Vasopressin V2 receptor expression during different phases of the estrous cycle in Sprague Dawley rats

Abstract

Women may be at greater risk than men for potential dehydration as it has been shown that women have greater water turnover than men, though the mechanism for this is unclear. Our lab recently demonstrated that water load excretion in conscious, euhydrated, adult female Sprague Dawley (SD) rats varies with estrous cycle phase. In this study we investigated whether estrous phase changes in renal sensitivity to vasopressin (VP), the hormone critical to water regulation, may play a role in water excretion differences via altered renal VP V2 receptor (V2R) expression. Blood samples for plasma osmolality (pOsm, mOsm/kg H2O) and plasma VP (μU/ml), and renal inner medulla (IM) samples were obtained from adult SD rats. V2R expression (relative units) was compared between males (M, n=12) and females (F) in anestrus (n=14), proestrus (n=11), estrus (n=10) and metestrus (n= 8). Results indicate that while female rats at all phases of the estrous cycle have a lower osmotic set-point than males at similar VP levels, there were no differences between estrous cycle phases. Likewise, estrous phase variations in V2R expression were not evident. Thus, V2R renal expression did not appear to be responsible for estrous cycle-dependant differences in water excretion. Instead, water excretion differences may be due to direct influence of steroid hormones on VP action. (Supported by Am Physiol Society UGSRF 2005, and USAMRAA DAMD170010673)