Furosemide and cerebrospinal fluid ions during acute respiratory acidosis

The purpose of this study was to investigate the effects of furosemide, an inhibitor of NaCl cotransport, on cisternal cerebrospinal fluid (CSF) acid-base balance during acute respiratory acidosis (ARA). We measured blood and CSF acid-base variables in two groups (n = 7 in each) of anesthetized, paralyzed, and mechanically ventilated dogs with bilateral ligation of renal pedicles (to eliminate saluresis). After base-line samples were obtained (-1 h), furosemide (50 mg/kg) was administered intravenously within 15 min (group II); group I received an equal volume of half-normal saline. ARA was induced 1 h later (0 h) and arterial CO2 tension was maintained between 55 and 60 Torr for 5 h. Mean cisternal CSF PCO2 was 42.8 +/- 2.6 and 39.5 +/- 1.7 Torr, respectively in groups I and II and rose approximately 20 Torr during ARA. In group I, CSF [HCO3-] was 22.0 +/- 1.0, 24.8 +/- 0.6, and 25.4 +/- 1.6 meq/l, respectively at 0, 2.5, and 5 h. Respective values for group II were 22.2 +/- 1.3, 24.3 +/- 1.8, and 24.6 +/- 1.0 meq/l. These values were not significantly different from each other. In each group, CSF [Na+-Cl-] increased significantly during ARA, but the changes were not significantly different when the two groups were compared. We conclude that furosemide at the dose used in the present study does not change ionic composition and acid-base balance of cisternal CSF compared with control. Because changes in CSF [Na+-Cl-] during ARA were similar in both groups, any inhibition of Cl- influx into CSF by furosemide should have been proportional to that of Na+.

Analysis of warfarin and its metabolites by reversed-phase ion-pair liquid chromatography with fluorescence detection

A high-performance liquid chromatographic method was developed for the determination of warfarin and its metabolites (diastereomeric warfarin alcohols and 6-, 7-, 8-, 4'- and 3'-hydroxywarfarin) in microbial cultures. Ion-pair chromatography with tetrabutylammonium ion as the counter ion allowed for the complete resolution of all compounds at pH 7.5 on a reversed-phase (C18) column, thus permitting direct fluorescence detection without the use of post-column pH switching techniques. Analysis of cell suspension cultures of the fungus Cunninghamella elegans (ATCC 36112) indicated that this organism metabolizes warfarin to all known mammalian metabolites, plus the previously unreported 3'-hydroxywarfarin. Detection limits for all compounds were in the low nanogram range.

Effects of cholestatic hepatic disease and chronic renal failure on alfentanil pharmacokinetics in children

The role of the liver and the kidney in alfentanil metabolism has not been defined. The effects of cholestatic hepatic disease and chronic renal failure on the pharmacokinetics of alfentanil were evaluated in 9 children undergoing liver transplantation and 10 children undergoing kidney transplantation. These findings were compared with data from 10 children with normal hepatic and renal function undergoing other surgical procedures. There was no statistical difference among the 3 groups with respect to apparent volume of distribution, half-life, or clearance. In a subgroup of 3 patients undergoing liver transplantation alfentanil kinetics were determined both before and after the allograft was incorporated into the recipient's circulation. Though both volume of distribution and elimination half-life increased in the posttransplantation period, only the decrease in clearance was statistically significant. Thus, it appears that alfentanil may be a useful anesthetic agent in pediatric patients with cholestatic hepatic disease or chronic renal failure. The dose of alfentanil in these patients need not be altered except in the period immediately after liver transplantation.

Stimulation in vitro of rabbit erythrocyte cytosol phospholipid-dependent protein kinase activity. A novel action of thyroid hormone

L-Thyroxine (T4) and 3,3',5-L-triiodothyronine (T3) at 10(-10) M stimulated phospholipid- and Ca2+-dependent protein kinase activity in rabbit red cell cytosol in vitro by 151 and 176%, respectively. Kinase of 30-fold greater specific activity, developed with 0.4 mM NaCl from cytosol applied to DEAE-cellulose, was also stimulated up to 2-fold by thyroid hormone. Hormone enhancement of kinase activity occurred after 60 min of incubation at 37 degrees C prior to enzyme assay. Thyroid hormone analogues triiodothyroacetic acid, 3,5-dimethyl-3'-isopropyl-L-thyronine, D-T3, D-T4, and 3,3',5'-L-triiodothyronine (reverse T3) were inactive. These results support a role for thyroid hormone endogenously in regulation of phospholipid-dependent protein kinase activity.

Microbial models of mammalian metabolism: conversion of warfarin to 4'-hydroxywarfarin using Cunninghamella bainieri

Warfarin, an anticoagulant and "metabolic probe" for cytochrome P-450 isozyme multiplicity, is metabolized to 4'-hydroxywarfarin, a principle mammalian metabolite, using the fungus Cunninghamella bainieri (UI-3065). The metabolite was isolated from cell suspension cultures and characterized by analytical (TLC, HPLC, GC-MS) and spectral (HRMS, EI-MS, PMR) comparisons with authentic 4'-hydroxywarfarin. The mechanism of aromatic hydroxylation was examined in C. bainieri using 4'-deuterowarfarin. The absence of a primary isotope effect (KH/KD = 1.13), migration and retention of deuterium in the phenolic product [80% migration and retention (M&R)], and inhibition of the hydroxylation by carbon monoxide (93% inhibition in a 50:50 CO:O2 atmosphere) are consistent with a cytochrome P-450-mediated hydroxylation involving the classic NIH shift (arene oxide) pathway.

Enzyme replacement therapy in fibroblasts from a patient with cholesteryl ester storage disease

Enzyme replacement has long been considered only a remote possibility in the treatment of a wide range of genetic disorders, many manifested as lysosomal storage diseases. The complexity of having a particular enzyme gain access to the lysosomal compartment in a specific cell seemed insurmountable. We report here on an attempt to introduce the enzyme cholesteryl esterase into fibroblasts from a patient with cholesteryl ester storage disease (CESD). The enzyme gains access to the lysosomal compartment and the accumulating cholesteryl ester by virtue of being carried into the cell conjugated to a ligand (insulin or apoprotein B [apoB]) that binds to its own specific receptor and is internalized by the well-described process of receptor-mediated endocytosis. Regardless of whether the enzyme enters the cell via the insulin receptor or via the low-density lipoprotein (ApoB) receptor, it can be found associated with a lysosomal fraction and is effective in lowering levels of accumulated substrate, cholesteryl ester. The time course of the substrate degradation and the dependence on the receptor density and receptor density and receptor-ligand interaction indicate that the enzyme is simply being carried to the site of substrate accumulation by virtue of the fact that that is the destination of the ligand (along with its conjugated enzyme) following internalization.

Retinoic acid is a modulator of thyroid hormone activation of Ca2+-ATPase in the human erythrocyte membrane

The thyroid hormones thyroxine (T4) and 3,3',5-L-triiodothyronine (T3) stimulate plasma membrane Ca2+-ATPase (EC 3.6.1.3) activity in human erythrocytes by a mechanism independent of the cell nucleus. The current studies were conducted to determine the effect of retinoic acid on the extranuclear activation by T4 and T3 of Ca2+-ATPase in the human red cell. The retinoid inhibited basal and T4-stimulatable activity of that enzyme in a dose-dependent manner. At the highest tested concentration (10(-6) M), retinoic acid inhibited basal enzyme activity by 25% and T4-stimulated activity by 72%. A concentration as low as 5 x 10(-10) M retinoic acid shifted the dose-response curve of both T4 and T3 so that the concentration of each associated with maximal enzyme stimulation was 10(-9) M instead of 10(-10) M. Retinoic acid displaced [125I]T4 binding to red cell membranes as effectively as unlabeled T4. Retinol failed to influence either basal or T4-stimulated enzyme activity or to displace T4 binding. These results indicate that retinoic acid can partially block the T4 and T3 stimulation of Ca2+-ATPase in human red cell membranes and suggest a physiologic role for the retinoid as a modulator of this peripheral action of thyroid hormone. They suggest that the red cell membrane is an important site of action for this active retinoid.

Thyroid hormone regulation of membrane Ca2(+)-ATPase activity

The Ca2(+)-ATPase of plasma membranes from a variety of tissues is subject to stimulation in vitro, and apparently in vivo, by physiological concentrations of iodothyronines regarded as biologically active in other bioassay systems. This calmodulin-dependent action of thyroid hormone is nongenomic, that is, directly on the cell membrane and independent of the cell nucleus. In the case of human erythrocyte Ca2(+)-ATPase, this assay of thyroid hormone bioactivity is attractive as an in vitro, readily-studied model of hormone action in a human cell. Enzyme activity is paralleled, as expected, by changes in calcium pump activity. Thyroid hormone action in this system is subject to modulation by glucose and by a variety of compounds which, like iodothyronines, are hydrophobic. The mechanism of thyroid hormone action on membrane Ca2(+)-ATPase involves, at least in part, membrane lipids, including components of the phosphatidylinositol cycle. The physiologic role of thyroid hormone action on cell membrane Ca2(+)-ATPase is speculative. In plasma membranes of nonexcitable and excitable tissues, ambient thyroid hormone may set basal activity of Ca2(+)-ATPase or magnitude of the enzymatic response to calmodulin Ca2+.

A method to increase recovery of fentanyl from urine

Fentanyl, a highly lipophilic drug (pk(a) 7.7), is a common drug of abuse. The current standard techniques to detect fentanyl in urine have low recovery rates and poor sensitivity. We report a modified solvent extraction technique that can recover between 63 and 86% of the drug with a detection limit of 0.2 ng/10 ml of urine. In addition, we report the duration of urinary fentanyl excretion in 11 adolescent patients administered either low (less than 10 mg/kg) or high (20-40 mg/kg) doses of fentanyl as part of anesthesia. The mean duration of urinary fentanyl excretion was similar in the two groups, with duration ranging from 1 to 5 days, and urine fentanyl concentration ranging from 0.1 ng to 10.3 ng/10 ml of urine.

Pharmacokinetics of alfentanil in newborn premature infants and older children

Because developmental pharmacokinetics appear to be closely associated with anatomic and physiologic changes that occur with growth, we were interested in determining the disposition and elimination of alfentanil in premature infants and older children. The pharmacokinetic profile of alfentanil was determined in 6 premature infants requiring sedation for medical management or analgesia for stressful intensive-care procedures. These pharmacokinetic profiles were compared with pharmacokinetic profiles determined in 9 older infants and children undergoing operative procedures that required invasive monitoring. In both groups the plasma decay curves best fit a 2-compartment model. Compared with older children, premature infants demonstrated a significantly larger apparent volume of distribution (1.0 +/- 0.39 vs. 0.48 +/- 0.19 l/kg), a smaller clearance (2.2 +/- 2.4 vs. 5.6 +/- 2.4 ml/kg/min) and a markedly prolonged elimination half-life (525 +/- 305 vs. 60 +/- 11 min).

Microbial models of mammalian metabolism: production of novel alpha-diketone metabolites of warfarin and phenprocoumon using Aspergillus niger

1. The coumarin anticoagulants warfarin and phenprocoumon were metabolized by Aspergillus niger via oxidative ring cleavage to yield the corresponding alpha-diketone metabolites. 2. Structural identification was based upon physical, spectral, and chromatographic comparisons of isolated metabolites and synthetic standards generated by the oxidative cleavage of warfarin or phenprocoumon with pyridinium chlorochromate. 3. This pathway of metabolism has been previously observed for coumarin anticoagulants in mammalian systems.

Analogue-specific action in vitro of atrial natriuretic factor on human red blood cell Ca2+-ATPase activity

Specific atrial natriuretic factor (ANF) analogues have been found to have inhibitory activity in vitro in a calmodulin-dependent, human red blood cell membrane Ca2+-adenosine triphosphatase (ATPase) model. Studied at 10(-8) to 10(-6) M concentrations, atriopeptin I (residues 127-147 of rat prepro-ANF sequence) and atriopeptin III (residues 127-150) progressively inhibited Ca2+-ATPase activity by up to 20% (p less than 0.001). This degree of inhibition was consistent with activities of other (calmodulin-independent) enzyme inhibitors in this model. Therefore, the C-terminal Phe-Arg-Tyr sequence (residues 148-150) is unnecessary for atriopeptin action on Ca2+-ATPase. Human and rat atrial peptides with amino acids 123-150 were inactive, indicating that the 123-126 sequence (Ser-Leu-Arg-Arg) must be cleaved to activate atriopeptins in this system. Human ANF fragment 129-150 also had no effect on Ca2+-ATPase, defining the importance of residues 127-128 (Ser-Ser) proximal to the disulfide bridge (joining 129 to 145). The addition of purified calmodulin to red blood cell membranes in the presence of inhibitory ANF did not restore Ca2+-ATPase activity to normal levels, indicating that the ANF effect on this enzyme is calmodulin-independent. Atriopeptin I and atriopeptin III had no effect on red blood cell Na+, K+-ATPase activity in vitro. Thus, the structure-activity relationships of ANF analogues in this novel human cell membrane model are highly specific. Although the inhibitory action of ANF analogues on Ca2+-ATPase, a calcium pump-associated enzyme, may be unique to the red blood cell, the calcium dependence of the gluconeogenic effects of ANF in the kidney would be supported by inhibition of this ATPase.

Abnormal response to calmodulin in vitro of dystrophic chicken muscle membrane Ca2+-ATPase activity

A skeletal muscle membrane fraction enriched in sarcoplasmic reticulum (SR) contained Ca2+-ATPase activity which was stimulated in vitro in normal chickens (line 412) by 6 nM purified bovine calmodulin (33% increase over control, P less than 0.001). In contrast, striated muscle from chickens (line 413) affected with an inherited form of muscular dystrophy, but otherwise genetically similar to line 412, contained SR-enriched Ca2+-ATPase activity which was resistant to stimulation in vitro by calmodulin. Basal levels of Ca2+-ATPase activity (no added calmodulin) were comparable in muscles of unaffected and affected animals, and the Ca2+ optima of the enzymes in normal and dystrophic muscle were identical. Purified SR vesicles, obtained by calcium phosphate loading and sucrose density gradient centrifugation, showed the same resistance of dystrophic Ca2+-ATPase to exogenous calmodulin as the SR-enriched muscle membrane fraction. Dystrophic muscle had increased Ca2+ content compared to that of normal animals (P less than 0.04) and has been previously shown to contain increased levels of immuno- and bioactive calmodulin and of calmodulin mRNA. The calmodulin resistance of the Ca2+-ATPase in dystrophic muscle reflects a defect in regulation of cell Ca2+ metabolism associated with elevated cellular Ca2+ and calmodulin concentrations.

Microbiologically Catalyzed Enantio- and Diastereoselective Oxidation of Chrysanthemol Stereoisomers to Chrysanthemic Acids

The diastereo- and enantioselective microbial oxidation of a mixture of racemic cis/trans -chrysanthemols to the corresponding stereoisomeric chrysanthemic acids by Aspergillus species is described. Of the three microorganisms which were found capable of oxidizing racemic cis/trans -chrysanthemols, A. ochraceus ATCC 18500 showed complete enantioselectivity for (+)-stereoisomers [(+)- trans -chrysanthemol and (+)- cis -chrysanthemol), whereas A. flavipes ATCC 1030 and ATCC 11013 showed complete enantioselectivity for the (+)- cis -chrysanthemol but a time-dependent enantioselectivity during oxidation of trans -chrysanthemol [oxidation of (+)- trans -chrysanthemol prior to (−)- trans -chrysanthemol]. The diastereoselectivity of all three microorganisms was time dependent, in that the trans -stereoisomers were oxidized prior to the cis -isomers.

Amino acids within hypervariable region 1 of avian coronavirus IBV (Massachusetts serotype) spike glycoprotein are associated with neutralization epitopes

The spike glycoprotein (S) gene of IBV codes for a precursor protein which is cleaved into the N-terminal S1 and C-terminal S2 glycopolypeptides. The S1 glycopolypeptide, which induces neutralizing antibody, comprises approximately 520 amino acid residues. We have determined the nucleotide sequence of S1 of seven strains of the Massachusetts (Mass) serotype and the first 337 bases of two additional Mass strains. Despite the fact that the strains had been isolated over three decades in Europe and the U.S.A. there was only 4% base and 6% amino acid variation within the group. Nearly one third of the 32 amino acid differences in S1 were in two hypervariable regions (HVRs 1 and 2) comprising residues 38-51 and 99-115, identified by Niesters et al. (1986), showing that HVRs 1 and 2 are a feature of the Mass serotype. Amino acid variation within HVRs 1 and 2 was 29% and 40% respectively. Five vaccine strains could be distinguished from each other by sequencing of the first 337 nucleotides. Variants of M41 which resisted neutralization by two monoclonal antibodies (A13 and A38) had the same, single base change at position 134, resulting in substitution of proline residue 45 by histidine. This indicates that residues within HVR 1 are associated with epitopes which induce neutralizing antibody.

Calcium channel blocker inhibition of the calmodulin-dependent effects of thyroid hormone and milrinone on rabbit myocardial membrane Ca2+-ATPase activity

The Ca2+-ATPase activity of rabbit myocardial membranes is stimulated in vitro by L-thyroxine and by milrinone, a bipyridine. These effects are concentration dependent and calmodulin requiring. The calcium channel blockers nifedipine and verapamil have been reported to have anti-calmodulin effects in other assay systems. In this study we have examined the effects of nifedipine and verapamil on rabbit myocardial membrane Ca2+-ATPase activity, in the absence (basal activity) and presence of exogenous L-thyroxine (T4), 10(-10) M, and milrinone, 10(-7) M. Basal enzyme activity was inhibited by a minimum of 10(-6) M nifedipine (IC50 of 3.4 X 10(-5) M) and 10(-5) M verapamil (IC50 of 1.5 X 10(-4) M). Both calcium antagonists inhibited enzyme stimulation by T4 and milrinone, with half-maximal inhibition of T4 and milrinone effects, respectively, at 2.9 X 10(-5) M and 9.0 X 10(-6) M nifedipine and 3.0 X 10(-5) M and 5.2 X 10(-5) M verapamil. The addition of exogenous purified calmodulin, 40 ng/micrograms membrane protein, in the presence of 10(-5) M nifedipine or verapamil restored T4-stimulated enzyme activity. Nifedipine and verapamil, each at a concentration of 10(-6) M, significantly inhibited binding of radioiodinated calmodulin to rabbit heart membranes in vitro. These studies provide evidence that nifedipine and verapamil have an anti-calmodulin effect in this myocardial enzyme system. Through interaction with calmodulin, the channel blockers inhibit thyroid hormone and milrinone stimulation of myocardial membrane Ca2+-ATPase.

Clinical pharmacology of doxacurium chloride (BW A938U) in children

The neuromuscular effects of doxacurium were studied in 26 children during halothane-nitrous oxide-oxygen anesthesia. Neuromuscular blockade was measured using electromyographic activity of the adductor pollicis muscle after supramaximal stimulation of the ulnar nerve at 2 Hz for 2 seconds at 10-second intervals. To estimate the cumulative dose-response relation, nine patients received incremental doses of doxacurium (2.5-10 micrograms/kg); nine patients received 27.5 micrograms/kg (the estimated ED95); eight patients received 50 micrograms/kg (1.8 X ED95). The ED25, ED50, ED75, and ED95 (estimated from linear regression plots of log dose vs probit of effect) were 11.5, 14.8, 19.0, and 27.3 micrograms/kg, respectively. Clinical duration (T25) was 27.8 +/- 10.3 (mean +/- SD) minutes at 1 X ED95 and 50.6 +/- 15.6 minutes at 1.8 X ED95. Time to recovery of the train-of-four ratio to 0.75 was 63.1 +/- 32.9 minutes at 1 X ED95 and 108.5 +/- 25.7 minutes at 1.8 X ED95. There were no significant changes in heart rate or mean arterial pressure after bolus administration of any dose of doxacurium.

Early abnormal development of calmodulin gene expression and calmodulin-resistant Ca2+-ATPase activity in avian dystrophic muscle

We have reported previously that the pectoralis muscle from three month-old dystrophic chickens with signs of myopathy exhibits increased calmodulin content, elevated calmodulin-specific mRNA (Biochem. Biophys. Res. Commun. 137:507-512, 1986), and reduced sarcoplasmic reticulum (SR) Ca2+-ATPase activity in response to calmodulin exposure in vitro (Clin. Res. 34: 725A, 1986). To determine the early time sequence for development of these abnormalities, we have studied muscle from embryos and post-hatched chickens at various ages. Quantitated by dot blot analysis, there was an approximate two-fold increase in calmodulin-specific mRNA in dystrophic muscle as early as 13 days ex ovo which was maintained throughout development up to three months ex ovo. Similarly, Ca2+-ATPase activity measured in SR membranes from chickens as early as 13 days post-hatch was also found to be resistant to stimulation in vitro by exogenous calmodulin, whereas the enzyme from normal muscle was calmodulin-stimulable. These findings suggest that the genetic lesion expressed in the avian dystrophic animal model involves the loss of normal control of intracellular calcium metabolism early in the maturation of the affected musculature and prior to appearance of disease signs.

Pharmacokinetics of sufentanil in adolescent patients with chronic renal failure

The role of the kidney in sufentanil elimination or metabolism has not been defined. The effects of chronic renal failure (CRF) on the pharmacokinetic profile of sufentanil were evaluated in six adolescent patients undergoing renal transplantation, and these findings were compared with data from age-matched control patients with normal renal function who were undergoing other surgical procedures. Patients with CRF weighed significantly less than did the control patients (28.7 +/- 5.7 vs 44.7 +/- 12.9 kg [mean +/- SD]). Although there was no statistical difference in the rate of clearance or apparent volume of distribution and half-life between the two groups, clearance and half-life were more variable among patients with CRF. In these patients, therefore, sufentanil dose must be carefully administered based on responses elicited in individual patients.

Evolution of avian coronavirus IBV: sequence of the matrix glycoprotein gene and intergenic region of several serotypes

We have sequenced 200 to 240 bases of the matrix (M) glycoprotein gene of 23 strains of infectious bronchitis virus (IBV) representing the A (D207), B (D3896), C (D3128), D (D212), Massachusetts (Mass), UK11 and UK12 serotypes. The bases examined code for the external, hydrophilic region and the first membrane-embedded hydrophobic region of M, both regions comprising approximately 20 amino acids. As predicted from protein Mr studies the A/D and B/C serotypes had two and one potential glycosylation sites respectively. This variation appeared to derive from a combination of base substitutions and deletions/insertions. The glycosylation sequence Asn-Cys-Thr was highly conserved. Overall, the exposed part of M exhibited a fourfold greater extent of amino acid variation than did the membrane-embedded sequence. The transcription-associated homology region sequence (CUUAACAA) in the 5' intergenic region was identical in all strains but there was considerable variation as to its location. The M gene of UK12 appeared to have evolved from a group A-like M gene by a two stage process involving a base substitution in the intergenic region which generated a new AUG translation start codon followed by deletion of the original AUG. Isolate UK11 closely resembled Mass strains in the intergenic region but was dissimilar from all strains in the protein coding region. The M sequences of serotypes B and C were identical and those of the A and D serotypes very similar. These results are discussed in relation to recent sequencing of part of the spike glycoprotein gene of some of these strains and the discovery of in vitro recombination of murine hepatitis coronavirus.

Adductor spastic dysphonia: heterogeneity of physiologic and phonatory characteristics

Physiologic and phonatory characteristics of 23 subjects with adductor spastic dysphonia were studied, including examination of the laryngeal appearance by fiberoptic nasoendoscopy, neurologic examination, and measurement of phonatory airflow and speaking fundamental frequency. These characteristics displayed considerable heterogeneity among the subjects investigated. Three patterns of laryngeal appearance during phonation were observed: vocal fold adduction, associated ventricular fold constriction, and approximation of the laryngeal inlet. Eight of 13 subjects demonstrated some neurologic abnormality. For the majority of subjects, the airflow demonstrated marked variability during sustained phonation; for different subjects, this variability was observed to be associated with either an oscillatory or irregular airflow pattern. The modal speaking fundamental frequency for the women and men with adductor spastic dysphonia was not significantly different from that for age- and sex-matched controls.

Action of long-chain fatty acids in vitro on Ca2+-stimulatable, Mg2+-dependent ATPase activity in human red cell membranes

Human red cell membrane Ca2+-stimulatable, Mg2+-dependent adenosine triphosphatase (Ca2+-ATPase) activity and its response to thyroid hormone have been studied following exposure of membranes in vitro to specific long-chain fatty acids. Basal enzyme activity (no added thyroid hormone) was significantly decreased by additions of 10(-9)-10(-4) M-stearic (18:0) and oleic (18:1 cis-9) acids. Methyl oleate and elaidic (18:1 trans-9), palmitic (16:0) and lauric (12:0) acids at 10(-6) and 10(-4) M were not inhibitory, nor were arachidonic (20:4) and linolenic (18:3) acids. Myristic acid (14:0) was inhibitory only at 10(-4) M. Thus, chain length of 18 carbon atoms and anionic charge were the principal determinants of inhibitory activity. Introduction of a cis-9 double bond (oleic acid) did not alter the inhibitory activity of the 18-carbon moiety (stearic acid), but the trans-9 elaidic acid did not cause enzyme inhibition. While the predominant effect of fatty acids on erythrocyte Ca2+-ATPase in situ is inhibition of basal activity, elaidic, linoleic (18:2) and palmitoleic (16:1) acids at 10(-6) and 10(-4) M stimulated the enzyme. Methyl elaidate was not stimulatory. These structure-activity relationships differ from those described for fatty acids and purified red cell Ca2+-ATPase reconstituted in liposomes. Thyroid hormone stimulation of Ca2+-ATPase was significantly decreased by stearic and oleic acids (10(-9)-10(-4) M), but also by elaidic, linoleic, palmitoleic and myristic acids. Arachidonic, palmitic and lauric acids were ineffective, as were the methyl esters of oleic and elaidic acids. Thus, inhibition of the iodothyronine effect on Ca2+-ATPase by fatty acids has similar, but not identical, structure-activity relationships to those for basal enzyme activity. To examine mechanisms for these fatty acid effects, we studied the action of oleic and stearic acids on responsiveness of the enzyme to purified calmodulin, the Ca2+-binding activator protein for Ca2+-ATPase. Oleic and stearic acids (10(-9)-10(-4) M) progressively inhibited, but did not abolish, enzyme stimulation by calmodulin (10(-9) M). Double-reciprocal analysis of the effect of oleic acid on calmodulin stimulation indicated noncompetitive inhibition. Addition of calmodulin to membranes in the presence of equimolar oleic acid restored basal enzyme activity. Oleic acid also reduced 125I-calmodulin binding to membranes, but had no effect on the binding of [125I]T4 by ghosts. The mechanism of the decrease by long chain fatty acids of Ca2+-ATPase activity in situ in human red cell ghosts thus is calmodulin-dependent and involves reduction in membrane binding of calmodulin.

Water excretion in the elderly

Osmoreceptor sensitivity is enhanced in healthy elderly subjects and AVP secretion is increased, relative to that of younger subjects, when plasma osmolality rises. Increased AVP secretion/unit increase in plasma tonicity reflects a decrease in collecting tubule sensitivity to AVP by an as yet unknown mechanism in the aged kidney. This change in sensitivity is not completely offset by increased ADH release, so that maximum Uosm achievable under hydropenic conditions (concentrating ability) is reduced in the elderly. CH2O in older subjects decreases in proportion to the fall in GFR; thus, CH2O is intact in older subjects with preserved GFR. In subjects with age-related reductions in GFR, minimal Uosm achievable is usually less than 100 mOsm per kg H2O and thus usually sufficient to meet the demands of solute-free water intake so that plasma hypo-osmolarity does not result. Increasing exposure of the elderly to pharmacologic agents that reduce CH2O is primarily responsible for the impression that aged patients are at increased risk for hyponatremia.

Laryngeal motoneurone activity in the rabbit during asphyxic gasping

Unitary activity was recorded from 44 recurrent laryngeal nerve (RLN) and 18 external laryngeal nerve (ELN) motoneurones in anaesthetized, paralysed rabbits during the development of periods of severe asphyxia caused by temporarily interrupting artificial ventilation. Ventilation was only recommenced when a simultaneously recorded phrenic neurogram showed the animal had attempted several gasps. Inspiratory-phased fibres (17 RLN, 14 ELN) displayed brief high frequency discharges with each gasp. Some inspiratory-phased ELN motoneurones (6/14) also displayed longer tonic discharges after each of the first few gasps. In the expiratory intervals immediately following each gasp many expiratory-phased fibres (13/21 RLN, 2/4 ELN) were active and 7 RLN fibres discharged a long train of impulses with a decrementing discharge pattern. In 3 anaesthetized rabbits, breathing spontaneously through a tracheostomy, a constant airflow was directed up through the larynx; successive gasps were associated with wide swings in translaryngeal pressure which were confirmed visually as reflecting rapid dilation of the glottis during gasps and intense constriction in the intervals between gasps.

Competition of milrinone, a non-iodinated cardiac inotropic agent, with thyroid hormone for binding sites on human serum prealbumin (TBPA)

Milrinone [2-methyl-5-cyano-(3,4'-bipyridin)-6(1H)-one] is a positive cardiac inotropic agent recently shown to have thyromimetic activity in vitro in a rabbit myocardial membrane Ca2+-ATPase system [K. M. Mylotte et al., Proc. natn. Acad. Sci. U.S.A. 82, 7974 (1985)]. In the present studies, milrinone was examined for activity as an inhibitor of iodothyronine binding by human serum thyroid hormone transport proteins, thyroxine-binding globulin (TBG), prealbumin (TBPA) and albumin. Polyacrylamide gel electrophoresis at pH 9.0 of sera equilibrated with [125I]thyroxine showed that milrinone competed with L-thyroxine (T4) for binding sites on TBPA (10 and 100 microM milrinone caused 61 and 73% reductions, respectively, in T4 binding to TBPA, P less than 0.01); T4 displaced from TBPA was bound by TBG and albumin. Comparable reductions in T4 binding to TBPA were observed in electrophoretic studies conducted at pH 7.4. Binding of triiodo-L-thyronine (T3) to TBPA was electrophoretically confirmed and shown to be decreased in the presence of milrinone. Electrophoresis of purified TBPA also demonstrated that [14C]milrinone co-migrated with this transport protein and that milrinone displaced tracer T4 from TBPA. Amrinone, the 2-H-5-NH2 analog of milrinone, had less than 5% of the activity of milrinone as an inhibitor of T4 binding in electrophoretic studies. Scatchard analysis of T4 and milrinone binding to purified TBPA, measured by equilibrium dialysis, showed two classes of binding sites, with association constants, respectively, of 6.1 X 10(7) M-1 and 1.6 X 10(6) M-1 for T4, and 1.7 X 10(6) M-1 and 8.9 X 10(2) M-1 for milrinone. Computer graphic modeling of the binding of milrinone to the T4 site in the crystal structure of TBPA showed that milrinone best occupied this site when the substituted bipyridine ring overlapped the phenolic ring of T4. In this orientation the 5-cyano group, which has an electronegativity similar to that of iodine, occupied the same volume as the 5'-iodine of T4. The 5-amino group of amrinone lacks these characteristics. In this orientation, the keto function of milrinone overlapped the T4 4'-hydroxyl and could participate in similar intermolecular interactions. Thus, milrinone, a non-iodinated bipyridine, and thyroid hormone share structural and biochemical homologies and compete for the same binding site on TBPA.

Action of erythropoietin in vitro on rabbit reticulocyte membrane Ca2+-ATPase activity

The mechanism of action of erythropoietin is thought to require specific interaction with the target cell surface and involve alteration of cellular calcium metabolism. Using the rabbit reticulocyte membrane as a model of the immature red cell membrane, we investigated the effects of human recombinant erythropoietin on membrane Ca2+-ATPase (calcium pump) activity in vitro. Erythropoietin in a concentration range of 0.025 to 3.0 U/ml progressively decreased membrane Ca2+-ATPase activity by up to 64% (P less than 0.01). These concentrations have been shown by others to stimulate in vitro erythroid growth. The action of erythropoietin on reticulocyte Ca2+-ATPase required an incubation time of 1 h before enzyme assay for maximum effect and was neutralized by antierythropoietin antiserum. Other nonhemopoietic growth factors (epidermal growth factor, insulin) had no effect in this assay. Ca2+-ATPase activity of membranes prepared from rabbit mature red blood cells was not inhibited by erythropoietin. The novel effect of erythropoietin on reticulocyte membrane Ca2+-ATPase activity is a mechanism by which erythropoietin can influence cellular Ca2+ metabolism.

Hypodontia and hyperdontia of permanent teeth in Hong Kong schoolchildren

This study was performed to determine the prevalence of hypodontia and hyperdontia of permanent teeth amongst Southern Chinese children in Hong Kong. The sample consisted of 1093 12-yr-old children on whom a panoramic radiograph was taken. The prevalence of congenitally missing teeth (third molars excluded) was 6.1% in boys, 7.7% in girls, and 6.9% for both sexes combined. On the average, each child was missing 1.5 teeth. The most commonly absent tooth was the mandibular incisor, affecting 58.7% of the children with hypodontia. Thirty children (2.7%) had supernumerary teeth, with a male:female ratio of 6.5:1; in four cases the tooth had erupted. Three children had fourth molars and one case of a supplemental premolar was recorded (all unerupted). Four cases of a maxillary supernumerary tooth and hypodontia in the mandible were seen.

Characteristics of calmodulin binding to purified human lymphocyte plasma membranes

We have explored the role of calmodulin in plasma membrane-related phenomena in lymphocyte activation by measurement of [125I]calmodulin binding to highly purified plasma membrane of human peripheral blood lymphocytes. Calcium-dependent calmodulin binding to lymphocyte membrane was found to reach equilibrium within 5 min of incubation at 37 degrees C and to be saturable and specific. A single class of high affinity-binding sites was identified, with a dissociation constant (Kd) of 1 to 3 X 10(-8) M and a total binding capacity (Bt) of 1 to 2 pmol/mg membrane protein. The free calcium concentration necessary for half-maximal binding was 100 to 300 nM. This was strikingly similar to the cytoplasmic-free calcium activity [Ca2+]i measured by the Quin-2 fluorescence technique, particularly after stimulation with phytomitogens. Calmodulin binding was inhibitable by trifluoperazine (TFP), W-7, and chloropramazine, all of which are calmodulin antagonists. The concentration of TFP that caused 50% inhibition of lymphocyte proliferative responses to phytomitogens was found to be identical to the concentration of TFP which causes 50% inhibition of calmodulin binding to lymphocyte plasma membrane. SDS-polyacrylamide gel electrophoresis followed by gel overlay and autoradiography with iodinated calmodulin revealed five calcium-dependent, TFP-inhibitable, calmodulin-binding polypeptides.

Characteristics of calmodulin binding to purified human lymphocyte plasma membranes

We have explored the role of calmodulin in plasma membrane-related phenomena in lymphocyte activation by measurement of [125I]calmodulin binding to highly purified plasma membrane of human peripheral blood lymphocytes. Calcium-dependent calmodulin binding to lymphocyte membrane was found to reach equilibrium within 5 min of incubation at 37 degrees C and to be saturable and specific. A single class of high affinity-binding sites was identified, with a dissociation constant (Kd) of 1 to 3 X 10(-8) M and a total binding capacity (Bt) of 1 to 2 pmol/mg membrane protein. The free calcium concentration necessary for half-maximal binding was 100 to 300 nM. This was strikingly similar to the cytoplasmic-free calcium activity [Ca2+]i measured by the Quin-2 fluorescence technique, particularly after stimulation with phytomitogens. Calmodulin binding was inhibitable by trifluoperazine (TFP), W-7, and chloropramazine, all of which are calmodulin antagonists. The concentration of TFP that caused 50% inhibition of lymphocyte proliferative responses to phytomitogens was found to be identical to the concentration of TFP which causes 50% inhibition of calmodulin binding to lymphocyte plasma membrane. SDS-polyacrylamide gel electrophoresis followed by gel overlay and autoradiography with iodinated calmodulin revealed five calcium-dependent, TFP-inhibitable, calmodulin-binding polypeptides.

Quantitative analysis of laryngeal mechanosensitivity in the cat and rabbit

1. Single afferent fibres in the internal branch of the superior laryngeal nerve which responded to light touch or gentle probing of discrete areas of the exposed epithelium of the opened larynx were identified in anaesthetized, paralysed cats (148 fibres) and rabbits (58 fibres). 2. A quantitative examination of the sensitivity of these laryngeal mechanoreceptors to both static (step indentations) and dynamic (vibratory) forms of mechanical stimulation was undertaken using a servo-controlled mechanical stimulator. 3. In both species two predominant classes of mechanoreceptors were observed (Boushey, Richardson, Widdicombe & Wise, 1974). One class was distinguished by a regular and continuous pattern of activity at a frequency of 10-70 Hz (tonic fibres, sixty-six in cat, thirty-five in rabbit). The other class was silent or (more rarely) irregularly active at a very low frequency (silent fibres, eighty-two in cat, twenty-three in rabbit). 4. The location of the receptive fields was determined by manual probing. Inter-species and regional variations in receptive field location were observed for the two fibre groups. 5. Conduction velocity was measured for twenty-one tonic and seven silent fibres in the rabbit by a pre-triggered averaging technique. The results obtained (tonic: range 10.8-30.0, mean +/- S.E. of mean 21.4 +/- 1.2 m/s; silent: 14.8-28.6, 20.4 +/- 1.8 m/s) were characteristic of group III afferent fibres but were not significantly different for the two classes. 6. Both classes of receptor showed a response at the onset of a step indentation of the region of the mucosa that corresponded to their receptive field. Subsequent to this brief initial response the behaviour of the two classes diverged markedly. Tonic fibres were invariably slowly adapting whereas most (forty-four out of fifty-five in cat; twenty-two out of twenty-three in rabbit) silent fibres were rapidly adapting, at least for smaller indentation amplitudes. 7. Receptors of both classes were readily entrained to discharge at the same frequency as the probe stimulator (1:1 entrainment) when this was made to vibrate upon the receptive area for test periods of 0.5 or 1.0 s. Tuning curves were constructed of the minimum amplitudes required to elicit 1:1 entrainment throughout an entire test period at various frequencies. 8. Individual fibres in the two classes could be entrained at frequencies up to 400 Hz or more at sensitive (e.g. less than 100 microns) vibratory amplitudes. However, all fibres were less sensitive at these higher frequencies than at some lower point on the frequency scale.(ABSTRACT TRUNCATED AT 400 WORDS)

Donor age-dependent decline in response of human red cell Ca2+-ATPase activity to thyroid hormone in vitro

The effect of increasing donor age on the susceptibility of human red blood cell Ca2+-ATPase activity to stimulation in vitro by thyroid hormone was studied in 26 normal subjects, aged 15-81 yr. Basal enzyme activity (no added thyroid hormone) was unaffected by donor age. Group analysis, young (less than or equal to 50 yr) vs. elderly (greater than 60 yr old), revealed a 23% decrease in responsiveness of the enzyme to L-T4 (P less than 0.001). Regression analysis confirmed an age-dependent decline in thyroid hormone stimulability of Ca2+-ATPase [r = -0.42 (T4 effect) and -0.38 (T3 effect); P less than 0.01]. Red cell membrane Na,K-ATPase activity was not affected by donor age. Plasma T4 and T3 concentrations in these normal subjects also did not change with age. Possible contributions of the following mechanisms to this age-correlated change in enzyme activity were examined: altered responsiveness to calmodulin of membrane Ca2+-ATPase; membrane content of endogenous calmodulin, endogenous plasma T4 and T3 concentrations, and plasma glucose concentrations. Calmodulin responsiveness is required for iodothyronine action on the enzyme, but the calmodulin responsiveness of cells from elderly donors was not significantly different from that of cells from younger donors (P greater than 0.10). There was no relationship between membrane immunoassayable calmodulin and donor age or membrane calmodulin and Ca2+-ATPase activity. There were positive correlations between donor plasma T4 level and basal enzyme activity (P less than 0.05) and between donor plasma T3 concentration and hormone-responsive Ca2+-ATPase (P less than 0.01), but these did not contribute to the age effect. Plasma glucose previously was found to modulate red cell Ca2+-ATPase activity, but did not correlate with decreased hormone responsiveness of the enzyme in elderly donors. In conclusion, we found that the susceptibility of human red cell Ca2+-ATPase to in vitro thyroid hormone stimulation declined significantly with advancing donor age. Several possible calmodulin-dependent mechanisms for this age-dependent change were excluded, and thus, we postulate that the altered hormone sensitivity of the enzyme is membrane phospholipid mediated.

Pharmacodynamics and pharmacokinetics of high-dose sufentanil in infants and children undergoing cardiac surgery

The pharmacodynamic and pharmacokinetic profiles of high-dose sufentanil (15 micrograms/kg) and oxygen were determined in 20 infants and children undergoing repair of congenital heart defects. Sufentanil provided marked hemodynamic stability after an infusion and during the stress periods of incision and sternotomy. Two patients required supplemental nitrous oxide because of an increase in blood pressure greater than 20% of baseline. Mean plasma catecholamine concentrations varied widely among patients and increased, although not significantly, during intraoperative stress. Pharmacokinetic data best fit a two-compartment model. In infants younger than 10 months (group 1) and children older than 10 months (group 2) who were not surface-cooled, elimination half-lives were similar (mean +/- SD, 53 +/- 15 min vs 55 +/- 10 min) as were clearance values (27.5 +/- 9.3 vs 18.1 +/- 10.7 ml X kg-1 X min-1). However, the volumes of distribution were significantly smaller in group 1 compared with group 2 (1.6 +/- 0.46 vs 3.0 +/- 1.3 L/kg). In infants younger than 10 months who were surface-cooled (group 3) elimination half-life was longer (120 +/- 36 min) and volume of distribution larger (3.7 +/- 1.1 L/kg), but clearance rate was similar (21.5 +/- 5.0 ml X kg-1 X min-1) compared with age- and weight-matched infants (group 1).

Bepridil and cetiedil reversibly inhibit thyroid hormone stimulation in vitro of human red cell Ca2+-ATPase activity

Thyroid hormone (10(-11) to 10(-10) M) stimulates plasma membrane Ca2+-ATPase activity in vitro in various tissues, including the human red cell (RBC), by a calmodulin-requiring mechanism. Bepridil and cetiedil are Ca2+ antagonists with an intracellular (calmodulin-antagonist) site of action, as well as an effect on the calcium channel in excitable tissues. We have studied the actions of bepridil and cetiedil on Ca2+-ATPase in a channel-free membrane (RBC) to determine effectiveness of these agents as inhibitors of thyroid hormone action on the enzyme. Dose-response studies showed that thyroid hormone stimulation of Ca2+-ATPase activity in vitro was significantly inhibited by as little as 2 x 10(-5) M bepridil and cetiedil. IC50 values of bepridil and cetiedil for thyroid hormone response of the enzyme were 5 x 10(-5) and 2 x 10(-5) M, respectively, whereas IC50s of these agents for enzyme activity in the absence of thyroid hormone were both 10(-4) M. Progressive addition of purified rat testis calmodulin in vitro (10-150 ng calmodulin/mg membrane protein) restored hormone responsiveness in the presence of bepridil and cetiedil. Binding of labeled thyroid hormone by RBC membranes was unaffected by bepridil and cetiedil (up to 2 x 10(-4) M). Thus, bepridil and cetiedil are Ca2+ antagonists that reversibly inhibit thyroid hormone action on human RBC Ca2+-ATPase by a calmodulin-dependent mechanism. Thyroid hormone effect on Ca2+-ATPase is more susceptible to bepridil and cetiedil inhibition than is basal enzyme activity.

Modulation of 3-hydroxy-3-methylglutaryl-CoA reductase by changes in microsomal cholesterol content or phospholipid composition

Microsomal preparations from normal human skin fibroblasts were used to investigate the role of free cholesterol in the endoplasmic reticulum in the control of cholesterol biosynthesis by regulation of 3-hydroxy-3-methylglutaryl-coenzyme A reductase (NADPH) [(S)-mevalonate:NADP+ oxidoreductase (CoA-acylating), EC 1.1.1.34]. Controlled changes in the cholesterol/phospholipid ratio of microsomes were introduced either in intact cells by incubating fibroblast cultures with whole serum or lipoprotein-deficient serum or by enrichment or depletion of cholesterol in microsomal preparations by incubating microsomes with cholesterol-rich or cholesterol-poor egg phosphatidylcholine unilamellar vesicles. Cholesterol enrichment resulted in suppression of reductase activity and increased ESR order parameters for 12-nitroxystearate in the microsomal preparations. Conversely, cholesterol depletion caused an activation of reductase and a decrease in order parameter. Enrichment of microsomal preparations with a "nonfluid" lipid, dipalmitoyl phosphatidylcholine, also suppressed enzyme activity and increased membrane order. The effect was reversed by subsequent enrichment of the microsomes with fluid egg phosphatidylcholine. Our findings suggest that cholesterol may regulate its own biosynthesis, at least in part, by suppression of hydroxymethylglutaryl-CoA reductase mediated through changes in membrane fluidity as measured by ESR order parameter.

Repression and the inaccessibility of affective memories

The fundamental assumption that repression involves an inaccessibility to affective memories has not been directly addressed in empirical research. In the present study we examined three groups of subjects (repressors, low anxious, and high anxious) under six conditions of recall (general, happy, sad, anger, fear, and wonder). Subjects were asked to recall personal experiences from childhood and to rate their current mood and the affective intensity of the memories. The results indicated that repressors recalled significantly fewer negative memories than did low-anxious and high-anxious subjects and, furthermore, that they were substantially older at the time of the earliest negative memory recalled. Compared with low-anxious subjects, repressors also recalled fewer positive affective memories as well. This pattern of findings is consistent with the hypothesis that repression involves an inaccessibility to negative emotional memories and indicates further that repression is associated in some way with the suppression or inhibition of emotional experiences in general. The concept of repression as a process involving limited access to negative affective memories appears to be valid.

Repression and the inaccessibility of affective memories

The fundamental assumption that repression involves an inaccessibility to affective memories has not been directly addressed in empirical research. In the present study we examined three groups of subjects (repressors, low anxious, and high anxious) under six conditions of recall (general, happy, sad, anger, fear, and wonder). Subjects were asked to recall personal experiences from childhood and to rate their current mood and the affective intensity of the memories. The results indicated that repressors recalled significantly fewer negative memories than did low-anxious and high-anxious subjects and, furthermore, that they were substantially older at the time of the earliest negative memory recalled. Compared with low-anxious subjects, repressors also recalled fewer positive affective memories as well. This pattern of findings is consistent with the hypothesis that repression involves an inaccessibility to negative emotional memories and indicates further that repression is associated in some way with the suppression or inhibition of emotional experiences in general. The concept of repression as a process involving limited access to negative affective memories appears to be valid.

Structure-activity relationships of sex steroid analogs determined in vitro in a thyroid hormone-responsive membrane Ca2+-ATPase model

Physiological concentrations of L-T4 were found previously to stimulate Ca2+-ATPase activity in vitro in reticulocyte membranes from female rabbits and to inhibit this enzyme in reticulocyte membranes from males. In these previous studies, preincubation of intact cells or ghosts with testosterone (5 X 10(-11) M) converted female-source reticulocyte membranes to male-type responsiveness to thyroid hormone (inhibition of Ca2+-ATPase activity). Preincubation of reticulocyte membranes with 17 beta-estradiol (5 X 10(-11) M) converted male-source membranes to female-type responsiveness (stimulation by L-T4 of membrane Ca2+-ATPase activity). Using this sex steroid-sensitive thyroid hormone-dependent membrane enzyme system, we investigated the structure-activity relationships of analogs of sex steroids and unrelated steroids. 5 beta-Androstanes were active compared to testosterone in assays using female-source membranes, while 5 alpha-androstanes were less active. Within the 5 beta-androstanes, activity was dependent on at least one hydroxyl group at the C3- or C17-position. Nongonadal steroids tested were less active, establishing specificity of the sex steroid effect in assays using female-source membranes. Assayed in male-source membranes, estrone and 3-hydroxy-1,3,5-(10)7-estratraen-17-one (equilin) were active compared for estrogen effect with 17 beta-estradiol, while estriol was less active. The activities of hydrocortisone and aldosterone were 76% and 71%, respectively, in this system. These structure-activity relationships are distinct from those described for gonadal steroid-cytoplasmic binding proteins or nuclear interactions, and represent a novel sex steroid-thyroid hormone effect on activity of a membrane enzyme.

Differential effect of common snack foods on caloric intake, growth and obesity in weanling male and female rats with hypothalamic obesity

In order to see whether weanling normophagic rats with hypothalamic obesity (VMNL rats) become hyperphagic and more obese than when fed lab chow, and to see in addition whether there is a possible sex difference in whatever response is found, male and female VMNL rats were fed lab chow for 14 days after lesion production and then, for the following 42 days, they received Hostess HoHos, potato chips, marshmallows and french fries in addition to lab chow. At termination, body weights were similar among the groups, but VMNL rats were fatter and shorter than controls. Also, female VMNL rats were fatter and shorter than male VMNL rats and layed down more fat per unit of food energy. Total caloric intake was greater in controls than in VMNL rats and in males than in females. However, the females showed a decrease in intake and the males an increase over time. Males ate more lab chow and french fries than females. Lab chow was the only food that VMNL rats ate more of than controls. The VMNL rats ate less french fries, HoHos and potato chips than controls, but similar amounts of marshmallows. There was no sex difference in macronutrient intake and per cent macronutrient intake. Moreover, controls ate as much carbohydrate and less per cent carbohydrate than VMNL rats, more fat than VMNL rats, but normal per cent fat and normal protein and per cent protein. Sex X lesion interactions indicated that female VMNL rats ate more per cent carbohydrate than female controls and male VMNL rats, ate more protein than male controls. The greater degree of obesity in the females despite the lower caloric intake may be due to enhanced food energy utilization. The data also show that weanling VMNL rats do not exhibit the great preference for palatable diets that have been reported for mature rats with ventromedial hypothalamic area lesions and that the only sex difference in intake is with french fries, which have neither the highest fat nor the highest carbohydrate content of the foods tested.

Differential activities of tolbutamide, tolazamide, and glyburide in vitro on rabbit myocardial membrane Ca2+-transporting ATPase activity

At clinically achievable concentrations (10(-9) to 5 X 10(-6) M), tolbutamide and tolazamide are in vitro inhibitors of Ca2+-transporting ATPase activity in sarcolemma-enriched rabbit myocardial membranes (sulfonylurea IC50, 10(-7) M). Thyroid hormone stimulation of this calcium pump-associated enzyme in vitro has been previously reported; in our study, this hormonal action was shown to be inhibited by tolbutamide and tolazamide. In contrast to these two sulfonylureas, glyburide (up to 5 X 10(-6) M) had no effect on basal or thyroid hormone-stimulable Ca2+-ATPase activity in vitro. Studies of binding of radiolabeled purified calmodulin to heart membranes showed that tolbutamide and tolazamide inhibited this interaction, whereas glyburide had no effect on calmodulin binding. Addition of purified calmodulin (5-40 ng/micrograms membrane protein) to myocardial membranes incubated with 10(-7) M tolbutamide or tolazamide restored Ca2+-ATPase activity and thyroid hormone responsiveness of the enzyme. Inhibition by tolbutamide and tolazamide of myocardial sarcolemmal Ca2+-ATPase is a mechanism by which these two sulfonylureas may at least transiently raise resting sarcoplasmic Ca2+ concentration. This effect of sulfonylureas on Ca2+-ATPase is not expressed in the presence of the benzamide side chain of glyburide. The inhibitory action of certain sulfonylureas on Ca2+-ATPase is mediated by interference of the agents with the binding of calmodulin to cardiac membranes.

Respiratory muscle activity during asphyxic apnoea and opisthotonus in the rabbit

The behaviour of submandibular, cervical, thoracic and abdominal respiratory muscles was examined in the pentobarbitone-urethane-anaesthetized rabbit during progressive asphyxia induced by rebreathing. During asphyxic hyperpnoea the external intercostal, interchondral and scalene inspiratory activities augmented until succeeded by the apnoeic period, in which all were inhibited with the diaphragm. Likewise, the genioglossus, sternohyoid and thyrohyoid muscles exhibited inspiratory augmentation during asphyxic hyperpnoea until the onset of apnoeic inhibition. However, late in the apnoea these muscles, together with the sternothyroid, sternomastoid and digastric muscles, generated an augmenting tonic discharge associated with an intense abdominal constriction, and with the extension of the limbs characteristic of opisthotonus. This intense tonic activity, which was never expressed by the diaphragm and thoracic inspiratory muscles, was immediately interrupted or terminated by the subsequent inspiratory efforts of gasping respiration, during which the abdominal muscles were inhibited but all the submandibular, cervical and thoracic inspiratory muscles greatly participated. The mylohyoid muscles presented augmenting expiratory activity during asphyxic hyperpnoea which declined during the apnoea. These muscles, however, did not exhibit the intense tonic discharge expressed by the expiratory abdominal and inspiratory submandibular and cervical muscles in late apnoea and were not active in gasping.

Bilirubin diffusion through lipid membranes

The possibility that bilirubin can diffuse through lipid bilayers is investigated with liposomes prepared from dipalmitoylphosphatidylcholine (DPPC), egg phosphatidylcholine (egg PC) with 22 mole percent cholesterol, and a lipid extract preparation from N115 neuroblastoma cells. Liposomes were prepared with internalized bilirubin and bovine or human serum albumin, and bilirubin efflux into an exogenous solution of human serum albumin was measured. Efflux from DPPC liposomes was significantly higher above the phase transition temperature than below it. This change was dependent on the lipid undergoing a phase transition and could not be accounted for by 6 K change in temperature. Maximum bilirubin efflux from egg PC-cholesterol liposomes was found to depend on the relative internal and external albumin pools, suggesting an equilibrium distribution of bilirubin between them. These observations demonstrate that bilirubin can diffuse freely through these lipid membranes.

Incorporation and modification of exogenous phosphatidylcholines by mycoplasmas

The uptake and modification of exogenous phosphatidylcholine (PC) by several Mycoplasma and Spiroplasma species was investigated. While in most Mycoplasma species and in all Spiroplasma species tested the PC appears to be incorporated unchanged from the growth medium, the PC of M. gallisepticum, M. pulmonis, and M. pneumoniae was disaturated PC, apparently formed by modification of 1-saturated-2-unsaturated PC from the growth medium. The modification of the exogenous PC by M. gallisepticum was inhibited by chloramphenicol under conditions that did not affect de novo synthesis of phosphatidylglycerol. A low activity of an endogenous phospholipase A was detected in native M. gallisepticum membranes. The activity was markedly stimulated by treating the membranes with low concentrations of the nonionic detergents. The PC modification was affected by the fatty acid composition of the exogenous PC species. Diunsaturated, 1-saturated-2-unsaturated, and 1-unsaturated-2-saturated PCs were modified to various extents, whereas the disaturated dipalmitoyl PC (DPPC) was not. Both modified and unmodified PCs were incorporated by the cells, but the unmodified DPPC was incorporated at a lower rate and to a lesser extent. The possibility that the incorporation of DPPC into M. gallisepticum cells is associated with the formation of intracytoplasmic membranes is discussed.