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Biomedical subjects

G Kirk

Publications and source records attributed to G Kirk.

28 records · Page 2Linked to original sources
PubMed1984

Effects of saline infusion on titratable acid generation and ammonia secretion.

Short-term hyperchloremic metabolic acidosis can decrease sodium reabsorption by the superficial proximal tubule (PT), increase tubular fluid flow rate, and stimulate aldosterone release. We studied the effects of increased tubular fluid delivery (graded saline infusion) and mineralocorticosteroid administration on tubular fluid pH (TFpH), titratable acid (TA) generation, and ammonium (NH+4) secretion by superficial proximal and distal tubules (DT) of acidotic, phosphate-loaded rats. The TFpH was 6.4 +/- 0.1 at the late proximal tubule (LP); it was unaltered at the early (ED) or late distal tubule (LD), but urine pH (UpH) was 1 unit lower. The major fraction of TA or NH+4 was formed in the superficial PT. There was no net TA generation by the superficial DT even during supplemental mineralocorticosteroid and increased Pi delivery during saline infusion. TA excretion was increased only slightly by saline infusion in acidotic rats despite increased buffer delivery (caused by decreased Pi reabsorption, primarily in the loop segment) because this was offset by a rise in UpH. Ammonia was secreted into tubular fluid in the superficial PT and DT; there was loss of NH+4 in the loop segment and addition after the LD. Saline infusion did not modify TFpH in the PT or DT but increased NH+4 secretion by the DT in direct proportion to tubular fluid flow. DOCA administration increased the addition of NH+4 between the LD and the urine. In conclusion 1) the superficial PT is of major importance for acidification, generation of TA, and secretion of NH+4 in short-term metabolic acidosis. 2) The superficial DT does not generate TA even during dramatically high rates of buffer delivery and mineralocorticosteroid administration. 3) Excretion of NH+4 is increased by saline infusion, which leads to flow-dependent NH+4 secretion by the superficial DT. 4) Chronic administration of DOCA stimulates NH+4 secretion predominantly in the terminal or deep nephrons.

Acidosis, Renal Tubular↗
PubMed1982

A method for rapid, continuous monitoring of solute uptake and binding.

A method has been developed for dynamically monitoring the free concentration of diffusible, tritiated solutes. The technique utilizes particles of a solid scintillator microencapsulated in gel beads that are permeable to diffusible label. Since tritium beta radioactivity has an effective range in water of only a few micrometers, only label that is free to diffuse through the gel can excite the scintillator, while sequestered label is effectively excluded. Thus, the scintillation light output monitors the freely diffusible concentration of label exclusively. A simple, preliminary encapsulation technique is described and tested, and the theory behind the method is discussed with regard to the time resolution attainable for a given label concentration and type of encapsulation. The feasibility of the method is demonstrated by measuring the uptake of [3H]tetraphenylphosphonium by Escherichia coli membrane vesicles in response to the generation of a membrane potential (interior negative).

Glucose↗
PubMed1981

A precision pump for simulated cardiographic studies.

A system simulating physiologic and pathologic changes in left-ventricular volume is presented. Its purpose is to provide a model to establish the accuracy of current equipment for assessing a heart's performance where the actual volume and size are measurable. The versatility of the model allows a wide range of variability of various parameters for simulation of many clinical situations.

Cardiac Output↗
PubMed1976

A novel mechanism for group translocation: substrate-product reutilization by gamma-glutamyl transpeptidase in peptide and amino acid transport.

Gamma-glutamyl transpeptidase (gamma-GTP) is suggested to act as a carrier in the group translocation of oligopeptides and possibly some amino acids across cellular membranes. It is proposed that the process may involve the repetitive transfer of gamma-glutamyl groups to acceptor peptides which are being translocated from the exterior of the cell to its interior. After group translocation of the peptides has occurred with concomitant formation of gamma-glutamyl peptide products, it is suggested that the products might then be utilized as substrate for the enzyme in order to permit the translocation of other peptides from the exterior. The system is economical and requires only that it be primed with an appropriate source of gamma-glutamyl peptides, such as glutathione. In contrast to most group translocation systems previously described, substrate-product reutilization by gamma-GTP would not be expected to accumulate peptides against a concentration gradient. Mechanisms for maintaining low intracellular concentrations of the translocated peptides are described. Studies on acceptor substrate specificity of gamma-GTP from bovine choroid plexus and rat kidney show some glycyl peptides are much better substrates than free amino acids in accord with the proposal that gamma-GTP might be primarily involved in peptide translocation. Both kinetic and topological evidence support the suggestion that repetitive transfer of gamma-glutamyl moieties by gamma-GTP could occur during group translocation of peptides and possibly some amino acids.

Amino Acids↗
PubMedDate not supplied

Cerebral arterial fenestration.

Fenestration or duplication of a cerebral vessel is a rare congenital variation which most commonly involves the vertebral artery and is usually of no clinical significance. Fenestrations may have associated aneurysms remote to the anomaly or involving the proximal bifurcation of the fenestration. They may also be associated with other vascular malformations e.g. arteriovenous malformations and venous angiomas. Four fenestrated cerebral vessels and their angiographic appearances are reported in this study.

Adolescent↗