Single-nephron adaptations to partial renal ablation in cats

To evaluate remnant nephron hyperfiltration, cats underwent sham surgery (group 1, n = 6) or three-fourths nephrectomy (group 2, n = 6). Four to six weeks later, micropuncture studies demonstrated increases (P < 0.01) of single-nephron glomerular filtration rate (SNGFR) in group 2 (28.1 +/- 2.8 vs. 56.0 +/- 5.9 nl/min). In group 2 the mean estimated glomerular capillary pressure of 74.0 +/- 1.7 mmHg exceeded (P < 0.01) the value for group 1 (62.6 +/- 1.4 mmHg). The mean effective filtration pressure (EFPm) for group 2 (28.7 +/- 3.1 mmHg) was greater (P < 0.05) than that in group 1 (20.8 +/- 1.9 mmHg). Similarly, the mean ultrafiltration coefficient (Kf) in group 2 of 2.03 +/- 0.24 nl.min-1.mmHg-1 exceeded (P < 0.05) the corresponding value for group 1 of 1.35 +/- 0.06 nl.min-1.mmHg-1. Morphological studies demonstrated glomerular enlargement and mesangial matrix expansion in group 2 (P < 0.05). Proteinuria, as assessed by the urine protein-to-creatinine ratio, was increased (P < 0.05) after partial renal ablation. These results demonstrate that increases in SNGFR in feline remnant nephrons occur in association with glomerular hypertension, glomerular hypertrophy, expansion of mesangial matrix, and proteinuria, and furthermore, that the observed increases in SNGFR are attributable to an augmentation of EFPm and Kf.

Arterial occlusion versus isofiltration pulmonary capillary pressures during very high flow

Pressure in the compliant middle segment of the pulmonary vascular bed (PM), as determined by arterial occlusion, was compared with pressure at the filtration site (effective filtration pressure, EFP), determined by the isofiltration technique, at very high (7–10 times normal) pulmonary flow in six in situ perfused canine left upper lobes. At these flow rates inflow and left atrial pressures averaged 41.9 +/- 1.3 and 2.5 +/- 0.5 (SE) mmHg, respectively. PM was 30.9 +/- 1.6 mmHg, and EFP was 32.3 +/- 1.9 mmHg with no significant difference between the two measurements by paired t test. The results indicate that the arterial occlusion technique yields a pressure that is equivalent to EFP even during very high pulmonary blood flow where the longitudinal distribution of resistance is quite different from that obtained during normal flow.

Effect of secretin on glomerular dynamics in dogs

These studies were performed to determine whether a role for increased renal plasma flow (RPF) in the regulation of glomerular filtration rate (GFR) could be demonstrated in dogs by infusing the polypeptide hormone secretin, a vasodilator that has been reported to increase GFR. Differences between control and recollection periods were compared by paired t test in five time-control dogs (group 1) and 10 secretin dogs (group 2). In group 2, secretin (100 mU . kg-1 . min-1, ia) significantly increased single-nephron glomerular filtration rate (SNGFR) 11.1 +/- 3.1 nl/min (20%) and glomerular plasma flow 59 +/- 11 nl/min (26%). Similar increases in GFR (26%) and RPF (29%) were observed. Secretin also increased glomerular capillary pressure 5.2 +/- 0.8 mmHg and free-flow proximal tubule pressure 5.5 +/- 1.0 mmHg. Secretin did not significantly affect average effective filtration pressure (EFP) but significantly increased the ultrafiltration coefficient (Kf) 0.74 +/- 0.14 nl . min-1 . mmHg-1. These differences were significantly greater than those observed in group 2. It is concluded that secretin increased SNGFR primarily by an effect on Kf. This is consistent with the marked effect that Kf is predicted to have on glomerular filtration in dogs. The maintenance of EFP agrees with other vasodilator studies and indicates that GFR is only moderately dependent on plasma flow in dogs.

Dynamics of glomerular filtration in the river lamprey, Lampetra fluviatilis L

Hydrostatic pressures decreased in the dorsal aorta (from 21.6 +/- 2.0 to 18.7 +/- 0.2 mmHg), proximal (from 19.5 +/- 1.6 to 16.2 +/- 1.7 mmHg) and distal (from 16.7 +/- 0.7 to 13.2 +/- 0.9 mmHg) renal arteries, and glomerular capillaries (from 16.1 +/- 1.1 to 12.3 +/- 0.6 mmHg) of anesthetized lampreys transferred from freshwater to isosmotic 20-30% seawater. Maximal vascular resistance appeared to be in the efferent arteriole; there was a 67% decrease in pressure between glomerular and peritubular capillaries. Plasma oncotic pressure was unchanged. The calculated afferent effective filtration pressure decreased by 87% after transfer and showed a good correlation with single nephron filtration rate. Effective renal plasma flow was high but variable in freshwater lampreys and decreased by 84% after transfer, but glomerular filtration rate did not decrease proportionately and there was a nonsignificant increase in mean filtration fraction from 0.045 +/- 0.022 to 0.080 +/- 0.021. Calculation of glomerular efferent oncotic pressure indicated that filtration equilibrium did not exist in freshwater lampreys but was attained after transfer. The mean coefficient of filtration of freshwater lampreys was 0.028 +/- 0.002 nl X s-1 X mmHg-1.

Effect of parathyroid hormone on the determinants of glomerular filtration in dogs

Elevated levels of parathyroid hormone (PTH) often are associated with reduced glomerular filtration rate (GFR) in humans. Although PTH has been reported to reduce the ultrafiltration coefficient (Kf) in rats, GFR declined only if they were plasma expanded. In contrast, PTH does not reduce GFR in dogs, despite filtration pressure disequilibrium. To evaluate this apparent discrepancy, the determinants of GFR were measured in acutely thyroparathyroidectomized dogs. In the absence (n = 8) and presence (n = 10) of synthetic bovine PTH, GFR was 29 +/- 3 and 26 +/- 2 ml/min; Single nephron glomerular filtration rate was 58 +/- 4 and 51 +/- 3 nl/min; glomerular plasma flow was 248 +/- 22 and 250 +/- 24 nl/min; glomerular capillary pressure was 58 +/- 2 and 61 +/- 3 mmHg; Bowman's space pressure was 19 +/- 2 and 19 +/- 1 mmHg; and systemic oncotic pressure was 19 +/- 0.8 and 18 +/- 0.5 mmHg. Average effective filtration pressure (EFP) was significantly greater in the presence (18.6 +/- 1.3 mmHg) than in the absence (14.6 +/- 0.9 mmHg) of PTH. Therefore, Kf per glomerulus calculated from these data was significantly (P less than 0.01) less in the presence than in the absence of PTH (2.91 +/- 0.29 and 3.98 +/- 0.16 nl X min-1 X mmHg-1, respectively). It is concluded that PTH reduced Kf. Whereas this effect predicts reduced GFR in dogs, given filtration pressure disequilibrium, a concomitant increase in EFP maintained GFR in the present study.

Measurement of hydrostatic pressure in salmonid eggs

A method is described, based on applanation tonometry of the human eye, for measurement of hydrostatic (internal, turgor) pressure in salmonid eggs. The area of an egg flattened by an external applanating force is related to the volume of the egg displaced by applanation. The hydrostatic pressure in steelhead trout eggs (Salmo gairdneri) (1248 h postfertilization, 5 °C) was 53 (−7, +8) mmHg (1 mmHg = 133.322 Pa). Unfertilized, flaccid eggs of the species, with an assumed zero internal pressure, had a measured pressure of 1.1 (−0.6, +1.1) mmHg, taken as equivalent to the force required to bend the relatively thick capsule (zona radiata) wall. Hence, the corrected internal pressure is estimated as 51.9 mmHg. Internal pressure in fertilized eggs of three species of Pacific salmon (Oncorhynchus nerka (sockeye), O. gorbuscha (pink), and O. tshawytscha (chinook)) increased during incubation at 10 °C. Between 2 and 8 h after fertilization, hydrostatic pressure was approximately 15 mmHg for sockeye, 25 mmHg for pink, and 40 mmHg for chinook. After 1000 h of incubation, the pressures (millimetres Hg) were approximately 76 for sockeye, 47 for pink, and 51 for chinook. Possible relations between hydrostatic and osmotic pressures are discussed with reference to effective filtration pressure, as well as the potential influence of the latter on oxygen transport across the capsule.

Urine Formation in the Lamellibranchs: Evidence for Ultrafiltration and Quantitative Description

1. Physical and chemical parameters were measured in the Japanese oyster Crassostrea gigas to investigate whether the first step of urine formation in the lamellibranchs could be an ultrafiltration and to give a quantitative description. 2. The effective filtration pressure was not constant, but a function of time, oscillating between 31.7 mmH2O and −3.8mmH2O. During the filtration, a separation of proteins took place: the protein concentration in the haemolymph was 17 μmoll−1 and the average molecular weight was 141 000. In the filtrate, the protein concentration was 2 μmoll−1 and the average molecular weight was 45 000. The marker substance inulin, applied via the gills, appeared successively within the haemolymph and the pericardial fluid. These findings establish the idea that the pericardial fluid is formed by ultrafiltration from the haemolymph. 3. The rate of filtration was found to be 0.4 μg−1 min−1 by quantitative analysis of the transport of the inulin. The coefficient of filtration was 4.5×10−6 mls−1 cm−2 mmHg−1.

Glomerular filtration dynamics during renal vasodilation with acetylcholine in the dog

The reason for the failure of glomerular filtration rate (GFR) to exhibit plasma flow dependency during pharmacologic vasodilation remains unclear although it has been suggested on the basis of experiments in rats that vasodilators may lead to a reduction in the glomerular filtration coefficient (Kf). To evaluate the applicability of this hypothesis to the dog, the effects of vasodilation with acetylcholine on glomerular dynamics and Kf were evaluated in two groups of dogs. One group (n = 19) was studied at spontaneous arterial pressures to allow maximum vasodilation to occur. In the other group (n = 5), renal arterial pressure was reduced and maintained at approximately 89 mmHg. Glomerular filtration rate and single nephron glomerular filtration rate were not altered significantly during acetylcholine infusion in either of the two groups. Both whole kidney and superficial filtration fractions decreased significantly. At spontaneous arterial pressures, transglomerular hydrostatic pressure was not altered significantly because of equivalent increases in proximal tubule pressure and in glomerular pressure. In the dogs studied at reduced renal perfusion pressure, glomerular capillary pressure did not change, but proximal tubule pressure increased slightly. Average effective filtration pressures and Kf were not significantly altered during the infusion of acetylcholine either at spontaneous or reduced renal perfusion pressures. These observations indicate that Kf in the dog is not significantly decreased by acetylcholine and that GFR is not affected during infusion of this agent because the effective filtration pressure is not significantly altered.

Filtration pressure equilibrium: a statistical analysis

Statistical analysis of data in published micropuncture studies was applied to determine: a) the number of rats and samples of glomerular capillary pressure (Pg), end-capillary oncotic pressure (COPE), and proximal tubule pressure (Pt), needed in a single study to state with 95% confidence that a measured mean net efferent effective filtration pressure (delta P*E) is within +/- mmHg of any true value, delta PE; b) the effect of intra-animal variation in Pg, COPE, and Pt values on the number of experiments needed; and c) the probability of obtaining a value for delta P*E that meets this criterion in multiple trials. Assuming no intra-animal variation in Pg, Pt, and COPE values and employing published interanimal variances, at least 42 rats should be studied in any series to show that -1 mmHg less than or equal to (delta P*E -- delta PE) less than or equal to 1 mmHg within 95% confidence limits. If intra-animal variances are 60% of the interanimal variances, 67 rats are needed to obtain that degree of confidence when a single measurement of Pt, Pg, and COPE is made in each rat, and 47 animals are required with five measurements per rat. A value for delta P*E within 2-3 mmHg of its true value is, however, attainable with confidence using a far smaller number of animals per series.

Corpuscles of Stannius and Renal Physiology in the Eel (Anguilla rostrata)

In freshwater eels there is a significant correlation between glomerular filtration rates (GFR) and urine flow rates suggesting that changes in GFR rather than tubular water reabsorption lead to the major adjustments in urine flow rates accompanying changes in environmental salinity.Removal of the corpuscles of Stannius was not followed by a significant change in GFR indicating that an adequate (normal) effective filtration pressure is independent of a corpuscular pressor substance.In 8 of 17 Stanniectomised eels urine flow rates exceeded GFR demonstrating that, under these experimental conditions, eel renal tubules secrete water.Multiple tissue electrolyte changes followed Stanniectomy; the 75% increase in the plasma calcium concentration is of particular interest. This increase was probably due to a reduction in the net rate of calcium deposition in bone and not to a change in the renal handling of calcium.