Hyponatremia induced by vasopressin or desmopressin in female and male rats

Abstract

Previous studies have demonstrated that hyponatremia induced by continuous sc infusion of desmopressin (dDAVP) in combination with a liquid diet allows brain volume adaptation with negligible morbidity and mortality in rats. In contrast, some studies of hyponatremia induced by injections of long-acting preparations of arginine vasopressin (AVP) have reported mortality rates as high as 20 to 80%. To evaluate the possibility that the use of AVP to produce antidiuresis may cause greater mortality as a result of increased brain edema, this study examined brain water and electrolyte contents of male and female rats after varying periods of hyponatremia induced by continuous sc infusions of either dDAVP (5 ng/h) or AVP (100 ng/h). Rats infused with AVP had AVP levels in plasma elevated into ranges reported in patients with the syndrome of inappropriate antidiuretic hormone secretion (17.5 ± 2.0 pg/mL); however, despite the production of comparably severe degrees of hyponatremia with both AVP and dDAVP infusions (105 to 115 mmol/L), no mortality occurred in any of the rats (N = 40 AVP infused and N = 40 dDAVP infused). AVP- and dDAVP-induced hyponatremia both caused transient brain edema in female and male rats, but brain water content returned to the levels of normonatremic controls after 5 days in the females and 10 days in the males. However, at no time during the 10-day study period did brain water content differ significantly between rats infused with AVP or dDAVP, either in females or males. Decreases in brain electrolytes were also equivalent in the AVP- and dDAVP-infused male and female rats. Thus, by methods that maintain AVP levels in plasma in pathophysiologically relevant ranges but below thresholds for precipitating AVP V1 receptor-mediated effects, no significant differences were observed between systemic infusions of AVP or dDAVP with regard to the degree of hyponatremic brain edema induced, losses of brain electrolytes, or the incidence of morbidity and mortality from neurologic deficits.