Nitrergic and opioidergic systems affect radiographic density and histomorphometric indices in bile-duct-ligated cirrhotic rats

Metabolic bone disease is a major issue in chronic liver disease. Increased production of nitric oxide (NO) and elevation of endogenous opioids have been suggested to occur during cholestasis/cirrhosis. We aimed to investigate the involvement of nitrergic and opioidergic systems in bone loss after bile-ductligation (BDL) in rats using optical density (OD) evaluation and histomorphometric analysis. BDL- and sham-operated (SO) rats received injections of 3 mg/kg N omega-Nitro-L-arginine methyl-ester-hydrochloride (L-NAME) as an NO-synthase inhibitor, 10 mg/kg naltrexone (NTX) as an opioid-receptors antagonist or saline once daily for 28 days. Lateral cephalometric radiographs were taken on days 0 and 28 and histomorphometric and biochemical indices were measured. Plasma levels of total bilirubin and alkaline-phosphate were markedly increased in BDL compared with SO rats (p=0.05). Among the studied variables, osteoclast number/mm trabecular surface showed significant increase in BDL animals compared to controls, which was significantly reduced following NO-synthase inhibition (p=0.05). Similarly, cortical area slightly decreased in BDL animals in comparison to controls, whereas both L-NAME and NTX significantly increased this variable. Following BDL, optical density increased in the skulls of cirrhotic animals and showed a significant decrease after blocking opioid-receptors (p=0.05). Inhibition of NO-synthase and/or opioid receptors caused significant changes in OD and histomorphometric parameters in BDL rats, both in favor of reducing bone loss. If confirmed by further studies, it seems that manipulation of these systems might be able to improve bone problems in subjects with cholestasis/cirrhosis.