Modulated hemodynamic response to clonidine in bile duct-ligated rats: The role of nitric oxide

Despite the well-known involvement of the peripheral sympathetic abnormalities in the development of cardiovascular complications of cholestasis, the role of the central sympathetic system is still elusive. The goal of this study was to evaluate the effects of central sympathetic tone reduction, through clonidine administration, on hemodynamic parameters of 7-day bile duct-ligated rats. The contributions of nitric oxide and endogenous opioids were also examined by acute intravenous (10 min before clonidine) or chronic daily subcutaneous administrations of N(ω)-nitro-l-arginine methyl ester (l-NAME, 3 mg/kg) or naltrexone (20 mg/kg). Seven days after bile duct ligation or sham operation, animals were anesthetized with sodium pentobarbital. After hemodynamic stabilization, clonidine (10 μg/kg) was injected intravenously, which elicited an initial hypertension (the peripheral effect) followed by persistent hypotension and bradycardia (the central effects). Cholestatic rats demonstrated significant basal bradycardia (P < 0.001) and hypotension (P < 0.05), which were corrected by chronic naltrexone but not l-NAME treatment. While the peripheral effect of clonidine was blunted, the central effects were exaggerated in cholestatic rats (P < 0.01). Acute l-NAME treatment accentuated the hypertensive phase in sham-operated and cholestatic rats (P < 0.05). However, the difference between the two groups was preserved (P < 0.01). This treatment attenuated the central effects in both sham-operated and cholestatic rats to the same level (P < 0.001). Chronic l-NAME treatment resulted in exaggeration of the peripheral response in cholestatic and central responses in sham-operated rats (P < 0.05), and abolished the difference between the groups. Naltrexone treatment had no significant effect on either the central or the peripheral responses to clonidine. This study shows that both central and peripheral hemodynamic responses to clonidine are altered in cholestasis. It also provides evidence that nitric oxide contributes to the development of these abnormalities.