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Biomedical subjects

D R Harder

Publications and source records attributed to D R Harder.

At least 55 records · Page 3Linked to original sources
PubMed1994

Myogenic activation of canine small renal arteries after nonchemical removal of the endothelium.

Myogenic activation of isolated small arteries (200-500 microns) of the dog kidney was evaluated by measuring vessel diameters during stepwise elevations of transmural pressure before and after removal of the endothelium by mechanical rubbing or air perfusion. Myogenic activation was unaffected by mechanical rubbing, but air perfusion caused the arteries to constrict and attenuated the myogenic response; i.e., vessel diameters increased as transmural pressure was elevated. However, air-perfused arteries still constricted in response to norepinephrine and dilated during superfusion with Ca(2+)-free solution, demonstrating that loss of the myogenic response did not result from an inability of the vessel to contract. Intact arteries contracted with 1 microM norepinephrine exhibited normal myogenic responses, demonstrating that loss of myogenic activation in the air-perfused vessels was not a nonspecific effect secondary to constriction of the artery. These results suggest that myogenic activation of small renal arteries is independent of the endothelium and that the method of endothelial removal may affect conclusions regarding the role of the endothelium in mediating the myogenic response.

Acetylcholine↗
PubMed1994

Guanine nucleotide-binding proteins in aortic smooth muscle from hypertensive rats.

To explore the hypothesis that altered vascular muscle signal transduction may underlie some of the vascular changes observed in hypertensive models, we measured expression of GTP-binding protein (G protein) alpha-subunits, Gs, G(i), and Gq, in aortic muscle of reduced renal mass and sham-operated rats and proximal and distal aortic segments from rats with interrenal aortic coarctation (IR-AC). G protein expression was measured by immunoblot analysis. When we probed aortic muscle membrane with G(i) and Gq alpha-subunit antibodies, we identified 41- and 42-kD immunoreactive proteins, respectively. Three immunoreactive bands specific to Gs alpha-subunit antibody were resolved. Immunoreactive blot densities were compared. In aortic muscle membrane of reduced renal mass rats (blood pressure, 148 +/- 7 mm Hg), we found significantly reduced Gs and G(i) blot densities compared with sham-operated controls (blood pressure, 99 +/- 12 mm Hg). There were no differences in Gq blot densities between reduced renal mass and control rats. Gs and G(i) blot densities were significantly lower in IR-AC proximal aortic segments (carotid pressure, 165 +/- 5 mm Hg) and distal aortic segments (femoral pressure, 121 +/- 4 mm Hg) than in aortas of sham-operated controls. In contrast, Gq expression was significantly increased in the high-pressure proximal aortic segments compared with low-pressure distal aortic segments from IR-AC rats. Thus, altered G protein expression occurs in aortic muscle from nongenetic rat models of hypertension.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1993

Modulation of vascular tone in renal microcirculation by erythrocytes: role of EDRF.

The effect of erythrocytes (red blood cells, RBC) on vascular tone in the renal microcirculation was examined using the juxtamedullary nephron microvascular preparation perfused in vitro with a physiological salt solution containing 5% albumin. The basal diameters of the arcuate, interlobular, proximal, and distal afferent arterioles averaged 444 +/- 24, 74 +/- 3, 29 +/- 1, and 19 +/- 1 micron, respectively, when perfused with a cell-free solution at a pressure of 80 mmHg. The diameters of the arcuate and interlobular arteries increased by 14 +/- 4 and 13 +/- 4%, respectively, whereas the diameter of the proximal and distal portions of the afferent arterioles decreased by 7 +/- 2% when perfusion pressure was elevated from 80 to 160 mmHg. The addition of RBC to the perfusate reduced the basal diameters of interlobular and afferent arterioles by 11 +/- 4 and 15 +/- 3%, respectively. The maximal vasoconstrictor response was seen after the addition of only 1% RBC to the perfusate. Removal of platelets did not block the vasoconstrictor response to addition of RBC to the perfusate. The role of endothelium-derived relaxing factor (EDRF) in the vasoconstrictor response to RBC was studied by addition of nitric oxide synthase inhibitor, N omega-nitro-L-arginine (L-NNA, 100 microM) to the perfusate. L-NNA reduced the basal diameters of interlobular and afferent arterioles by 7 +/- 3 and 9 +/- 3%, respectively, and abolished the vasoconstrictor response to RBC. L-NNA had no effect on the pressure-diameter relationships of the preglomerular vasculature when added to perfusates already containing RBC.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1993

Elevated renovascular tone in young spontaneously hypertensive rats. Role of cytochrome P-450.

The present study examined the role of cytochrome P-450 metabolites of arachidonic acid in elevating renal vascular resistance in young spontaneously hypertensive rats (SHR). Differences in vascular tone were assessed in the preglomerular vasculature of 3- to 4-week-old prehypertensive SHR (n = 11) and normotensive Wistar-Kyoto (WKY, n = 10) and Wistar-Lewis (n = 10) rats. Pressure-diameter relations to changes in renal perfusion pressure were compared using the juxtamedullary nephron microvascular preparation perfused in vitro with a physiological salt solution. At a pressure of 60 mm Hg, the basal diameters of the interlobular arteries and proximal and distal afferent arterioles of the SHR averaged 43 +/- 2, 17 +/- 0.3, and 11 +/- 0.4 microns, respectively. The diameters of the interlobular arteries and afferent arterioles were 9% to 14% smaller than those of corresponding vessels in WKY and Wistar-Lewis rats. Addition of P-450 inhibitors, ketoconazole (100 mumol/L) or 7-ethoxyresorufin (1 mumol/L), to the perfusate dilated the afferent arteriole of SHR by 7% to 12%, whereas it increased the diameter by only 0% to 6% in control rats and significantly reduced the differences in the pressure-diameter relation in the preglomerular vasculature of SHR and control rats. Inhibitors of P-450 eliminated the contractile response of afferent arterioles to increases in renal perfusion pressure in all three groups. Removal of calcium from the perfusate eliminated differences in the diameters of the preglomerular vasculature in SHR and normotensive rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Acetylcholine↗
PubMed1993

20-Hydroxyeicosatetraenoic acid is an endogenous vasoconstrictor of canine renal arcuate arteries.

Recent studies have indicated that renal arteries can produce 20-hydroxyeicosatetraenoic acid (20-HETE) and suggest the potential involvement of a P450 metabolite of arachidonic acid in the myogenic activation of canine renal arteries. In the present study, the effects of 20-HETE on isolated canine renal arcuate arteries were studied. Administration of 20-HETE to the bath or the lumen at concentrations of 0.01-1 microM produced a graded reduction in the diameter of these vessels. In contrast, 19(R)-HETE was a vasodilator, whereas 19(S)-HETE was relatively inactive. The vasoconstrictor response to 20-HETE was not altered by the cyclooxygenase inhibitor indomethacin, endoperoxide/thromboxane receptor antagonist SQ29548, or combined blockade of the cyclooxygenase, lipoxygenase, and P450 pathways using indomethacin, baicalein, and 7-ethoxyresorufin. The response to 20-HETE was associated with depolarization and a sustained increase in the intracellular calcium concentration in renal vascular smooth muscle cells. Patch-clamp studies indicated that 20-HETE significantly reduced mean open time, the open-state probability, and the frequency of opening of a 117-pS K+ channel recorded from renal vascular smooth muscle cells in the cell-attached mode. Microsomes prepared from the renal cortex of dogs produced 20-HETE and 20-carboxyarachidonic acid when incubated with [14C]arachidonic acid. These results indicate that 20-HETE is an endogenous constrictor of canine renal arcuate arteries. The vasoconstrictor response to 20-HETE resembles the myogenic activation of these vessels after elevations in transmural pressure and suggests a potential role for this substance in the regulation of renal vascular tone.

Animals↗
PubMed1993

Cellular and ionic signal transduction mechanisms for the mechanical activation of renal arterial vascular smooth muscle.

Elevations in transmural pressure increase active vascular tone in arteries from most vascular beds, and this myogenic response has been shown to play an important role in the regulation of blood flow in the kidney and other organs. The myogenic response in isolated perfused arteries is associated with depolarization of vascular smooth muscle cells and a rise in intracellular calcium concentration, which is dependent on calcium influx through voltage-sensitive calcium channels. Recent studies have indicated that the myogenic response in renal arteries is associated with the activation of phospholipase C and that arachidonic acid potentiates, whereas inhibitors of cytochrome P-450 and protein kinase C attenuate, this response. Renal arteries produce 20-hydroxyeicosatetraenoic acid (20-HETE) via the cytochrome P-450 pathway when incubated with arachidonic acid. 20-HETE is a potent constrictor of canine and rat renal arterioles. It inhibits K+ channel activity, depolarizes renal vascular smooth muscle cells, and produces a sustained increase in intracellular calcium concentration. In this regard, the vasoconstrictor response to 20-HETE mimics the myogenic activation of renal arteries after elevations in transmural pressure. These studies suggest that the activation of phospholipase C and subsequent increases in the intracellular levels of diacylglycerol, 1,4,5 inositol triphosphate, and cytochrome P-450 metabolites of arachidonic acid may participate in the myogenic response of renal arteries and in the regulation of renal vascular tone.

Animals↗
PubMed1992

Spontaneous flow oscillations in the cerebral cortex during acute changes in mean arterial pressure.

The purpose of this study was to characterize spontaneous oscillations of blood flow in the cerebral cortex of anesthetized rats under control conditions and after mean arterial pressure was altered by various means. Blood flow was monitored using a laser-Doppler flowmeter through the closed cranium. Spontaneous flow oscillations with amplitudes of 14-30% of the mean flow and frequencies of 4-11 cycles/min were recorded when arterial pressures were less than 90 mm Hg. Stepwise hemorrhagic hypotension and unilateral carotid occlusion increased the amplitude of oscillations. The amplitude of oscillations was negatively correlated with the level of mean arterial pressure after manipulation with norepinephrine or sodium nitroprusside. The oscillations were reversibly abolished during dilation of the cerebral circulation by elevating the inspired carbon dioxide content to 5%. The frequency of flow oscillations was very stable during all of the above maneuvers except during the infusion of norepinephrine, which increased the oscillation frequency slightly. The results suggest that flow oscillations are determined primarily by cerebral arterial pressure.

Animals↗
PubMed1992

Mechanism of action of cerebral epoxyeicosatrienoic acids on cerebral arterial smooth muscle.

Microsomal preparations of cat brain incubated with [14C]arachidonic acid produced epoxyeicosatrienoic acids (EETs) that eluted with the same retention times as synthetically prepared 5,6-, 8,9-, and 11,12-EETs. These compounds dilated serotonin-preconstricted, pressurized cat cerebral arteries in a dose-dependent fashion. Epoxide formation was not found in mitochondrial fractions and was dependent on the presence of NADPH. The maximum effects of 8,9-EET and 11,12-EET were greater than those of 5,6-EET. The cellular basis of this vasodilation was further investigated by examining the effects of 8,9-EET and 11,12-EET on K+ channel activity in vascular muscle cells freshly isolated from cat cerebral arteries. Both 8,9-EET and 11,12-EET increased the frequency of opening, mean open time, and open-state probability of a 98-pS K+ channel recorded in the cell-attached mode with 145 mM KCl in the pipette and 4.7 mM KCl in the bath. Blockade of K+ channel activity with tetraethylammonium attenuated the vasodilatory effects of 11,12-EET on serotonin-preconstricted cat cerebral arteries. These results suggest that endogenously formed EETs may participate in local regulation of cerebral blood flow by dilating cerebral arteries through a mechanism that involves activation of K+ channels.

8,11,14-Eicosatrienoic Acid↗
PubMed1992

An angiographic method for in vivo study of arteries of the circle of Willis in small animals.

An X-ray imaging technique designed to allow sequential diameter measurements of the cerebral vessels in intact, anesthetized small animals under relatively physiological conditions is described. The ferret and the rabbit were chosen as potentially useful animal models for studying the cerebrovascular system because of the advantageous anatomic characteristics of these relatively small species. A commercially available and relatively inexpensive X-ray imaging system with a small focal spot provides good spatial resolution. An external carotid perfusion loop allows for 1) the introduction of low-osmolality contrast medium without changing perfusion pressure or flow and 2) measurement of internal carotid and circle of Willis pressures at the same time that the vessel images are obtained. In the present study, detection of small changes in the diameters of the small vessels is facilitated by an algorithm utilizing the X-ray absorption by the entire vessel cross section. This avoids some of the problems of edge detection for small cylindrical vessels wherein the contrast is less than optimal and diminishes as the vessel perimeter is approached.

Animals↗
PubMed1992

Distensibility of small veins of the dog lung.

To determine the distensibility of the intrapulmonary veins (250-2,900 microns diam) of the dog lung, we obtained X-ray angiograms from isolated lung lobes over a vascular pressure range of approximately 0-30 Torr. Over this pressure range the diameter vs. pressure curves tended to flatten out at the high pressures. In the pressure range of 0-19 Torr, we characterized the vessel distensibility by alpha (the ratio of the slope, beta, of the graph of diameter vs. intravascular pressure to the intercept, Do). The average value of alpha was approximately 1.2%/Torr. There was a weak negative correlation (r = -0.32) between alpha and Do. Infusion of enough norepinephrine to produce approximately 50% increase in total lobar vascular resistance produced a decrease in Do and alpha of approximately 33 and 32%, respectively.

Angiography↗
PubMed1991

Characterization of an outward K+ current in freshly dispersed cerebral arterial muscle cells.

This study was carried out to define some of the cellular ionic mechanisms controlling cerebral arterial muscle. Muscle cells were enzymatically dispersed from cat cerebral arteries. Cells were dialyzed and voltage-clamped using patch pipettes and whole-cell currents measured. Using pipette solutions allowing us to record K+ currents we identified an outward current elicited by depolarizing voltage steps beyond -20 mV. This outward current exhibited properties of delayed outward rectification having a peak macroscopic current at +90 mV of 504 +/- 236 pA. The current was sensitive to 4-aminopyridine, but was sensitive to tetraethylammonium only at very high doses. When CsCl was in the recording pipette, macroscopic outward currents could not be recorded. Variations in the extracellular Ca2+ concentration from 0.5 to 5.0 mM had no effect on current amplitude or voltage dependence; similarly the Ca2+ channel blockers nifedipine and Mn2+ were without effect on this outward current. The current inactivated slowly with no decay seen even with 3-s command pulses. Repetitive voltage pulses from -60 to +90 mV at a frequency of 1 Hz resulted in "cumulative reduction", depressing peak current by 60% after ten pulses. Upon reduction of pH from 7.43 to 7.20 we observed a 350% increase in peak outward current in 7 of 12 cells studied in this regard. Thus, the cellular mechanism responsible for cerebral vascular dilation to acidosis and/or hypercapnia may involve an increase in outward K+ current.

4-Aminopyridine↗
PubMed1991

Effects of 12-HETE on isolated dog renal arcuate arteries.

12-Hydroxy-5,8,10,14-eicosatetraenoic acid (12-HETE) is one of the major noncyclooxygenase eicosanoids formed in vascular tissue. The vasoactive effects of the cytochrome P-450 product, 12(R)-HETE and the lipoxygenase product, 12(S)-HETE, on isolated, perfused renal arcuate arteries of the dog were investigated using videomicroscopy. R and S refer to stereoconfiguration of the hydroxy group at the twelfth position of this fatty acid structure. Cumulative doses of 12(R)-HETE produced a concentration-dependent vasoconstriction (n = 9) with a threshold dose of 10(-9) M. At a concentration of 3 x 10(-7) M, 12(R)-HETE reduced vascular diameter by 63 +/- 8 microns (from 306 +/- 17 microns), which was 37 +/- 6% of the maximal vasoconstrictor response to norepinephrine (10(-6) M). The effects of 12(R)-HETE were not altered by indomethacin (10(-6) M, n = 8). The vasoconstrictor response was associated with depolarization of vascular smooth muscle from -47 +/- 1 (15 cells) to -32 +/- 1 mV (12 cells). 12(S)-HETE was also a vasoconstrictor (n = 6), but the threshold concentration for vasoconstriction was 10(-8) M. Small renal arteries obtained from ischemic-injured, but not normal, kidneys produced a metabolite when incubated with arachidonic acid, which coeluted with a 12-HETE standard using reverse-phase high-pressure liquid chromatography. The rate of synthesis of this 12-HETE-like metabolite by renal arteries obtained from ischemic-injured and normal kidneys averaged 1.2 +/- 0.4 (n = 9) and 0.1 +/- 0.1 (n = 7) pmol.h-1.mg tissue-1, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

12-Hydroxy-5,8,10,14-eicosatetraenoic Acid↗
PubMed1991

Distensibility of small arteries of the dog lung.

To obtain in situ measurements of the distensibility of small (100- to 1,000-microns-diam) pulmonary arterial vessels of the dog lung, X-ray angiograms were obtained from isolated lung lobes with the vascular pressure adjusted to various levels. The in situ diameter-pressure relationships were compared with the diameter-pressure relationships for small arteries that were dissected free from the lungs and cannulated with small glass pipettes for the measurement of diameter and transmural pressure. The diameter-vascular or diameter-transmural pressure curves from both in situ and cannulated vessels were sufficiently linear in the pressure range studied (0-30 Torr) that they could be characterized by linear regression to obtain estimates of D0, the diameter at zero vascular pressure, and beta, the change in diameter (micron) per Torr change in pressure. The vessel distensibility coefficient (alpha) was defined as alpha = beta/D0. The mean values of alpha were approximately 2.0 +/- 0.8%/Torr (SD) for the in situ vessels and 1.7 +/- 0.6%/Torr for the cannulated vessels, with no statistically significant difference between the two methods. The influence of vasoconstriction elicited by serotonin was evaluated in the in situ vessels. Serotonin-induced vasoconstriction caused a decrease in D0 and little change in alpha.

Animals↗
PubMed1991

Inhibitors of cytochrome P-450 attenuate the myogenic response of dog renal arcuate arteries.

The role of cytochrome P-450 in the myogenic response of isolated, perfused renal arcuate arteries of dogs to elevations in transmural pressure was examined. The phospholipase A2 inhibitor oleyloxyethylphosphorylcholine (1 and 10 microM) inhibited the greater than threefold increase in active wall tension in these arteries after an elevation in perfusion pressure from 80 to 160 mm Hg. Inhibition of cyclooxygenase activity with indomethacin (1 or 10 microM) had no effect on this response. The cytochrome P-450 inhibitors ketoconazole (10 and 100 microM) and beta-diethyl-aminoethyldiphenylpropylacetate (SKF 525A, 10 and 100 microM) also inhibited the myogenic response. At a pressure of 160 mm Hg, SKF 525A (10 microM) and ketoconazole (100 microM) reduced active wall tension in renal arteries by approximately 70%. Partial inhibition of the myogenic response was obtained after perfusion of the vessels with mechanism-based inhibitors of P-450, 1-aminobenzotriazole (75 microM) and 12-hydroxy-16-heptadecynoic acid (20 microM). The thromboxane receptor antagonist SQ 29,548 (1 or 10 microM) had no effect on the pressure-induced increase in active wall tension in renal arteries. Arachidonic acid (50 microM) constricted isolated perfused renal arteries and potentiated the myogenic response in the presence of indomethacin. This response was completely reversed by ketoconazole (100 microM) or SKF 525A (100 microM). Microsomes (1 mg/ml) prepared from small renal arteries (200-500 microns) and incubated with [1-14C]arachidonic acid (0.5 mu Ci, 50 microM) produced a metabolite that coeluted with 20-hydroxyeicosatetraenoic acid (20-HETE) during reversed-phase high-performance liquid chromatography. The formation of this product was inhibited by both ketoconazole and SKF 525A at concentrations of 10 and 100 microM. These results are consistent with the involvement of the vasoconstrictor 20-HETE and other cytochrome P-450 metabolites of endogenous fatty acids in the myogenic response.

Animals↗
PubMed1991

Effects of hypoxia on a potassium channel in cat cerebral arterial muscle cells.

We have shown that exposure of isolated cat cerebral arterial muscle cells to hypoxic environments increases K+ channel activity when recorded in the cell-attached mode. Inhibition by glibenclamide of the "hypoxia-induced" increase in K+ channel activity may suggest that increased activity is mediated by an ATP sensitive K+ channel. Thus, the level of O2 may modulate cerebral vascular tone by an action on membrane K+ channels, possibly mediated by the concentration of intracellular ATP.

Animals↗
PubMed1990

Enhanced norepinephrine sensitivity in renal arteries at elevated transmural pressure.

The electrical and mechanical responses of vascular smooth muscle to norepinephrine were compared at three different levels of transmural pressure (60, 100, and 140 mmHg) in cannulated small arteries that were isolated from dog kidneys. Elevation of transmural pressure caused depolarization of the vascular smooth muscle and a significant increase in vessel sensitivity to norepinephrine. Norepinephrine produced less depolarization as transmural pressure was elevated. Comparison of the relationship between transmembrane potential and norepinephrine concentration at these different transmural pressures suggests that membrane depolarization contributes to, but is not the sole explanation of, the increased norepinephrine sensitivity at higher transmural pressures. The results of this study suggest that transmural pressure in a blood vessel may be an important determinant of its sensitivity to vasoactive agonists.

Animals↗
PubMed1990

Mechanoreception by the endothelium: mediators and mechanisms of pressure- and flow-induced vascular responses.

Mechanoreception, a widely distributed sensory modality, has been shown to be present in certain blood vessels. Changes in physical forces, like sudden increase of transmural pressure or flow velocity (shear stress), trigger changes in blood vessel diameter; the former reduces it while the latter increases vessel caliber. These changes in diameter, which are the result of contraction and relaxation of vascular smooth muscle in the blood vessel media, can serve the purpose of physiological regulation of blood flow (autoregulation) and protection of the intima against damages from high shear forces. The precise location of mechanosensor(s) and the mechanism of mechanoreception and signal transduction are poorly understood. Accumulating evidence suggests that the endothelium may be a site of mechanoreception and that changes in the synthesis/release of endothelium-derived relaxing (EDRF, EDHF, PGI2) and contracting factors (EDCF) result in altered vascular smooth muscle tone and vessel caliber. Increased shear stress stimulates the release of EDRF and PGI2 probably via activation of a K+ channel (inward rectifier) in endothelial cell membrane. Endothelium-dependent vascular contraction evoked by increased transmural pressure may be the result of (1) reduced release of EDRF (canine carotid artery) and (2) stimulation of the release of a still unidentified EDCF(s) (feline cerebral artery). Thus the endothelium can serve as pressure and flow sensor and is capable of transducing changes in mechanical forces into changes of vascular smooth muscle tone by modulating the release of endothelium-derived vasoactive factors. The physiological importance of the mechanoreception by endothelial cells in the intact circulation remains to be determined.

Animals↗