in insulin-infused kidney compared to vehicle-infused kidney (199.4±17 vs. 145.5±3.6nm, n=3, p<0.05). Conclusion: Acute HI increased CBF, that was completely reversed by ENaC inhibition implying a possible role of enhanced CTGF. Chronic renal-HI caused GBM thickening. Perspective: HI observed in obesity or type-2 diabetes may cause renal hyperperfusion by increasing CTGF and contribute to the ORD.

NMDA attenuates the neurovascular response to hypercapnia in the neonatal cerebral cortex

Cortical spreading depolarization (SD) involves activation of NMDA receptors and elicit neurovascular unit dysfunction. NMDA cannot trigger SD in newborns, thus its effect on neurovascular function is not confounded by other aspects of SD. The present study investigated if NMDA affected hypercapnia-induced microvascular and electrophysiological responses in the cerebral cortex of newborn pigs. Anesthetized piglets were fitted with cranial windows over the parietal cortex to study hemodynamic and electrophysiological responses to graded hypercapnia before/after topically applied NMDA assessed with laser-speckle contrast imaging and recording of local field potentials (LFP)/neuronal firing, respectively. NMDA increased cortical blood flow (CoBF), suppressed LFP power in most frequency bands but evoked a 2.5 Hz δ oscillation. The CoBF response to hypercapnia was abolished after NMDA and the hypercapnia-induced biphasic changes in δ and θ LFP power were also altered. MK-801 prevented NMDA-induced increases in CoBF and the attenuation of microvascular reactivity to hypercapnia. The neuronal nitric oxide synthase (nNOS) inhibitor (N-(4 S)-4-amino-5-[aminoethyl]aminopentyl-N′-nitroguanidin) also significantly preserved the CoBF response to hypercapnia after NMDA, although it didn’t reduce NMDA-induced increases in CoBF. In conclusion, excess activation of NMDA receptors alone can elicit SD-like neurovascular unit dysfunction involving nNOS activity.

Effect of radial nerve stimulation on regional cerebral blood flow in anesthetized mice

In urethane anesthetized mice, we measured the regional blood flow in the frontal, parietal and occipital regions of the neocortex and in the olfactory bulb, bilaterally and simultaneously, by laser speckle contrast imaging, and the effect of unilateral electric stimulation of the radial nerve. In CNS-intact mice, radial nerve stimulation increased arterial pressure and increased cortical blood flow. After spinal cord transection at the 1st thoracic level, radial nerve stimulation had no effect on blood pressure but maintained its widespread effect on blood flow in the cerebral cortex. In contrast, nerve stimulation slightly decreased blood flow in the olfactory bulb. Cortical blood flow increased when the radial nerve was stimulated at an intensity above the threshold of C-fiber excitation and was maximal when the frequency was as low as 2–5 Hz. The increase in cortical blood flow with nerve stimulation was much reduced by intravenous administration of an acetylcholine receptor antagonist. We conclude that electric stimulation of afferent C-fibers in the radial nerve of anesthetized mice induces widespread cholinergic vasodilatation and increased blood flow in the main neocortical areas but not in the olfactory bulb.

Renal vasculature reactivity to agonist of P2X7 receptor is increased in streptozotocin-induced diabetes.

Diabetic nephropathy is characterized by the dysfunction of renal microvasculature. The involvement of the P2X7 receptor, being a part of the purinergic system, is presumable in this process. The aim of our study was to investigate the P2X7 receptor-mediated renal microvasculature response and renal metabolism of extracellular adenine nucleotides in diabetic rats. Study was performed on streptozotocin-induced diabetic Wistar rats. The vascular response to BzATP, an agonist of the P2X7 receptor, was monitored based on the changes of cortical blood flow (CBF), glomerular filtration rate (GFR) and glomerular inulin space (GIS). The renal interstitial fluid (RIF) was probed by microdialysis technique and concentrations of ATP and adenosine were measured. Activity on NTDPase and 5'-nucleotidases was measured on renal membranes. Diabetic kidneys were characterized by decreased ATP RIF and increased adenosine RIF concentrations with accompanied enhancement of NTDPase and 5'-nucleotidase activities. BzATP induced a more pronounced increase of CBF and decrease of GFR and GIS in diabetes rats. These effects were abolished by A438079, an antagonist of the P2X7 receptor. It is possible that increased P2X7 receptor reactivity may be involved in the pathogenesis of diabetic nephropathy.

Abstract 89: Nitrite After Cardiac Arrest Has Mitochondrial Antioxidant Effects Reducing Reperfusion Cerebral Hyperemia

Background: Nitrite confers neuroprotection after asphyxial cardiac arrest (ACA) through uncertain mechanisms though others have demonstrated antioxidant effects and improved blood flow after ischemia. We hypothesized that nitrite would modulate reperfusion blood flow and reduce reactive oxygen species (ROS). Methods: Adult male SD rats were intubated and catheterized. Cardiac output (CO) was measured using an ultrasonic flow probe (ascending aorta), cortical blood flow (CBF) was measured using laser speckle imaging (5mm craniotomy). 5m post-ROSC from 8m ACA, animals were randomized to a 500 ul 10m infusion of 8 uM nitrite or plasmalyte placebo. Physiology was measured for 1h and normalized to pre-arrest baseline. Brains were removed at 1h and homogenized for ascorbate measurement (ac-TEMPO). Separately, brains removed 15m post-ROSC had mitochondria isolated by Percoll gradient. Respiration was measured using a Clark electrode and ROS generation quantified by Amplex Red fluorescence +/- UV pretreatment to lyse S-nitrosothiols. Pyruvate/malate or succinate +/- ADP were the substrates. Results: Animals had similar baseline physiology. In placebo animals, post-RSOC hypertension resulted in significant increases in CBF (187%) compared to nitrite treated animals (136%; p<0.01; Figure): This difference persisted until 20 min after ROSC at which point groups converged. Nitrite treated animals had significantly higher levels of ascorbate (33.09 nmol/mg protein) compared to placebo treated animals (26.17; p=0.027). ROS generation with pyruvate substrate was reduced with nitrite therapy with minimal effects on respiration ( Figure ). This difference was reversed with UV pretreatment and not present with succinate. Conclusion: Nitrite is antioxidant after ROSC, preserving ascorbate, reducing mitochondrial ROS generation at complex I presumably via S-nitrosation and blunting loss of autoregulation and hyperemia.

Resolving the transition from negative to positive blood oxygen level-dependent responses in the developing brain

The adult brain exhibits a local increase in cortical blood flow in response to external stimulus. However, broadly varying hemodynamic responses in the brains of newborn and young infants have been reported. Particular controversy exists over whether the "true" neonatal response to stimulation consists of a decrease or an increase in local deoxyhemoglobin, corresponding to a positive (adult-like) or negative blood oxygen level-dependent (BOLD) signal in functional magnetic resonance imaging (fMRI), respectively. A major difficulty with previous studies has been the variability in human subjects and measurement paradigms. Here, we present a systematic study in neonatal rats that charts the evolution of the cortical blood flow response during postnatal development using exposed-cortex multispectral optical imaging. We demonstrate that postnatal-day-12-13 rats (equivalent to human newborns) exhibit an "inverted" hemodynamic response (increasing deoxyhemoglobin, negative BOLD) with early signs of oxygen consumption followed by delayed, active constriction of pial arteries. We observed that the hemodynamic response then matures via development of an initial hyperemic (positive BOLD) phase that eventually masks oxygen consumption and balances vasoconstriction toward adulthood. We also observed that neonatal responses are particularly susceptible to stimulus-evoked systemic blood pressure increases, leading to cortical hyperemia that resembles adult positive BOLD responses. We propose that this confound may account for much of the variability in prior studies of neonatal cortical hemodynamics. Our results suggest that functional magnetic resonance imaging studies of infant and child development may be profoundly influenced by the maturing neurovascular and autoregulatory systems of the neonatal brain.

Action of 4-aminopyridine on the cerebral circulation.

4-Aminopyridine (4-AP) facilitates both inhibitory and excitatory synaptic activity in the central nervous system, and may, therefore, be a drug of potential therapeutic use in brain diseases with a disturbed synaptic transmission. In the present study the vasomotor effects upon isolated feline brain vessels, and regional cerebral blood flow and brain cortical metabolism in rats were examined. At high concentrations (above 10-6 M) a minor vasoconstriction was obtained of isolated pial vessels. Measurements of regional cerebral blood flow using the 14C-ethanol technique resulted in a significant increase in blood flow of caudate nucleus (93%), thalamus (74%) and cerebellum (82%). The arteriovenous oxygen difference of cortical tissue was reduced from 3.20 mmol O2/ml to 1.69 mmol O2/ml by 4-AP. This was not associated with an increase in cortical blood flow. Calculation of the cortical metabolic rate of oxygen, however, failed to demonstrate any significant change.

N-Methyl-d-Aspartate Induces Cortical Hyperemia through Cortical Spreading Depression-Dependent and -Independent Mechanisms in Rats

N-methyl-d-aspartate (NMDA) is a powerful cerebrovascular dilator in vivo. Cortical spreading depression (CSD) has recently been shown to contribute to the pial arteriolar dilation in mice. Our main aim was to examine the participation of CSD in the overall cerebrovascular response to NMDA in the rat. Anesthetized Wistar rats (eight weeks old) were equipped with a closed cranial window to allow topical application of NMDA (10(-5)-10(-3) M) to the parietal cortex. Cortical blood flow (CoBF) under and outside the cranial window was simultaneously monitored by using a two-channel laser-Doppler flowmeter. CSDs were detected by recording the changes in the cortical DC potential. Concentrations of 10(-4) and 10(-3) M of NMDA evoked single CSDs associated with rapid, transient hyperemia, followed by a sustained, but reduced, increase in CoBF. The latency and magnitude of the CoBF responses were dose dependent. The higher dose resulted in shorter latency (100+/-5* vs. 146+/-11 seconds, *P<0.05; mean+/-standard error of the mean) and larger overall flow response (77+/-12* vs. 28+/-3% from baseline) under, but not outside, the cranial window. NMDA elicits dose-dependent increases in CoBF that are composed of CSD-dependent and -independent components in rats.

N-methyl-D-aspartate increases cortical blood flow in part by evoking cortical spreading depression in Wistar, and insulin resistant Zucker rats

Event Abstract Back to Event N-methyl-D-aspartate increases cortical blood flow in part by evoking cortical spreading depression in Wistar, and insulin resistant Zucker rats Laura Lenti1, 2*, Ferenc Domoki1, 2, David W. Busija2 and Ferenc Bari1 1 Department of Physiology, University of Szeged, Hungary 2 Department of Physiology & Pharmacology, Wake Forest University Health Sciences, United States NMDA dilates pial arterioles via evoking cortical spreading depression (CSD) in mice; however, a dose-dependent action was described in piglets. The mechanism of the cerebral vascular response in rats is unclear. The purpose of our study was to critically examine the effect of NMDA on the cortical blood flow (CoBF) in this model. Further, we sought to determine whether this microvascular response is reduced in the Zucker obese rats, since insulin resistance (IR) impairs vascular reactivity of large cerebral arteries. Anesthetized, ventilated Wistar (8 weeks old), Zucker obese and lean (12 weeks old, n=8-8) rats were equipped with closed cranial window. NMDA (10-4 10-3 M) was applied to the parietal cortex, while CoBF (using Laser-Doppler flowmetry) and cortical DC potential were monitored. NMDA evoked CSD at both concentrations in all experimental groups. After a rapid, transient hyperemia, sustained increases in CoBF were observed. The latency and peak amplitude of the CoBF response to CSD was dose-related: the higher dose resulted in shorter latency (100±5* vs. 146±11 s, all data from Wistars, *p<0.05) and larger amplitude (237±45* vs. 168±34, % of baseline). The sustained CoBF elevation after the CSD was also dose-dependent: 51±10* vs. 19±4% (average of 2-6th minutes after the peak values). CoBF responses were similar in lean and obese rats. In conclusion, the cerebrovascular response to NMDA in rats is partially due to CSDs. The unchanged CoBF response to NMDA/CSD in Zucker obese rats indicates that the microvascular response to this stimulus remains intact in IR. Supported by OTKA (K63401 and IN69967) Conference: 12th Meeting of the Hungarian Neuroscience Society, Budapest, Hungary, 22 Jan - 24 Jan, 2009. Presentation Type: Poster Presentation Topic: Pathophysiology and neurology - degenerative disorders Citation: Lenti L, Domoki F, Busija DW and Bari F (2009). N-methyl-D-aspartate increases cortical blood flow in part by evoking cortical spreading depression in Wistar, and insulin resistant Zucker rats. Front. Syst. Neurosci. Conference Abstract: 12th Meeting of the Hungarian Neuroscience Society. doi: 10.3389/conf.neuro.01.2009.04.162 Copyright: The abstracts in this collection have not been subject to any Frontiers peer review or checks, and are not endorsed by Frontiers. They are made available through the Frontiers publishing platform as a service to conference organizers and presenters. The copyright in the individual abstracts is owned by the author of each abstract or his/her employer unless otherwise stated. Each abstract, as well as the collection of abstracts, are published under a Creative Commons CC-BY 4.0 (attribution) licence (https://creativecommons.org/licenses/by/4.0/) and may thus be reproduced, translated, adapted and be the subject of derivative works provided the authors and Frontiers are attributed. For Frontiers’ terms and conditions please see https://www.frontiersin.org/legal/terms-and-conditions. Received: 05 Mar 2009; Published Online: 05 Mar 2009. * Correspondence: Laura Lenti, Department of Physiology, University of Szeged, Szeged, Hungary, lauralenti@yahoo.com Login Required This action requires you to be registered with Frontiers and logged in. To register or login click here. Abstract Info Abstract The Authors in Frontiers Laura Lenti Ferenc Domoki David W Busija Ferenc Bari Google Laura Lenti Ferenc Domoki David W Busija Ferenc Bari Google Scholar Laura Lenti Ferenc Domoki David W Busija Ferenc Bari PubMed Laura Lenti Ferenc Domoki David W Busija Ferenc Bari Related Article in Frontiers Google Scholar PubMed Abstract Close Back to top Javascript is disabled. Please enable Javascript in your browser settings in order to see all the content on this page.

N‐methyl‐D‐aspartate (NMDA) increases cortical blood flow in part by evoking cortical spreading depression (CSD) in insulin resistant Zucker rats

Insulin resistance (IR) leads to selective impairment of responsiveness of larger cerebral arteries but effects on total cortical blood flow (CoBF) have not been examined. The purpose of our study was to test whether NMDA‐induced cerebral vasodilation is altered in the Zucker obese rat, a genetic model of IR. Anesthetized, ventilated, 12 week old male Zucker obese (n=8) and lean (n=8) rats were equipped with closed cranial windows. NMDA (10‐4, 10‐3 M) was applied to the parietal cortex, while CoBF (Laser‐Doppler flowmetry) and cortical DC potential were monitored. NMDA evoked CSD often at 10‐4 and always at 10‐3 M concentration. The amplitude of the response was similar in the two groups at all doses. After the transient CSD‐induced hyperemia, sustained increases in CoBF occurred with both 10‐4–10‐3 M NMDA at 6–10 minutes and there were no differences between obese and lean rats. Increases in CoBF during application of 10‐4 and 10‐3 M NMDA (% of baseline, 6–10th min of NMDA, *p&lt;0.05 compared to vehicle) were 12±6 and 40±9*% in lean and 19±8% and 40±8*% in obese rats. Thus, similar to mice, the total cerebral vascular response to NMDA is due to direct effects by individual neurons as well as evoked CSDs. The retention of normal increases in CoBF in obese rats to NMDA/CSD indicates microvascular responses to some stimuli are intact in IR animals. Supported by the NIH (HL30260, HL65380, HL77731) and by the OTKA (K68976 and K63401).

Adenosine mediates decreased cerebral metabolic rate and increased cerebral blood flow during acute moderate hypoxia in the near-term fetal sheep.

Exposure of the fetal sheep to moderate to severe hypoxic stress results in both increased cortical blood flow and decreased metabolic rate. Using intravenous infusion of 8-cyclopentyl-1,3-dipropylxanthine (DPCPX), a selective adenosine A1 receptor antagonist that is permeable to the blood brain barrier, we examine the role of adenosine A1 receptors in mediating cortical blood flow and metabolic responses to moderate hypoxia. The effects of DPCPX blockade are compared to controls as well as animals receiving intravenous 8-(p-sulfophenyl)-theophylline) (8-SPT), a non-selective adenosine receptor antagonist which has been found to be blood brain barrier impermeable. Laser Doppler flow probes, tissue PO2, and thermocouples were implanted in the cerebral cortices of near-term fetal sheep. Catheters were placed in the brachial artery and sagittal sinus vein for collection of samples for blood gas analysis. Three to seven days later responses to a 30-min period of fetal hypoxemia (arterial PO2 10-12 mmHg) were studied with administration of 8-SPT, DPCPX, or vehicle. Cerebral metabolic rate was determined by calculation of both brain heat production and oxygen consumption. In response to hypoxia, control experiments demonstrated a 42 +/- 7 % decrease in cortical heat production and a 35 +/- 10 % reduction in oxygen consumption. In contrast, DPCPX infusion during hypoxia resulted in no significant change in brain heat production or oxygen consumption, suggesting the adenosine A1 receptor is involved in lowering metabolic rate during hypoxia. The decrease in cerebral metabolic rate was not altered by 8-SPT infusion, suggesting that the response is not mediated by adenosine receptors located outside the blood brain barrier. In response to hypoxia, control experiments demonstrated a 35 +/- 7 % increase in cortical blood flow. DPCPX infusion did not change this increase in cortical blood flow, however 8-SPT infusion attenuated increases in flow, indicating that hypoxic increases in cerebral blood flow are mediated by adenosine but not via the A1 receptor. In summary, adenosine appears to play a key role in fetal hypoxic defences, acting to increase O2 delivery via adenosine A2 receptors and to decrease metabolic rate via A1 receptors inside the blood brain barrier. These data show for the first time in the mammalian fetus that the adenosine A1 receptor is an important mediator of brain metabolic rate during moderate hypoxia.

Intrarenal blood flow distribution in hyperdynamic septic shock: Effect of norepinephrine.

To measure changes in medullary and cortical renal blood flow during experimental hyperdynamic sepsis and the effect of subsequent norepinephrine infusion on such flows. DESIGN Experimental animal study. Animal laboratory of university-affiliated physiology institute. SUBJECTS Eighteen anesthetized merino sheep. A transit-time flow probe was placed around the left renal artery. Laser Doppler flow probes were inserted in the left renal medulla and cortex by micromanipulation to measure changes in regional intrarenal blood flow. Systemic pressures, cardiac output, renal, and intrarenal blood flows were measured continuously. A bolus of Escherichia coli (7.5 x 10(9) colony forming units) was given intravenously to induce hyperdynamic sepsis. After the onset of hyperdynamic sepsis, all animals were randomly allocated to either norepinephrine (0.4 microg.kg-1.min-1 for 30 mins) or observation for 30 mins in random order. E. coli injection induced a significant decrease in mean arterial pressure (102.2 +/- 15.2 mm Hg to 74.3 +/- 16.1 mm Hg, p <.05) and an increase in mean cardiac output (4.60 +/- 1.62 L/min to 5.93 +/- 1.18 L/min, p <.05). However, renal blood flow did not change significantly (326.4 +/- 139.4 mL/min to 293.1 +/- 117.5 mL/min, not significant) despite a 30% increase in renal conductance (3.27 +/- 1.52 to 4.13 +/- 2.01 mL.min-1.mm Hg-1, p <.05). Cortical blood flow decreased by 15% (not significant) and medullary flow by 5% (not significant) during sepsis, but individual changes were unpredictable. On the other hand, norepinephrine infusion caused a significant improvement in mean arterial pressure (74.3 +/- 16.1 to 105.7 +/- 17.7 mm Hg, p <.05) and a further increase in cardiac output (5.93 +/- 1.18 to 7.13 +/- 1.52 L/min, p <.05). Mean renal blood flow also increased (293.1 +/- 117.5 to 384.5 +/- 168.1 mL/min, p <.05) despite decreased renal conductance (4.13 +/- 2.01 to 3.73 +/- 1.91 mL.min-1.mm Hg-1, p <.05). Infusion of norepinephrine significantly increased medullary blood flow by 35% compared with baseline (p <.05) and by 54% compared with untreated sepsis (p <.05), whereas the increases in cortical blood flow (16 and 53%, respectively) were not significant. Hyperdynamic sepsis caused renal vasodilation but had limited effects on regional intrarenal blood flow. Norepinephrine infusion (0.4 microg.kg-1.min-1) during sepsis significantly increased global and medullary renal blood flow and restored renal vascular tone toward but not above normal.

Role of nitric oxide in hypoxic cerebral vasodilatation in the ovine fetus.

To investigate the role of nitric oxide (NO) in fetal cerebral circulatory responses to acute hypoxia, near-term fetal sheep were instrumented with laser Doppler probes placed in the parasagittal parietal cortices and vascular catheters in the sagittal sinus and brachiocephalic artery. After a 3 day recovery period, responses of cortical blood flow (CBF) to hypoxia were compared with and without inhibition of nitric oxide synthase (NOS). After an initial 30 min baseline period, fetuses were given a bolus followed by a continuous infusion of Nomega-nitro-L-arginine methyl ester (L-NAME), or saline vehicle as control. After administration of L-NAME, CBF decreased by 14 +/- 6 % (P < 0.01) despite increases in arterial blood pressure of 15 mmHg, resulting in an ~60 % increase in cerebrovascular resistance. Thirty minutes following initiation of L-NAME or vehicle infusion, fetal systemic hypoxia was induced by allowing the ewes to breathe 10-11 % oxygen. In control fetuses CBF increased progressively to 145 +/- 9 % of baseline (P < 0.01) after 30 min, while cortical release of cyclic guanylate cyclase (cGMP), an index of NOS activity, increased 26 +/- 8 % (P < 0.05). In contrast, CBF in L-NAME-treated fetuses increased to only 115 % of the reduced CBF baseline, whereas cortical release of cGMP did not change significantly. In summary, basal levels of NO lower resting cortical vascular resistance by ~15 % in the fetal sheep. Inhibition of NO synthesis attenuates hypoxic cerebral relaxation but does not completely prevent the characteristic increases in CBF. Hypoxic increases in NO directly increase cortical production of cGMP and inhibition of NO synthesis ablates these changes in cGMP.

Isocortical hyperemia and allocortical inflammation and atrophy following generalized convulsive seizures of thalamic origin in the rat.

1. Generalized convulsive seizures can be elicited by a single unilateral microinjection of the cholinergic muscarinic agonist, carbachol, into the specific sites of the thalamus including ventral posterolateral and the reticular thalamic nuclei. The implication of the thalamic specific and reticular neurons is reviewed and discussed. 2. On the basis of the c-fos regional expression and well-known efferent and afferent pathways linking these regions, a neuronal network relating the limbic, thalamo-striatal-cortical, and central autonomic systems, was constructed. 3. The pattern of Fos immunoreactivity associated with long-lasting isocortical vasodilatation elicited by generalized convulsive seizures in anesthetized rat following cholinergic stimulation of the thalamus can be attributed to both the electrocortical activity and the long-lasting increase in cortical blood flow. We propose that the sustained cerebral cortical blood flow response during convulsive epileptic seizures may implicate intracerebral vasodilatory and vasoconstrictory neural mechanisms. Double-labeled NADPH-d and Fos-positive neurons implicated in maintaining the sustained isocortical vasodilatory response were found in the anterior lateral hypothalamic area. Inhibition of these neurons prevented the increase in cortical blood flow despite an increased metabolic demand manifested by the ictal electrocortical activity. 4. Medial temporal lobe atrophy, including hippocampus, amygdala, and parahippocampal gyrus (piriform and entorhinal cortices) are the most common pathology in man. However the origin of medial lobe atrophy remain uncertain. Our results provide evidence that the allocortical microvascular inflammation may be in origin of the neurovascular degenerative processes leading to atrophy.

Effects of the contrast medium iopromide on renal hemodynamics and oxygen tension in the diabetic rat kidney.

We investigated the effects of the contrast medium (CM) iopromide on regional renal blood flow and oxygen tension (pO2) in the streptozotocin (STZ)-induced diabetic Wistar Furth rats. In normoglycemic rats, CM injection induced a transient decrease followed by an increase in renal cortical blood flow (CBF), whereas CBF increased directly in the diabetic animals. Renal outer medullary blood flow (OMBF) increased in controls, while it decreased in the diabetic animals following CM injection. In control rats a marked initial decrease in OM pO2 following injection of CM was observed. In animals diabetic for 4 weeks only a slight decrease was seen, whereas in 9-week diabetic animals a persistent increase was recorded. An altered oxygen tension and hemodynamic response to CM was found in diabetic rats. If these disturbances may contribute to the development of renal dysfunction by CM in the diabetic rat kidney remains to be elucidated.

Intracerebral temperature alterations associated with focal seizures

Because focal seizures produce an increase in local cerebral metabolism and blood flow, we wanted to determine whether they might lead to changes in brain temperature. We induced focal neocortical seizures by microinjection of 4-aminopyridine (4-AP) into the rat motor cortex. The temperature on the dura immediately over the injection site, or 8 mm away, was measured with a thermocouple and in some experiments relative blood flow was monitored with a laser Doppler probe. In animals that did not receive 4-AP, brain and rectal temperature remained fairly constant at 33.5 and 37.2 °C, respectively, over a 2 h monitoring period. In animals treated with 4-AP, brain temperature over the seizure focus rose an average of 0.3 °C, within a few seconds of seizure onset, while rectal temperature remained constant. The seizure-induced temperature rise was preceded by an increase in cortical blood flow. The temperature, but not blood flow, was also elevated 8 mm away from the seizure focus. When blood flow was increased independently of neuronal activity, by elevating pCO 2, brain temperature also rose by about 0.3 °C. Focal seizures in anesthetized rats produce a small, but statistically significant increase in local brain temperature, as a result of increased blood flow that brings brain temperature closer to body temperature. In humans, seizures could actually cause a reduction in brain temperature, because brain temperature is normally higher than body temperature.

Changing dopaminergic activity through different pathways: consequences for renal sodium excretion, regional blood flow and oxygen tension in the rat.

Dopamine (DA) is an intrarenal natriuretic hormone involved in sodium homeostasis, but the regulation of renal dopaminergic tonus is unclear. We evaluated different pathways for elevating DA tonus to determine which are important for the ability of the kidney to produce natriuresis and studied the accompanying effects on regional renal blood flow and oxygen tension. Thus, we compared the effects of a catechol-O-methyl transferase (COMT)-inhibitor, an unspecific monoamine oxidase (MAO)-inhibitor, a D1-like receptor agonist and a DA precursor in anaesthetized rats. Sodium excretion increased sixfold after COMT inhibition, eightfold after administration of the D1-like agonist, whereas it was similar to control after MAO inhibition and infusion of DA precursor. Urinary dopamine excretion increased 42% by COMT inhibition, 55% by MAO inhibition and 12-fold after DA precursor, but remained unchanged after infusion of the D1-like agonist. The D1-like receptor agonist led to a 38% increase in the cortical blood flow and a 21% increase in outer medullary blood flow. Regional renal blood flow was unaffected by all other treatments. Cortical and outer medullary oxygen tension was unaffected in all treatment groups. To conclude, the natriuretic and haemodynamic properties of an elevation in DA tonus depends on the route by which the elevation occurred. Systemic administration of a D1-like receptor agonist, results in a natriuretic response which, as opposed to the natriuresis seen after COMT inhibition, coincides with an increase in renal cortical and outer medullary blood flow. Precursor delivery or MAO inhibition did not change neither urinary sodium excretion nor renal blood flow.

Regulation of regional cerebral blood flow by cholinergic fibers originating in the basal forebrain

The intracranial neural vasodilative system of cholinergic fibers projecting from the basal forebrain to the cortex was discovered by Biesold, Inanami, Sato and Sato (Biesold, D., Inanami, O., Sato, A., Sato, Y., 1989. Stimulation of the nucleus basalis of Meynert increases cerebral cortical blood flow in rats. Neurosci. Lett. 98, 39–44) using laser Doppler flowmetry in anesthetized rats. This cholinergic vasodilative system, which operates by increasing extracellular ACh release, relies upon activation of both muscarinic and nicotinic cholinergic receptors in the parenchyma of the cortex. Further, the involvement of nitric oxide in this cholinergic vasodilation, indicates the necessity to this system of neurons, which contain nitric oxide synthase. The increase in cortical blood flow elicited by this cholinergic vasodilative system is independent of systemic blood pressure and is not coupled to cortical metabolic rates. This cholinergic vasodilative system may be activated by somatic afferent stimulation. Most of the data presented here were obtained in anesthetized animals.