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Melatonin inhibits hypothalamic gonandotropin-releasing hormone release and reduces biliary hyperplasia and fibrosis in cholestatic rats

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AJP Gastrointestinal and Liver Physiology

Published online on

Abstract

Melatonin is a hormone produced by the pineal gland with increased circulating levels shown to inhibit biliary hyperplasia and fibrosis during cholestasis. Melatonin also has the capability to suppress the release of hypothalamic gonadotropin releasing hormone (GnRH), a hormone that promotes cholangiocyte proliferation when serum levels are elevated. However, the interplay and contribution of neural melatonin and GnRH to cholangiocyte proliferation and fibrosis in bile duct-ligated (BDL) rats has not been investigated. In order to test this, cranial levels of melatonin were increased by implanting osmotic minipumps that performed an intracerebroventricular (ICV) infusion of melatonin or saline for 7 days starting at the time of BDL. Hypothalamic GnRH mRNA and cholangiocyte secretion of GnRH and melatonin was assessed. Cholangiocyte proliferation and fibrosis was measured. Primary human hepatic stellate cells (HSCs) were treated with cholangiocyte supernatants, GnRH, or the GnRH receptor 1 (GnRHR1) antagonist, cetrorelix acetate and cell proliferation and fibrosis gene expression were assessed. Melatonin infusion reduced hypothalamic GnRH mRNA expression and led to decreased GnRH and increased melatonin secretion from cholangiocytes. Infusion of melatonin was found to reduce hepatic injury, cholangiocyte proliferation and fibrosis during BDL-induced liver injury. HSCs supplemented with BDL cholangiocyte supernatant had increased proliferation and this increase was reversed when HSCs were supplemented with supernatants from melatonin-infused rats. GnRH stimulated fibrosis gene expression in HSCs and this was reversed by cetrorelix acetate co-treatment. Increasing bioavailability of melatonin in the brain may improve outcomes during cholestatic liver disease.