Sex Differences in the Regulation of Vasopressin and Oxytocin Secretion in Bile Duct-Ligated Rats

Abstract

Introduction: Hyponatremia due to elevated arginine vasopressin (AVP) secretion increases mortality in liver failure patients. No previous studies have addressed sex differences in hyponatremia in liver failure animal models. Objective: This study addressed this gap in our understanding of the potential sex differences in hyponatremia associated with increased AVP secretion. Methods: This study tested the role of sex in the development of hyponatremia using adult male, female, and ovariectomized (OVX) female bile duct-ligated (BDL) rats. Results: All BDL rats had significantly increased liver to body weight ratios compared to sham controls. Male BDL rats had hyponatremia with significant increases in plasma copeptin and FosB expression in supraoptic AVP neurons compared to male shams (all p < 0.05; 5–7). Female BDL rats did not become hyponatremic or demonstrate increased supraoptic AVP neuron activation and copeptin secretion compared to female shams. Plasma oxytocin was significantly higher in female BDL rats compared to female sham (p < 0.05; 6–10). This increase was not observed in male BDL rats. Ovariectomy significantly decreased plasma estradiol in sham rats compared to intact female sham (p < 0.05; 6–10). However, circulating estradiol was significantly elevated in OVX BDL rats compared to the OVX and female shams (p < 0.05; 6–10). Adrenal estradiol, testosterone, and dehydroepiandrosterone (DHEA) were measured to identify a possible source of circulating estradiol in OVX BDL rats. The OVX BDL rats had significantly increased adrenal estradiol along with significantly decreased adrenal testosterone and DHEA compared to OVX shams (all p < 0.05; 6–7). Plasma osmolality, hematocrit, copeptin, and AVP neuron activation were not significantly different between OVX BDL and OVX shams. Plasma oxytocin was significantly higher in OVX BDL rats compared to OVX sham. Conclusions: Our results show that unlike male BDL rats, female and OVX BDL rats did not develop hyponatremia, supraoptic AVP neuron activation, or increased copeptin secretion compared to female shams. Adrenal estradiol might have compensated for the lack of ovarian estrogens in OVX BDL rats.