Biomedical subjects

D W Good

Publications and source records attributed to D W Good.

60 records · Page 4Linked to original sources

PubMed1984

Ammonia production by individual segments of the rat nephron.

Ammonia production was measured directly in 10 segments of the rat nephron to determine the relative importance of the segments as sites of renal ammonia production. Tubules were microdissected from normal rats and rats drinking 0.28 M NH4Cl or 0.28 M NaHCO3 for 3-8 d. The segments were incubated in vitro with and without 2 mM glutamine. Ammonia concentrations in the incubation fluid were measured by microfluorometry to determine ammonia production rates. All segments produced ammonia from glutamine. In normal rats, production with glutamine was highest (greater than 5 pmol/min per mm) in the proximal convoluted (S-1), proximal straight (S-3), and distal convoluted tubules, and lowest (less than or equal to 2) in cortical and medullary collecting ducts and thin descending limbs. Metabolic acidosis increased production by 60% in the S-1 segment of the proximal convoluted tubule and by 150% in the S-2 segment of the proximal straight tubule without significant effect in any other segment. Bicarbonate loading decreased production by S-1 but had no effect on S-2 or S-3. Thus, acid-base changes altered production only in specific segments of the proximal tubule. We infer that the bulk of ammonia production occurs in the proximal tubules and that production by collecting ducts can account for only a few percent of renal ammonia production and excretion in the rat.

Ammonia↗

PubMed1983

Picomole quantitation of ammonia by flow-through fluorometry.

A new fiber optic fluorometer has been used to measure picomole amounts of ammonia. The method is based on the enzymatic conversion of alpha-ketoglutaric acid and ammonium ion to glutamate with associated oxidation of NADH. The decrease in NADH fluorescence is used to quantify sample ammonia content. The method is rapid and reproducible and is capable of resolving differences as small as 0.3 pmol between samples containing 0-7 pmol.

Ammonia↗

PubMed1982

Luminal influences on potassium secretion: chloride replacement with sulfate.

Electrolyte transport by the renal distal tubule of rats was studied by in vivo continuous microperfusion to determine whether replacing luminal chloride with sulfate would stimulate net potassium secretion. Results in a first series of experiments showed that replacing all Cl in the perfusion fluid with SO4 reduced net Na absorption, reversed the direction of net Cl transport from net absorption to net secretion, increased the lumen-negative transepithelial voltage, and increased net K secretion. In a second series of experiments adding NaCl to a perfusion fluid containing SO4 increased net Na absorption, reversed the direction of net Cl transport from net secretion to net absorption, decreased the transepithelial voltage, and decreased net K secretion. In a third series of experiments addition of 10(-6) M amiloride to a SO4-containing perfusion fluid reduced the transepithelial voltage but did not prevent the increase in K secretion, indicating that the changes in K secretion cannot be explained solely by changes in electrical driving forces. Since net fluid absorption was controlled, the changes in K secretion cannot be attributed to solvent drag effects. In all three series of experiments the rate of net K secretion was increased when luminal Cl concentration was reduced to less than 10 mM. The results suggest the existence of a cotransport system mediating K and Cl absorption by the distal tubule. Inhibition of K absorption by low lumen Cl may contribute to the increased net K secretion seen when nonchloride anions are present in distal fluid.

Animals↗

PubMed1980

Luminal influences on potassium secretion: transepithelial voltage.

In vivo microperfusion techniques were used to evaluate whether changes in luminal fluid flow rate affect late distal tubule transepithelial voltage (VTE) and to determine whether flow-dependent changes in K secretion by the renal distal tubule of the rat that we observed previously could be attributed to changes in electrical driving forces. Results showed that increasing the perfusion rate from 6 to 26 nl/min of solutions containing either 94, 46, or 15 mM sodium and 2 mM potassium caused VTE to become 10-12 mV less lumen negative. Since increasing perfusion rate decreases VTE, a flow-dependent voltage change is not responsible for the effect of increasing luminal flow rate to increase distal K secretion. To evaluate the possible contribution of changes in luminal Na and K concentrations to the flow-dependent changes in VTE, the effects of changing either Na or K concentration at constant flow rate were examined. These studies showed that 1) changes in luminal Na concentration within the physiological range (44-94 mM) have no detectable effect on VTE; 2) increases in luminal K concentration within the physiological range (5-16 mM) significantly increase VTE; and 3) the flow-dependent depolarization of VTE is primarily caused by flow-dependent changes in luminal K concentration.

Animals↗

PubMed1979

Luminal influences on potassium secretion: sodium concentration and fluid flow rate.

Two methods of in vivo continuous microperfusion were used to evaluate separately luminal sodium concentration and fluid flow rate as factors regulating potassium secretion by the renal distal tubule of the rat. Emphasis was placed on evaluating changes in sodium concentration (43-97 mM) and flow rate (4-27 nl/min) within the physiological range. Absolute rates of Na, K, Cl, and H2O transport were measured. Results showed that increasing early distal flow rate without increasing early distal Na concentration significantly increased the absolute rate of potassium secretion by the distal tubule. In contrast, increasing early distal Na concentration, distal Na delivery, and distal Na absorption did not affect potassium secretion if flow rate was not changed. Further studies showed that reducing early distal Na concentration below the physiological range (to 15 mM) caused the direction of net sodium transport to be reversed but did not significantly reduce potassium secretion. Increasing early distal K concentration (to 34 mM) caused the direction of net potassium transport to be reversed. The rate of potassium secretion appears to depend in part on the luminal potassium concentration. Increases in luminal flow rate may increase the rate of potassium secretion by lowering the luminal K concentration.

Animals↗

PubMed1976

Group home program.

The success in this program was defined in terms of staying out of the hospital or in not regressing to a more intensive level of care requirement. By these criteria, we have been successful. Nine chronic patients have lived in the group home. Of these nine, two have become totally independent, five live in the group home, one went to a family care home, and one to a nursing home due to physical disease. Not one of the group is in a psychiatric institution, and only one had a setback. Presently, plans to expand this program with the assistance of a community group are being formulated.

Chronic Disease↗