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B R Edwards

Publications and source records attributed to B R Edwards.

34 records · Page 2Linked to original sources
PubMed1980

Concentration of urine in the absence of ADH with minimal or no decrease in GFR.

It is known that large (more than 50%) reductions in glomerular filtration rate (GFR) can lead to formation of hyperosmotic urine in the absence to depend critically upon reduced delivery of luid to the loops of Henle. In the present study, we tried to determine whether a much lesser decrease in GFR could also result in hyperosmotic urine when ADH is absent. The following mean values (control vs. 3 h of partial aortic constriction) were obtained in 21 conscious diabetes insipidus rats: GRF, 909 +/- 35 (SE) vs. 835 +/- 49 microliter . min-1 . 100 g body wt-1 (8% decrease; P less than 0.02); urinary osmolality (Uosmol), 125 +/- 6 vs. 309 +/- 14 mosmol/kg H2O (P less than 0.001; peak Uosmol 350 +/- 22). Analysis of individual responses revealed that Uosmol increased as much when there was no measurable decrease in GFR as when such decrease occurred. Neither GFR nor filtration fraction bore any systematic relationship to Uosmol or to each other. We conclude that in the absence of ADH Uosmol can increase with minimal or no change in GFR. Changes in filtration fraction--a potential mediator of reduced delivery to the loops--could not explain the increased Uosmol, even in those instances in which GFR remained unchanged.

Animals↗
PubMed1979

Urinary concentrating ability during dehydration in the absence of vasopressin.

Despite the apparent absence of vasopressin (ADH), Brattleboro homozygotes [diabetes insipidus (DI) rats] can concentrate their urine when deprived of drinking water. Since other investigators have shown that reducing glomerular filtration rate (GFR) improves the concentrating ability of water-loaded dogs, the present studies were undertaken to quantify the magnitude and time course of changes in GFR during dehydration. Clearance experiments were performed in 10 conscious DI rats before and following 3, 6, 9, 12, 15, and 24 h of dehydration. Urine osmolality increased from 155.0 +/- 12.6 (SE) to 696.7 +/- 8.4 mosmol/kg H2O after 24 h. GFR averaged 984.3 +/- 79.6 microliters . min-1 . 100 g body wt-1 in the control phase, fell to about 80% of this value over the first 12 h of dehydration, and then declined to 27% at 24 h. The rats lost 20% of their body weight over the 24 h. The osmolality of the papillary tip averaged 896 +/- 44 mosmol/kg H2O at 24 h compared to a control value of 493 +/- 28. The lack of osmotic equilibration between urine and papillary interstitium suggests that dehydration did not appreciably increase the water permeability of the distal nephron. These experiments clearly show a progressive decline in GFR as urine becomes concentrated during dehydration in the absence of ADH; these events may or may not be causally related.

Animals↗
PubMed1978

Calcium and sodium excretion in rats in response to prolonged treatment with polythiazide.

The hypocalciuric response to prolonged polythiazide (PTZ) administration has been investigated in intact and thyroparathyroidectomized (TPTX) rats. After 3 control days, PTZ was given for 6 days (0.1 mg/100 g body weight . 24 h p.o.). In both groups, calcium excretion fell on day 1 of PTZ and remained depressed thereafter. In the intact rats, this decrease was associated with increased sodium excretion and urine output on treatment day 1. In the TPTX rats, hypocalciuria occurred without change in sodium excretion or body weight; urine output increased on the first 2 days. Thus PTZ can reduce calcium excretion in the absence of parathyroid hormone, changes in sodium excretion, and changes in body weight (an estimate of body fluid balance with constant food intake).

Animals↗
PubMed1977

Renal clearances of 14C-inulin and polyfructosan in the rat. Effect of increased ureteral pressure.

Polyfructosan has been used as a substitute for inulin in GFR determinations. However, the validity of this substitution in conditions where renal tubular permeability to other substances, such as mannitol, sucrose and other substances, such as mannitol, sucrose and iothalamate, is increased has not been tested. Experiments were performed on 8 rats to compare the clearances of polyfructosan (CPF) and 14C-inulin (CIN) during hydropenia, 3% BW saline expansion, elevation of one ureteral catheter by 30 cm, and following return of increased ureteral pressure to the control level. No significant difference between CPF and CIN could be detected except in the kidney subjected to increased ureteral pressure. However, the magnitude of this difference--which may relate to the different molecular weights of the two compounds--was so small that we conclude that the use of CPF, as an index of GFR, is no less reliable than CIN under the conditions tested.

Animals↗
PubMed1976

The deiodination of thyroxine in hyperthyroid rats as determined by renal clearance of iodide.

Other investigators have reported that whole body clearance of thyroxine (T4) is increased in hyperthyroid rats isotopically equilibrated with radioactive T4, using the 24 h post-injection serum T4 concentration in the clearance calculation. Data from this laboratory indicate that serum T4 concentration is lowest at this point yielding falsely high clearance values, particularly when high doses of T4 are injected. To investigate this problem further, two types of experiments were performed. First, rats were equilibrated with [125I]T4, 5 or 20 mug/day, and the urinary clearance of iodide derived from T4 (deiodinative clearance) was measured from 0-7 and 7-24 h after a T4 injection, using the T4 concentration in serum obtained at the midpoint of each urine collection period. Urine was then collected from the ureters for several 1 h periods during the 4th to 8th h following T4 injection, calculating clearances using the midpoint plasma T4 concentration. Second, normal rats were given a single dose of [125I]T4, 5 or 55 mug/rat, and deiodinative clearance was determined during the subsequent 0-7 and 7-24 h periods. The first experiment indicated that deiodinative clearance was significantly enhanced in rats equilibrated with the large dose of T4 under all conditions studied. In contrast, the clearance in normal rats given a single large dose of T4 was not significantly different from that of normal rats given a small dose of T4. These results support the view that T4 clearance is increased in hyperthyroidism, due in part to an increase in the deiodination of T4.

Animals↗
PubMed1973

Micropuncture study of diuretic effects on sodium and calcium reabsorption in the dog nephron.

A close relationship has been observed between the clearance rates of sodium and calcium under a variety of diuretic conditions. The thiazide diuretics act differently in dissociating the renal tubular reabsorption of sodium and calcium. This phenomenon has been further investigated using recollection micropuncture and clearance techniques in a group of 14 dogs subjected to three consecutive experimental phases: expansion to 3% of body weight (BWt) with Ringer's solution, chlorothiazide infusion at 20 mg/kg/h, and furosemide in a prime of 10 mg/kg/ and a 10 mg/kg/h infusion. Diuretic losses were balanced with infusion of equal volumes of Ringer's solution throughout the experiment. Chlorothiazide increased the fractional excretion (FE) of sodium almost threefold while FE(Ca) was not significantly altered. Furosemide increased FE(Na) and FE(Ca) to an approximately equal, and more marked, degree. This dissociation of sodium and calcium reabsorption after chlorothiazide was also evident in the superficial distal tubule, where (tubule fluid/plasma sodium) (TF/P(Na)) increased from 0.32 to 0.49 (P < 0.01) and TF/(ultrafiltrate)UF(Ca) was unchanged (0.35-0.31). Furosemide markedly reduced the transtubular concentration gradient for both sodium (0.86) and calcium (0.94). TF/P(Inul in) decreased progressively from 3.79 to 2.78 to 2.33 in three phases. In the late proximal tubule, chlorothiazide induced a fall of TF/P(Inul in) from 1.57 to 1.44 (P < 0.01), but the ratio TF/UF(Ca): TF/P(Na) was unchanged. Furosemide had no significant proximal effect. It is concluded that acute administration of chlorothiazide reduces sodium reabsorption in the distal hephron, presumably the cortical diluting segment, without affecting calcium reabsorption.

Animals↗