The interactions of prostaglandins and vasopressin in the kidney

Atypical Causes of Urinary Tract Obstruction

Acute kidney injury due to urinary tract obstruction invariably suggests lower urinary tract obstruction or bilateral ureteric obstruction since obstruction of a single kidney while the contralateral kidney is normal and not obstructed would not cause a perceptible rise in creatinine. Assuming a total body volume of 42 L, 70 kg male that generates approximately 1400 mg of creatinine daily (20 mg/kg/day) who has complete urinary tract obstruction would experience a 3.33 mg/dL per day increase in serum creatinine. Thus, for an individual who had prior normal renal function and who presents with a creatinine of 30 mg/dL, one could surmise that the obstructive pathology had lasted at least 10 days. However, the rise in serum creatinine is a poor marker of renal injury and subsequent prognosis. Urinary tract obstruction leading to AKI can be due to a variety of causes, and its management is tailored to the underlying etiology. This case series describes the varied clinical course of four patients at our center who experienced AKI from atypical causes of obstructive uropathy. Current and future diagnostic modalities and caveats in the treatment of this disease entity are also discussed.

Transient gestational diabetes insipidus: report of two cases and review of pathophysiology and treatment

Gestational diabetes insipidus is a rare disorder characterized by polyuria and polydipsia due to the inability of the kidneys to concentrate urine. We report two cases of transient gestational diabetes insipidus in which patients responded to intranasal DDAVP (1-deamino-8-D-arginine vasopressin) with greater than 50% increase in urine osmolality and marked reduction in urine output. Intranasal DDAVP was discontinued after their discharge and both patients maintained normal urine output and appropriate urine osmolality. In determining whether diabetes insipidus is present in a patient who is polyuric and hypernatremic, a urine osmolality below that of the plasma suggests the presence of diabetes insipidus. Understanding of the pathophysiology may soon lead to improved methods of prevention, diagnosis and treatment.

Transient gestational diabetes insipidus diagnosed in successive pregnancies: review of pathophysiology, diagnosis, treatment, and management of delivery

Gestational diabetes insipidus (GDI) is a rare disorder characterised by polyuria, polydypsia, and excessive thirst usually manifesting in the third trimester of pregnancy. The etiology is thought to depend on excessive vasopressinase activity, a placental enzyme that degrades arginine-vasopressin (AVP), but not 1-deamino-8-D: -arginine vasopressin (dDAVP), which is a synthetic form. This is a transient syndrome and may be associated with acute fatty liver of pregnancy and preeclampsia. The use of dDAVP in symptomatic cases has been proven as a safe method for both the mother and the fetus during the pregnancy. We report a case of recurrent gestational diabetes insipidus in successive pregnancies, which responded to dDAVP and subsided after delivery.

Resistance of the renal biosynthesis of prostaglandin E2 to the inhibitory effect of indomethacin in the rat in vivo

Our recent observation that the chronic administration of indomethacin (3.0 mg.kg-1.day) to hypertensive rats, while profoundly inhibiting the urinary excretion of 6-oxo-PGF1 alpha, dinor-6-oxo-PGF1 alpha and thromboxane B2, failed to reduce the urinary levels of PGE2, prompted us to study in more details the influence of indomethacin and of meclofenamate on the urinary excretion of prostaglandins in normal rats. A dose of 1.5 mg.kg-1 of indomethacin administered intraperitoneally was sufficient to cause a 70-75% reduction in the urinary excretion of dinor-6-oxo-PGF1 alpha and of 6-oxo-PGF1 alpha for a period of at least 12 hours. Doses of indomethacin lower than 2.5 mg.kg-1.12h beta 1 or a dose of meclofenamate equal to 5 mg.kg-1.12h beta 1 did not influence the urinary excretion of PGE2. Doses of indomethacin equal to or higher than 2.5 mg.kg-1 were needed to obtain a 50% reduction in the urinary levels of PGE2 for a period of 10-14 h. During these experiments, no circadian rhythm for the urinary excretion of 6-oxo-PGF1 alpha and of dinor-6-oxo-PGF1 alpha could be observed whereas the urine volume and the urinary excretion of PGE2 were found to be greater at night than during the day.(ABSTRACT TRUNCATED AT 250 WORDS)

Post-obstructive urinary concentrating defect. A case study in the role of prostaglandins

A child with post-obstructive urinary concentrating defect was studied for the possible pathophysiological role of prostaglandins and an eventual therapeutic approach. Increased urinary excretion of prostaglandins was corrected by indomethacin, with resultant increased nephrogenous cyclic AMP and partial improvement in the concentrating defect. The addition of a thiazide restored urinary concentration. These results add clinical support to the conception of the important role of prostaglandins in the mechanism of post-obstructive hyposthenuria. This therapeutic regimen is advocated for prolonged post-obstructive concentrating defect.

Extreme unilateral hydronephrosis with normal glomerular filtration rate: physiological studies in a case of obstructive uropathy

A 30-year-old man presented with massive left hydronephrosis caused by congenital stricture of the ureteropelvic junction. Glomerular filtration rate of the post-released kidney (inulin clearance and creatinine clearance) was preserved completely. Simultaneous individual kidney function tests showed the following values expressed as the ratio of post-obstructed to normal kidney: inulin clearance 142 per cent, urine flow rate 475 per cent, sodium clearance 221 per cent and urinary excretion of prostaglandin E2 617 per cent. Urinary osmolality was 257 and 791 mOsm./kg. in the obstructed and normal kidneys, respectively. Administration of indomethacin, a cyclo-oxygenase inhibitor, caused decreased urinary excretion of prostaglandin E2 in both kidneys, with drastic antinatriuresis manifested predominantly in the normal kidney. We conclude that the glomerular filtration rate may be preserved despite huge hydronephrosis, which suggests that the human kidney is salvageable even after a prolonged period of unilateral ureteral obstruction, and the contralateral normal kidney mitigates the volume losses from the obstructed kidney.

Potentiating effects of leukotriene B4 and prostaglandin E2 on urinary sodium excretion by the dog kidney

A synergistic vasodilatation was recently demonstrated with leukotriene B4 (LTB4) and prostaglandin E2 (PGE2) in the cutaneous microcirculation. The present study addresses this question to the renal microcirculation, with respect to its eventual influence on the net transport of sodium, infusing small doses of LTB4 (100 ng/min) and PGE2 (3 ng/min) in the left renal artery, and using the contralateral kidney as control in anesthetized Mongrel dogs. In group 1 (hydropenic animals), LTB4 alone failed to influence natriuresis (UNaV) while PGE2 increased UNaV from 152 +/- 20 to 225 +/- 18 uEq/min. The combined infusion of LTB4 and PGE2 resulted in a marked elevation of natriuresis to 368 +/- 26, 317 +/- 30 and 342 +/- 52 uEq/min. In group 2, water diuresis was induced to examine the eventual site of action of these compounds, and to assess the response of the diluting segment of the nephron. In these dogs, PGE2 was first administered and UNaV rose modestly from 51 +/- 12 to 77 +/- 15 uEq/min. LTB4 again had no significant influence on UNaV, but LTB4 and PGE2 produced a marked increment from 75 +/- 16 to 374 +/- 24 uEq/min. Urine volume, as well as free water clearance, increased from 3.3 +/- 0.2 to 6.5 +/- 0.7 ml/min, and from 2.3 +/- 0.2 to 3.7 +/- 0.4 ml/min, respectively, during LTB4 + PGE2. No significant change occurred in the right control kidney during these manoeuvers. Since renal hemodynamics (glomerular filtration and plasma flow) remained relatively stable in both groups of dogs, it is suggested that the combined infusion of LTB4 and PGE2 exerts a direct influence on the net transport of sodium, probably in the proximal tubule, as inferred by the results obtained in group 2. These two important metabolites of arachidonic acid could be involved in the modulation of renal sodium excretion under normal and/or pathophysiological conditions.

Water balance in the Brattleboro rat: single or multiple defects?

The total restoration of urinary concentrating ability of the DI rat given daily injections of vasopressin takes several weeks, although complete osmotic equilibrium across the collecting duct is manifest within hours. This suggests that there may be other deficiencies of the renal concentrating mechanism that, if corrected by vasopressin treatment, are corrected more slowly. I have focussed on just three possibilities. First, the morphology of the medullary interstitium is different from normal rats. Perhaps associated with this finding are alterations in the levels of medullary glycosaminoglycans which may have a role to play in water balance. Functional and morphological changes in the juxtamedullary nephrons are also evident. Second, the possibility exists that the countercurrent multiplier of the DI rat operates less efficiently than in the normal animal. Finally, reduced synthesis of PGs in the renal medulla of DI rats may also influence the concentrating mechanism, although in a favorable direction. While most (if not all) of these differences are secondary to the lack of vasopressin, in some instances it appears that it is the high water turnover (possibly the altered chemical composition of the medullary interstitium) that is the primary culprit. While the DI rat remains an excellent model for the study of water balance and the action of vasopressin, the presence of multiple defects within the system should be borne in mind. This is particularly true when comparing data obtained following acute treatment with vasopressin versus that following chronic treatment.