On the relationship between urinary PGE2 and PGF2 alpha excretion rates and urine flow, osmolar excretion rate and urinary osmolality in anesthetized rats

Is there a role for PGE2 in urinary concentration?

Prostanoids are prominent, yet complex, components in the maintenance of body water homeostasis. Recent functional and molecular studies have revealed that the local lipid mediator PGE2 is involved both in water excretion and absorption. The biologic actions of PGE2 are exerted through four different G-protein-coupled receptors; designated EP1-4, which couple to separate intracellular signaling pathways. Here, we discuss new developments in our understanding of the actions of PGE2 that have been uncovered utilizing receptor specific agonists and antagonists, EP receptor and PG synthase knockout mice, polyuric animal models, and the new understanding of the molecular regulation of collecting duct water permeability. The role of PGE2 in urinary concentration comprises a variety of mechanisms, which are not fully understood and likely depend on which receptor is activated under a particular physiologic condition. EP3 and microsomal PG synthase type 1 play a role in decreasing collecting duct water permeability and increasing water excretion, whereas EP2 and EP4 can bypass vasopressin signaling and increase water reabsorption through two different intracellular signaling pathways. PGE2 has an intricate role in urinary concentration, and we now suggest how targeting specific prostanoid receptor signaling pathways could be exploited for the treatment of disorders in water balance.

Acute effects of the anti-inflammatory cyclooxygenase-2 selective inhibitor, flosulide, on renal plasma flow and glomerular filtration rate in rats

Nephrotoxicity of nonsteroidal anti-inflammatory drugs is associated with other risk factors (volume-depletion) and may be secondary to functional changes mediated by the inhibition of renal cyclooxygenases. Acute anti-inflammatory doses of flosulide and indomethacin were determined on carrageenan paw edema and its effects on renal plasma flow (RPF) and glomerular filtration rate (GFR) were studied in normovolemic and hypovolemic rats. In normovolemic rats, flosulide increased RPF and GFR (25 mg/kg) and indomethacin (5-10 mg/kg) was without effect. Volume-depleted rats were obtained by oral furosemide (32 mg/kg), urinary eicosanoids were determined. After furosemide, plasma volume, RPF and GFR and PGE2 decreased. Treatment of hypovolemic rats with flosulide (5-25 mg/kg) or indomethacin 10 mg/kg reduced RPF and GFR. Flosulide at 5 mg/kg reduced 6-keto-PGF1alpha whereas at 25 mg/kg and after indomethacin at 10 mg/kg a fall in 6-keto-PGF1alpha and TXB2 appeared. Our data suggest that acute COX-2 selective inhibition may alter renal function.

A biphasic response of urinary prostaglandin E2 excretion to water deprivation in conscious diabetes insipidus Brattleboro rats

The effects of water deprivation on the urinary excretion rate of prostaglandin E2 (PGE2) were examined in conscious Brattleboro rats. In order to study the time course of the changes in the PGE2 excretory rate, urine was collected in 6 periods,

CONTROL

0-1 hour (h.). 1: 3-4.5 h., 8-10 h., III: 12-15 h., IV: 24-28 h. and V: 32-36 h. after removal of water and food. It was found that the PGE2 excretion rate changed in a biphasic pattern. During the first 2 experimental periods it increased. Thereafter it decreased towards the control value. There was an increase in PGE2 excretion with urinary flows down to 3 microliter/(min*100 g b. wt). At further reductions in urinary flow rate, PG excretion decreased towards basal levels.

Association of prostaglandin metabolism with urine volume; dissociation from excretion of Na+ and K+ by stress

Stress induced by routine cage cleaning causes retention of Na+ and K+, and increased water and prostaglandin metabolite excretion when measured either against concurrent-controls or against self-control values. This novel stress completely masked the diuretic effects of a long-acting prostaglandin synthetase inhibitor previously observed in a stress-free environment. The results show that prostaglandin synthesis and urine volume regulation are closely associated. They also demonstrate a complete dissociation of urine volume and prostaglandin synthesis regulation from electrolyte regulatory mechanisms in a stressful environment.

Renal venous and urinary PGE2 output during intrarenal arachidonic acid infusion in dogs

Inferences about total renal (venous and urinary) PGE2 output from determinations of urinary excretion rates (U PGE2 V) cannot be made unless the distribution of PGE2 between renal venous plasma and urine is known. Therefore, in the present study on intact kidneys of anesthetized dogs both urinary excretion of PGE2 and the renal venous output (the product of plasma flow and venous concentration of PGE2) was determined during low and high rates of renal PGE2 synthesis. PGE2 was measured in urine and arterial and renal venous plasma by radioimmunoassay during the following conditions: (1) Hydropenia. In the control condition U PGE2 V averaged 0.041 +/- 0.012 pmol/g . min and varied between 4 and 70% of the total PGE2 output. With infusion of arachidonic acid (AA, 160 micrograms/kg . min) into the renal artery total PGE2 output increased from 0.18 +/- 0.03 to 3.23 +/- 0.51 pmol/g . min, whereas arterial concentrations of PGE2 were unchanged. The urinary fraction still varied between 6 and 46% of total renal PGE2 output. (2) High urine flows caused by mannitol, saline or saline and ethacrynic acid (ECA) infusion. These procedures did not stimulate total renal PGE2 output and the urinary fraction varied between 4 and 49%. ECA combined with saline infusion increased the urinary fraction significantly to 34.7 +/- 4.0%. AA increased the total PGE2 output as during hydropenia, but the urinary fraction fell to 13% in 13 dogs and was unchanged at about 8% in six dogs. On average the urinary fraction of total PGE2 output was significantly lower than in hydropenia. Thus, the urinary fraction of total renal PGE2 output is not constant, and urinary excretion of PGE2 does not give reliable information about renal synthetic rates of prostaglandins.

The relationship between urinary prostaglandin excretion rates and urine flow in conscious rats. Evaluation of the radioimmunoassay by gas chromatography-mass spectrometry

In conscious rats prostaglandin E2- and F2 alpha excretion rates increased from about 20 to more than 100 pg/min/g kidney weight as urine flow decreased from about 10 to below 1 microliter/min/g kidney weight following 24 h of water deprivation confirming previous data from surgically prepared rats (Leyssac & Christensen 1981 b). There was no difference in this response between rats on a normal sodium diet and severely sodium depleted rats. Additional supply of polyunsaturated fatty acids in the food did not influence the results. Elevated levels of prostaglandin excretion did not correlate with urine osmolality. The reliability of the radioimmunoassays used was documented by comparison with measurements by gas chromatography-mass spectrometry. The analysis showed that these two methods provide almost identical estimates of urinary PGE2 and PGF2 alpha content. It is concluded that renal prostaglandin production is activated by a negative feedback mechanism as tubular and/or urine flow rate decreases towards subnormal values.

Effects of halothane-nitrous oxide inhalation anesthesia and Inactin on overall renal and tubular function in Sprague-Dawley and Wistar rats

Real function, plasma renin concentration (PRC) and prostaglandin (PG) excretion rate was studied in groups of Sprague-Dawley (SPRD) and Wistar (WIST) rats anesthetized with either Halothane-N2O or Inactin. Conscious rats were used as controls. A. In Halothane-N2O anesthesia inulin clearance (CIN) and absolute proximal reabsorption rate (APR) was moderately decreased (by about 20%), while renal plasma flow (RPF), urine flow and solute excretion remained unchanged as compared to conscious rats. There was a linear relationship between the reciprocal of the proximal occlusion time (OT) and CIN in Halothane anesthesia indicating that the proximal luminal diameter was constant and independent of CIN. B. Inactin anesthesia CIN was similarly reduced but APR was more depressed (by about 35%). RPF and solute excretion rate decreased only in SPRD rats, while urine flow was significantly reduced in both strains. 1/OT was invariant to changes in CIN indicating luminal diameter variations in proportion to CIN. Urinary PGE2-and PGF2 alpha excretion rates and PRC were moderately elevated in operated animals of both strains regardless of the anesthetics used. It is concluded that renal functional parameters in surgically prepared rats are more severely depressed by Inactin than by Halothane-N2O anesthesia. The gas anesthesia is equally well tolerated by both strains of rats.