Biomedical subjects

B K Mallick

Publications and source records attributed to B K Mallick.

10 recordsLinked to original sources

PubMed2000

Postnatal changes of plasma amino acids in suckling pigs.

Amino acids, ammonia, urea, orotate, and nitrate plus nitrite (stable oxidation products of nitric oxide) were determined in plasma of 1- to 21-d-old suckling pigs. Jugular venous blood samples were obtained from pigs at 1, 3, 7, 14, and 21 d of age for analysis of plasma amino acids and metabolites by HPLC and enzymatic methods. Plasma concentrations of arginine and its immediate precursors (citrulline and ornithine) decreased (P < 0.01) progressively (20 to 41%) with increasing age from 3 to 14 d. Plasma concentrations of glutamine declined (P < 0.01) progressively (10 to 31%) during the 1st wk of life. Plasma concentrations of branched-chain amino acids, threonine, and alanine decreased (P < 0.01) (5 to 12%) in 14- and 21-d-old pigs, compared with 1- and 3-d-old pigs. There were no postnatal changes (P > 0.05) in plasma concentrations of other amino acids. Plasma concentrations of ammonia increased (P < 0.01) by 18 and 46%, whereas those of nitrate plus nitrite decreased (P < 0.01) by 16 and 29%, in 7- and 14-d-old pigs, respectively, compared with 1- to 3-d-old pigs. Because arginine plays a crucial role in ammonia detoxification via the hepatic urea cycle and is the physiological substrate for nitric oxide synthesis, our results of the decreased plasma concentrations of arginine and nitrate plus nitrite, as well as the increased plasma ammonia concentration, indicate a hitherto unrecognized deficiency of arginine in 7- to 21-d-old suckling pigs. Arginine is an essential amino acid for piglets and has a great potential to enhance neonatal growth; therefore, further studies are necessary to elucidate the mechanism responsible for arginine deficiency in sow-reared piglets and to identify hormonal and metabolic means for improving neonatal arginine nutrition and growth.

Amino Acids↗

PubMed1999

A Bayesian semiparametric accelerated failure time model.

A Bayesian semiparametric approach is described for an accelerated failure time model. The error distribution is assigned a Pólya tree prior and the regression parameters a noninformative hierarchical prior. Two cases are considered: the first assumes error terms are exchangeable; the second assumes that error terms are partially exchangeable. A Markov chain Monte Carlo algorithm is described to obtain a predictive distribution for a future observation given both uncensored and censored data.

Algorithms↗

PubMed1999

Bayesian survival analysis using a MARS model.

A Bayesian multivariate adaptive regression spline fitting approach is used to model univariate and multivariate survival data with censoring. The possible models contain the proportional hazards model as a subclass and automatically detect departures from this. A reversible jump Markov chain Monte Carlo algorithm is described to obtain the estimate of the hazard function as well as the survival curve.

Algorithms↗

PubMed1995

Bayesian analysis of proportional hazards models built from monotone functions.

We consider the usual proportional hazards model in the case where the baseline hazard, the covariate link, and the covariate coefficients are all unknown. Both the baseline hazard and the covariate link are monotone functions and thus are characterized using a dense class of such functions which arises, upon transformation, as a mixture of Beta distribution functions. We take a Bayesian approach for fitting such a model. Since interest focuses more upon the likelihood, we consider vague prior specifications including Jeffreys's prior. Computations are carried out using sampling-based methods. Model criticism is also discussed. Finally, a data set studying survival of a sample of lung cancer patients is analyzed.

Algorithms↗

PubMed1992