Enhanced Ca response to AVP in preglomerular vessels from rats with genetic hypertension during different hydration states

Vagnes, Øyvind B., Frank H. Hansen, Jian J. Feng, Bjarne M. Iversen, and William J. Arendshorst. Enhanced Ca response to AVP in preglomerular vessels from rats with genetic hypertension during different hydration states. Am J Physiol Renal Physiol 288: F1249–F1256, 2005. First published January 18, 2005; doi:10.1152/ajprenal.00363.2004.—Exaggerated arginine vasopressin (AVP)-induced calcium signaling and renal vasoconstriction, characteristic in young spontaneously hypertensive rats (SHR) during euvolemia, are related to greater amounts of V1a receptor mRNA and V1a protein in preglomerular resistance arterioles. The present study determined whether V1a receptor density and calcium signal transduction in the renal vasculature of young SHR is regulated appropriately during physiological changes in hydration state. [H]AVP ligand binding documented twoto threefold greater density of V1a receptors in euvolemic SHR vs. WistarKyoto (WKY) rats. Parallel changes in V1a receptor density were observed in both strains during chronic water loading (plus 50 fmol/mg) and during dehydration (minus 50 fmol/mg). Affinity was unchanged. Real-time RT-PCR demonstrated that V1a mRNA in preglomerular arterioles was three times greater in euvolemic SHR. Dehydration decreased expression 50% in renal vessels independent of rat strain; water loading increased V1a mRNA. Thus V1a receptor regulation correlated with changes in mRNA in a normal manner in response to chronic changes in AVP concentration, albeit set at a higher level in SHR. In dehydrated animals, AVP increased the cytosolic Ca concentration ([Ca ]i) by 60 5 and 112 13 nM cytosolic Ca in WKY and SHR, respectively (P 0.01), whereas in hydrated animals the [Ca ]i increase was 168 10 and 220 18 nM, respectively (P 0.05). In all hydration states, calcium signaling was greater in SHR compared with WKY (P 0.05). Calcium signaling paralleled changes in the receptor density and mRNA. Mechanisms other than hydration state per se are likely to be responsible for the twoto threefold difference in the V1a receptor density between WKY and SHR in the renal vasculature at the critical age of 6 wk.