PubMed Health⌕ Search

Biomedical subjects

R W Schrier

Publications and source records attributed to R W Schrier.

At least 19 recordsLinked to original sources
PubMed1992

High specific activity 125I- and 35S-labeled vasopressin analogues with high affinity for the V1 and V2 vasopressin isoreceptors.

Since iodination of the tyrosine residue in the pressin ring of vasopressins abolishes binding to the V2 (renal) isoreceptor, the low specific activity tritiated vasopressins have been the only radioligands available for this receptor. Alternative vasopressin radioligands are described in the present study. N-tert-Butoxycarbonyl- (N-t-Boc) 125I-tyrosine or [35S]methionine were conjugated to the 8th amino acid of lysine- (LVP) or deamino-ornithine-vasopressin via active succinimidyl esters. Following the purification on C-18 reverse-phase high pressure liquid chromatography, t-Boc removal, and a second high pressure liquid chromatography purification, specific activities of 2200 and 1300 Ci/mmol were obtained for the 125I- and the 35S-labeled ligands, respectively. These vasopressin analogues, conjugated outside the pressin ring, were found to bind with high affinity to the V1A (vascular) and V2 vasopressin isoreceptors (Kd less than or equal to 10(-9) M) and to retain the full biological activity of intact vasopressin. The present study demonstrates the possibility of producing high specific activity radioligands with high affinity for the V1A and V2 vasopressin isoreceptors by conjugating labeled moieties to the 8th amino acid of vasopressin analogues. Since these new radioligands have specific activities much higher than the tritiated ligands (1300-2200 versus 10-30 Ci/mmol), they should provide considerable advantages in the future study of the physiology and biochemistry of the AVP receptors.

Adenylyl Cyclases↗
PubMed1992

Demonstration of processing and recycling of biologically active V1 vasopressin receptors in vascular smooth muscle.

The present study examines the binding and postbinding cellular processing and recycling of the V1 arginine vasopressin (AVP) receptor in cultured vascular smooth muscle cells (VSMCs). The surface binding of AVP to VSMCs was temperature dependent and reached equilibrium within 60 min at 4 degrees C. Displacement studies with unlabeled AVP or a specific V1 AVP antagonist revealed a single class of V1 receptors (Bmax, 1.99 pmol [corrected] per mg of protein; Kd, 2.15 nM). Incubation of VSMCs with unlabeled 10 nM AVP to promote receptor internalization resulted in a time- and temperature-dependent loss of AVP surface binding. At 37 degrees C, maximum loss of binding sites (65%) occurred within 20 min. Recovery of AVP binding occurred rapidly (t1/2, 15-20 min at room temperature) and was uninfluenced by inhibiting protein synthesis with cycloheximide. Pretreating VSMCs with chloroquine prevented AVP receptor recycling, indicating that the AVP-receptor complex requires endosomal processing. The biological competence of the recycled AVP receptor was shown by AVP-induced Ca2+ uptake. The results of these studies therefore indicate that, after surface binding, the AVP-receptor complex internalizes and dissociates in an endosomal compartment. It is demonstrated that in VSMCs biologically active V1 AVP receptors recycle back to the cell surface, thus attenuating the loss of AVP surface binding sites.

Animals↗
PubMed1992

Short-term hypothyroidism and vasopressin gene expression in the rat.

Hypothyroidism is associated with abnormalities in renal water handling, which include a delay in excretion of an acute water load, decreased urinary concentrating ability, and increased urine volume. In the present study, we investigated the role of vasopressin in aminotriazole-induced hypothyroidism by measuring vasopressin concentration in the plasma and pituitary along with vasopressin mRNA levels in the hypothalamus. After 5 weeks of aminotriazole treatment, L-thyroxine levels were significantly lower in the experimental animals (122 +/- 8 v 26 +/- 1 nmol/L [9.5 +/- 0.6 v 2.0 +/- 0.1 micrograms/dL]; P less than 0.001). Serum sodium (148 +/- 0.5 v 144 +/- 1.2 mmol/L [mEq/L]; P less than 0.01), and plasma osmolality (311 +/- 2.5 v 304 +/- 1.8 mmol/kg [mOsm/kg] H2O; P less than 0.05) were also lower in the experimental animals. There were no differences in plasma (1.9 +/- 0.4 v 1.5 +/- 0.2 pg/mL) or pituitary (1.5 +/- 0.4 v 1.5 +/- 0.2 microgram/pituitary) vasopressin levels. In addition, steady-state vasopressin mRNA levels were not different between the two groups (1,286 +/- 210 v 1,093 +/- 138 pg/hypothalamus). One week of L-thyroxine replacement resulted in significant increases in serum thyroxine levels without changes in the other variables measured. These results indicate that short-term hypothyroidism, which has been shown to exert substantial effects on renal function, causes only a modest central alteration in the plasma vasopressin-osmolality relationship, which occurs in the absence of detectable changes in vasopressin synthesis.

Amitrole↗
PubMed1992

Atrial natriuretic peptide kinetic studies in patients with cardiac dysfunction.

Three studies were performed: (1) a controlled investigation of alpha-human atrial natriuretic peptide (alpha-hANP) total body production and metabolic clearance rates using a bolus infusion technique (controls, patients 1 to 6); (2) a study of alpha-hANP kinetics in cardiac dysfunction patients using a constant infusion method (patients 7 to 14); and (3) a right heart catheterization study to determine the amount of alpha-hANP released into the circulation at the level of the right heart, estimated by the step-up in alpha-hANP concentration between the superior and inferior vena cava and the pulmonary artery, in the patients with left ventricular dysfunction. Baseline venous plasma alpha-hANP was 27.3 +/- 16.5 pg/ml in the controls (mean +/- SD; N = 6), 141.6 +/- 138.0 pg/ml in patients 1 to 6 (P less than 0.05 compared to controls), and 167.5 +/- 145.7 pg/ml in patients 7 to 14. Total body alpha-hANP production rate was markedly elevated in patients 1 to 6 compared to controls (0.45 +/- 0.36 vs. 0.11 +/- 0.06 micrograms/min, P less than 0.05) and was similar to that determined by the continuous infusion technique in patients 7 to 14 (0.62 +/- 0.44 micrograms/min, P = 0.49 compared to patients 1 to 6). alpha-hANP release into the right heart (0.17 +/- 0.11 micrograms/min), however, was significantly lower than total body production rate in the cardiac dysfunction patients, indicating that total body alpha-hANP secretion occurs from sites in addition to drainage into the right heart via the coronary sinus and anterior cardiac veins. Right atrial pressure correlated with the alpha-hANP released into the right heart.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1992

Acute phosphate depletion and in vitro rat proximal tubule injury: protection by glycine and acidosis.

The effects of phosphate (PO4) removal from Krebs Henseleit buffer on freshly isolated rat proximal tubules (rPT) were assessed by measuring Ca2+ uptake (nmol/mg protein), cellular adenosine triphosphate (ATP) (nmol/mg), tissue K+ content (nmol/mg) and lactate dehydrogenase (LDH) as an index of cell integrity. Ca2+ uptake increased by 50% in rPT incubated in zero PO4 medium as compared to control (2.6 +/- 0.1 vs. 3.9 +/- 0.19, P less than 0.001) and LDH release increased 2.5-fold from 14.2 +/- 0.6 to 31.6 +/- 1.6%, P less than 0.001. Neither verapamil (200 microM) nor mepacrine (50 microM) reduced Ca2+ uptake or decreased LDH release suggesting that the increased Ca2+ uptake was not occurring through potential operated channels and that phospholipase-induced cell injury was not the cause of increased LDH release. Either glycine (2 mM) or extracellular fluid acidosis (pH 7.06), however, significantly diminished rPT injury and Ca2+ uptake. Specifically, as compared to the increased LDH released in untreated. PO4-depleted rPT, LDH release was diminished significantly by glycine treatment (31.0 +/- 0.9 vs. 15.5 +/- 1.6%, P less than 0.001) or acidosis (30.3 +/- 0.04 vs. 19.2 +/- 0.9%, P less than 0.01). Ca2+ uptake did not increase in glycine treated tubules (2.6 +/- 0.1 vs. 2.8 +/- 0.2 nmol/mg, NS) or in the presence of acidosis (2.6 +/- 0.1 vs. 2.97 +/- 0.17 nmol/mg, NS). ATP concentrations were markedly reduced by PO4 depletion (2.8 +/- 0.2 vs. 4.8 +/- 0.3 nmol/mg, P less than 0.001) and remained at low levels during either acidosis or glycine-induced protection.(ABSTRACT TRUNCATED AT 250 WORDS)

Acidosis↗
PubMed1992

Prevention and attenuation of acute renal failure.

Recent progress in our understanding of the pathogenetic processes involved in ischemic acute renal failure is considerable. Blockade of the production of endothelium-derived relaxing factor may markedly improve survival in patients with septic shock. Atrial natriuretic peptide and growth factors enhance renal recovery in animal models of acute renal failure, even when administered well after the ischemic insult. Aminoglycosides and radiocontrast agents are the most common causes of drug-induced acute renal failure. Once-daily administration of aminoglycosides is an effective treatment modality that may limit the occurrence of nephrotoxicity. Awareness of the patient's volume status has decreased the incidence of radiocontrast-induced acute renal failure. The new, expensive, nonionic, low-osmolar radiocontrast agents do not offer apparent benefits in patients with normal or slightly decreased renal function. However, use of such agents may decrease the incidence of radiocontrast-induced renal failure in diabetic patients with severe renal failure. The prognosis for patients with renal vasculitis has improved greatly in the past decade. The discovery of antibodies directed against antigenic targets in the cytoplasm of neutrophils has facilitated the diagnosis of renal vasculitides, has improved our knowledge of the pathogenesis of these diseases, and may guide rational treatment.

Acute Kidney Injury↗
PubMed1992

Comparative effects of arginine vasopressin and oxytocin in cell culture systems.

Arginine vasopressin (AVP) and oxytocin (OXT) induced contraction in cultured vascular smooth muscle cells (VSMC) and glomerular mesangial cells (GMC). The contractile response of AVP and OXT was paralleled by Ca2+ mobilization as assessed by 45Ca2+ efflux in a dose-dependent manner. The effects of AVP were blocked by pretreating VSMC and GMC with a V1 antagonist. OXT-stimulated effects, however, were not affected by preexposure of VSMC and GMC to an OXT antagonist but were inhibited by the V1 antagonist. Competition studies demonstrated displacement of [3H]AVP from its receptors by unlabeled AVP, the V1 antagonist, and high doses of OXT. The OXT antagonist was the least effective in displacing [3H]AVP. Thus occupancy of the V1 receptor by OXT may initiate signal transduction and contraction in VSMC and GMC in a manner qualitatively similar to that of the AVP agonist. Cultured myometrium cells (MMC) also contracted in response to AVP and OXT. Moreover, 45Ca2+ efflux increased in response to both hormones in a dose-dependent manner. AVP-stimulated contraction and 45Ca2+ efflux were blocked in MMC by pretreatment with V1 antagonist. OXT-induced effects were inhibited by the OXT antagonist but not by the V1 antagonist. Binding experiments showed that [3H]AVP was displaced equally by unlabeled AVP and V1 antagonist. Very high concentrations of OXT antagonist also demonstrated displacement.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1992

Glucose-induced downregulation of angiotensin II and arginine vasopressin receptors in cultured rat aortic vascular smooth muscle cells. Role of protein kinase C.

Early diabetes mellitus is characterized by impaired responses to pressor hormones and pressor receptor downregulation. The present study examined the effect of elevated extracellular glucose concentrations on angiotensin II (AII) and arginine vasopressin (AVP) receptor kinetics in cultured rat vascular smooth muscle cells (VSMC). Scatchard analysis of [3H]AVP and 125I-AII binding to confluent VSMC showed that high glucose concentrations (20 mM) similarly depressed AVP and AII surface receptor Bmax but did not influence receptor Kd. This receptor downregulation was not reproduced by osmotic control media containing either L-glucose or mannitol. Receptor downregulation was maximal at a glucose concentration of 15-20 mM and required 24-48 h for a maximum effect. Normalization of the extracellular glucose concentration allowed complete recovery of AVP and AII binding within 48 h. Receptor downregulation was associated with depressed AVP and AII-stimulated intracellular signaling and cell contraction. High glucose concentrations induced a sustained activation of protein kinase C (PKC) in VSMC, which was prevented by coincubation with H-7. H-7 also markedly attenuated glucose-induced downregulation of AVP and AII receptors on VSMC. This study demonstrates a novel cellular mechanism whereby high extracellular glucose concentrations directly and independently downregulate pressor hormone receptors and their function on vascular tissue via glucose-stimulated PKC activation.

Angiotensin II↗
PubMed1992

Atrial natriuretic peptide and urinary cyclic guanosine monophosphate in patients with chronic heart failure.

Circulating concentrations of human atrial natriuretic peptide (hANP) are elevated in patients with heart failure; however, the natriuretic effect of hANP is blunted in these patients. In this study, the relationship between urinary cGMP, the second messenger for the natriuretic effect of hANP in vivo, and endogenous hANP was examined in six patients with heart failure and four normal subjects. In addition, right heart catheterization for the determination of central hemodynamics was performed in the heart failure patients. The heart failure patients were in New York Heart Association Classes II to IV and were receiving no medications at the time of the study. Supine plasma hANP and urinary cGMP concentrations were determined on two occasions in each subject, as were right and left atrial pressures in the heart failure patients. At the time of study, the patients were in positive sodium balance, and control subjects were in normal sodium balance. Plasma hANP and urinary cGMP excretion rates were elevated in heart failure patients as compared with those in controls: hANP, 139.0 +/- 42.0 versus 22.0 +/- 6.1 pg/mL (P less than 0.05); urinary cGMP, 1.14 +/- 0.31 versus 0.35 +/- 0.05 nmol/min (P less than 0.05). In heart failure patients, right atrial pressure correlated positively with plasma hANP (r = 0.96; P less than 0.01) and urinary cGMP concentrations (r = 0.93; P less than 0.05) and the excretion rate (r = 0.92; P less than 0.05). Moreover, plasma hANP was strongly correlated with urinary cGMP concentration (r = 0.91; P less than 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1992

Characterization of glucose-induced in situ protein kinase C activity in cultured vascular smooth muscle cells.

The VSMC is an important target for the injurious effects of hyperglycemia in vivo. PKC plays a key role in the regulation of VSMC contraction and growth. This study examines whether elevated extracellular glucose concentrations (10-30 mM [180-540 mg/dl]) activate PKC in cultured rat VSMCs in vitro. A new, rapid, and highly specific assay was used to determine in situ PKC activity in digitonin-permeabilized VSMCs. PKC activity in VSMCs responded rapidly to variations in extracellular glucose concentrations. PKC was activated significantly within 10 min of exposure to D-glucose (20 mM) versus glucose (5 mM). Moreover, with continued exposure to D-glucose (20 mM), PKC activation was sustained for up to 48 h. Reducing D-glucose concentrations to 5 mM restored PKC activity to control values within 1 h. PKC activation was also glucose-concentration dependent. A threshold of only 15 mM (270 mg/dl) was required to significantly and maximally activate PKC in VSMC. PKC was not activated in the presence of osmotic control media that contained either elevated mannitol or L-glucose concentrations. In marked contrast to the sustained PKC activation induced by D-glucose in VSMCs, the normal physiological PKC response to the pressor hormones, AII and AVP, was short-lived and returned to base line within minutes. Sustained PKC activation in the presence of elevated D-glucose concentrations in vitro could disturb the normal physiological regulation of VSMC function and growth and thereby may contribute to the apparent vasotoxicity of hyperglycemia in vivo.

1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine↗
PubMed1992

Calcium channel blockers: protective effects in ischemic acute renal failure.

Studies in heart, liver, and kidney have provided evidence that calcium is an important factor in cell injury. Calcium channel blockers are used with increasing frequency in ischemic and toxic renal failure. In this review the available data on the effects of calcium channel blockers in animal models of ischemic renal failure are presented and possible mechanisms of protective actions are discussed.

Acute Kidney Injury↗
PubMed1992

Pathogenesis of sodium and water retention in liver disease.

The "Peripheral Arterial Vasodilation" hypothesis most completely explains the clinical spectrum of cirrhosis ranging from compensated to decompensated to the hepatorenal syndrome (Figure 15-1). As the systemic peripheral vasodilation increases, the neurohumoral responses to arterial underfilling are stimulated with resultant renal vasoconstriction, sodium and water retention. Hypoalbuminemia and portal hypertension, as well as local effects of vasodilation at the capillary level, also contribute to ascites formation and peripheral edema. The suppressed plasma renin activity and aldosterone concentrations and exaggerated natriuresis, which are observed in some patients with early cirrhosis during HWI and the supine position, probably indicate greater central translocation of splanchnic fluid in these volume expanded cirrhotic patients when compared with normal subjects. This interpretation is supported by the greater increases in ANF during HWI in these patients when compared with controls. The neurohumoral responses to arterial vasodilation in cirrhosis combine to decrease distal sodium and water delivery, an event which impairs escape from the sodium retaining effects of aldosterone and causes resistance to the distal tubular effect of ANF (Figure 15-3). As discussed, the peripheral arterial vasodilation of cirrhosis is no doubt multifactorial in nature and the resultant arterial underfilling may be worsened by events that could impair the cardiac response to afterload reduction, including bile salt accumulation, alcoholic cardiomyopathy, and tense ascites decreasing cardiac preload. This pathogenetic schema of cirrhosis is compatible with the unifying body fluid volume hypothesis (Figure 15-3), which we have recently proposed.

Body Water↗
PubMed1992

Effect of elevated extracellular glucose concentrations on calcium ion uptake by cultured rat vascular smooth muscle cells.

Blood flow autoregulation is impaired in early diabetes mellitus, predisposing the microvasculature to injury. Blood flow autoregulation is in part a myogenic response that is critically dependent on Ca2+ uptake via voltage-sensitive calcium channels in vascular smooth muscle cells (VSMC). Recent evidence suggests that impairment of blood flow autoregulation in diabetes may be responsive to variations in glycemic control. The present study thus examined the independent effect of an elevated extracellular glucose concentration on Ca2+ uptake by cultured rat VSMC in vitro. A threshold glucose concentration of 15-20 mmol/l markedly and maximally depressed basal and voltage sensitive Ca2+ channel activated (BAY K 8644, 10(-7) M) Ca2+ uptake. This effect was apparent within 3 h of incubating VSMC with the high glucose medium and was maximal after 48 h incubation. Osmotic control media containing either mannitol or L-glucose did not inhibit Ca2+ uptake by VSMC, thus confirming the effect was specific for elevated extracellular glucose concentrations and unrelated to changes in extracellular osmolality. Glucose-induced inhibition of basal and voltage-sensitive transmembrane fluxes of Ca2+ in VSMC may provide a metabolic mechanism for impaired calcium-dependent blood flow autoregulatory responses in early diabetes mellitus.

Animals↗