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Biomedical subjects

B J Lin

Publications and source records attributed to B J Lin.

13 recordsLinked to original sources
PubMed1979

Glucose oxidation in fresh guinea pig cornea.

The rate of glucose oxidation of fresh corneas of guinea pigs at different ages has been determined. Full-thickness corneal discs, 4 mm in diameter, were incubated in radioactive glucose solution. The quantity of the released CO2 was expressed in terms of the corneal discs, their dry weights, and DNA and protein contents. The rate of glucose metabolized to CO2 per hour was about 300 pmol/microgram DNA for guinea pigs weighing approximately 800 g. Glucose oxidation decreased as the age of the animals increased. Our results compared well with those obtained in other species. We therefore feel that the guinea pig should be a suitable model for research on the metabolism of corneas.

Animals↗
PubMed1979

Does the number of cells in the cornea decrease with age? A biochemical study.

We used biochemical techniques to investigate whether the cornea becomes more acellular with age. Guinea pigs of different body weights (age) were killed. From each cornea, a central full-thickness button (4 mm in diameter) was punched out. The DNA content of the corneal buttons was determined. Using spleen cells, the DNA content per diploid cell of guinea pig was also estimated. It was found that as the body weights of the animals increased, the amount of DNA per corneal disc decreased. This indicated that as the animal grows older the total cellular content of the cornea is reduced.

Aging↗
PubMed1979

Biochemical analysis of the cornea stored in steroid medium.

We wished to measure changes in the tissue mass and the deoxyribonucleic acid and protein content of guinea pig corneas stored for up to 21 days in tissue culture medium with or without 1 microM hydrocortisone. Full-thickness discs 4 mm in diameter were cut from the corneas for measurement of the three variables. Whether the disc came from a steroid-treated cornea or not, and whether it came from a fresh cornea, hydrocortisone did not appear to have any adverse effect on the features studied.

Animals↗
PubMed1978

Electroncytochemical and biochemical demonstration of guanylate cyclase activity in the pancreatic islet.

With a cytochemical method using guanylyl imidodiphosphate as a substrate, the guanylate cyclase activity was localized on the plasma membrane of A, B and D cells of islets of Langerhans isolated from the rat. Adequate control experiments were performed by a double-blind method. Parallel biochemical assay showed that guanylate cyclase activity was not completely lost after fixation with 1% glutaraldehyde and incubation with 4 mM lead nitrate. Furthermore, the depressed activity was still stimulatable with acetylcholine.

Acetylcholine↗
PubMed1977

An apparent inhibition of insulin biosynthesis resulting from inhibition of transport of neutral amino acids by arginine.

At concentrations higher than 10 mM, the cationic amino acid, arginine, inhibited the incorporation of neutral amino acids such as alanine, threonine, valine and leucine into insulin in the presence of glucose. This inhibitory effect probably did not result from the stimulatory effect of argnine on insulin release because, in the absence of glucose, arginine failed to stimulate insulin release but nevertheless inhibited the incorporation of leucine into insulin. This inhibitory effect of arginine was shared by another basic amino acid, histidine, but not by lysine. Arginine inhibited the incorporation of leucine not only into insulin but also into other islet proteins. This inhibition was not accompanied by any disturbance of glucose metabolism in the islet cells. Further studies indicated that the inhibition of incorporation resulted primarily from the interference of uptake of the neutral amino acids by arginine.

Alanine↗
PubMed1977

Differential effect of D-glucose anomers on proinsulin biosynthesis by the pancreatic islets.

Pancreatic islets of Langerhans of the rat were used to study effects of D-glucose anomers on the incorporation of [3H]leucine into proinsulin and other islet proteins. At low (1 mg/ml), but not at high (2 mg/ml) glucose concentration, the alpha-anomer stimulated more proinsulin biosynthesis than the beta-anomer. This observation adds to the growing list of islet functions showing anomeric preference for alpha-D-glucose.

Animals↗
PubMed1976

Effects of iodoacetate and fluoride on islate respiration and insulin biosynthesis.

Fluoride and iodoacetate inhibited the oxidation of glucose by islets of Langerhans isolated from the rat pancreas. Fifty % inhibition occurred with either 17 mM fluoride or 0.5 mM iodoacetate. The rate of insulin biosynthesis was more strongly inhibited by these inhibitors, especially fluoride. Fifty % inhibition occurred with approximately 1.5 mM fluoride. At high concentrations of iodoacetate and fluoride, the inhibitory effect on insulin synthesis was not reversed to a significant degree by the addition of pyruvate in the incubation medium. In addition to inhibiting the glycolysis and depriving islets of energy essential for the biosynthesis of insulin, fluoride probably exerts a direct inhibitory influence on the biosynthetic mechanism. A separate experiment with [6-14C]glucose indicated that 0.2 mM iodoacetate does not inhibit glycolysis completely.

Animals↗
PubMed1976

Interaction of alloxan and anomers of D-glucose on glucose-induced insulin secretion and biosynthesis in vitro.

The direct effects of alloxan on glucose-induced insulin secretion and biosynthesis and the interaction of alloxan and D-glucose anomers were studied in vitro by use of isolated islets from rat pancreas. Islets were pretreated by incubation for five minutes in media containing alloxan (0.2 mg./ml.) alone or alloxan with either the alpha or beta anomer of D-glucose (3 mg./ml.). After washing, batches of five islets were incubated in the medium supplemented with glucose (1.8 mg./ml.) for 60 minutes to observe insulin secretion and for 90 minutes to observe insulin biosynthesis. Prior exposure to alloxan alone produced marked inhibition of subsequent glucose-induced insulin secretion and biosynthesis. A significantly greater protection against these inhibitory effects of alloxan was observed by using the alpha anomer of D-glucose than the beta anomer. The anomeric preference of D-glucose for protecting islet cells from the inhibitory effect of alloxan on glucose-induced insulin secretion and biosynthesis was similar to that for triggering insulin secretion. Possible mechanisms of the inhibitory effect of alloxan and the protective effect of D-glucose anomers in connection with those of other sugars are discussed. It is suggested that a glucoreceptor, stereospecific to the alpha anomer of D-glucose, may exist for both insulin secretion and biosynthesis.

Alloxan↗
PubMed1975

Insulin biosynthesis: the monoaminergic mechanisms and the specificity of "glucoreceptor".

Islets of Langerhans, isolated from the rat, did not synthesize insulin in the presence of L-glucose, fructose, galactose, 3-0-methyl glucose or sorbitol. A small amount of insulin was synthesized in the presence of glucosamine. Addition of caffeine to these compounds did not enhance the biosynthesis of insulin. It is suggested that the specificity of the membrane surface "glucoreceptor", if it exists, may be rather narrow, at least with respect to insulin biosynthesis. Serotonin, dopamine and isoproterenol did not inhibit or enhance insulin biosynthesis induced by glucose. Propranolol also failed to modify insulin synthesis in the absence or presence of isoproterenol. It is concluded that the monoaminergic mechanisms do not affect insulin biosynthesis in spite of their significant regulatory influence on insulin release. Methysergide, at the concentration reported to potentiate insulin release induced by glucose and tolbutamide in rabbit, strongly inhibited insulin biosynthesis.

Amines↗