Renal excretory responses to mu-opioids and volume expansion in ketamine/xylazine anesthetized rats

Intravenous infusion of the α₂-agonist, xylazine, significantly augments urine flow rate and urinary sodium excretion in ketamine-anesthetized rats. The present studies examined whether these anesthetized rats respond to acute isotonic saline volume expansion (VE) or the centra] administration of mu-opioids in the same manner as conscious rats. Sprague-Dawley rats were chronically implanted with arterial and venous catheters. For opioid studies, an intracerebroventricular (ICV) cannula was also implanted. Rats were anesthetized by using a continuous i.v. infusion of ketamine (1.0 mg/kg/min) and xylazine (50 μg/kg/mtn) in isotonic saline vehicle, and a urinary bladder cannula implanted. In the first group (n=5), VE (5 % body weight over 30 min) produced a diuretic (23±3 to 104±17 μl/min/gkw) and natriuretic (1.7±.7 to 16.0±2.4 μeq/min/gkw) response. These VE-induced responses were similar to those previously observed in conscious rats (JPET. 222:199, 1995). In separate studies (n=5), ICV injection of the mu-opioid agonist, dermorphin (0.1 nmol/kg) produced a diuretic (27±2 to 67±2 μl/min/gkw) and antinatriuretic response (3.8±.2 to 1.3±.2 μeq/min/gkw) in anesthetized rats. These responses were also similar to those previously observed in coascious rats (JPET, 205:134, 1993). These results suggest that the changes in urine flow rate and urinary sodium excretion elicited by VE or ICV dermorphin in ketamine/xylazine-anesthetized rats are comparable to those observed in conscious rats Whether the renal responses to these physiologic and pharmacologie stimuli are mediated via the same mechanism(s) in ketamine/xylazine-anesthetized and conscious rats remains to be determined. Support DK 43337 and DA 08255.