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J R Bronk

Publications and source records attributed to J R Bronk.

50 records · Page 3Linked to original sources
PubMed1973

Changes in the adenine nucleotide content of preparations of the rat small intestine in vitro.

1. The adenine nucleotide content of rat jejunal mucosa has been measured. For fresh tissue the concentrations of the three nucleotides in the total water are approximately: ATP, 1.4 mM; ADP, 1.0 mM; and AMP, 0.5 mM.2. The adenine nucleotide content of mucosal slices prepared from rat jejunum was about 80% of that of fresh tissue, but the slices rapidly lost nucleotides when they were incubated in vitro. After a 4 min incubation the mucosal tissue contained about 1 mumole/g dry wt. of each of the three nucleotides. This represented only 14% of the ATP, 20% of the ADP and 36% of the AMP originally present. Further incubation had little effect on the ATP and ADP content, but some additional AMP was lost.3. Additions of glucose, amino acids, phosphate, pyruvate, butyrate or glucose-6-phosphate did not prevent the loss of nucleotides from the mucosal slices. The addition of ADP (1 mM) did restore the ATP content of slices to a value close to that of fresh tissue within 2 min, but the nucleotide content declined again on further incubation.4. The respiration rate of mucosal slices falls progressively during incubation in vitro. This decline was largely prevented by the addition of ADP.5. Although nucleotide loss occurred most rapidly from mucosal slices, it was also observed with rings of whole intestinal wall and, less rapidly, with everted sacs.6. ATP added to incubations of mucosal slices disappeared at a rate of about 30 mumole/min. g dry wt.7. These results suggest that the adenine nucleotide content of preparations of rat small intestine studied in vitro is likely to be severely reduced. The addition of nucleotides to the incubation medium produces only a temporary increase in the nucleotide content of the tissue.

Adenosine Diphosphate↗
PubMed1968

Studies on the physiological and structural characteristics of rat intestinal mucosa. Mitochondrial structural changes during amino acid absorption.

Sections from mucosal strips and rings of rat jejunum were studied with the light microscope and the electron microscope before and after incubation in a modified Krebs bicarbonate Ringer. Various additions were made to the incubation medium, and their effects on both the structure and the respiratory activity of the mucosal tissue were noted. In those cases in which an amino acid mixture was added, there was a pronounced increase in the rate of respiration. When strips of intestine were used, the presence of the amino acid mixture more than doubled the rate of oxygen consumption. Along with the increased levels of respiration there was a sharp rise in the percentage of mitochondria assuming a condensed ultrastructural conformation. The amino acid mixture did not cause the condensation of jejunal mitochondria if glucose was included in the incubation medium or if 2,4-dinitrophenol was present. The evidence suggests that a high proportion of the jejunal mitochondria assumes a condensed conformation in response to an increased energy demand. Apparently glucose can prevent the amino acid mixture from increasing the energy drain on the oxidative processes in these cells. Although a high rate of respiration was obtained in the presence of dinitrophenol, the studies indicated that mitochondrial condensation was only associated with a high rate of coupled oxidative phosphorylation.

Amino Acids↗
PubMed1966

Thyroid hormone: effects on electron transport.

Thyroidectomy markedly reduces the oxidative capacity of rat liver mitochondria. After the injection of triidothyronine about half of the lost capacity is recovered within 3 hours. This rapid recovery is not associated with any change in the amounts of electron transport components, although the activities of cytochromes b and c are significantly increased by the hormone.

Animals↗
PubMed1966

The influence of thyroid gland on amino acid accumulation and protein synthesis by rat small intestine in vitro.

1. A method is described for measuring the accumulation of amino acids and also the extent to which the absorbed amino acids are incorporated into the tissue protein of rings of rat intestine in vitro.2. With this method rat jejunum was found to accumulate a mixture of amino acids to give a concentration in the tissue water which was 2-3 times that in the medium after 8 min incubation. More than 10% of the absorbed amino acids were found to be incorporated into protein.3. In surgically thyroidectomized animals there was no impairment of the capacity of the intestine to accumulate amino acids nor was there any loss of ability to incorporate these amino acids into protein. Similarly, treatment of the thyroidectomized animals with 3,5,3'-triiodothyronine (T(3)) did not produce any significant change either in the rate of accumulation or in the extent of the incorporation of the amino acids.4. The omission of glucose from the incubation medium was found to cause a large increase in the respiration of mucosal slices in the presence of the amino acid mixture. Thyroidectomy significantly reduced this high respiration rate. Treatment of thyroidectomized animals with T(3) restored the respiration to high value.

Amino Acids↗
PubMed1966

Amino acid accumulation and incorporation in rat intestine in vitro.

1. Rings of rat jejunum incubated in vitro accumulate a mixture of amino acids at a rate of about 3 mumoles/cm. hr. The rate of incorporation of the accumulated amino acid into the tissue protein corresponds to a rate of synthesis of 50% of the protein of the whole wall in five days.2. Replacement of the Na(+) in the NaCl of the incubation medium by choline or by Li(+) did not prevent amino acid accumulation by the tissue. However, replacement of the Na(+) by K(+) prevented the accumulation.3. The accumulation of amino acids by rat jejunum in vitro proceeded at normal rates not only in the presence in the incubation medium of oxygen tensions below 10 Torr but also in the presence of 2,4-dinitrophenol. Reasons are given for supposing that the findings are compatible with the view that the energy upon which depend the processes of amino acid accumulation by the tissue could be derived from the movement of ions across cellular boundaries.4. The amino acid incorporation into the tissue proteins was reduced to one tenth of the control rate in the presence of 2,4-dinitrophenol or by hypoxia so that the processes of incorporation depend upon energy derived from oxidative metabolism. In the presence of oligomycin the tissue respiration was depressed but the amino acid incorporation into the tissue protein was not inhibited. The view that the amino acid incorporation may be able to function with energy intermediates other than ATP is discussed.

Amino Acids↗