Biomedical subjects

R J Roman

Publications and source records attributed to R J Roman.

At least 55 records · Page 3Linked to original sources

PubMed1999

20-HETE agonists and antagonists in the renal circulation.

The present study examined the effects of a series of 20-hydroxyeicosatetraenoic acid (20-HETE) derivatives on the diameter of renal arterioles to determine the structural requirements of the vasoconstrictor response to 20-HETE. The vascular responses to 5-, 8-, 12-, 15-, 19-, 20-, 21-HETEs, arachidonic acid (AA), and saturated, partially saturated, dimethyl, carboxyl, and 19-carbon derivatives of 20-HETE (10(-8) to 10(-6) M) were assessed in rat renal interlobular arteries (65-125 micrometer). 20-HETE, 21-HETE, dimethyl-20-HETE, and a partially saturated derivative of 20-HETE, 20-hydroxyeicosa-5(Z),14(Z)-dienoic acid, reduced vessel diameter by 19 +/- 3, 17 +/- 3, 16 +/- 2, and 28 +/- 2%, respectively. In contrast, 5-, 8-, 12-, 15-, and 19-HETE, AA, saturated, partially saturated, carboxyl, and the 19-carbon derivatives of 20-HETE had no effect on vessel diameter. Pretreatment with 5-, 15-, and 19-HETE, the 19-carbon derivative or 20-hydroxyeicosa-6(Z),15(Z)-dienoic acid (1 microM) completely blocked the vasoconstrictor response to 20-HETE in renal arterioles. Pretreatment with AA, carboxyl, saturated 19-carbon, and saturated 20-HETE derivatives (1 microM) partially blocked the response, whereas 8- and 12-HETE (1 microM) had no effect on the vasoconstrictor response to 20-HETE. These findings suggest that 20-HETE agonists and antagonists require a carboxyl or an ionizable group on carbon 1 and a double bond near the 14 or 15 carbon. 20-HETE agonists also require a functional group capable of hydrogen bonding on carbon 20 or 21, whereas antagonists lack this reactive group.

Animals↗

PubMed1999

Role of tyrosine kinase and PKC in the vasoconstrictor response to 20-HETE in renal arterioles.

The present study examined the hypothesis that activation of protein kinase C (PKC), components of the mitogen-activated protein (MAP) kinase pathway, or both contributes to the inhibitory effects of 20-hydroxyeicosatetraenoic acid (20-HETE) on K+-channel activity and its vasoconstrictor response in renal arterioles. 20-HETE (0.1 to 50 micromol/L) dose-dependently produced a 30% increase in PKC activity and a fivefold rise in the expression of active extracellular signal-regulated kinase 1 (ERK1) and ERK2 proteins in renal microvessels. 20-HETE (0.01 to 1 micromol/L) reduced the diameter of isolated perfused renal interlobular arterioles by 33+/-2%. Blockade of PKC activity with an N-myristoylated PKC pseudosubstrate inhibitor (Myr-PKCi, 100 micromol/L) or calphostin C (0.5 micromol/L) had no significant effect on the vasoconstrictor response to 20-HETE. In contrast, the tyrosine kinase inhibitors genistein (30 micromol/L) and tyrphostin 25 (10 micromol/L) reduced the response to 20-HETE by 76.5+/-2.1% and 67.5+/-1.8%, respectively. A specific inhibitor of mitogen-activated extracellular signal-regulated kinase (MEK), PD98059, had no effect on the vasoconstrictor response to 20-HETE. In cell-attached patches on renal vascular smooth muscle cells, 20-HETE reduced the open state probability of a large-conductance K+ channel (from 0.0026+/-0.0004 to 0.0006+/-0.0001). The Myr-PKCi (100 micromol/L) did not alter the inhibitory effects of 20-HETE on this channel. In contrast, the tyrosine kinase inhibitor genistein (30 micromol/L) blocked the inhibitory effects of 20-HETE on the large-conductance K+ channel. These data suggest that 20-HETE activates the MAP kinase system in renal arterioles and that the activation of a tyrosine kinase, which is proximal to MEK in this cascade, contributes to the inhibitory effects of 20-HETE on K+-channel activity and its vasoconstrictor effects in the renal arterioles.

Animals↗

PubMed1999

Role of 20-HETE in elevating chloride transport in the thick ascending limb of Dahl SS/Jr rats.

This study examined the role of endogenous 20 hydroxyeicosatetraenoic acid (20-HETE) in elevating Cl- transport in the medullary thick ascending loop of Henle (MTAL) of 9-week-old male Dahl salt-sensitive (SS/Jr) and salt-resistant (SR/Jr) rats perfused in vitro. Basal transepithelial voltage (Vte; 14.9+/-0.9 versus 10.1+/-0.5 mV) and net lumen-to-bath Cl- flux (JCl) (155+/-6 versus 127+/-5 pEq. min-1. mm-1) were significantly greater in MTAL isolated from SS/Jr rats (n=16) than in those obtained from SR/Jr rats (n=16). Blockade of the synthesis of 20-HETE with 17-octadecynoic acid (17-ODYA; 10 micromol/L) increased Vte from 9. 9+/-0.8 to 13.1+/-1.0 mV and JCl from 127+/-7 to 152+/-8 pEq. min-1. mm-1 in the MTAL of SR/Jr rats (n=8), but it had no significant effect on Vte or JCl in the MTAL of SS/Jr rats (n=8). Exogenous 20-HETE (1 micromol/L) decreased Vte from 14.8+/-0.6 to 10.5+/-0.6 mV and JCl from 155+/-10 to 116+/-6 pEq. min-1. mm-1 in MTAL of SS/Jr rats (n=8), but it had no effect on Vte or JCl in the MTAL of SR/Jr rats (n=8). The expression of P4504A2 protein in the MTAL of SS/Jr rats was approximately half of that seen in the MTAL of SR/Jr rats. These results indicate that endogenously formed 20-HETE regulates transepithelial voltage and Cl- transport in the MTAL and that a diminished production of 20-HETE contributes to an elevation in Cl- transport in the MTAL of SS/Jr rats.

Animals↗

PubMed1999

Contribution of 20-HETE to vasodilator actions of nitric oxide in the cerebral microcirculation.

BACKGROUND AND PURPOSE: The present study examined the contributions of a rise in cGMP versus a fall in 20-HETE levels to the vasodilator response to nitric oxide (NO) in the cerebral circulation of the rat. METHODS: Intact rat middle cerebral and basilar arteries were bathed in physiological saline solution containing indomethacin (5 micromol/L) and baicalein (0.5 micromol/L) and pressurized at 90 mm Hg. Relaxations to sodium nitroprusside (SNP) were studied before and after addition of [1H-[1,2,4]oxadiazole[4,3-a]quinoxalin-1-one] (ODQ, a guanylyl cyclase blocker), 8R,9S, 11S-(-)-9-methoxy-carbamyl-8-methyl-2,3,9,10-tetrahydro-8, 11-epoxy-1H,8H,11H-2,7b,11a-trizadibenzo-(a,g)-cycloocta-(c, d, e)-trinden-1-one (KT5823, a protein kinase G blocker), and 20-hydroxyeicosatetraenoic acid (20-HETE). Cerebral blood flow was measured by using a laser Doppler flow probe over a thin cranial window in anesthetized rats, and the effects of intracerebroventricular infusion of 1-hexamine, 6-(2-hydroxy-1-methyl-2-nitrosohydrazino)N-methyl (MAHMA nonoate) and dibromododecenyl methylsulfimide (DDMS) were determined. RESULTS: SNP-induced dilation of serotonin-preconstricted (0.2 micromol/L) middle cerebral arteries (10(-7) to 10(-3) mol/L) was attenuated in arteries treated with ODQ (10 micromol/L) or KT5823 (1 micromol/L) by 52% and 27%, respectively. Preventing the NO-induced fall in intracellular 20-HETE, by adding 20-HETE (100 nmol/L) to the bath, reduced the dilation to SNP by 62%. Simultaneous administration of ODQ and 20-HETE markedly attenuated the SNP-induced dilation by 90%. In basilar arteries, ODQ (10 micromol/L) alone completely blocked the response to SNP. Infusion of MAHMA nonoate (10 nmol/min ICV) in anesthetized rats increased cerebral blood flow by 52% before and 8% after blockade of the endogenous production of 20-HETE with DDMS (50 pmol/min). CONCLUSIONS: These results suggest that NO dilates cerebral arteries through both cGMP-dependent and cGMP-independent pathways and that inhibition of 20-HETE formation contributes to the cerebral vasodilator response to NO both in vitro and in vivo.

Adenosine↗

PubMed1999

Acute and chronic renal effects of recombinant human TGF-beta2 in the rat.

The expression of transforming growth factor-beta (TGF-beta) correlates with the incidence of renal glomerular and interstitial injury, however, nothing is known of the effect of these proteins on renal hemodynamics. This study examines the renal hemodynamic and morphologic effects of recombinant human TGF-beta2 in normal male Sprague Dawley rats. Acute infusion of TGF-beta (1.2 microg/kg per min) induced no hemodynamic changes, except for a modest though significant fall in mean arterial pressure. Administering TGF-beta2 at varying doses (20, 100, and 400 microg/kg) for 9 wk caused modest increases in systolic BP and proteinuria and minimal tubular interstitial fibrosis, however, renal hemodynamic end points were not significantly altered. TGF-beta2 (800 microg/kg) was also administered to volume-depleted rats for 7 consecutive days. In contrast to the findings in volume-replete animals, administration of TGF-beta2 to volume-depleted rats caused a marked reduction in GFR and medullary blood flow. Histologic fibrosis of the medullary vasa recta and cortical interstitium was seen, but glomeruli were unaffected. Thus, acute and short-term chronic TGF-beta2 administration did not induce major renal changes in the volume-replete state, however, TGF-beta2 combined with volume depletion caused medullary hypoperfusion and reduced GFR.

Analysis of Variance↗

PubMed1999

Altered expression and activity of G-proteins, mitogen activated protein kinases, and tyrosine kinases in aging kidney cortex.

BACKGROUND: Renal function declines with age and this may be related to changes in the expression or activity of various signal transduction proteins in the kidney. METHODS: The present study compared the expression and activity of G alpha i(1-3) and G alpha s phosphorylation of mitogen activated protein kinases (MAP-K) (44 and 42 kd) and the activity of tyrosine kinase in renal cortical homogenates of young (4-month-old) and aging (14-month-old) rats. RESULTS: The GTP/(GTP + GDP) binding ratio of G alpha s was significantly decreased in the kidney cortex of aging rats compared to young rats, while the GTP/(GTP + GDP) binding ratio of G alpha i(1-3) increased significantly in kidney cortex of aging rats. Tyrosine kinase activity and phosphorylation of MAP-K (44 and 42 kd) were also reduced in the kidney cortex of aging rats compared to young rats. CONCLUSIONS: These results suggest that diminished phosphorylation of MAP-K and tyrosine kinase activity as well as changes in the binding of GTP/(GTP + GDP) to G alpha i(1-3) and G alpha s may contribute to the age-related decline in renal tubular and vascular function seen in aging animals.

Aging↗

PubMed1998

Nitric oxide-20-hydroxyeicosatetraenoic acid interaction in the regulation of K+ channel activity and vascular tone in renal arterioles.

The present study examined whether inhibition of P4504A enzyme activity and the formation of 20-HETE contributes to the activation of K+ channels and vasodilator effects of nitric oxide (NO) in renal arterioles. Addition of an NO donor to the P4504A2 enzyme that produces 20-HETE increased visible light absorbance at 440 nm indicating that NO binds to heme in this enzyme. NO donors also dose-dependently inhibited the formation of 20-HETE in microsomes prepared from renal arterioles. In patch-clamp experiments, NO donors increased the open-state probability of a voltage-sensitive, large-conductance (195+/-9 pS) K+ channel recorded with cell-attached patches on renal arteriolar smooth muscle cells. Blockade of guanylyl cyclase with [1H-[1,2,4]Oxadiazolo[4,3-a] quinoxalin-1-one] (ODQ, 10 micromol/L), or cGMP-dependent kinase with 8R,9S,11S-(-)-9-methoxycarbamyl-8-methyl-2,3,9,10-tetrahydro-8, 11-epoxy-1H,8H,11H-2,7b,11a-trizadibenzo-(a,g)-cy-cloocta-(c ,d, e)-trinden-1-one (KT-5823) (1 micromol/L) did not alter the effects of NO on this channel. In contrast, inhibition of the formation of 20-HETE with 17-octadecynoic acid (1 micromol/L) activated this channel and masked the response to NO. Preventing the NO-induced reduction in intracellular 20-HETE levels also blocked the effects of NO on this channel. Sodium nitroprusside (SNP) increased the diameter of renal interlobular arteries preconstricted with phenylephrine to 80+/-4% of control. Blockade of guanylyl cyclase with ODQ (10 micromol/L) attenuated the response to SNP by 26+/-2%; however, fixing 20-HETE levels at 100 nmol/L reduced the response by 67+/-8%. Blockade of both pathways eliminated the response to SNP. These results indicate that inhibition of the formation of 20-HETE contributes to the activation of K+ channels and the vasodilator effects of NO in the renal microcirculation.

Animals↗

PubMed1998

Effects of intrarenal infusion of 17-octadecynoic acid on renal antihypertensive mechanisms in anesthetized rabbits.

To characterize the role of cytochrome P450 metabolism of fatty acids in the renal response to increased renal perfusion pressure, we tested the effects of renal arterial infusion of 17-octadecynoic acid (17-ODYA, 450 nmol/min) on renal and systemic hemodynamic, and renal excretory responses to step-wise increases in renal perfusion pressure (RPP) in anesthetized rabbits, using an extracorporeal circuit for renal autoperfusion. Inhibition of cytochrome P450-dependent fatty acid metabolism was estimated by comparing the metabolism of arachidonic acid in microsomes prepared from the kidneys of control and 17-ODYA-treated animals. Step-wise increases in RPP decreased mean arterial pressure, which previous studies have indicated is attributable to the release of a depressor hormone from the renal medulla. Elevations in RPP also increased renal blood flow and glomerular filtration rate, and the absolute and fractional excretions of urine and sodium. Intrarenal infusion of 17-ODYA reduced the metabolism of arachidonic acid to 20-hydroxyeicosatetraenoic acid by 41%, but it did not significantly influence the responses to increased renal perfusion pressure. We conclude that either the responses elicited by increased renal perfusion pressure in anesthetized rabbits do not depend on cytochrome P450-dependent fatty acid metabolism, or that cytochrome P450 activity must be inhibited by more than was achieved in the present study (41%), before functional effects on the response to increased renal perfusion pressure are observed.

Anesthesia↗

PubMed1998

Lovastatin reduces renal vascular reactivity in spontaneously hypertensive rats.

We have reported that lovastatin attenuates the development of hypertension in spontaneously hypertensive rats (SHR). The fall in arterial pressure is associated with an elevation in renal medullary blood flow, normalization of the pressure-natriuresis relationship, and diminished hypertrophy of renal arterioles. However, the mechanism by which lovastatin alters renal vascular tone is unknown. The present study examined the effects of lovastatin on renal vascular tone and the expression of G proteins. Four-week-old SHR were chronically treated with lovastatin (20 mg/kg/day) or vehicle by gavage for 4 weeks. At the end of the study, mean arterial pressure averaged 131 +/- 4 (n = 5) and 160 +/- 4 mm Hg (n = 6) in lovastatin- and vehicle-treated SHR, respectively. Renal arterioles isolated from lovastatin-treated SHR were significantly less responsive to norepinephrine and vasopressin than those obtained from vehicle-treated rats (ED50: 5.0 v 1.8 x 10(-7) mol/L for norepinephrine, and 8.0 v 5.2 x 10(-10) mol/L for vasopressin). The fall in renal vascular reactivity in lovastatin-treated SHR was associated with reduced levels of ras and rho proteins in renal arterioles, whereas the expressions of heterotrimeric G proteins (Gs Gq, Gi) were similar in renal arterioles from vehicle- and lovastatin-treated SHR. Overnight culture of renal arterioles with media containing lovastatin also diminished the expression of ras and rho proteins and the response to vasoconstrictors. These findings indicate that lovastatin diminishes the response to vasoconstrictors and the expression of small G proteins in the renal vasculature of SHR and suggest that a fall in the levels of ras and rho proteins in these vessels may contribute to the antihypertensive effects of lovastatin.

Animals↗

PubMed1998

A common pathway for regulation of nutritive blood flow to the brain: arterial muscle membrane potential and cytochrome P450 metabolites.

Perfusion pressure to the brain must remain relatively constant to provide rapid and efficient distribution of blood to metabolically active neurones. Both of these processes are regulated by the level of activation and tone of cerebral arterioles. The active state of cerebral arterial muscle is regulated, to a large extent, by the level of membrane potential. At physiological levels of arterial pressure, cerebral arterial muscle is maintained in an active state owing to membrane depolarization, compared with zero pressure load. As arterial pressure changes, so does membrane potential. The membrane is maintained in a relatively depolarized state because of, in part, inhibition of K+ channel activity. The activity of K+ channels, especially the large conductance Ca(2+)-activated K+ channel (KCa) is dependent upon the level of 20-HETE produced by arterial muscle. As arterial pressure increases, so does cytochrome P450 (P4504A) activity. P4504A enzymes catalyse omega-hydroxylation of arachidonic acid and formation of 20-hydroxyeicosatetraenoic acid (20-HETE). 20-HETE is a potent inhibitor of KCa which maintains membrane depolarization and muscle cell activation. Astrocytes also metabolize AA via P450 enzymes of the 2C11 gene family to produce epoxyeicosatrienoic acids (EETs). Epoxyeicosatrienoic acids are released from astrocytes by glutamate which 'spills over' during neuronal activity. These locally released EETs shunt blood to metabolically active neurones providing substrate to support neuronal function. This short paper will discuss the findings which support the above scenario, the purpose of which is to provide a basis for future studies on the molecular mechanisms through which cerebral blood flow matches metabolism.

Animals↗

PubMed1998

Localization of cytochrome P-450 4A isoforms along the rat nephron.

The expression of P-450 4A isoforms responsible for the formation of 20-hydroxyeicosatetraenoic acid (20-HETE) was examined using the reverse transcription and polymerase chain reaction in various nephron segments and preglomerular arterioles microdissected from the kidneys of Sprague-Dawley rats. Expression of cytochrome P-450 4A1, 4A2, 4A3, and 4A8 mRNA could be detected in RNA extracted from the whole kidney. The expression of P-450 4A1, 4A3, and 4A8 mRNA was similar in the kidney of male and female rats, whereas the expression of 4A2 mRNA was fourfold greater in the kidney of male vs. female rats. At the single-nephron level, P-450 4A1 mRNA could not be detected in either preglomerular arterioles or any nephron segments. P-450 4A2 mRNA was readily detected in preglomerular arterioles, glomeruli, proximal convoluted tubule (PCT), proximal straight tubule (PST), medullary thick ascending limb (MTAL), cortical thick ascending limb (CTAL), cortical collecting duct (CCD), outer medullary collecting duct (OMCD), and inner medullary collecting duct (IMCD). P-450 4A3 mRNA was also detected in every nephron segment, but the expression of this isoform was barely detectable in preglomerular arterioles. The expression of P-450 4A8 mRNA was detected in the glomerulus, PCT, PST, CTAL, and CCD. It was not detectable in preglomerular arterioles, MTAL, OMCD, or IMCD. Immunoblot analysis using a P-450 4A antibody exhibited a strong signal for P-450 4A protein in the proximal tubule. Smaller signals were also observed in glomerulus, MTAL, and preglomerular arterioles, but no signal could be detected in the IMCD. A similar pattern of P-450 4A protein expression was seen in kidney sections immunostained with this antibody. These results indicate that the expression of P-450 4A isoforms in the kidney of rats is sex dependent and that different P-450 4A isoforms are expressed throughout various nephron segments and the renal vasculature of rats.

Animals↗

PubMed1998

Contribution of 20-HETE to the vasodilator actions of nitric oxide in renal arteries.

The present study examined the contribution of elevations in cGMP versus inhibition of cytochrome P-4504A enzymes and the production of the vasoconstrictor 20-hydroxyeicosatetraenoic acid (20-HETE) to the vasodilator actions of NO in renal arterioles. The NO donor sodium nitroprusside (SNP) at 10(-5), 10(-4), and 10(-3) M reduced the production of 20-HETE in microsomes prepared from renal arterioles to 80 +/- 2, 43 +/- 5, and 7 +/- 1% of control, respectively (n = 4). In other experiments, the vasodilator response to SNP (10(-7) to 10(-3) M) was examined in rat renal interlobular arteries (<90 micron ID), preconstricted with phenylephrine (1 microM) under control conditions and after blockade of the cGMP and P-4504A pathways. Inhibition of guanylyl cyclase with 1H-[1,2, 4]oxadiazole[4,3-a]quinoxalin-1-one (ODQ) (10 microM, n = 6) or of cGMP-dependent protein kinase with 8R,9S, 11S-(-)-9-methoxy-carbamyl-8-methyl-2,3,9,10-tetrahydro-8, 11-epoxy-1H,8H,11H-2,7b,11a-trizadibenzo-(a,g)-cycloocta-(c, d, e)-trinden-1-one (KT-5823, 1 microM; n = 5) attenuated the vasodilator response to SNP by 26 and 30%, respectively. In contrast, inhibition of the endogenous production of 20-HETE with a suicide substrate, irreversible inhibitor [17-octadecynoic acid (17-ODYA), 1 microM, n = 5], or a selective, competitive inhibitor of 20-HETE formation (dibromo-dodecenyl-methylsulfimide, 25 microM, n = 5) markedly impaired the vasodilator response to SNP by 76 and 78%, respectively. Similarly, when 20-HETE levels were fixed at 100 nM (n = 6), the response to SNP was attenuated by 73%. Blockade of both pathways with ODQ and 17-ODYA completely abolished the response to SNP (n = 6). These results indicate that the vasodilator response to NO is largely cGMP independent and that inhibition of 20-HETE formation contributes to the cGMP-independent effects of NO in the renal microcirculation.

Alkaloids↗

PubMed1998

Effects of lipid-lowering agents in the Dahl salt-sensitive rat.

Inducing renal cytochrome P4504A (P4504A) activity with clofibrate prevents the development of hypertension in Dahl salt-sensitive (Dahl S) rats. To determine if this also occurs with other antilipidemic agents, we compared the effects of a related drug, fenofibrate, with those of an unrelated agent, pravastatin, on blood pressure, renal histology, and P4504A activity. Dahl S rats were pretreated with fenofibrate (95 mg/kg per day), pravastatin (70 mg/kg per day), or vehicle for 7 days before and after being switched from a low-salt (0.1% NaCl) to a high-salt (8.0% NaCl) diet. After 3 weeks on the high-salt diet, mean arterial pressures averaged 183+/-13 (n=9), 126+/-10 (n=9), and 148+/-11 mm Hg (n=8), respectively, in vehicle-, fenofibrate-, and pravastatin-treated animals. Both drugs reduced the degree of proteinuria and glomerular injury. P4504A protein levels and the synthesis of 20-hydroxyeicosa-5,8,11,14-tetraenoic acid (20-HETE) were increased in the liver and kidney of fenofibrate-treated, but not pravastatin-treated rats. We also administered these agents to Dahl S rats in which hypertension had previously been induced by a high-salt diet. Mean arterial pressures averaged 164+/-10, 113+/-23, and 160+/-15 mm Hg in rats treated with vehicle, fenofibrate, or pravastatin for 3 weeks. Fenofibrate-treated rats exhibited a natriuresis. Proteinuria and glomerular injury were reduced by pravastatin but not by fenofibrate. These results indicate that fenofibrate prevented the development of hypertension and reduced subsequent glomerular injury in Dahl S rats, probably secondary to increased renal production of 20-HETE. Although pravastatin did not induce renal P4504A activity in these animals, it reduced the severity of hypertension and renal damage through some other mechanism.

Animals↗

PubMed1998

Induction of P4504A activity improves pressure-natriuresis in Dahl S rats.

Clofibrate has been reported to prevent the development of hypertension in Dahl S rats, but its mechanism of action remains to be determined. The present study examined the effects of clofibrate on renal P4504A activity and the pressure natriuresis relationship in Dahl S rats. Dahl S and R rats fed a low-salt diet (0.4% NaCl) were given either clofibrate (240 mg/kg/d) or vehicle (20 mmol/L Na2CO3) in their drinking water for 1 week and then switched to a high salt diet (8% NaCl) while continuing drug treatment. After 3 weeks, mean arterial pressure in ketamine-Inactin anesthetized rats averaged 121+/-2 (n=8) in Dahl R, 173+/-8 (n=6) in Dahl S, and 139+/-4 mm Hg (n=7) in clofibrate-treated Dahl S rats. Increasing renal perfusion pressure (RPP) from 100 to 150 mm Hg in Dahl R rats increased sodium excretion (U(Na)V) from 2.9+/-0.7 to 9.7+/-3.2 micromol/min/g kwt. In contrast, the pressure natriuresis relation was blunted in Dahl S rats and U(Na)V only increased from 2.7+/-0.9 to 6.1+/-1.3 micromol/min/g kwt. The pressure natriuresis relation was improved in clofibrate-treated Dahl S rats and U(Na)V increased from 5.1+/-1.3 to 16.7+/-2.6 micromol/min/g kwt. At similar levels of RPP, the fractional excretion of sodium tended to be higher in clofibrate-treated than in vehicle-treated Dahl S rats, but not significantly. Glomerular filtration rate (GFR) was 40% higher in clofibrate- compared to vehicle-treated Dahl S rats (0.9+/-0.2 versus 0.6+/-0.2 mL/min/g kwt), and was not significantly different from the values seen in Dahl R rats (0.9+/-0.1 mL/min/g kwt). Clofibrate induced the expression of P4504A protein in the renal cortex and outer medulla of Dahl S rats. These data suggest that induction of renal P4504A activity with clofibrate improves the pressure natriuresis relation in Dahl S rats by primarily increasing GFR.

Animals↗

PubMed1998

Functional hyperemia in the brain: hypothesis for astrocyte-derived vasodilator metabolites.

BACKGROUND: Cerebral blood flow is tightly coupled to neuronal metabolic activity, a phenomenon referred to as functional hyperemia. The mechanisms underlying functional hyperemia in the brain have been extensively studied, but the link between neuronal activation and nutritive blood flow has yet to be defined. Recent investigations by our laboratory and others have identified a potential role for astrocytes as an intermediary cell type in this process. SUMMARY OF REVIEW: This short review will develop the hypothesis that cytochrome P450 epoxygenase activity in astrocytes catalyzes formation of epoxyeicosatrienoic acids (EETs), which act as potent dilators of cerebral vessels and are released in response to glutamate receptor activation within astrocytes. Neuronal activity stimulates release of arachidonic acid from the phospholipid pool of astrocytic membranes. We provide evidence that the arachidonic acid released on stimulation of glutamate receptors within astrocytes is metabolized by cytochrome P450 2C11 cDNA enzymes into EETs. CONCLUSIONS: The EETs thus formed will be released and activate K+ channels, increase outward K+ current, and hyperpolarize the plasma membrane. The resulting membrane hyperpolarization inhibits voltage-gated Ca2+ channels and leads to arteriolar dilation, thereby increasing regional nutritive blood flow in response to neuronal activity.

8,11,14-Eicosatrienoic Acid↗

PubMed1998

Role of inducible nitric oxide synthase and cyclooxygenase-2 in endotoxin-induced cerebral hyperemia.

BACKGROUND AND PURPOSE: Bacterial lipopolysaccharide (LPS), an endotoxin, has been reported to induce the expression of inducible isoforms of both nitric oxide synthase (iNOS) and cyclooxygenase (COX-2) in various cell types. LPS is also known to dilate systemic vasculature, including cerebral vessels. This study aimed to determine to what extent LPS induces iNOS and COX-2 expression in the brain and whether NO and/or cyclooxygenase metabolites derived from iNOS and/or COX-2 contribute to the LPS-induced cerebral hyperemia. METHODS: Regional cerebral blood flow (rCBF) was measured by laser-Doppler flowmetry in halothane-anesthetized, artificially ventilated rats for 4 hours after intracerebroventricular administration of LPS. RESULTS: LPS at doses of 0.01 mg/kg to 1 mg/kg caused dose-dependent, progressive increases in rCBF at 1 to 4 hours after administration. The increase in rCBF was attenuated by systemic administration of the selective iNOS inhibitor aminoguanidine (100 mg/kg IP) or the selective COX-2 inhibitor NS-398 (5 mg/kg IP), and it was abolished by preventing induction of these isoforms with dexamethasone (4 mg/kg IP). LPS significantly increased iNOS and COX-2 mRNA, iNOS protein, and iNOS and cyclooxygenase enzyme activity. The increases in iNOS and cyclooxygenase enzyme activity were eliminated by aminoguanidine and NS-398, respectively. Dexamethasone also prevented the increase in iNOS and cyclooxygenase activity. CONCLUSIONS: These results indicate that induction of iNOS and COX-2 expression and the increased production of NO and vasodilator prostanoids in the brain contribute to the elevation in CBF after intracerebroventricular administration of LPS.

Animals↗

PubMed1998

Tissue sources of cytochrome P450 4A and 20-HETE synthesis in rabbit lungs.

We previously reported that 20-hydroxyeicosatetraenoic acid (20-HETE) is an endogenous cytochrome P450 (cP450) 4A metabolite of arachidonic acid (AA) in human lung tissue, and is a potent cyclooxygenase-dependent vasodilator of isolated pulmonary arteries. In the present investigations, we identified sources of cP450 4A immunospecific protein, messenger RNA (mRNA), and 20-HETE synthesis in rabbit lungs. Microsomes of peripheral lung tissue, airways, small and large vessels, and lysates of alveolar macrophages all express proteins of approximately 50 kD which cross-reacted with a primary antibody raised against rat liver cP450 4A1. Peripheral lung tissue, small and large pulmonary arteries, airways, and isolated vascular smooth muscle cells from small pulmonary arteries produced 20-HETE when incubated with AA. Expression of cP450 4A6/4A7 mRNA was readily detectable by reverse transcription-polymerase chain reaction using isoform-specific probes and 5 microg total RNA extracted from microdissected small pulmonary arteries. These data demonstrate that small pulmonary arteries express cP450 4A proteins and vascular smooth muscle cells derived from these arteries synthesize 20-HETE. Furthermore, cP450 4A appears to be widely distributed in rabbit tissue, raising the possibility that 20-HETE generated from nonvascular tissue could serve as a paracrine factor in the pulmonary circulation.

Animals↗

PubMed1997

Isoflurane-induced cerebral hyperemia in neuronal nitric oxide synthase gene deficient mice.

BACKGROUND: Nitric oxide (NO) has been reported to play an important role in isoflurane-induced cerebral hyperemia in vivo. In the brain, there are two constitutive isoforms of NO synthase (NOS), endothelial NOS (eNOS), and neuronal NOS (nNOS). Recently, the mutant mouse deficient in nNOS gene expression (nNOS knockout) has been developed. The present study was designed to examine the role of the two constitutive NOS isoforms in cerebral blood flow (CBF) response to isoflurane using this nNOS knockout mouse. METHODS: Regional CBF (rCBF) in the cerebral cortex was measured with laser-Doppler flowmetry in wild-type mice (129/SV or C57BL/6) and nNOS knockout mice during stepwise increases in the inspired concentration of isoflurane from 0.6 vol% to 1.2, 1.8, and 2.4 vol%. Subsequently, a NOS inhibitor, N omega-nitro-L-arginine (L-NNA), was administered intravenously (20 mg/kg), and 45 min later, the rCBF response to isoflurane was tested again. In separate groups of wild-type mice and the knockout mice, the inactive enantiomer, N omega-nitro-D-arginine (D-NNA) was administered intravenously in place of L-NNA. Brain NOS activity was measured with radio-labeled L-arginine to L-citrulline conversion after treatment with L-NNA and D-NNA. RESULTS: Isoflurane produced dose-dependent increases in rCBF by 25 +/- 3%, 74 +/- 10%, and 108 +/- 14% (SEM) in 129/SV mice and by 32 +/- 2%, 71 +/- 3%, and 96 +/- 7% in C57BL/6 mice at 1.2, 1.8, and 2.4 vol%, respectively. These increases were attenuated at every anesthetic concentration by L-NNA but not by D-NNA. Brain NOS activity was decreased by 92 +/- 2% with L-NNA compared with D-NNA. In nNOS knockout mice, isoflurane increased rCBF by 67 +/- 8%, 88 +/- 12%, and 112 +/- 18% at 1.2, 1.8, and 2.4 vol%, respectively. The increase in rCBF at 1.2 vol% was significantly greater in the nNOS knockout mice than that in the wild-type mice. Administration of L-NNA in the knockout mice attenuated the rCBF response to isoflurane at 1.2 and 1.8 vol% but had no effect on the response at 2.4 vol%. CONCLUSIONS: In nNOS knockout mice, the cerebral hyperemic response to isoflurane is preserved by compensatory mechanism(s) that is NO-independent at 2.4 vol%, although it may involve eNOS at 1.2 and 1.8 vol%. It is suggested that in wild-type mice, eNOS and nNOS contribute to isoflurane-induced increase in rCBF. At lower concentrations (1.2 and 1.8 vol%), eNOS may be involved, whereas at 2.4 vol%, nNOS may be involved.

Anesthetics, Inhalation↗