JUXTAMEDULLARY MICROVASCULAR RESPONSES TO ARGININE-VASOPRESSIN IN RAT-KIDNEY

Experiments were performed to determine the site of arginine vasopress in (AVP)induced vascular resistance adjustments that result in decreas es in papillary blood flow. Simultaneous measurements of luminal diame ter and centerline erythrocyte velocity allowed estimation of single-v essel blood flow in in vitro blood-perfused juxtamedullary nephrons. A VP (0.1-1,000 pM) caused concentration-dependent reductions in outer m edullary descending vasa recta (OMDVR) blood flow (10 pM) without alte ring OMDVR diameter. Afferent arteriolar diameter was significantly de creased by 1 pM AVP, whereas arcuate artery diameter was decreased by 100 pM AVP. Increasing the concentration of AVP to 1,000 pM resulted i n significant reductions of vessel diameter in interlobular arteries, distal afferent arterioles, and efferent arterioles. The effects of AV P to decrease afferent arteriolar diameter and blood flow were blocked in the presence of V-1 receptor antagonist. These data indicate that afferent arterioles exhibit the greatest sensitivity to the vasoconstr ictor effects of AVP, whereas OMDVR appear insensitive. We conclude th at the change in OMDVR blood flow produced by AVP is not due to a dire ct effect of the peptide on this vascular segment but to its effect on upstream vessels.