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Biomedical subjects

A M Kumar

Publications and source records attributed to A M Kumar.

At least 55 records · Page 3Linked to original sources
PubMed1990

Effect of early exposure to delta-9-tetrahydrocannabinol on the levels of opioid peptides, gonadotropin-releasing hormone and substance P in the adult male rat brain.

The effects of neonatal exposure to delta-9-tetrahydrocannabinol (THC) on the adult animal brain neurochemistry and pain perception were evaluated. Newborn rat pups were culled to a litter size of 8 (males and females) and treated either with THC (2 mg/kg) or oil (control) daily, during days 1-4 after birth. After weaning, the THC-treated males were housed 4 per cage. During the juvenile period (day 50), the THC-treated animals exhibited significantly lower baseline tail-flick values (a measure of pain perception) than the control. However, as adults, the THC-treated animals exhibited significantly higher sensitivity to pain following 5 mg/kg morphine challenge. Furthermore, the THC-treated animals had significantly elevated beta-endorphin and methionine-enkephalin levels in almost all the brain areas sampled for the study. In addition, the neonatally THC-treated rats exhibited significantly higher levels of substance P (SP) and significantly lower levels of gonadotropin releasing hormone (GnRH) in the anterior hypothalamus-preoptic area. The SP and GnRH levels did not differ among the THC-treated and control animals in the medial basal hypothalamus. The results of this study indicate that even a very low dose of THC administered during the neonatal period has a long-lasting effect on the brain neurochemistry. In particular, neonatal administration of THC appears to alter functioning of the endogenous opioid system.

Animals↗
PubMed1990

A spectrophotometric method for detection of 5'-fluorouracil in plasma.

A quantitative method using spectrophotometry was devised for the detection of 5'-Fluorouracil (FUra) in plasma. Plasma samples obtained at different time intervals from drug treated rabbits were deproteinised using phenol. The aqueous phase was lyophilised and dissolved in 0.01 N NaOH and absorption was monitored at 305 nm. Levels of FUra in the plasma were calculated by comparing with a standard graph generated from known concentrations of FUra. As low as 1 microgram of the drug per ml of plasma could be detected by this method.

Animals↗
PubMed1990

Electron and light microscopy of pancreatic islets of Langerhans isolated by Trowell's T8 medium.

The isolation and purification of high yields of islets of Langerhans are important areas of investigation. Although it is well established that warm and cold ischemia affect islet yield and function, little information is available about the damage that occurs during the digestion period. We used Trowell's T8 medium and conventional Hank's balanced salt solution to obtain high yields of islets with morphologically-intact cells. Light and electron microscopy were used to characterize the islets isolated by the two media. Results reveal that the islets isolated by Trowells T8 medium were less fragmented and had better fine-structural integrity than those isolated by the conventional medium.

Animals↗
PubMed1990

A modified HPLC technique for simultaneous measurement of 5-hydroxytryptamine and 5-hydroxyindoleacetic acid in cerebrospinal fluid, platelet and plasma.

A sensitive, reliable and simplified HPLC assay for simultaneous measurement of 5-hydroxytryptamine (5-HT) and 5-hydroxyindoleacetic acid (5-HIAA) in human cerebrospinal fluid (CSF), platelets and plasma is described. Perchloric acid is used for one step precipitation of proteins and extraction of 5-HT and 5-HIAA. Precision of the assay has been increased by calibration of the instrument using serotonin-free plasma spiked with known amount of standards and N-w-methyl-5-hydroxytryptamine as internal standard. Integration of the peaks and calculations are achieved by a preprogrammed data module using ratio method. As little as 20 pg/ml of serotonin in the deproteinated sample can be detected using this procedure. In a group of surgical patients, plasma 5-HT concentration is (Mean +/- S D) 3.4 +/- 2.7 ng/ml and that of platelet 748.3 +/- 448.3 ng/10(9) platelets. In CSF, 5-HT is found to be 3.3 +/- 3.4 ng/ml and 5-HIAA is 15.1 +/- 7.3 ng/ml. A good correlation (r = 0.648, p less than .0001) is observed between 5-HT and 5-HIAA in CSF.

Adult↗
PubMed1988

Rapid isolation of lysyl-tRNA synthetase from rat liver.

The high molecular weight aminoacyl-tRNA synthetase complex (the 24S complex) was isolated from rat liver by ultracentrifugation. The lysyl-tRNA synthetase (E.C. 6.1.1.6) was selectively dissociated by hydrophobic interaction chromatography on 1,6 diaminohexyl agarose followed by hydroxylapatite chromatography and DEAE chromatography. The lysyl-tRNA synthetase dissociated from the 24S synthetase complex was purified approximately to 2700 fold with 14% yield.

Amino Acyl-tRNA Synthetases↗
PubMed1988

Renal reabsorption of phosphate during development: tubular events.

Studies performed in our laboratory on the isolated perfused kidney of the guinea pig have demonstrated that the rate of Pi reabsorption is substantially greater in the newborn than in the adult, when appropriate corrections are being made either for differences in glomerular filtration rate (GFR) or in renal tubular mass. In order to determine the location of this enhanced reabsorption along the nephron, micropuncture experiments were performed on euvolemic, non-fasted guinea pigs 5-14 and 42-49 days of age, maintained on standard guinea-pig chow diet (0.76% Pi). Concomitant measurements of overall kidney function were also obtained. The results confirmed that fractional reabsorption of Pi (TRPi%) across the entire kidney was significantly higher (P less than 0.01) in the newborn (89.93 +/- 2.55%) than in the adult (78.25 +/- 2.89%) animals. The difference was also significant (P less than 0.05) when TRPi was expressed in mol/ml GFR (1.87 +/- 0.14 vs 1.53 +/- 0.12, respectively). At comparable locations along the proximal tubule (TF/Pin of 1.90 +/- 0.16 in the newborn, and 1.79 +/- 0.15 in the adult, P greater than 0.70), the fraction of the filtered load of Pi reabsorbed was significantly higher (P less than 0.001) in the immature (76.66 +/- 2.74%) than in the mature (67.21 +/- 2.74%) guinea pigs. Estimates based on the differences between proximal Pi reabsorption and the urinary excretion of Pi indicate that the reabsorption of Pi in tubular segments located beyond the proximal tubule is also enhanced in the newborn when compared with the adult (15.62 +/- 2.11% vs 10.51 +/- 1.83%, respectively, P less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1988

Intracellular sodium in proximal tubules of diabetic rats. Role of glucose.

Renal hypertrophy is a common consequence of diabetes mellitus that precedes and possibly accounts for the increased glomerular filtration rate. We have postulated that the glucose-mediated increase in the intracellular concentration of sodium [Na]i initiates the chain of events leading to the increase in cell size and eventually cell number. Experiments were conducted on Sprague-Dawley rats made diabetic by the intravenous injection of 45 mg/kg body wt of streptozotocin dissolved in a 5 mM citrate buffer solution. Control animals were injected with the vehicle alone. Ninety-six hours and 11 weeks later, measurements of [Na]i were done by NMR spectroscopy on suspensions of proximal tubules, using dysprosium tripolyphosphate as an extracellular shift reagent. At 96 hours after the induction of the diabetes, there was a 60% increase in [Na]i compared to control (P less than 0.01). No further increase in [Na]i was observed during the subsequent 11 weeks of observation. Addition of ouabain (1.0 mM) resulted in a fourfold increase in [Na]i in tubules from control animals, and a 2.5-fold increase in tubules from 96-hour diabetic rats. Ouabain-inhibitable Na+-K+-ATPase activity was substantially higher in the renal tubules of diabetic rats, the increase being proportional to that of [Na]i. In order to ascertain the effect of hyperglycemia on [Na]i, proximal tubules prepared from kidneys of normal and diabetic rats were exposed to low (5 mM) and high (25 mM) concentration of glucose in the media.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1987

Factors affecting proximal tubular reabsorption during development.

Studies performed in several animal species have demonstrated that glomerulotubular balance is maintained throughout development despite the many changes that occur in the factors known to control it. In an attempt to understand the nature of this phenomenon we quantified the magnitude and described the profile of these changes in guinea pigs. The changes in physical forces were assessed from measurements of hydrostatic and oncotic pressures, whereas those in the permeability characteristics of the proximal tubule epithelium were estimated from permeance to macromolecules of graded radii, histologic measurements of the intercellular channels, and measurements of end-proximal ratio of tubular fluid-to-plasma osmolality (TF/Posm). Between 1 and 50 days of age the net pressure for reabsorption increased from 15.0 to 30.9 mmHg (P less than 0.01, n = 15) with the major change occurring during the first 2-3 wk of postnatal life. The urinary recovery of inulin, sucrose, and creatinine, injected in the early segment of proximal tubules did not vary with age. The urinary recovery of mannitol (MW 180 daltons, Stokes-Einstein radius 4.0 X 10(-10) m) increased from 92% at birth to 100% at 49 days of age (P less than 0.001, n = 24), consistent with a decrease of approximately 0.5 X 10(-10) m in the luminal openings of the paracellular channels. The length of the zonulae occludens and the width of the intercellular channels did not change during this period; however, the length of the channels increased from 5.0 +/- 0.17 to 8.9 +/- 0.48 micron (P less than 0.01, n = 16). These changes should result in an increase in resistance across the intercellular channels. Consistent with this assertion is the observation that the mean TF/Posm of the fluid collected toward the end of the proximal convoluted tubule decreased as a function of age from 1.05 at day 2 to 0.98 at day 80 (P less than 0.001, n = 24). The findings support the hypothesis that during early postnatal life glomerulotubular balance is made possible by a high permeability of the proximal tubule, which compensates for the low net reabsorptive pressure. As the animal matures and the proximal tubule epithelium becomes tighter, for glomerulotubular balance to be maintained, an increase in the number of intercellular channels and in the active transport of sodium need to be postulated.

Aging↗
PubMed1986

NMR measurement of intracellular water volume in rat kidney proximal tubules.

Knowledge of cell water volume is essential for the measurement of concentrations of intracellular ions and metabolites in kidney proximal tubules. We have developed a method which utilizes 35Cl-NMR as a measure of extracellular volume and 2H-NMR, in combination with a membrane-impermeable shift-reagent [Dy-DTPA]2-, as a measure of the ratio of intra- and extracellular water volumes. Measurement of extracellular volume by 35Cl-NMR is possible, since the resonance of intracellular 35Cl is too broad to be detectable in kidney cells. The 2H-NMR measurement exploits the fact that only extracellular water is in direct contact with [Dy-DTPA]2-. However, rapid exchange of water across the cell membrane results in only a single 2H2O resonance at a chemical shift which is a weighted average of the shifted extra- and unshifted intracellular water resonances. Expression of the extracellular volume as a fraction of the total volume by fCl and as a fraction of the total water-volume by fD, permits the calculation of the fractional cell-water content fw = [(1/fD)-1]/[(1/fCl)-1]. This approach was applied to proximal tubular suspensions prepared from the rat kidney. The water content was found to be 76.9 +/- 1.8% (n = 6) at 37 degrees C. Increasing extracellular osmolality from 295 to 390 mOsm/kg H2O, by addition of mannitol, decreased the water content by 21%. Our results are in good agreement with those obtained by the gravimetric method.

Animals↗
PubMed1986

23Na NMR spectroscopy of proximal tubule suspensions.

Intracellular sodium concentrations in proximal tubule suspensions of rat kidney were measured by NMR spectroscopy. A simple method for the preparation of proximal tubule suspension is described. Examination by light microscopy revealed these preparations to contain 93.6 +/- 0.6% (N = 5) proximal tubules, and electron microscopy demonstrated that the tubules were open. When incubated with trypan blue for five min, only 2% of tubules picked-up the dye. The basal oxygen consumption rate was 0.42 +/- 0.01 microliter min-1 mg protein-1 (N = 6). Addition of succinate (5 mM) resulted in a fivefold increase in the rate of oxygen consumption. The 23Na spectra were obtained in proximal tubules incubated for 30 min in the aqueous shift reagent dysprosium tripolyphosphate Dy(PPPi)2(7-). The NMR observable sodium concentration was 34.1 +/- 1.8 mM at room temperature and 16.3 +/- 0.6 mM (P less than 0.001) at 37 degrees C. Addition of ouabain (10(-4) M) at 37 degrees C resulted in an increase in intracellular sodium to 30.9 +/- 2.9 mM (P less than 0.001), while nystatin increased the concentration of sodium to 72.0 +/- 9.1 mM (P less than 0.001), compared to basal concentration. Thus NMR permits the measurement of intracellular concentration of sodium in proximal tubules under basal conditions and to monitor, in the same preparation, the changes that occur under various experimental conditions without interfering with the morphologic integrity of the cells.

Animals↗
PubMed1986

Early exposure to delta 9-tetrahydrocannabinol influences neuroendocrine and reproductive functions in female rats.

Sexual differentiation of the rat brain is affected by certain compounds administered during the neonatal period. We evaluated the effects of exposure to THC during the critical period of sexual differentiation of the female rat brain on postpubertal estrous cycles and brain neurotransmitter levels. Newborn female rats were injected either with vehicle (oil) or with different doses of THC (0.38; 1.9 or 3.8 mg/100 g) subcutaneously during the first 5 days after birth. The rats were examined daily by vaginal lavage smears from 3 to 10 months of life for phases of estrous cyclicity. The animals were then sacrificed and the anterior hypothalamus preoptic area (AHPOA) and medial basal hypothalami (MBH) were collected, processed and the methionine-enkephalin (met-enkephalin), beta-endorphin-like immunoreactivity (beta-end LI), LHRH and substance-P were measured by radioimmunoassays. In addition, serum LH and prolactin levels were measured by radioimmunoassay. Compared with the control rats, the rats perinatally exposed to THC exhibited either constant metestrus diestrus type vaginal smears or irregular estrous cycles. In the THC-treated animals, the met-enkephalin and beta-end LI levels were lower in the AHPOA and higher in the MBH. The LHRH levels of THC-treated rats were significantly lower in the MBH. The substance-P levels were significantly lower in the AHPOA of THC treated animals. In the THC-treated rats, serum LH was low but, the prolactin levels were not significantly different from the control animals.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1983

Evidence for PAH extraction from superficial cortical efferent vessel plasma.

Consistent with its anatomical association with the proximal tubule we have previously shown that superficial cortical efferent vessel blood contains an admixture of early and late proximal tubular reabsorbate. Since tubular secretion of p-aminohippurate (PAH) occurs predominantly in the late proximal tubule, extraction of this compound should occur preferentially from efferent vessel blood. As a result, the midportion of the proximal convoluted tubule supplied by the more downstream peritubular capillaries would receive blood containing a disproportionately reduced concentration of PAH. To study this, proximal and distal tubular fluid and efferent vessel blood samples were collected from rats. The data confirm that preferential secretion of PAH occurs in the pars recta and demonstrate that PAH is extracted from efferent vessel plasma by the pars recta. This in turn preferentially reduces PAH concentration in early postglomerular blood before it reaches the peritubular capillary network. We speculate that PAH and similar substances secreted by the pars recta are short-circuited by rapid extraction from early postglomerular blood, reducing their delivery to the mid-proximal convoluted tubule. Such circumstances must be considered in any analysis of organic compound secretion by the in vivo proximal tubule.

Aminohippuric Acids↗
PubMed1969

Protein quality of the bacterium Hydrogenomonas eutropha.

Hydrogenomonas eutropha cells harvested from semicontinuous autotrophic culture and washed free of substrate contain about 13% of nitrogen on a dry-solids basis. Biological value and digestibility of the bacterial nitrogen were determined in the rat by use of an abbreviated Mitchell-Thomas nitrogen balance technique and casein as the standard protein. Casein nitrogen was 99% digestible, and that of both whole boiled and sonically ruptured bacterial cells was 93%. Biological value of casein and the bacterial preparations was uniformly 77%. Amino acid composition of the bacteria, as in the case of casein, indicates a first limitation of sulfur-containing amino acids. These compositional features suggest that H. eutropha may be potentially valuable as a protein supplement in animal feeds.

Amino Acids↗