Experimental study in bile duct-ligated rats of vasopressin and preoperative volume loading to prevent hypotensive crises

Are bile acids involved in the renal dysfunction of obstructive jaundice? An experimental study in bile duct ligated rats

BACKGROUND

Surgery on patients with obstructive jaundice is associated with a significant risk of postoperative renal failure. Bile acids are implicated as nephrotoxins because they accumulate in the plasma and the kidney becomes their only excretory route in cholestasis. The experimental evidence favoring this proposal is inadequate and unconvincing. Therefore, we designed an animal experiment involving bile duct ligated (BDL) rats in which we could correlate variations in serum and urine bile acids with indices of nephrotoxicity and renal function.

HYPOTHESIS

Bile acids are putative nephrotoxins.

MATERIALS AND METHODS

Total serum and urine bile acid concentrations and profiles were determined using liquid chromatography/gas chromatography/mass spectrometry selected ion monitoring. Nephrotoxicity was assessed by renal histopathology and by determination of the urinary activities of the following enzymes: muramidase, glutamate dehydrogenase, alkaline phosphatase, N-acetyl-beta-D-glucosaminidase, and lactate dehydrogenase. Renal function was assessed by measuring urine osmolality, daily osmolar excretion, sodium excretion (U(Na)V), potassium excretion (U(K)V), and total protein and albumin excretion.

RESULTS

Maximum plasma concentrations and renal clearance of bile acids occurred between the third or fourth postoperative day following BDL. This peak coincided with maximal disruption of proximal convoluted tubule architecture and postoperative changes in renal function-increased urine flow rate and decreases in urine osmolality and sodium excretion. Thereafter, 1) plasma levels of bile acids returned toward normal levels, 2) urinary bile acid clearance declined, 3) normal renal histology was restored, and 4) normal renal function was reestablished. Throughout this period, fluctuations in enzymuria were evident. However, these shifts did not coincide with plasma and urine bile acid concentrations and histological and functional changes.

DISCUSSION AND CONCLUSIONS

Transient functional impairment of renal cation and water transport and nonspecific morphological changes in the proximal convoluted tubule occur 3 to 4 days following bile duct ligation in rats. These functional and morphological changes occurred when plasma total and urinary bile acids were at their peaks. Although it is tempting to equate association with causality, we cannot implicate bile acids as being responsible for the aberrations in renal function and structure following BDL. Accordingly, we have concluded that elevated plasma concentrations of bile acids are renal exacerbates acting in concert with other factors, be they prerenal or renal in origin to precipitate a cascade of events leading to postoperative renal failure in cholestasis.

Effects of experimental obstructive jaundice on contractile responses of dog isolated blood vessels: role of endothelium and duration of bile duct ligation

1. We examined the effects of experimental obstructive jaundice caused by bile duct ligation (BDL) on vascular smooth muscle function, as well as the underlying mechanisms involved, by recording responses to noradrenaline (NA), 5-hydroxytryptamine (5-HT) and acetylcholine (ACh) in canine isolated renal arteries and to NA in isolated mesenteric arteries in vitro. All studies were performed 7 days after the onset of BDL in renal arteries and 3, 7 and 15 days after the onset of BDL in mesenteric arteries. 2. The maximum contraction evoked by both NA and 5-HT was significantly attenuated with no change in agonist potency (pD2 value) in renal arteries with endothelium obtained from 7 day BDL dogs when compared with those from sham-operated controls (SO). However, the reduction almost disappeared when the endothelium was removed. In contrast, no change in the responsiveness of renal arteries to KCl could be detected at 7 day BDL. Endothelium-dependent relaxations produced by ACh were significantly increased in renal artery rings from 7 day BDL dogs, but the endothelium-independent relaxations produced by papaverine in BDL preparations were not changed when compared with SO controls. 3. At 7 and 15 days after BDL, the Emax values of the mesenteric ring of BDL dogs to NA were significantly lower than that of SO controls, whereas 3 days after surgery there was no significant difference. The pD2 values in arteries obtained from 15 day BDL animals were significantly lower than those obtained from SO control animals. However, no significant changes in pD2 values were seen 3 and 7 days after the onset of BDL. 4. In conclusion, it is suggested that enhanced production and/or release of nitric oxide, mainly of endothelial origin, is associated with reduced vascular responses to contractile agents in experimental obstructive jaundice and that this effect is related to the duration of obstructive jaundice. These results may explain, at least in part, a cause of hypotension that leads to renal failure in patients with obstructive jaundice.

Drinking and blood pressure during sodium depletion or ANG II infusion in chronic cholestatic rats

After a chronic ligation of the common bile duct (BDL), Long-Evans rats are hypotensive and have elevated saline intake during both sodium-depleted and nondepleted conditions. We tested whether BDL rats have exaggerated hypotension during sodium depletion or an elevated dipsogenic response to angiotensin II (ANG II) that might help to explain the saline intake. After 4 wk of BDL, rats were hypotensive at baseline and developed exaggerated hypotension during acute furosemide-induced diuresis. Without saline to drink, BDL rats increased water intake during depletion equal to sham-ligated rats. However, with saline solution available at 22 h after sodium depletion, the BDL rats drank more water and saline than did sham-ligated rats. This rapid intake temporarily increased their mean arterial pressure to equal that of sham-ligated rats. Intravenous infusion of ANG II induced equal drinking responses despite reduced pressor responses in the BDL rats relative to sham-ligated rats during both ad libitum and sodium-depleted conditions. Thus BDL rats have exaggerated hypotension during diuresis, and their hypotension is corrected by drinking an exaggerated volume of saline, but they do not have an increased drinking response to ANG II.