Balance between tubular flow rate and net fluid reabsorption in the proximal convolution of the rat kidney. II. Reabsorptive characteristics during constriction of the renal artery

Polycystic kidney disease and renal injury repair: common pathways, fluid flow, and the function of polycystin-1

The root cause for most cases of autosomal-dominant polycystic kidney disease (ADPKD) is mutations in the polycystin-1 (PC1) gene. While PC1 has been implicated in a perplexing variety of protein interactions and signaling pathways, what its normal function is and why its disruption leads to the proliferation of renal epithelial cells are unknown. Recent results suggest that PC1 is involved in mechanotransduction by primary cilia measuring the degree of luminal fluid flow. PC1 has also recently been shown to regulate the mTOR and signal transducers and activators of transcription (STAT) 6 pathways. These two pathways are normally dormant in the healthy kidney but are activated in response to injury and appear to drive a proliferative repair response. This review develops the idea that a critical function of PC1 and primary cilia in the adult kidney may be to sense renal injury by detecting changes in luminal fluid flow and to trigger proliferation. Constitutive activation of these pathways in ADPKD would lead to the futile attempt to repair a nonexisting injury, resulting in cyst growth. The existence of many known cellular and molecular similarities between renal repair and ADPKD supports this model.

Distribution of ferrocyanide along the proximal tubular lumen of the rat kidney: its implications upon hydrodynamics

1. Simultaneous determination of the single nephron glomerular filtration rate (s.n.g.f.r.) and the amount of [14C]ferrocyanide contained per unit length (Fe/mm) of the proximal tubule makes it possible to calculate the tubular radius and flow velocity along this structure. These measurements were made in normal rats, chronically salt-loaded rats, and rats rendered hypotensive by controlled haemorrhage or aortic constriction. 2. In normal rats, Fe/mm remains constant along the proximal tubule, indicating a gradual decrease in tubular radius and constant flow velocity. 3. In salt-loaded rats, with high s.n.g.f.r.s, Fe/mm also remains constant along the proximal tubule, but at a higher level than in normal rats. This indicates larger tubular radii, but the same evolutionary pattern for tubular radius and flow velocity along the proximal tubule, as in normal rats. 4. In rats with controlled haemorrhage, Fe/mm values are low but rise slightly along the proximal tubule. Tubular radius is reduced, and again, gradually decreases along the length. Considering the very low s.n.g.f.r.s, this implies that a large drop in reabsorption along the proximal tubule accompanies the reduction in s.n.g.f.r. 5. In rats with aortic construction, Fe/mm exhibits a large increase along the proximal tubule, suggesting a huge Fe concentration along the tubule, which in turn would indicate that water reabsorption may not diminish in proportion to the reduction in s.n.g.f.r. In some cases, this disruption of the glomerulo-tubular balance led to the cessation of tubular flow in the proximal tubule. 6. In all cases, Fe/mm and the calculated radius in the initial portion of the proximal tubule were correlated to the s.n.g.f.r., suggesting passive adaptation of tubular radius to fluid delivery.

Sauvagine, a new polypeptide from Phyllomedusa sauvagei skin. Occurrence in various Phyllomedusa species and pharmacological actions on rat blood pressure and diuresis

1. The occurrence of sauvagine, a new polypeptide from amphibian skin, and its actions on rat blood pressure and diuresis were studied. 2. Sauvagine was found to be present in the skin of all the 10 Phyllomedusa species so far studied, amounts ranging from a few micrograms to 240 micrograms per g fresh skin. 3. The polypeptide displayed in the rat an intense, long-lasting hypotensive action accompanied by tachycardia. Hypotension was not modified by either atropine or propranolol, excluding the participation of the autonomic nervous system in its production. Tachycardia, on the contrary, was partially inhibited by propranolol. 4. Hypotension is probably the main cause of the intense antidiuresis seen in hydrated rats following sauvagine administration. Reduction in urina volume was accompanied by a decrease in GFR and an increase in tubular NA+ reabsorption.

Renal tubular flow dynamics during angiotensin diuresis in the rat

1. Tubular size and lissamine green transit times were measured in rat kidneys undergoing a diuretic response to angiotensin II (0.5 mug/kg per min), and compared with the changes observed during diuresis induced by osmotic diuretics, noradrenaline and chlorothiazide.2. Angiotensin always caused a marked prolongation in proximal and distal tubular transit times; individual distal convolutions were coloured for prolonged periods, and lissamine green appeared in high concentration in distal tubules.3. Marked changes were observed in superficial tubular calibre during a stable diuretic response to angiotensin. Where distal tubular diameter was normal for the rate of urine flow, proximal tubular volume was generally reduced. In a number of experiments, however, distal tubules were markedly dilated, and in these cases proximal tubular volume was also often increased. Angiotensin may therefore be capable of causing a degree of internal hydronephrosis in the rat kidney.4. Prolongation of dye transit times, and the appearance of a concentrated lissamine green bolus in distal tubules, was suggestive of a decreased superficial nephron flow rate, indicating that the diuretic effect of angiotensin may take place only through deeper nephrons.