Effects of prostaglandin inhibition on intrarenal hemodynamics in acutely saline-loaded rats

Acute prostaglandin reduction with indomethacin and chronic prostaglandin reduction with an essential fatty acid deficient diet both decrease plasma flow to the renal papilla in the rat

Renal distribution of prostaglandin synthetase is mainly medullary, whereas the major degrading enzyme, prostaglandin dehydrogenase is primarily cortical. This suggests that prostaglandins (PG) released from the renal medulla could affect the medullary blood vessels. In two different experiments we studied the role of PG in the regulation of renal papillary plasma flow in the rat. First study: PG synthesis were stimulated in 34 adult Sprague-Dawley rats by bleeding from the femoral artery 1% of the body weight over a period of 10 minutes. Following this, indomethacin (a PG inhibitor, 10 mg/kg i.v.) was given slowly and then renal papillary plasma flow was measured 25 minutes after the end of infusion. In 17 indomethacin rats the renal papillary plasma flow averaged 18.8 ml/100 g/minute, whereas it averaged 23.0 in 17 non-indomethacin rats given diluent, an 18% reduction (p less than .025). Second study: Male Sprague-Dawley rats were made prostaglandin deficient by fasting rats for one week, followed by 10% dextrose fluid for one week and subsequent institution of an essential fatty acid (EFA) deficient diet for two weeks. With urinary PG excretion in prostaglandin deficient rats 28 ng/24 hours compared to 149 ng in control rats, they could be considered as prostaglandin deficient. When renal papillary plasma flow was measured, the 16 prostaglandin deficient rats had a 16% lower papillary plasma flow than 16 control rats, 21.6 vs 25.6 (p less than .005). These results clearly demonstrate that PG inhibition in rats decreases plasma flow to the papilla, strongly suggesting that PG are vasodilators for the vessels supplying the renal papilla.

Effect of alterations in extracellular fluid volume on urinary kallikrein in the conscious rat

The effect of alterations in extracellular fluid volume (ECV) and solute concentration on excretion of urinary kallikrein was examined in conscious Sprague-Dawley rats. Animals were given infusions of either dextrose and water, saline, or albumin according to a variety of protocols. These were designed to evaluate possible relationships between excretion of kallikrein, volume, sodium, and potassium. A reproducible pattern of kallikrein excretion was noted in all volume expanded groups. This consisted of a short lived increase during the initial hour of expansion with a subsequent fall to lower levels than baseline and a gradual recovery. To define the role of aldosterone in these studies, an adrenalectomized group and a group of appropriately prepared sham controls were expanded with saline. Adrenalectomy did not effect this pattern. We postulate a tubular "washout" phenomenon as the etiology of these observations. Results of these studies fail to demonstrate a consistent relationship between urinary volume, sodium, or potassium and the simultaneous amount of kallikrein found in the urine.

[Hepato-renal syndrome (author's transl)]

The hepato-renal syndrome is defined as potentially reversible functional renal failure associated with acute fulminant hepatitis or, more often, with advanced chronic liver failure. It is characterized by oliguria, azotemia, retention of sodium and water with formation of ascites, and hyponatremia. While urinary sodium concentration of less than 10 mEq/l reflects intact tubular sodium absorption, the kidney lacks the ability for adequate free-water generation. This condition must be separated from specific renal diseases which may arise during the course of intra-or extrahepatic diseases and which must be classified accordingly. Pathophysiological aspects of the hepa-to-renal syndrome include hemodynamic factors, such as changes in intrarenal blood flow distribution in the presence of elevated intrarenal and reduced peripheral vascular resistance. The functional relationship of vasoconstrictor, sodium retaining, and anti-diuretic hormones (e.g., renin-angiotensin, aldosterone, and vasopressin) to vasodilator, diuretic, and natriuretic hormonal factors (e.g., prostaglandins, kinins, and natriuretic hormone) may be altered as well. Finally, a pre- and intrahepatic spillover resulting in decreased endotoxin clearance must be considered. Due to the lack of understanding of their complex interactions, so far pharmacological and therapeutic approaches remained ineffective to correct at least some of these factors. Today, recovery from hepato-renal syndrome will, therefore, mainly depend on the course of the underlying liver disease.

Prostaglandin-independent protection by furosemide from oliguric ischemic renal failure in conscious rats

In 38 conscious rats divided into seven groups, acute unilateral ischemic renal failure was induced by 1 hour of complete occlusion of the left renal artery while the contralateral kidney remained intact. Renal excretory function of the left kidney was monitored up to 144 hours after ischemia and revealed a typical course of oliguric renal failure with oligoanuria persisting for more than 48 hours. Urinary osmolality and sodium concentration became plasma isotonic after release of renal artery occlusion and approximated control values on day 6 after ischemia. In nine rats, the i.v. infusion of furosemide before (6 microgram/min/100 g body wt) and after (12 microgram/min/100 g body wt) renal artery occlusion protected the ischemic kidney from oligoanuria with endogenous creatinine clearance of 0.42 +/- 0.11 ml/min/g kidney wt 5 hours after ischemia. Tubular absorption of sodium and water was at least partially preserved 36 hours after ischemia when infusion of furosemide was stopped. The loop diuretic significantly (P less than 0.01) increased total urinary prostaglandin (PG) E2 excretion before and after renal artery occlusion; and 5 hours after ischemia, PGE2 excretion from the ischemic kidney significantly exceeded that from the intact kidney (P less than 0.05). Indomethacin (1 mg/100 g body wt) administered in six animals markedly suppressed control PGE2 excretion (P less than 0.05) as well as the furosemide-induced rise in urinary PG excretion before and after ischemia but did not modify the protective effect of the diuretic in this experimental model. Inhibition of PG synthesis, however, reduced urinary flow rate and sodium and potassium excretion of the contralateral intact kidney and almost completely prevented its compensatory rise in creatinine clearance. The results indicate that mechanisms other than the intrarenal prostaglandin system must be considered to mediate the protective effects of furosemide in acute ischemic renal failure.

[Comparison of the effects of gastroenteric and parenteral saline loading on kidney function after inhibition of prostaglandin synthesis (author's transl)]

We inhibited the prostaglandin synthesis with indomethacin in rats during a 7-h (periods: 1--4h; 4--5.5h; 5.5--7h) gastroenteric and parenteral infusion of isotonic saline. Indomethacin was given in a dosis of 10 mg/kg of b. wt. by stomach tube after 5.5-h infusion of saline. We studied how far prostaglandins are involved in the different function of the kidney by measuring the water and sodium excretion and the cortico-medullary osmotic and albumin concentrations of the kidney.

RESULTS

1. a) Studies Without Indomethacin. As compared to infusion of isotonic saline into the stomach water excretion is decreased by 30% (P less than 0.02) and 35% (P = n.s.) in the second and third 90 min period during parenteral infusion of saline. As compared to gastroenteric infusion we found an increase of the total osmolarity by 13% (P less than 0.02) in the cortex of the kidney. b) Studies with Indomethacin. As compared to saline infusion into the stomach indomethacin-treated rats decrease their urinary flow rates in 90 min by 26% (P = n.s.) in the presence of equivalent saline infusion into the aorta. Total osmolarity of the parenteral loaded rats increases by 17% (P less than 0.01) in the cortex of the kidney. 2. Indomethacin leads to an increased concentrating ability of the kidney in both gastroenteric and parenteral loaded rats. 3. In the presence of indomethacin plasma albumin of the kidney increases in the cortex and in the outer medulla of the kidney. In the inner medulla, and in the papillary tip, however, albumin concentration decreases significantly. As compared to gastroenteric saline infusion, the osmolarity of the kidney tissue increases and the urinary flow rate decreases during equivalent parenteral infusion of isotonic saline. The prostaglandins are not responsible for the pronounced diuresis during infusions of isotonic saline into the stomach.

The hemodynamic effects of prostaglandins in the rat. Evidence for important species variation in renovascular responses

The hemodynamic effects of prostaglandins E2, F2alpha, D2, and I2, and of indomethacin and arachidonic acid were studied in Sprague-Dawley rats, by means of the radioactive microsphere technique. In contrast to effects in other species, PGE2, PGD2, and arachidonic acid were renal vasoconstrictors in the rat, although PGE2 and arachidonic acid reduced total vascular resistance. PGF2alpha and indomethacin had no effect on the renal vasculature, but PGI2 produced renal and systemic vasodilation. These data indicate that if prostaglandin-mediated renal vasodilation occurs in the rat, PGI2 may be the substance responsible. In view of the species differences in renal vascular responses to the prostaglandins, the rat may not be an appropriate model for study of the prostaglandin system as it relates to other species.

Effects of inhibition of prostaglandin-synthesis on renal electrolyte excretion and concentrating ability in healthy man

In five healthy subjects inhibition of prostaglandin (PG)-synthesis with indomethacin did not significantly alter glomerular filtration, urinary flow rate or sodium and potassium excretion during control urine collection periods or i.v. hypertonic saline infusion. Saline administration was accompanied by a fall in urinary PGEI-excretion from 0.58 +/- 0.14 to 0.26 +/- 0.09 ng/min (p less than 0.05). While indomethacin had no effect on basal urinary osmolality (Uosm), renal concentrating ability following hypertonic saline or i.v. administration of 100 mU lysine-vasopressin significantly increased in the presence of indomethacin with Uosm rising from 805 +/- 25 to 970 +/- 53 mosm/L (p less than 0.01) and from 839 +/- 47 to 996 +/- 62 mosm/L (p less than 0.01), resp. Since this was not accompanied by respective changes in urinary excretion of cyclic adenosine monophosphate (cAMP) mechanisms other than PG-antagonism of vasopressin, such as decreased medullary washout of solute, may contribute to enhanced renal concentrating ability following inhibition of PG-synthesis with indomethacin.