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S K Podder

Publications and source records attributed to S K Podder.

At least 37 records · Page 2Linked to original sources
PubMed1991

Pharmacokinetic basis for nonadditivity of intraocular pressure lowering in timolol combinations.

The authors determined whether the ocular absorption of topically applied timolol in the pigmented rabbit was affected significantly by coadministration with either pilocarpine or epinephrine in the same drop to explain the nonadditivity in intraocular pressure lowering (IOP) seen clinically. They instilled 25 microliters of 0.65% timolol maleate solution (equivalent to 0.5% timolol), both in the presence and absence of 2.6% pilocarpine nitrate or 1% epinephrine bitartrate, into pigmented rabbit eyes. The time course of timolol concentration in the conjunctiva, anterior sclera, corneal epithelium, corneal stroma, aqueous humor, iris-ciliary body, and lens was monitored for 360 min by using reversed-phase high-performance liquid chromatography. The area under the timolol concentration-time curve in all but one of the anterior segment tissues was reduced by 20-50% (mean, 40%) when timolol was coadministered with pilocarpine and by 20-70% (mean, 42%) when timolol was coadministered with epinephrine. Such an effect was not a result of alterations in corneal permeability or aqueous humor turnover rate, nor was it related to the extent of systemic absorption caused by pilocarpine and epinephrine. Rather, the reduction in ocular timolol absorption may have been caused by the accelerated washout of timolol by tears stimulated by the coadministered drugs and, to a lesser extent, by the loss of timolol through binding to the increased amount of tear proteins induced by the coadministered drugs. Thus, the nonadditivity in IOP lowering from timolol-pilocarpine and timolol-epinephrine combinations is probably caused by changes in precorneal timolol clearance.

Absorption↗
PubMed1990

Complex carbohydrate-lectin interaction at the interface: a model for cellular adhesion. I. Effect of vesicle size on the kinetics of aggregation between a fatty acid conjugate of lectin and a liposomal asialoganglioside.

Two types of phospholipid vesicles capable of mutual recognition have been tailor-made to serve as a model system for the study of carbohydrate-mediated cellular adhesion. One of the vesicles contained a fatty acid conjugate of a galactose specific lectin (lectin vesicle) and the other an asialoganglioside with a reactive terminal galactose residue (galactose vesicle). The kinetics of aggregation of these two types of vesicles was followed by monitoring time-dependent change in turbidity. A 10-100-fold enhancement in the forward rate constant (kf ranging from 7.1 x 10(5) to 4.5 x 10(7) M-1.s-1 at 27 degrees C) was observed when compared with that for the lectin-galactose system in solution (kf being 4.5 x 10(5) M-1.s-1), reported in the literature. A study of the influence of vesicle size on the rate of aggregation showed that enhancement depended on the curvature of the galactose vesicle rather than the density of asialoganglioside suggesting a possible diffusion in the plane of the membrane. The ratio, kf/kd is found to be approx. 10(10) M-1 indicating that the formation of multiple bonds plays a role for stable adhesion.

Cell Adhesion↗
PubMed1989

Disposition of phenacetin in rabbits pretreated orally and intraperitoneally with 3,4-benzpyrene.

Disposition of phenacetin (PHT) administered intravenously was investigated in rabbits pretreated orally and intraperitoneally with 3,4-benzpyrene. 3,4-Benzpyrene pretreatment intraperitoneally 24 and 48 h before the disposition experiments resulted in enhanced PHT metabolism as was shown from the decreased levels of PHT and the increased levels of acetaminophen sulfate (NAPAS) in the blood after intravenous administration of PHT. Following the oral pretreatment with 3,4-benzpyrene 24 h before the disposition experiments, no effect was found on the metabolism of PHT compared to the control. 3,4-Benzpyrene pretreatment orally 48 h before the disposition experiments resulted in enhanced PHT metabolism as was shown from the decreased levels of PHT and the increased levels of acetaminophen glucuronide and NAPAS in the blood. From these results, the response to oral and intraperitoneal pretreatment with 3,4-benzpyrene appears to be profoundly different. A technique for selective enzyme induction in the intestine by the route of administration of inducer is discussed.

Acetaminophen↗
PubMed1988

Comparison of salicylamide and acetaminophen and their prodrug disposition in dogs.

Comparative studies on the disposition of two pairs of drugs and their prodrugs, i.e., (1) salicylamide (SAM) and ethenzamide (ETB), (2) acetaminophen (NAPA) and phenacetin (PHT), were performed in dogs following intravenous and oral administration of the drugs. ETB and PHT were largely metabolized to SAM and NAPA, respectively, and SAM and NAPA thus formed or those directly administered were conjugated with sulfuric acid and glucuronic acid. It was found that the prodrugs, ETB and PHT, were more susceptible to first-pass metabolism than the corresponding parent drugs, SAM and NAPA, respectively at 30 mg/kg dose of each drug. Free NAPA levels in the blood of dogs receiving PHT were found to be considerably high, whereas free SAM levels in the blood of dogs receiving ETB were very low. These are consistent with results in humans which have been reported earlier, suggesting the similarity between dogs and humans. The ratio of sulfate to the sum of sulfate and glucuronide (S-ratio) as the area under blood concentration-time curve and urine were examined. The prodrugs (ETB and PHT) showed higher S-ratios than the corresponding parent drugs (SAM and NAPA). The S-ratios were greater than 0.6 in ETB and SAM and less than 0.5 in PHT and NAPA, indicating that sulfate formation was predominant in the former pair while glucuronide formation was predominant in the latter pair. No intestinal metabolism was found in the prodrugs. In the parent drugs, however, conjugation with sulfuric acid and glucuronic acid was observed.(ABSTRACT TRUNCATED AT 250 WORDS)

Acetaminophen↗
PubMed1986

Conjugation of salicylamide in the intestinal wall of dogs and rabbits.

The intestinal conjugation of salicylamide (SAM) the formation of SAM sulfate (SAMS) and SAM glucuronide (SAMG) were investigated in dogs and rabbits by using in situ intestinal sac preparation with mesenteric vein cannulation. SAM, SAMS and SAMG in the mesenteric venous blood, sampled at successive intervals after injection of SAM solutions into the sac, were determined. Total recoveries in 1 h were not significantly different in dogs (71%) and rabbits (64%). Both animals, however, showed a quantitative difference in intestinal conjugation. Sulfation predominated over glucuronidation in dog intestine while the formation of the glucuronide was exclusively high in rabbit intestine. Furthermore, the dose-dependent conjugation of SAM was investigated in dog intestine at four doses, 2, 3, 6 and 10 mg/one animal. Upon increasing the doses from 2 to 10 mg, the amounts of SAMS appearing in the blood remained unchanged, those of SAMG increased about two times and those of free SAM increased about six times, while the total recoveries increased parallel to the doses, suggesting saturation kinetics in the formation step of the two conjugates. Simultaneous computer-fitting of the experimental data for 2 and 10 mg doses to a simplified model, containing Michaelis-Menten kinetics in the formation of the conjugates, was examined and good agreement between the observed data and the theoretical values was obtained.

Animals↗
PubMed1984

Specificity of protein-nucleic acid interaction and the biochemical evolution.

The water soluble carbodiimide mediated condensation of dipeptides of the general form Gly-X was carried out in the presence of mono- and poly-nucleotides. The observed yield of the tetrapeptide was found to be higher for peptide-nucleotide system of higher interaction specificity following mainly the anticodon-amino acid relationship (Basu, H.S. & Podder, S.K., 1981, Ind. J. Biochem. Biophys., 19, 251-253). The yield of the condensation product of L-peptide was more because of its higher interaction specificity. The extent of the racemization during the condensation of Gly-L-Phe, Gly-L-Tyr and Gly-D-Phe was found to be dependent on the specificity of the interaction--the higher the specificity, the lesser the racemization. The product formed was shown to have a catalytic effect on the condensation reaction. These data thus provide a mechanism showing how the specific interaction between amino acids/dipeptides and nucleic acids could lead to the formation of the 'primitive' translation machinery.

Biological Evolution↗
PubMed1982

Reactivity of glycoconjugates in membranes. I. Determination of transbilayer distribution of gangliosides in lipid vesicles by chemical methods.

Two simple chemical methods are described for the determination of the transbilayer distribution of gangliosides GD1a and GM1 in phosphatidylcholine vesicles. The data presented here show an increase in the percentage of GD1a exposed on the outer surface of vesicles with increasing mole fraction of GD1a. The percentage of GD1a exposed on 1:50 and 1:5 GD1a-dipalmitoylphosphatidylcholine vesicles were found to be 67% and 83%, respectively. The same trend is seen for vesicles with dimyristoylphosphatidylcholine and distearoylphosphatidylcholine. Extrapolation of the data to infinite dilution gives 65% of GD1a exposed on the surface of GD1a-dipalmitoylphosphatidylcholine vesicles. The results indicate that composition-dependent changes in transbilayer distribution of GD1a can only partly account for the observed increase in the reactivity of GD1a in vesicles towards neuraminidase from clostridium perfringens as the ratio of GD1a to phosphatidylcholine increases.

Chemical Phenomena↗