Mechanism of palmityl coenzyme A inhibition of liver glycogen synthase

Palmityl-CoA inhibits free liver glycogen synthase; the concentration required for half-maximum inhibition is 3 to 4 micrometer. Almost complete inhibition was observed at 50 micrometer. Palmityl-CoA inhibition is associated with dissociation of the tetrameric enzyme into monomers, and binding of palmityl-CoA to the monomers. Glycogen-bound enzyme is also inhibited by palmityl-CoA, resulting in dissociation of the enzyme into monomers and concomitant release of the enzyme from the primer glycogen. Palmityl-CoA inhibition of the enzyme is partially reversed by the glycogen synthase activator, glucose-6-P, whereas sodium lauryl sulfate-inhibited enzyme is not reactivated by glucose-6-P. Sodium lauryl sulfate inhibition results in the dissociation of the tetramer into the monomers. Bovine serum albumin and cyclodextrin can prevent palmityl-CoA inhibition only when they are added prior to palmityl-CoA addition. The possible physiological role of palmityl-CoA in glucose homeostasis is discussed.

Surface tension lowering and dissolution rate of hydrocortisone from solid solutions of selected n-acyl esters of cholesterol

The dissolution of hydrocortisone into simulated intestinal fluid from lipid delivery systems followed second-order kinetics. As the ratio of hydrocortisone to lipid was increased from 1:1 to 1:6, the dissolution rate decreased. Solvent deposition of solid solutions of hydrocortisone and lipid on lactose resulted in the enhancement of the dissolution rate. For the 1:1 hydrocortisone-lipid solid solutions, the rank order of the dissolution rate was hydrocortisone-cholesteryl stearate, hydrocortisone, hydrocortisone-cholesterol, hydrocortisone-cholesteryl acetate, hydrocortisone-cholesteryl palmitate, hydrocortisone-cholesteryl n-butyrate, hydrocortisone-cholesteryl laurate, and hydrocortisone-cholesteryl n-decylate. A direct correlation was found between the dissolution rate of hydrocortisone and the surface tension lowering of simulated intestinal fluid by the corticoid and various lipids.

Quantitative structure-activity relationships for 5-substituted 8-hydroxyquinolines as inhibitors of dental plaque

Fourteen 8-hydroxyquinolines were tested for antiplaque activity by measuring their minimum inhibitory concentrations [MIC (M)] against Streptococcus mutans No. 6715. Linear regression analysis was conducted with the MIC (M) values and hydrophobic (log P), electronic (beta, pKaOH, pKaN), and steric [molar refractivity (MR), molecular weight (mol wt)] parameters. The best correlation (r2 = 0.90) was obtained with MR, log P, and beta. The smaller the steric contribution of the 5-substituent, the more active the compound. The parent 8-hydroxyquinoline was the most active. The negative contribution toward activity by 5-substituents larger than hydrogen can be overcome by the positive contributions of groups that are lipophilic and electron withdrawing; for example, the 5-chloro derivative is as active as the parent 8-hydroxyquinolines.

Pharmacokinetics of gentamicin during peritoneal dialysis in children

The pharmacokinetics of gentamicin were examined on two occasions using intravenous and intraperitoneal routes in five children undergoing intermittent peritoneal dialysis for chronic renal failure. Serum, urine and dialysis fluid (DF) were assayed microbiologically for gentamicin and the data were subjected to computer analysis using equations evolved for a two-compartment model which considered the bi-directional flux of the drug. Following i.v. injection of 1 mg/kg of gentamicin, the apparent volume of distribution averaged 23% (range, 13 to 36%) of body wt (similar to normal), the mean half-life was 21 hr (range 9 to 37 hr; normal, 2 hr) and the peritoneal clearance averaged 4.0 ml/min/m2 (range, 1.2 to 7.0 ml/min/m2). During peritoneal administration of gentamicin (15 mg/liter of DF, 0.7 liters/m2 administered in each cycle over 9 to 12 cycles), serum concentrations increased towards extrapolated steady-state levels which averaged 42% (range, 25 to 68%) of DF concentrations. The mean renal clearance of gentamicin was only 1.6 ml/min/m2 while total body clearance ranged from 2.3 to 8.0 ml/min/m2 mostly occurring by a variable degree of dialysance. Peritoneal clearances and half-lives of gentamicin were similar in each patient following either treatment mode. The appreciable variability in gentamicin pharmacokinetics among adolescent patients with renal insufficiency necessitates dosage adjustments based on measurements of serum concentrations.