Synthesis and degradation of interconvertible enzymes. Kinetic equations of a model system

Steady-state and kinetic equations have been developed which characterize the rates of formation, interconversion, and degradation of an enzyme protein subject to reversible phosphorylation. The theoretical model system incorporates separate fractional degradative rate constants for the phosphorylated and dephosphorylated protein species. The classical models for interconvertible enzymes, and for protein turnover, are special limiting situations of the general model presented here.

The holographic storage of study models

The storage and recall of dental study models pose major problems for orthodontists. This problem may be solved by taking holographic films of study models. A method is described for their fabrication and some preliminary measurements are reported. The image produced by this method has a measurable three-dimensionality which can be produced at a very reasonable cost.

Population redistribution within the rural-urban fringe: a typology of small towns and rural municipalities in the state of New Jersey

Population redistribution within the rural-urban fringe of the United States is examined using the state of New Jersey over the period 1970-1980 as an example. "This article provides additional evidence for the redistribution of population to the rural-urban fringe and identifies those types of municipalities that experienced the greatest growth during the 1970s. Furthermore, it finds that the factors that account for population growth at the rural-urban fringe are not only those associated with suburbanization, but also those associated with nonmetropolitan growth. It also demonstrates that population growth at the rural-urban fringe varies not only by municipal type but also by race."

Acute renal failure in toxic shock syndrome owing to rhabdomyolysis

Toxic shock syndrome is frequently complicated by renal dysfunction. The mechanism of this functional disturbance is unclear. The present report concerns a 33-year-old woman with reversible renal failure in the course of toxic shock syndrome owing to rhabdomyolysis. It is suspected that the renal consequences of muscle injury play a pathophysiological role in the acute renal failure of toxic shock syndrome.

Assessment of the forced expiration technique, postural drainage and directed coughing in chest physiotherapy

The Forced Expiration Technique (FET), postural drainage (PD) and directed coughing have been evaluated in 10 patients with copious sputum (mean value 63.3 ml/24 h) with an inhaled radioaerosol method over a 30-min treatment period. FET alone and FET + PD (but not directed coughing) cleared more radioaerosol than during the control period (P less than 0.01). The wet weight of sputum obtained following FET, FET + PD and directed coughing were all significantly greater than control (P less than 0.01). However, sputum obtained by FET + PD was significantly greater than FET alone (P less than 0.05). Both FET and particularly FET + PD have been shown to be more effective than directed coughing alone and it is suggested that these manoeuvres should be incorporated into standard chest physiotherapy.

Morphometric analysis of the human endometrium in relation to peripheral hormone levels

Twelve indices were quantitated at three sites in 68 endometrial biopsies from 14 women in five cycles each in which daily plasma levels of luteinizing hormone (LH), estradiol (E2), and progesterone (P) were measured. It was found that a single biopsy specimen is representative of the entire endometrium. Using classic dating, 59% of the biopsies were correct. The error rate increased with the distance from the LH surge. The morphometric indices revealed significant differences am ong all 48-hour secretory phase periods except days LH + 7 to LH + 10. The glandular diameter was positively correlated with proliferative phase E2 levels and with secretory phase P levels; the latter were negatively correlated with stromal mitoses. Basal vacuoles were negatively correlated with E2 and positively with P levels.

Sex-related differences in the susceptibility of rats to gentamicin nephrotoxicity

Age-matched male and female Fischer 344 rats were treated with gentamicin, 40 mg/kg of animal body weight per day, for three to 21 days. Renal dysfunction was less severe in females as measured by concentrations of blood urea nitrogen and creatinine and by cortical slice uptake of p-aminohippuric acid and N1-methylnicotinamide chloride. Also, cortical concentrations of gentamicin in females were lower than in males. Neither exogenous testosterone administered to adult females nor castration of prepubertal males changed the pattern of dysfunction. These results show that sex affects susceptibility to aminoglycoside nephrotoxicity by mechanisms that are undefined but that are apparently unrelated to testosterone. The variable of sex needs to be considered in interpreting the results of studies of experimental aminoglycoside nephrotoxicity.

A randomized, double-blind study of two combined and two progestogen-only oral contraceptives

A randomized double-blind study of two combined oral contraceptives and two progestogen-only oral contraceptives was conducted using the same protocol at WHO Collaborating Centres for Clinical Research in Human Reproduction in Bombay and Ljubljana of the 518 women admitted to the trial, 123 received mestranol 50 micrograms + norethisterone 1mg (MES 50 + NET 1); 137 received ethinyl estradiol 30 micrograms + levonorgestrel 150 micrograms (EE 30 + LNG 150); 130 received norethisterone 350 micrograms/NET 350); and 128 received levonorgestrel 30 micrograms (LNG 30). At one year, between 52.6 and 61.0 percent of those recruited had discontinued oral contraceptive use for all reasons, and by two years, between 70.5 and 76.5 percent had discontinued the treatment. These rates did not differ between the four treatment groups. However, discontinuation rates for all medical reasons at one and two years, and at two years pregnancy rates and discontinuation rates for bleeding disturbances, were significantly lower in the EE/LNG preparation. The groups receiving the MES/NET, LNG and NET had similar pregnancy rates, discontinuation rates for all medical reasons and all bleeding disturbances. There were two ectopic pregnancies among the 22 pregnancies in the progestogen-only groups. Discontinuation because of headache, dizziness and other central nervous system symptoms were significantly more common in those receiving MES/NET compared to EE/LNG. In contrast, discontinuation for gastro-intestinal disturbances were significantly higher in the EE/LNG combined preparation. Bleeding disturbances in the first few cycles tended to be higher in NET than in the LNG group. The data suggest that greater consideration be given to the benefits and risks of including progestogen-only oral contraceptives in the family planning programmes of some countries.

Effect of basis amino acids and aminoglycosides on 3H-gentamicin uptake in cortical slices of rat and human kidney

The uptake of 3H-gentamicin was assessed in renal cortical slices of Fischer 344 male rats and four human cadaver kidneys not utilized for renal transplantation. In both species the uptake was maximal at 90 min and maintained a steady state thereafter. The characteristics of the energy-dependent component of 3H-gentamicin uptake were not altered by various basic amino acids, but competitive inhibition was induced by other aminoglycosides in a dose-dependent fashion. Thus aminoglycosides appear to share a transport process that is distinct from those of organic bases or other cationic substances. In addition, under the experimental conditions employed, the basolateral membrane of the tubular cell is capable of energy-dependent uptake of gentamicin. The role of this route of cellular uptake of aminoglycoside in clinical nephrotoxicity is speculative.

Short-term regulation of hydroxymethylglutaryl coenzyme A reductase by reversible phosphorylation: modulation of reductase phosphatase in rat hepatocytes

Hydroxymethylglutaryl CoA reductase catalyzes the limiting step in cholesterol synthesis in liver and other tissues. Beginning in 1973 studies with subcellular systems established that microsomal reductase is inactivated with ATP(Mg) and reductase kinase, and restored to full activity with phospho-protein phosphatase. By contrast reductase kinase is inactivated with phosphatase and reactivated with a second protein kinase (reductase kinase kinase). This bicyclic system has now been confirmed in terms of homogeneous enzyme components and by direct reversible phosphorylation with [gamma 32P]ATP in several laboratories. Short-term endocrine control of reductase and reductase kinase has been demonstrated in intact rat hepatocytes. Preincubation of cells with glucagon brought about a fall in the expressed activity of reductase and a rise in reductase kinase consistent with net phosphorylation of both enzymes. Total reductase levels were also severely depressed after glucagon. Addition of insulin to suspensions of hepatocytes had the reverse effect on expressed activity of reductase (elevated) and reductase kinase (depressed). Insulin also prevented the decay in total reductase activity. Since both protein kinases identified in this system are cAMP-insensitive, it was possible that hormonal signaling is mediated through the protein phosphatase that acts on both reductase kinase and reductase. In recent studies we have shown that the rate of activation of endogenous reductase in hepatocyte extracts (microsomes plus cytosol) is responsive to hormonal modulation. Pretreatment of hepatocytes with insulin increases apparent reductase phosphatase activity in extracts while glucagon diminishes the rate of reductase activation. HMG CoA is converted to mevalonate by the reductase enzyme. In hepatocytes mevalonate is rapidly converted to cholesterol and to a variety of isoprene derivatives. Expressed reductase activity falls precipitously when hepatocytes are incubated with mevalonate (added in the form of mevalono-lactone). As in the case with glucagon pretreatment reductase phosphatase is rapidly diminished. (Mevalonate itself is not inhibitory to reductase or reductase phosphatase activity in subcellular systems.) It is probable that a product of mevalonate metabolism generated in intact cells may act as a reductase phosphatase inhibitor. Among these added inorganic pyrophosphate inhibited reductase phosphatase at low concentrations.

Comparative nephrotoxicity of dibekacin and gentamicin in rats

To evaluate the nephrotoxicity of the new aminoglycoside, dibekacin, relative to gentamicin, we administered both drugs in doses of 40 and 120 mg/kg per day to male and female Fischer 344 rats. At sacrifice, we determined serum creatinine, in vitro renal cortical uptake of 14C N-methyl nicotinamide and para-aminohippurate, renal cortical antibiotic concentrations, and real histology. Dibekacin and gentamicin were similar in overall toxicity. Dibekacin differed from gentamicin and other aminoglycosides (1) in failing to cause early transient stimulation of para-aminohippurate uptake in male rats and (2) in the location of histologic damage at the 120 mg/kg dose. We conclude that: 1) in this model, dibekacin is comparable to gentamicin in nephrotoxic potential, and 2) the lack of early stimulation of para-aminohippurate uptake in male rates after dibekacin treatment may be related to greater initial injury to the late proximal tubule than is caused by gentamicin.

Vaginal bleeding disturbances associated with the discontinuation of long-acting injectable contraceptives. From the World Health Organization Special Programme for Research, Development, and Research Training in Human Reproduction; Task Force on Long-acting Systemic Agents for the Regulation of Fertility

A randomized comparative trial of 832 women receiving norethisterone oenanthate (NET-OEN) and 846 women receiving depot medroxyprogesterone acetate (DMPA) injections at 12 week intervals was conducted in 10 centers. The pregnancy rate with NET-OEN was significantly higher than with DMPA. The termination rate for amenorrhoea was substantially lowe with NET-OEN than DMPA, whereas the discontinuation rates for bleeding problems were similar with the two drugs. Analysis of bleeding patterns among continuing and discontinuing users suggests that women tolerated frequent bleeding episodes, but found prolonged bleeding or prolonged bleeding-free intervals unacceptable. Bleeding for more than 30 days during an injection interval and complete amenorrhoea for a whole injection interval were jointly associated with 43.7% of all terminations among NET-OEN users and 64.5% of all terminations among DMPA users. In future efforts to improve the acceptability of long-acting injectable contraceptives, more attention should be given to the control of prolonged amenorrhoea and prolonged bleeding.

Comparative nephrotoxicities of high-dose netilmicin and tobramycin in rats

The nephrotoxic potentials of netilmicin and tobramycin given in doses of 180 mg/kg per day for up to 14 days were compared in Fischer rats. At this dosage, tobramycin produced mortality and significant changes in renal structure and function; netilmicin evoked minimal nephrotoxicity.

Drug therapy in renal failure: dosing guidelines for adults. Part II: sedatives, hypnotics, and tranquilizers; cardiovascular, antihypertensive, and diuretic agents; miscellaneous agents

Data providing guidelines for drug use in adult patients with renal insufficiency are presented in tabular form with supporting references. The data are derived from the current medical literature. If specific information about a drug is unavailable or conflicting, emphasis is given to normal pharmacokinetic variables in arriving at recommendations for therapy. Nephrotoxicity or adverse effects in patients with renal disease are noted and adjustments for dialysis suggested.

Drug therapy in renal failure: dosing guidelines for adults. Part I: Antimicrobial agents, analgesics

Data are presented in tabular form that provide guidelines for drug use in adult patients with renal insufficiency. The data are derived from the current medical literature. If specific information about a drug is unavailable or conflicting, emphasis is given to normal pharmacokinetic variables in arriving at recommendations for therapy. Nephrotoxicity or adverse effects in patients with renal disease are noted and adjustments for dialysis suggested.

The use of quinesterol for the control of vaginal bleeding irregularities caused by DMPA

A comparative clinical trial examined the effect of oral administration of a long-acting estrogen (quinesterol) on the vaginal bleeding pattern of 214 Thai women receiving 3 monthly injections of the contraceptive depot-medoxyprogesterone acetate. Although the proportion of subjects with amenorrhea was lower in the group receiving quinesterol, there was no substantial increase in the proportion of women with normal bleeding patterns.

Effect of sodium bicarbonate and ammonium chloride ingestion in experimental gentamicin nephrotoxicity in rats

To examine the possibility that gentamicin binding to renal tubular epithelium is electrostatic, the effect of sodium bicarbonate-induced alkaline diuresis and ammonium chloride administration on the course of gentamicin nephrotoxicity in male Fischer 344 rats was examined. After 14 days of gentamicin, sodium bicarbonate drinking animals did not differ significantly from tap water drinking controls in the degree of nephrotoxicity as determined by serum creatinine, in vitro para-aminohippurate and N-methylnicotinamide uptake, histology and renal cortical gentamicin concentrations. However, 7/10 sodium bicarbonate drinking animals had extensive intratubular renal calcifications as compared to 0/29 tap water drinkers. Ammonium chloride drinking animals had more severe toxicity than tap water drinking controls. We conclude that in our model, sodium bicarbonate administration does not reduce experimental gentamicin toxicity and is associated with intratubular calcification. Ammonium chloride potentiates gentamicin nephrotoxicity.

Percutaneous aspiration biopsy of renal allografts using ultrasound localization

Percutaneous aspiration of renal allografts was done employing ultrasound localization and the Jamshidi renal biopsy needle-syringe. Adequate tissue for pathologic assessment was obtained in 19 of 20 biopsy attempts. There were no complications. Ultrasound provides a convenient, nonradiologic means of renal localization for allograft biopsy. The aspiration needle-syringe is well suited for percutaneous transplant biopsy.

The influence of dosage regimen on experimental gentamicin nephrotoxicity: dissociation of peak serum levels from renal failure

Peak serum levels of gentamicin were varied in rats by administering a standard nephrotoxic dosage of 40 mg/kg per day in one (QD), two, or three (TID) daily doses. The QD animals had the highest peak serum levels but showed no appreciable increase of serum creatinine concentrations over a 10-day treatment period. The TID rats had the lowest peak serum levels, but, after 10 days of drug administration, the serum creatinine concentration (2.8 +/- 0.2 mg/100 ml, mean +/- SE) was significantly higher than in control rats (0.6 +/- 0.01 mg/100 ml) (P less than 0.001). After two days of gentamicin treatment, the renal concentration of gentamicin was 269 +/- 77 micrograms/g in the QD rats and 820 +/- 29 micrograms/g in the TID rats (P less than 0.001). In this rat model, the frequency of doses was a more important factor in the development of nephrotoxicity than the peak serum concentration of gentamicin. The results suggest that dose frequency should be considered when data from different laboratories are compared.

RMI 15,731 (1-[5-tetradecyloxy-2-furanyl]-ethanone), a new antirhinovirus compound

RMI 15,731 (1-[5-tetradecyloxy-2-furanyl]-ethanone) is a new antiviral compound with activity specific for rhinoviruses. Virus synthesis in R-HeLa cells was susceptible to low concentrations (0.25 micrograms/ml) of the compound. RMI 15,731 was effective if added for 1 h before infection and removed or if added as late as 6 h postinfection. Low concentrations of the compound directly inactivated infectious rhinovirus in a time- and temperature-dependent fashion. RMI 15,731 appears to be a promising new antirhinovirus compound for clinical evaluation since it (i) blocks intracellular virus synthesis (without cellular toxicity), and (ii) directly inactivates virions. The last property may be important in limiting virus shedding from an infected host.

5-(Tetradecyloxy)-2-furancarboxylic acid and related hypolipidemic fatty acid-like alkyloxyarylcarboxylic acids

5-(Tetradecyloxy)-2-furancarboxylic acid (91, RMI 14514) was found to lower blood lipids and to inhibit fatty acid synthesis with minimal effects on liver weight and liver fat content. This fatty acid-like compound represents a new class of hypolipidemic agent; it is effective in rats and monkeys. The compound resulted from discovery of hypolipidemic activity in certain beta-keto esters, postulation and confirmation of the corresponding benzoic acids as active metabolites, and systematic exploration of the structure--activity relationships.

Insulin secretion in the fetal and neonatal sheep

The effect on plasma insulin of elevating plasma glucose levels was studied in exteriorized sheep fetuses of 68 to 142 days conceptual age and in 2 lambs, 1 and 7 days old. Fetuses of less than 110 days showed, at most, only a very small and delayed rise in plasma insulin following an injection of glucose (1.67–3.45 g/kg body weight) into the umbilical vein. In 5 out of 6 fetuses of 110 days and older intravenous glucose (0.54–1.38 g/kg) was followed by a marked but delayed rise in plasma insulin reaching a peak 25–100 min after glucose administration. In the lambs intravenous glucose (1 g/kg) gave an immediate response in plasma insulin. Intraduodenal glucose was also seen to give a marked rise in plasma insulin in a 123 day fetus and 2 lambs. Intravenous fructose (0.65 and 0.55 g/kg) to two older fetuses caused no rise in plasma insulin although glucose given subsequently evoked a marked response. The onset of appearance of a marked response to glucose in the fetus was preceded by a proliferation of secondary islets in the pancreas. The changes in plasma insulin in the exteriorized fetuses and in 2 isolated fetuses suggest that the placenta must be relatively impermeable to insulin, fetal insulin must largely be derived from the fetal pancreas and fetal tissues must take up insulin.

The effect of a sulphated mucopolysaccharide (RO1-8307) on adrenal and kidney morphology and function in the rat

RO1–8307, a heparinoid with low anticoagulant activity, was injected into male rats on a controlled diet. The width of the zona glomerulosa decreased, in relation to dosage and duration of treatment. Other endocrine organs were histologically unchanged, but there was involution of the thymus in rats given large doses. Vacuolation occurred in the proximal convoluted renal tubule, without derangement of tubule function. Coincident with the histologically altered zona glomerulosa was a marked reduction in aldosterone levels in the adrenal venous plasma, without significant change in deoxycorticosterone or corticosterone levels. Plasma sodium and potassium values were unchanged. The juxtaglomerular index increased in most animals, but extractable renin, measured by direct bioassay, increased significantly only with maximal dosage of RO1-8307. The findings confirm the hypothesis that heparin and heparinoids with diuretic properties act selectively on the zona glomerulosa to reduce aldosterone secretion, but the exact mechanism remains unknown.

A quantitative study of skeletal-muscle purines and pyrazolo(3,4-d)pyrimidines in gout patients treated with allopurinol

1. Hypoxanthine, xanthine, uric acid, allopurinol and oxipurinol have been determined in skeletal-muscle biopsies by quantitative high-resolution mass spectrometry.

2. The results obtained in six untreated gout patients and in seven gout patients who had been treated with the xanthine oxidase inhibitor allopurinol for periods of about 2 years, have been compared with those obtained on muscle tissue from non-gouty subjects and with the results of previous microscopical studies of the same biopsies.

3. Measurable amounts of xanthine were detected more frequently in the allopurinol-treated gout patients than in the untreated patients. The concentration of uric acid was generally lower in the allopurinol-treated than in the untreated gout patients' muscle; and all except one of the allopurinol-treated subjects' tissue contained a measurable amount of oxipurinol. Allopurinol was detected less frequently than oxipurinol.

4. The concentrations of hypoxanthine and xanthine in the allopurinol-treated patients' muscle tissue are very much less than those which have been reported in congenital xanthine oxidase deficiency.

5. It is concluded that allopurinol can still be recommended as a useful drug in the treatment of gout but that longer studies during the clinical use of the drug would be of value.

Steroid secretion by the adrenal gland of foetal and neonatal sheep

From the left adrenal of ten sheep foetuses and four lambs aged from 110 days after conception to 14 days after birth, adrenal venous blood was collected and assayed for cortisol, corticosterone and aldosterone. These steroids were secreted at all ages but the rate of secretion was greatly increased toward term and after birth. The increase coincided with morphological changes in the adrenal gland. At no stage was the rate significantly increased by corticotrophin, and in two young foetuses it was not decreased by dexamethasone. In two foetuses and one lamb, angiotensin II did not increase the rate of secretion of any of the three steroids significantly, and the blood pressure was raised only in the lamb. It is probable that the secretion of the steroids was maximal under the conditions of the experiments.