Angiotensin converting enzyme inhibition blocks interstitial hyaluronan dissipation in the neonatal rat kidney via hyaluronan synthase 2 and hyaluronidase 1.

A functional renin-angiotensin system (RAS) is required for normal kidney development. Neonatal inhibition of the RAS in rats results in long-term pathological renal phenotype and causes hyaluronan (HA), which is involved in morphogenesis and inflammation, to accumulate. To elucidate the mechanisms, intrarenal HA content was followed during neonatal completion of nephrogenesis with or without angiotensin converting enzyme inhibition (ACEI) together with mRNA expression of hyaluronan synthases (HAS), hyaluronidases (Hyal), urinary hyaluronidase activity and cortical lymphatic vessels, which facilitate the drainage of HA from the tissue. In 6-8days old control rats cortical HA content was high and reduced by 93% on days 10-21, reaching adult low levels. Medullary HA content was high on days 6-8 and then reduced by 85% to 12-fold above cortical levels at day 21. In neonatally ACEI-treated rats the reduction in HA was abolished. Temporal expression of HAS2 corresponded with the reduction in HA content in the normal kidney. In ACEI-treated animals cortical HAS2 remained twice the expression of controls. Medullary Hyal1 increased in controls but decreased in ACEI-treated animals. Urine hyaluronidase activity decreased with time in control animals while in ACEI-treated animals it was initially 50% lower and did not change over time. Cells expressing the lymphatic endothelial mucoprotein podoplanin in ACEI-treated animals were increased 18-fold compared to controls suggesting compensation. In conclusion, the high renal HA content is rapidly reduced due to reduced HAS2 and increased Hyal1 mRNA expressions. Normal angiotensin II function is crucial for inducing these changes. Due to the extreme water-attracting and pro-inflammatory properties of HA, accumulation in the neonatally ACEI-treated kidneys may partly explain the pathological renal phenotype of the adult kidney, which include reduced urinary concentration ability and tubulointerstitial inflammation.

Determination of the charge of the plasma proteins and consequent Donnan equilibrium across the capillary barriers in the rat microvasculature.

AIM: Due to the negatively charged proteins in plasma, a Donnan equilibrium will be formed between plasma and interstitium or, as in the glomerulus, between glomerular plasma and Bowman's space. The phenomenon is of great physiological significance in the sense that the electro-osmotic pressure offered by the small ions attracted to the proteins may account for an important part of the total colloid osmotic pressure and also as the electric potential consequent to the Donnan distribution will affect the transcapillary transport of all charged molecular compounds. The present study aimed at estimating the protein charge in rat plasma in order to validate its importance for colloid osmotic pressure and potential. METHODS: The charge of the plasma proteins was determined in vitro from the concentration of sodium across a cellophane membrane separating a rat plasma sample from saline alone. However, in order to improve the sensitivity of the method, the studies were carried out at an ionic strength of 1/10 of physiological saline. RESULTS: The average charge of plasma was estimated at 0.23 +/- 0.003 mEq g(-1) protein (mean +/- SE), and the standard variation at +/-0.01 mEq g(-1), i.e. about 5%. At the normal protein concentration in Wistar rats of 50 g L(-1), the charge of the proteins in systemic plasma was calculated to be 11.5 mEq L(-1), whereas in glomerular and peritubular capillary plasma, the larger protein concentration increases the protein charge to 14.4 mEq L(-1). CONCLUSION: The results verify that the plasma protein charge accounts for about one-third of the total colloid osmotic pressure and that the obtained potential will constitute a major driving force for the transport of charged molecular compounds.

Renal hyaluronan content during experimental uncontrolled diabetes in rats.

With diabetes mellitus, the ability of the kidneys to maintain fluid balance is affected. Hyperglycaemia increases production of hyaluronan in cultured kidney cells implying that diabetes promotes induction of hyaluronan in the kidney. The aim of the present study was to determine if the interstitial matrix component hyaluronan is differently distributed within the kidney in diabetic rats compared to non-diabetic rats. Furthermore, to test if diabetic rats are able to respond with diuresis upon a hypotonic fluid load. The normal heterogeneous intrarenal distribution of hyaluronan was confirmed in non-diabetic control rats, with 60-fold more in the papilla than in the cortex. In diabetic animals, the cortical hyaluronan was unaffected but the papillary hyaluronan content was 3-fold higher than in non-diabetic rats. This increase correlated with a more than three-fold induction of the papillary hyaluronan-synthase 2 mRNA expression. In non-diabetic animals, 2 h water loading increased papillary hyaluronan (+93%) and diuresis (17-fold). In diabetic animals, baseline diuresis was 8-fold higher than in non-diabetic animals, which correlated with hyperglycaemia, glucosuria and proteinuria. Water loading in diabetic animals did not further increase papillary hyaluronan or diuresis: the urine flow rate decreased. To conclude, papillary hyaluronan is elevated in diabetic rats, which coincides with induction of hyaluronan-synthase 2 mRNA, hyperglycaemia, glucosuria, proteinuria and overt diuresis. The inability to respond to a water load with further diuresis may be related to the already elevated papillary hyaluronan and the inability to change hyaluronan during water loading.

Hormonal regulation of renomedullary hyaluronan.

AIM: Hyaluronan (HA) is involved in renomedullary water handling through its water-binding capacity. This study addressed the effect of hormones involved in regulating fluid-electrolyte homeostasis on renomedullary HA content in vivo and in vitro. METHODS: The kidneys from rats treated with L-NAME, indomethacin, vasopressin (AVP) or methylprednisolone (MP) during euvolaemia or water loading were analysed for HA by RIA, ELISA and histochemical staining. HA was measured in renomedullary interstitial cells treated with AVP, angiotensin II (Ang II) or a combination of AVP and Ang II. RESULTS: Baseline renal cortical and medullary HA content was unaffected by 2 h of intravenous treatment with L-NAME (NOS inhibitor) or indomethacin (cyclo-oxygenase inhibitor), whereas AVP reduced medullary HA by 33%. During 2 h of acute water loading, diuresis was accompanied by an increase in renomedullary HA (+45%), but cortical HA was unaffected. In both L-NAME- and indomethacin-treated animals, the water loading-induced increase in renomedullary HA was absent, indicating involvement of NO and prostaglandins. After 7 days of MP treatment, medullary HA was reduced by 40%, but the water loading-induced elevation in HA remained. In cultured renomedullary interstitial cells, AVP reduced the HA content in the supernatant by 63%, and simultaneous treatment with Ang II reduced the HA content even further (95%). CONCLUSION: AVP reduces HA content, and NO and prostaglandins are needed for the increase in HA during water loading.