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Biomedical subjects

N G Levinsky

Publications and source records attributed to N G Levinsky.

At least 19 recordsLinked to original sources
PubMed1990

Endotoxin inhibits contraction of vascular smooth muscle in vitro.

Decreased responsiveness of the vasculature to vasoconstrictors has been implicated in the pathogenesis of endotoxic shock, yet the mechanism of diminished responsiveness has not been determined. In these studies, exposure of rat aortic rings to purified Escherichia coli lipopolysaccharide (endotoxin) in vitro inhibited subsequent contractions caused by vasoconstrictors. Contractions caused by the alpha-adrenoceptor agonist phenylephrine, as well as those induced by potassium depolarization, were depressed by endotoxin. The effect of endotoxin on vascular contractions was delayed. Phenylephrine-induced contractions were not decreased during a 1-h exposure to endotoxin (10 micrograms/ml), but they were markedly decreased when tested several hours after the exposure period. A large part of the inhibition caused by a 1-h exposure to endotoxin was endothelium dependent. In contrast, endotoxin inhibited contractions equally in rings with or without endothelium exposed to endotoxin for a longer period (3 h). The inhibitory effect of endotoxin was not affected by indomethacin, but it was eliminated in aortic rings treated with the protein synthesis inhibitor cycloheximide. These studies indicate that endotoxin potently inhibits vascular contraction in vitro. The effect of endotoxin is apparently independent of prostanoids but may involve protein synthesis and effects on both vascular smooth muscle and endothelial cells.

Acetylcholine↗
PubMed1990

Rat aortic smooth muscle cells in culture express kallikrein, kininogen, and bradykininase activity.

We have studied rat vascular smooth muscle (VSM) cells in culture for the presence of key elements of the glandular kallikrein-kinin system. Direct radioimmunoassay (RIA) using antiserum against rat urinary kallikrein detected a glandular kallikrein-like enzyme (GKLE) in VSM cells and in media. VSM homogenates and culture media had kininogenase activity, generating kinins from dog kininogen. About half of the GKLE was enzymatically inactive which could be activated with trypsin. Kininogenase activity was inhibited completely by aprotinin but only 20% by soybean trypsin inhibitor (SBTI). Trypsin liberated kinins from homogenates and media, demonstrating that VSM cells contain kininogen. Homogenates and media rapidly degrade bradykinin. GKLE, kininogen, and bradykininase activity were all present in VSM cells grown in defined media that contain no serum, thus eliminating any contamination or artefacts from fetal calf serum in standard culture media. Blood vessels of the rat have been reported to contain GKLE. Our observations indicate that GKLE is synthesized by VSM cells, not deposited from plasma. Furthermore, VSM cells synthesize kininogen and bradykininase(s), the other key elements of the glandular kallikrein-kinin system. Thus it is possible that the system functions as an autocoid mechanism that regulates local vascular tone.

Animals↗
PubMed1989

A micro-kininogenase assay for studies of kallikrein in renal micropuncture/microperfusion.

We report the development of a micro-kininogenase assay suitable in studying the dynamics of kallikrein at intranephron segmental level. The detection limit is 119 fg or 2.6 attomoles of kallikrein. Activation of microquantities of kallikrein is possible with the use of Triton X-100. Because of its extremely high sensitivity and reproducibility the assay is likely to also prove useful in physiological studies in which only very small amounts of kallikrein containing samples can be obtained.

Animals↗
PubMed1989

Renal ischemia and reperfusion impair endothelium-dependent vascular relaxation.

We studied the hemodynamic response of the isolated erythrocyte-perfused kidney to 25 min of ischemia and found that renal vascular resistance (RVR) was increased in the reflow period (16.7 +/- 1.4 mmHg.ml-1.min.g following ischemia vs. 10.2 +/- 0.8 mmHg.ml-1.min.g in control kidneys). Endothelial independent vasodilators [atrial natriuretic factor (ANF) and sodium nitroprusside] prevented the increase in RVR that occurred after ischemia. In contrast, acetylcholine and the calcium ionophore A23187, two vasodilators that act by releasing endothelium-derived relaxing factor (EDRF), had no effect on the increased RVR that occurs on reflow. Two inhibitors of EDRF, methylene blue and gossypol, increased RVR in nonischemic kidneys by 45 +/- 6 and 46 +/- 11%, respectively, an increase that was comparable to that found with ischemia alone (55 +/- 7%). The increase in RVR found with the combination of EDRF inhibition and ischemia (59 +/- 5%) was the same as that found with ischemia alone. We conclude that EDRF activity is impaired following ischemia and reperfusion. This abnormality in EDRF may be an important mechanism contributing to postischemic vasoconstriction in the renal vasculature.

Animals↗
PubMed1989

Interleukin 1 inhibits contraction of vascular smooth muscle.

Interleukin 1 has been implicated as a mediator of both systemic and local responses to infection and injury. Since systemic and local vasodilatation are hallmarks of sepsis and infection, we studied the direct effect of IL-1 on vascular contractility. We report here that human recombinant IL-1-beta potently inhibits the response of rat thoracic aorta to vasoconstrictor agents. Exposure of isolated rat aortic rings to IL-1 (20 ng/ml) for 1 h did not affect phenylephrine-induced contractions during the exposure period. However, when rings were retested 150-200 min after initiation of IL-1 exposure, contractions were markedly decreased. The cytokine had a similar effect in rings from which the endothelium was removed. Contractions caused by potassium depolarization also were depressed, indicating the effect of IL-1 is not specific to the alpha-adrenoceptor agonist. The inhibitory effect of IL-1 was concentration-dependent (0.2 to 20 ng/ml), and eliminated by pretreatment with cycloheximide (20 micrograms/ml). Indomethacin (10(-5) M) did not prevent the inhibition caused by IL-1. These studies identify IL-1 as a potent inhibitor of vascular contraction, via an endothelium-independent mechanism. Studies with inhibitors suggest that the action of IL-1 is independent of prostanoid synthesis, and may involve synthesis of protein.

Animals↗
PubMed1987

Hemodynamic effects of different preparations of stroma free hemolysates in the isolated perfused rat kidney.

We have examined the effects of Stroma Free Hemolysate (SFH) solutions in the isolated perfused rat kidney. Three types of SFH, stored for 6 to 8 months at 4 degrees C, were tested: 1) unmodified, 2) glyoxalated and lightly cross linked and 3) pyridoxalated and polymerized. All three SFH solutions, added to the perfusate at a concentration of approximately 420 mg/100ml, increased renal vascular resistance (RVR) and reduced glomerular filtration rate (GFR). Unmodified, glyoxalated and lightly cross linked and pyridoxalated polymerized SFH resulted in a rise in RVR of 55%, 38% and 33% respectively and a fall in GFR of 42%, 57% and 83% respectively. In order to determine whether storage had altered the effect of SFH on renal function, one of the forms of SFH (glyoxalated and lightly cross linked) was studied only 4-6 weeks after preparation. While this preparation caused an increase in RVR of 41% it did not alter GFR; filtration fraction (FF) rose. However, after further storage of this preparation for 6-7 months, the solution resulted in a marked decrease in GFR of 47% as well as a rise in RVR of 23%. We conclude that three different SFH preparations resulted in marked vasoconstriction and reductions in GFR. These deleterious effects on renal hemodynamics were noted at a concentration of hemoglobin well below that necessary to effectively improve oxygen content. Storage of the SFH solutions may cause or contribute to their effects on renal function. SFH solutions intended for use as blood substitutes should be tested for vasoconstrictor activity.

Animals↗
PubMed1987

Micropuncture localization of kallikrein secretion in the rat nephron.

We have used free-flow micropuncture to study the tubular locus at which kallikrein enters the urine. Kallikrein was measured by a newly developed, very sensitive assay for kininogenase activity; active kallikrein was measured directly by this assay and total kallikrein after activation of inactive kallikrein. Kallikrein was readily detected in all of 17, late distal tubular fluid-samples. In contrast, kallikrein was too low to detect in 15 of 17 proximal or in 11 of 14 early distal tubular fluid samples. Calculations indicate that less than 10% of urinary kallikrein could have derived from filtration or from proximal secretion of kallikrein. We conclude that urinary kallikrein enters the urine via secretion in the distal tubule. Filtration or proximal secretion of kallikrein does not contribute significantly to urinary kallikrein excretion.

Animals↗
PubMed1987

Interactions between ADH and prostaglandins in isolated erythrocyte-perfused rat kidney.

Interactions between antidiuretic hormone (ADH) and renal prostaglandins in the regulation of sodium reabsorption and urinary concentrating ability were studied in isolated erythrocyte-perfused rat kidneys (IEPK). In this model, hemodynamic characteristics are comparable to those found in vivo, and tubular morphology is preserved throughout the period of perfusion. [Deamino]-D-arginine vasopressin (dDAVP) markedly reduced fractional sodium excretion (FE Na) in the IEPK from 3.5 +/- 0.6 to 0.45 +/- 0.14%. After indomethacin, FE Na fell still further to 0.08 +/- 0.02%. In the absence of dDAVP indomethacin had no effect on sodium excretion; FE Na was 2.4 +/- 0.6% in control and 2.0 +/- 0.4% in indomethacin-treated groups. dDAVP increased urine osmolality in the IEPK to 741 +/- 26 mosmol/kg. When prostaglandin synthesis was blocked with indomethacin, urinary osmolality increased further to 1,180 +/- 94 mosmol/kg. In isolated kidneys perfused without erythrocytes (IPK), dDAVP decreased FENa from 14.5 +/- 1.8% to 9.6 +/- 1.2%; addition of indomethacin had no further effect. dDAVP increased urine osmolality only modestly to 350 +/- 12 mosmol/kg in the IPK and indomethacin did not increase concentrating ability further (342 +/- 7 mosmol/kg). Thus the IEPK (unlike the IPK) can excrete a markedly hypertonic urine in response to ADH. ADH also enhances tubular reabsorption of sodium in the IEPK. Prostaglandins inhibit both these actions of ADH but do not directly affect sodium excretion in the absence of the hormone.

Absorption↗
PubMed1987

Effect of erythrocytes on the function and morphology of the isolated perfused rat kidney.

We have examined the effects of erythrocytes on the function and morphology of isolated rat kidneys perfused with a physiological concentration of bovine albumin (45 g/l). (1) In kidneys perfused without red cells, renal vascular resistance (RVR) was low (4.2 +/- 0.3 mm Hg/ml/min/g), fractional sodium excretion (FeNa) was high (14.5 +/- 1.8%) and concentrating ability impaired (maximum urine osmolality 343 +/- 4 mmol/kg). The erythrocyte-free kidney also developed necrosis of the cells of the medullary thick ascending limb (mTAL). (2) Erythrocytes at a hematocrit of 4-6% did not alter RVR but prevented ischemic changes in the mTAL and reduced FeNa to 9.4 +/- 0.03%. Concentrating ability was not improved by a hematocrit of 4-6% despite the presence of a morphologically normal mTAL. (3) At a hematocrit of 40-45%, RVR was increased (to 11.2 +/- 0.4 mm Hg/ml/min/g) and FeNa was further lowered to 3.5 +/- 0.6%. Also, urinary concentrating ability was markedly improved (maximum urine osmolality 640 +/- 35 mmol/kg). (4) The isolated perfused kidney (IPK) at a hematocrit of 40-45% was able to autoregulate renal perfusate flow rate of GFR but autoregulation was incomplete. A 50% increase in perfusion pressure from 100 to 150 mm Hg increased renal perfusate flow rate and GFR 27 and 29%, respectively. Thus the IPK is not able to autoregulate as efficiently as the kidney in vivo, even in the presence of red cells at a normal hematocrit.

Animals↗
PubMed1986

Health care for veterans: the limits of obligation.

The federal government has a generally unquestioned obligation to provide health care to veterans for diseases or disabilities acquired during military service. Much argued, however, is the government's obligation to offer care for nonservice-connected disorders. The Reagan administration has sharpened the debate recently by attempting to impose a means test on veterans over sixty-five who are seeking such care. But the controversy focuses on the wrong issue. Society has a moral obligation to provide adequate health care to all citizens but has no special obligation to care for nonservice-connected health problems of veterans.

Delivery of Health Care↗