Pharmacodynamic and kinetic considerations on diuretics as a basis for differential therapy

Summary Diuretics are classified according to their site of action in the nephron: loop diuretics, thiazides, and antikaliuretics. During peak diuresis the pattern of electrolyte excretion is constant and characteristic for a class of diuretics. The ratio of diuretic-induced excretion of K⁺ to Na⁺ is 0.12 for loop diuretics, 0.20 for thiazides, and –0.21 for antikaliuretics. The ratio of Ca²⁺ to Na⁺ is 0.02 for loop diuretics and 0.003 for thiazides. Mg²⁺ excretion follows K⁺ excretion in a ratio of 0.15. The natriuretic effect of a diuretic directly depends on the renal clearance of the drug and is proportionate to the number of intact nephrons. Not only loop diuretics but also thiazides and antikaliuretics were demonstrated to be effective natriuretic drugs down to end-stage renal disease. In renal failure FE_Na is doubled with every halfening of GFR. Loop diuretics increase FE_Na to a maximum of 24%, thiazides to 10–15%, and FE_Na is doubled by antikaliuretics. Comedication of loop diuretics with thiazides in renal failure may therefore be more effective than increasing monotherapy. In liver disease, nonrenal drug clearance is reduced the more the patient's direct bilirubin rises thus causing an increase in AUC and urinary excretion of parent drug and metabolites. Despite increased A_e, the cirrhotic patient may become resistant to diuretics as may patients with congestive heart failure or nephrotic syndrome. This is considered to be due to reduced Na⁺ load available at the diuretic's site of action following avid proximal Na⁺ reabsorption. In reduced EABV a short-term comedication of loop diuretics with carboanhydratase inhibitors is considered a more effective diuretic strategy than vigorously increasing monotherapy.Abbreviations GFR glomerular filtration rate (ml/min) - A_e amount of drug excreted into the urine (% of given dose) - AUC area under the plasma level time curve (g·h/ml) - Cl_pl total plasma clearance=Dose_i.v./AUC (ml/min) - Cl_r renal clearance=A_e/AUC (ml/min) - Cl_nr nonrenal clearance=Cl_pl-Cl_r (ml/min) - FE_Na fractional sodium excretion (%)=Na excreted x 100/Na filtered=urine sodium × urine volume per minute x 100/plasma sodium x GFR - CHF congestive heart failure - EABV effective arterial blood volume - RAA Renin angiotensin aldosterone system - NE Norepinephrin - NSAIDs Nonsteroidal anti-inflammatory drugs Gratefully dedicated to Prof. Dr. K.J. Ullrich     

PGE2 concentrations in renal venous plasma and renal lymph during basal and stimulated conditions in the dog

PGE₂ concentration (pg/ml ± SEM) was measured in canine renal lymph (394±115), renal venous plasma (276±55), arterial plasma (172±34) and urine (1290±934). Control periods were followed by an infusion of the sodium salt of arachidonic acid (AA) (40 g/kg min) into the renal artery to stimulate prostaglandin synthesis. During infusion of AA PGE₂ concentrations increased significantly in renal lymph (672±155) renal venous plasma (549±123), and urine (6768±1420), but not in the arterial plasma (176±31). Concentrations in renal lymph and renal venous plasma were not significantly different under either condition. These findings indicate that PGE₂ concentration in renal venous plasma is, by and large, representative of mean PGE₂ concentrations in the cortical renal interstitium, although focal inhomogeneities in PGE₂ concentration in the different areas of the renal interstitium cannot be excluded. Since flow rate of renal lymph is insignificant in comparison with renal venous plasma flow rate total renal PGE₂ output can be estimated from measurements in renal venous plasma and urine.This work was supported by the Friedrich-Baur-Stiftung, München     

Glucose kinetics during prolonged exercise in euglycaemic and hyperglycaemic subjects

To determine the limits to oxidation of exogenous glucose by skeletal muscle, the effects of euglycaemia (plasma glucose 5 mM, ET) and hyperglycaemia (plasma glucose 10 mM, HT) on fuel substrate kinetics were evaluated in 12 trained subjects cycling at 70% of maximal oxygen uptake (VO_{2, max}) for 2 h. During exercise, subjects ingested water labelled with traces of U-¹⁴C-glucose so that the rates of plasma glucose oxidation (R _ox) could be determined from plasma ¹⁴C-glucose and expired ¹⁴CO₂ radioactivities, and respiratory gas exchange. Simultaneously, 2-³H-glucose was infused at a constant rate to estimate rates of endogenous glucose turnover (R _a), while unlabelled glucose (25% dextrose) was infused to maintain plasma glucose concentration at either 5 or 10 mM. During ET, endogenous liver glucose R _a (total R _a minus the rate of infusion) declined from 22.4±4.9 to 6.5±1.4 mol/min per kg fat-free mass [FFM] (P<0.05) and during HT it was completely suppressed. In contrast, R _ox increased to 152±21 and 61±10 mol/min per kg FFM at the end of HT and ET respectively (P<0.05). HT (i. e., plasma glucose 10 mM) and hyperinsulinaemia (24.5±0.9 U/ml) also increased total carbohydrate oxidation from 203±7 (ET) to 310±3 mol/min per kg FFM (P<0.0001) and suppressed fat oxidation from 51±3 (ET) to 18±2 mol/min per kg FFM (P<0.0001). As the rates of oxidation at more physiological euglycaemic concentrations of glucose were limited to 92±9 mol/ min per kg FFM, and were similar to those reported when carbohydrate is ingested, the results of the current study suggest that the concentrations of glucose and insulin normally present during prolonged, intense exercise may limit the rate of muscle glucose uptake and oxidation.     

Tubular transport processes in proximal tubules of hypothyroid rats. Lack of relationship between thyroidal dependent rise of isotonic fluid reabsorption and Na+−K+-ATPase activity

Hypothyroid rats reconstituted with 10 g/kg b.w. per day of tri-iodothironine (T₃) for 4 days resulted in normal free T₃ and TSH levels. FT₃ levels were: 0.53±0.3 pg/ml in hypothyroid rats; 2.78±1.21 pg/ml in hormone reconstituted rats and 2.90±0.90 pg/ml in euthyroid rats. TSH levels were 3,508±513 g/ml in hypothyroid rats; 1,008±204 g/ml in reconstituted rats and 270±184 ng/ml in euthyroid rats.When hypothyroid rats were reconstituted with 50 g T₃/kg b.w. per day, TSH levels were nearly normal after 4 days (1,157±621 ng/ml). However FT₃ levels after 1–4 days were always higher than in euthyroid rats.Hypothyroid rats show a decrease in isotonic fluid reabsorption (J _v) in the proximal tubule (1.50±0.08 versus 4.96±0.23 10^–2 nl·mm^–1·s^–1 in euthyroid animals). 1 day after T₃ (10 g/kg b.w./day) injectionJ _v was increased significantly to 2.05±0.20 10^–2 nl·mm^–1·s^–1 and continued to increase during 4 days of T₃ reconstitution.When 50 g T₃/kg b.w./day was used,J _v increased to 2.75±0.07 after 1 day and to 3.10±0.42 10^–2 nl·mm^–1·s^–1 after 4 days.J _v was never reaching a value close to that of euthyroid rats because the tubular radius in hypothyroid rats (14.7±1.8 m) is less than that of euthyroid rats (19.2±0.5 m). The radius in hypothyroid rats treated with T₃ was unchanged over a 4 day course with either high or low doses of T₃.Na⁺–K⁺-ATPase activity was found to be 2.91±0.16 M P_i/h×mg protein in homogenates of kidney cortex from hypothyroid rats. Treatment of hypothyroid rats with 10 g or 50 g of T₃ resulted in an initial decrease in ATPase activity, followed by an increase to base level in hypothyroid rats with 10 g and a significantly higher level with 50 g. This decrease in ATPase activity was contrasted to the increase inJ _v.These data indicate that there is a dissociation between the effects of physiological doses of thyroid hormones on proximal tubular reabsorption and the effects of T₃ on Na⁺–K⁺-ATPase activity of kidney cortex. This leads to question the relationship between sodium transport and ATPase activity under physiological doses of thyroid hormones. An early effect of physiological doses of thyroid hormones on brush border Na⁺ permeability is suggested.     

Cytogenetic effects of chloroquine in human lymphocyte cultures

Addition of chloroquine to a culture of human lymphocytes at the G₁ stage showed that the compound, in a concentration of 15 g/ml, does not affect the level of chromosomal aberrations, but in concentrations of 60 and 100 g/ml it suppresses mitotic activity of the cells virtually completely. By its actions of the G₂ stage chloroquine, in a concentration of 100 g/ml, significantly increases the number of chromosomal aberrations, but in a concentration of 15 g/ml it has no appreciable action.Presented by Academician N. P. Dubinin.Translated from Byulleten' Éksperimental'noi Biologii i Meditsiny, Vol. 82, No. 7, pp. 879–881 (1976).     

Phosphaturic response of hydrocortisone in the presence and the absence of parathyroid hormone

The effect of hydrocortisone (HC) on the renal Pi transport in the presence and in the absence of parathyroid hormone (PTH) in the rat was examined using clearance techniques. During constant infusion of PTH in parathyroidectomized (PTX) rats, HC decreased the reabsorption of Pi from 2.84 to 2.33 mol/min (P<0.001), the Tm_Pi from 4.55 to 3.83 mol/min (P<0.001), the reabs. Pi/GFR values from 0.93 to 0.74 (P<0.001) and the Tm_Pi/GFR from 1.73 to 1.42 mol/ml (P<0.001). In the absence of PTH, HC diminished the Tm_Pi from 8.36 to 6.58 mol/min (P<0.005) and the Tm_Pi/GFR from 3.36 to 2.51 mol/ml (P<0.001). It is concluded that the phosphaturic response of hydrocortisone may be important in the homeostasis of inorganic phosphate in the body.This work was supported by a grant from the Deutsche Forschungsgemeinschaft (Fr 239/8)     

Transport properties of a C. albicans amino-acid permease whose putative gene was cloned and expressed in S. cerevisiae

Using a gene bank of C. albicans, the lysine-permease deficiency in a strain of S. cerevisiae was complemented, and the restriction map of the corresponding C. albicans DNA fragment was constructed. Its expression in S. cerevisiae showed that the permease of C. albicans actively transports arginine (K_T=18 mol/l, J_max=26 nmol/min per mg dry weight), lysine (K_T=12 mol/l, J_max=18 nmol/min per mg dry weight), histidine (K_T=37 mol/l, J_max=9.7 nmol/min per mg dry weight), as well as their toxic analogues canavanine and thialysine, with high affinity. The intracellular concentration of basic amino acids transported into S. cerevisiae by the C. albicans permease reaches more than a thousand-times-higher value compared to the external concentration in the medium. Accumulated amino acids do not leave the cells. The uptake is strongly reduced by the protonophores and inhibitors of plasma membrane H⁺-ATPase.     

Interaction of allopurinol and hydrochlorothiazide during prolonged oral administration of both drugs in normal subjects

The kinetics of allopurinol and hydrochlorothiazide were investigated in seven healthy male subjects during prolonged coadministration of two drugs. Subjects were maintained on an isoenergetic, purine-free formula diet with RNA supplementation for 24 days. Allopurinol (300 mg) was given orally on days 1–24. Hydrochlorothiazide (50 mg daily) was added to days 11–21. On day 43 a single oral dose of 50 mg hydrochlorothiazide was administered. Plasma concentration-time profiles of allopurinol and its main metabolite oxipurinol were obtained on days 1, 10, and 21; hydrochlorothiazide profiles were assessed on days 21 and 43. In addition, 24-h plasma concentrations of oxipurinol were measured repetitively, and 24 h urine samples were collected for the determination of allopurinol, oxipurinol, and hydrochlorothiazide. For oxipurinol, meanC _max was not altered on hydrochlorothiazide treatment (13.8 ± 1.4 g/ ml and 14.7 ± 2.6 g/ml, respectively); mean AUC_0–24 was 259 and 290 g h^–1 ml^–1, respectively. The small difference in AUC_0–24 values does not explain the increase in plasma uric acid concentration during hydrochlorothiazide treatment, nor do the variations in allopurinol and hydrochlorothiazide kinetics.Abbreviations AUC_0–24 area under the plasma concentration-time curve from time zero to 24 h - AUC _0– area under the plasma concentration-time curve from time zero to infinity - Allo allopurinol - Oxi oxipurinol - HCT hydrochlorothiazide Correspondence to: J.X, de Vries     

The source of urinary epidermal growth factor in humans

Summary To clarify the source of human urine EGF, we studied EGF renal clearance in 20 healthy, young adult subjects. Immunoreactive EGF was measured hourly in EDTA plasma, heparin plasma, serum and urine of 12 males and 8 females during a 3 h study period. Plasma and urine creatinine and creatinine clearance were measured and calculated hourly. Mean (and SEM) creatinine clearance was similar in males and females (118±12 vs 105±6 ml/min). EGF was not detectable in plasma, whereas relatively high levels were measured in serum (2.5±0.25 vs 1.5±0.18 ng/ml in males and females respectivelyp<0.05). Urine EGF excretion averaged 1641±233 ng/h in males and 1507±191 ng/h in females (p>0.05). A significant correlation was observed between urine creatinine and urine EGF concentrations in both male (r = 0.98,p<0.01) and female (r=0.94,p< 0.01) subjects. EGF immunoreactivity in urine and serum eluted from G-75 sephadex columns similarly to recombinant 6000 Mr hEGF. Urine excretion of EGF approximated 1.5 g/h or 25 ng/mg creatine. The high concentrations of EGF found in urine in the face of non-detectable levels of EGF in plasma favor the hypothesis that EGF in urine is derived from kidney synthesis and secretion. The significant positive correlation between urine creatinine and urine EGF suggests a functional correlation between glomerular filtration and the process of tubular EGF excretion.Abbreviations EGF epidermal growth factor - hEGF human epidermal growth factor - IGF insulin-like growth factor - TGF alpha transforming growth factor - TGF beta transforming growth factor - NGF nerve growth factor - PDGF platelet derived growth factor - CPDA citrate phosphate dextrose adenine buffer - EDTA ethylenedinitrilotetraacetic acid - PBS phosphate saline buffer     

Steady-state kinetics of bezafibrate retard in hyperlipidemic geriatric patients

Summary The pharmacokinetics of a slow-release formulation of bezafibrate were investigated under steady-state conditions in 19 hyperlipidemic patients between the age of 61 and 87 years and compared to the kinetics in 20 healthy volunteers (age 19–42 years). Maximum serum levels were 1.6-fold higher in the elderly, which was partly due to a diminished renal clearance caused by the reduction in renal function (CL_CR 23–81 ml/min) and partly due to a decrease in extrarenal clearance (probably hydroxylation and hydrolysis). Evidence for the additional decrease in extrarenal clearance was provided by the greater decline in total drug clearance than would be anticipated from a mere reduction in glomerular filtration. Thus, dose adjustment of slow-release bezafibrate in elderly patients cannot be based merely on creatinine clearance. In general, it is recommended that bezafibrate retard is substituted by a reduced dose of normal-release bezafibrate below a creatinine clearance of 60 ml/min.Abbreviations AUC_ss area under the curve within the dosing interval during steady-state - C_max maximum concentration - CL total clearance - CL_CR creatinine clearance - CL/f clearance divided by bioavailability - CL_R renal clearance - f bioavailability - lambda_z (_z) elimination rate constant - t _max time to C_max - t _1/2 elimination half-life     

Fibrinogen and fibrinogen/fibrin degradation products in the urine of rabbits infected with Trypanosoma (Trypanozoon) brucei

Summary Studies have been carried out on the urine of rabbits infected with Trypanosoma (Trypanozoon) brucei to determine whether fibrinogen or fibrinogen/fibrin degradation products (FDP) could be detected. No fibrinogen was found but during the last two weeks of this 7-week infection low levels of FDP were present in the urine which did not exceed 5 g/ml. Rabbit urine was shown to contain a potent proteolytic enzyme capable of breaking down rabbit fibrinogen and both early and late FDP were present in the cleavage products. No deposits of fibrin were detected in the kidney, but casts were present in the urine suggesting renal damage. The most likely explanation of the urinary FDP is that either an increase in the glomerular permeability occurs allowing filtration of plasma FDP or a local fibrinogenolysis in the kidney tubules.     

Characterization of L-glutamate uptake into and release from astrocytes and neurons cultured from different brain regions

Summary The uptake of L-glutamate was studied in astrocytes cultured from different brain areas of newborn rats as well as in two different cultures of neurons obtained from mouse brain. Both astrocytes and neurons exhibited high-affinity glutamate uptake with K_m values ranging from 34 [M to 82 M. V_max values for astrocytes cultured from the different brain regions were: prefrontal cortex: 13.9; occipital cortex: 11.4; neostriatum: 27.3 and cerebellum: 5.8 nmol · min^–1 · mg^–1 cell protein. For cerebellar granule cells and cerebral cortical neurons the V_max values were found to be 10.2 and 5.9 nmol · min^–1 · mg^–1 cell protein, respectively. The effect on L-glutamate uptake in astrocytes cultured from prefrontal cortex and in cultured cerebellar granule cells of a series of compounds structurally related to glutamate was studied, and detailed kinetic analyses of the inhibitory patterns of three potent inhibitors were performed. L-aspartate and L-aspartate--hydroxamate were found to be competitive inhibitors of L-glutamate uptake in both cell types with K_i values for astrocytes of 60 M and 91 [M, respectively, and for granule cells of 48 M and 72 M, respectively. D-aspartate was found to be a mixed-type noncompetitive inhibitor of L-glutamate uptake in astrocytes (K;: 106 M), but in granule cells this compound showed simple competitive inhibition with a K_i of 49 M. Sodium dependency of L-glutamate uptake in both cell types was studied at a series of Lglutamate and Na⁺ concentrations. It was found that the uptake of glutamate in astrocytes is coupled with one Na⁺ ion in contrast to two Na⁺ ions in granule cells. The K_m value for sodium was found to be 15 mM in both cell types. It was shown that release of exogenously supplied [³H] -L-glutamate from cerebel lar granule cells could be stimulated in a Ca²⁺-dependent manner by high concentrations (55 mM) of K⁺. In contrast to this no K⁺-induced release of glutamate could be demonstrated in cultured astrocytes.Supported by grants from The Danish Natural Science Research Council (512-20817) and The NOVO Foundation to Arne Schousboe, and from The Danish Medical Research Council (512-20569) to The Biochemical Laboratory, Royal Danish School of Pharmacy     

Localization and properties of NAD+-dependent 15-hydroxyprostaglandin dehydrogenase activity in the rat kidney

Localization of NAD⁺-dependent (type I) 15-hydroxyprostaglandin dehydrogenase (15PGDH) in the rat kidney was examined using an ultramicro assay of the enzyme activity based on the enzymatic cycling method. The enzyme activities during first 3 weeks of age were 30- to 40-fold higher than the adult and rapidly decreased by 4th week. 15PGDH activities measured with either PGE₂ or PGF₂ as a substrate were five times higher in slices from midcortical or juxtamedullary layers than in slices from the superficial cortex of 3 week-old rat kidney. Little activity was found in inner medulla and papilla. When the enzyme activity was assayed using isolated nephron segments dissected from collagenase treated slices of 3 week-old rat kidneys, the activity was localized only in the proximal convoluted and straight tubules with either PGs (PGE₂: 1.75±0.25 in PCT, 7.70±1.19 in PST, and PGF₂: 1.63±0.39, 6.18±1.52 pmoles NADH/mm/40 min). The kinetic analysis for renal 15PGDH of 3 week-old rats revealed thatK _m for PGE₂ (8.4 M) was lower than that for PGF₂ (22.6 M) with constant NAD⁺, whileV _max for both was similar. In contrast, bothK _m andV _max for NAD⁺ were identical with either PGs. These data suggest that the rate-limiting factor of type I 15PGDH is the concentration of prostaglandins in the kidney rather than the concentration of NAD⁺. It is thought that the enzyme may be physiologically significant in inactivating the prostaglandins reaching the proxial tubule in order to ensure that the classical prostaglandins (PGE₂ and PGF₂) produced in the medullary interstitium and collecting tubules can effectively regulate the distal nephron function.     

Calcium sensitivity and unloaded shortening velocity of hypertrophied and non-hypertrophied skinned human atrial fibres

The mechanical properties of myocardium of different animals are modified by a chronic increase in haemodynamic load. In this study differences in calcium sensitivity and maximum unloaded shortening velocity of hypertrophic and non-hypertrophic chemically skinned human atrial fibres are characterized. Investigating right atria of 34 patients, possible correlations are studied between preoperative atrial pressure, degree of hypertrophy (estimated from the muscle fibre diameter), calcium responsiveness (pCa₅₀ eliciting half-maximum contraction) and V _max (unloaded shortening velocity). Hypertrophic fibres from atrial appendages of patients having an increased right atrial pressure (RAP 8.5±1.6 mm Hg) and suffering from mitral valve disease (stenosis and insufficiency combined) had a fibre diameter of 18.0±0.9 m. They also had a higher calcium sensitivity (pCa₅₀ 5.65±0.08) and a lower unloaded shortening velocity (1.7±0.1 muscle lengths/s) than non-hypertrophic fibres from the appendages of patients with normal right atrial pressure (RAP 3.2±0.5 mm Hg) and coronary heart disease (CHD: pCa₅₀ 5.45±0.04; V _max= 3.4±0.2 muscle lengths/s; fibre diameter 12.8±0.4 m). Thus non-hypertrophic fibres from control CHD patients differed significantly (p < 0.01) from hypertrophied atrial fibres of patients with mitral valve disease and with combined valve disease (MAV, pCa₅₀=5.58±0.05, V _max 2.0±0.3 muscle lengths/s, fibre diameter 14.6±0.9 m) or aortic valve disease (stenosis combined with insufficiency, fibre diameter 14.8±1.4 m, pCa₅₀ 5.56±0.03, V _max 2.0±0.24 muscle lengths/s; RAP 11.0±2.6 mm Hg). Such alterations of calcium responsiveness, shortening velocity and fibre thickness may reflect an adaptation to the chronic overload in atria from patients with various forms of heart valve disease.     

Caffeine elimination: A test of liver function

Summary Fasting plasma caffeine concentration and various parameters of caffeine elimination from plasma obtained after a standardized oral dose of 140 mg caffeine have been compared in nine patients with liver cirrhosis, eight patients with non-cirrhotic liver disease and ten healthy volunteers with regard to their ability to discriminate between the different groups. Fasting plasma caffeine concentrations were significantly higher in cirrhotics (11.1±10.5 mol/l) than in healthy volunteers (1.5±0.8 mol/l). The respective values measured in patients with non-cirrhotic liver disease (3.1±3.1 mol/l) did not differ significantly from the controls. Plasma disappearance rate and clearance of caffeine were significantly decreased in cirrhotics (0.11±0.02 h^–1; 1.0±0.3 ml/min per kg) and in patients with non-cirrhotic liver disease (0.18±0.04 h^–1; 2.2±0.7 ml/min per kg) as compared to healthy volunteers (0.23±0.04 h^–1; 3.1±0.9 ml/min per kg). Plasma caffeine concentration determined 12 h after administration of the test dosage discriminated best between patients with cirrhosis (5.4±1.6 mol/l), patients with noncirrhotic liver disease (2.0±1.4 mol/l) and healthy volunteers (0.8±0.2 mol/l). These results, the safety of the test compound and the simplicity of a single caffeine determination in plasma 12 h after a standardized dose of caffeine make this test attractive for evaluation of liver function.     

Dermal inflammation in primates,mice, and guinea pigs: Attenuation by second-generation leukotriene B4 receptor antagonist,SC-53228

Granulocyte infiltration is a prominent feature of human psoriasis. Psoriatic lesional skin contains abnormally high amounts of immunoreactive leukotriene B₄ (LTB₄), a potent granulocyte chemotaxin in vivo and in vitro. SC-53228 [(+)-(S)-7-(3-{2-(cyclopropylmethyl)-3-methoxy-4-[(methylamino)carbonyl]phenoxy}propoxy)-3, 4-dihydro-8-propyl-2H-1-benzopyran-2-propanoic acid], a second-generation LTB₄ receptor antagonist, was tested topically and orally in phorbol ester-induced dermal inflammation in three species. Skin inflammation was induced by topical application of phorbol-12-myristate-13-acetate-(PMA/TPA) and assessed by ear thickness, levels of the neutrophil marker enzyme myeloperoxidase (MPO) and histological examination. In mice, SC-53228 inhibited inflammation with a topical ED₅₀ value of 200 ± 18 g. When applied to guinea pigs, SC-53228 (100 g) inhibited the MPO increase by 86%, while 1000 g abrogated inflammation in rhesus macaques with no plasma accumulation of the drug. A 1 % gel formulation was also efficacious in guinea pig PMA-induced epidermal inflammation. Furthermore, single oral dose administration to mice was efficacious (ED₅₀ < 2.5 mg/kg) as was multidose administration to rhesus macaques. PMA-induced skin inflammation possesses some of the attributes of human psoriasis and an agent such as SC-53228 may have utility in the medical management of this condition.     

A combined study of sodium current and T-type calcium current in isolated cardiac cells

Sodium currents (I _Na) and T-type calcium currents (I _Ca,T) of isolated guinea-pig ventricular myocytes were recorded using the whole-cell voltage-clamp technique. Separation of the two currents was obtained by using the difference current method in the presence and absence of 2 mM extracellular Na (Na_o). Time to peak and the time constant of inactivation of. I_Na were about 5 times faster than that of I _Ca,T (test potential –30 mV). and I _Ca,T had an activation range positive to –50 mV, were inactivated at –50 mV, and their current/voltage relationships peaked at –22.3±1.8 mV (n=18) and –29.3±0.5 mV (n=18) respectively, with a reversal potential of +40.3±4 mV (n=18) and +30±10 mV (n=18), respectively [2 mM Na_o; 5.4 mM extracellular Ca (Ca_o)]. I _Na was blocked by 30 M tetrodotoxin (TTX), 500 M lidocaine, partly inhibited by 1 mM amiloride, but not affected by 100 M nickel (Ni). I _Ca,T was neither affected by 30 M TTX nor 500 M lidocaine, but blocked by 100 M Ni, 1 mM amiloride, 10 M R 56865 and use-dependently reduced by 5 M flunarizine. Adenosine (500 M) affected neither I _Na nor I _Ca,T, whereas 1 M isoprenaline did not affect I _Ca,T, but slightly increased I _Na. Our results demonstrate that the characteristics of I _Ca,T are not affected by the concomitant activation of I _Na, and vice versa. We conclude that I _Ca,T are not Ca currents through Na channels.     

Mediated transport of chloride from blood into cerebrospinal fluid

Summary The kinetics of transport of chloride from blood into CSF have been studied in the adult cat in vivo for a wide range of concentrations of chloride in arterial plasma: 1. In studies employing isosmotic replacement of body chloride with isethionate by means of extracorporeal hemodialysis, the chloride content in cerebral cortex and corpus callosum and concentration in CSF were relatively resistant to change despite the fact that plasma chloride was varied over the range 120.5 to 8.1 mM. 2. During hemodialysis the ratio of the concentration of chloride in CSF (or content in cerebral cortex) versus the concentration of chloride in arterial plasma was maintained for at least 1 or 2 h at as much as 10 times the ratios present in normal animals. 3. In studies with ³⁶Cl, the rate of entry of chloride from blood into CSF followed Michaelis-Menten kinetics with the V_max=0.55 mole/ ml/min and with the K_m < 60 mM and possibly < 8.1 mM. On the other hand the rate of entry of chloride from blood into cerebral cortex and corpus callosum was much slower and followed simple diffusion kinetics. 4. Evidence is presented indicating that chloride is transported from blood to CSP at the choroid plexus as well as at other sites. 5. On the basis of the rate of entry of chloride into CSF, the rate of bulk production of CSF in the adult cat was calculated to be 17.1 l/min at normal plasma concentrations of chloride, a value in close agreement with previous estimates of the rate of production of CSF in the adult cat. 6. The relationships of the content of chloride in skeletal muscle and in liver to the concentration of chloride in plasma are presented, when the latter is varied over the range 120.5 to 8.1 mM.     

In vitro activity of ciprofloxacin against methicillin-susceptible and methicillin-resistant staphylococci

Ciprofloxacin was found to be active against selected strains of methicillin-resistant as well as methicillin-susceptible Staphylococcus aureus and Staphylococcus epidermidis, having minimal inhibitory concentrations <0.8 g/ml with inocula of approximately 10⁴ CFU/ml. When killing kinetic studies were done with inocula of approximately 10⁶ CFU/ml and various ciprofloxacin concentrations, the killing effect was low (<3 log₁₀ in 6h) and regrowth of the culture was seen after 24 h in at least one Staphylococcus aureus strain. After 48 h incubation, mutants with MICs eightfold that of the parental strain had grown to a number of approximately 10¹⁰ CFU/ml.     

The inotropic effect of atrial natriuretic factor in the anesthetized rabbit

This study was designed to investigate whether atrial natriuretic factor (ANF) administered over the physiological, pathological and pharmacological range has a negative inotropic action on the heart. Anesthetized rabbits were infused with increasing doses of ANF (0.05, 0.25 and 0.5g kg^–1min^–1), while measuring hemodynamic variables including the maximum rate of change of left ventricular pressure (dP/dt _max) as an index of inotropic state. Plasma levels of immunoreactive ANF (iANF) were measured to relate the hemodynamic changes to actual plasma levels of the peptide. Administration of ANF was associated with decreases in blood pressure, left ventricular pressure and dP/dt _max so that after 0.5 g kg^–1 min^–1 infusion, these variables had decreased by 21±2 mmHg, 21±5.3 mmHg and 925±175 mmHg/s, respectively (P<0.01). There were no significant changes in right atrial pressure, left ventricular end-diastolic pressure or heart rate. Since dP/dt _max can be influenced by changing hemodynamic variables and baroreflex changes, a second group of rabbits was studied in which afterload and heart rate were held artificially constant. Again, in this group of rabbits, infusions of ANF led to decreasing inotropic state, so that at the highest infusion rate, a 14% decrease in dP/dt _max was observed (P<0.05). By comparison, hydralazine, a drug which causes active vasodilatation but no direct inotropic action, significantly (P<0.01) decreased blood pressure, left ventricular pressure and dP/dt _max when infused at a rate of 10 g kg^–1 min^–1. However, in animals in which afterload was controlled, hydralazine did not affect any of the variables measured. The results indicate that ANF does have a negative inotropic action in the anesthetized rabbit.