Renal hemodynamics in young and old spontaneously hypertensive rats duringintrarenal infusion of arginine vasopressin

Background/Aims: To gain insight into the effect of arginine vasopressin AV P) on renal hemodynamics in hypertensive rats, we investigated the vasocons trictive response to AVP on total renal blood flow (RBF) and total and zona l glomerular filtration rate (GFR) in young and old spontaneously hypertens ive rats (SHR). A hypothesis of increased AVP sensitivity in the juxtamedul lary cortex of SHR was tested. Methods: Total RBF and total and zonal GFR w ere studied in 10- and 40-week-old SHR and normotensive Wistar-Kyoto rats ( WKY). RBF was recorded by a flowmeter before infusion of AVP and immediatel y after injection of a bolus dose of 10 ng AVP. Whole kidney GFR and its in tracortical distribution was measured by the tubular uptake of I-125- and I -131-labelled aprotinin before and during a continuous infusion of AVP 5 ng /min. Ligand binding measurements of preglomerular V-1a receptors were perf ormed in young and old rats. Results: RBF decreased by 43 +/- 3% in 10-week SHR (9.2 +/- 0.5 vs. 5.2 +/- 0.3 ml.min(-1).g(-1)), significantly more tha n 10-week WKY where RBF decreased by 35 3% (9.6 +/- 0.7 vs. 6.5 +/- 0.5 ml. min(-1).g(-1)) (p < 0.05). The effect of AVP on RBF was attenuated in 40-we ek-old rats where the decline in RBF was 29 +/- 5% in SHR and 23 +/- 4% in WKY (p > 0.05). GFR decreased by 6 +/- 3% (1.03 +/- 0.04 vs. 0.96 +/- 0.04 ml.min(-1).g(-1), p < 0.05) in 10-week SHR and was unchanged in 10-week WKY (1.10 +/- 0.07 vs. 1.08 +/- 0.04 ml.min(-1).g(-1), p > 0.10). GFR decrease d by 11 +/- 10% in 40-week SHR and by 4 +/- 4% in 40-week WKY (p > 0.05). A VP infusion significantly increased filtration fraction in all groups excep t 40-week SHR, indicating that AVP has the strongest vasoconstrictive effec t on postglomerular vessels. The intrarenal distribution of GFR was unchang ed in the normotensive and hypertensive groups. Vla receptor density was up regulated in young SHR compared to young WKY (p < 0.05), but downregulated in old compared to young SHR (p = 0.05). Conclusion: The results indicate t hat AVP sensitivity is not increased in the juxtamedullary cortex in SHR an d the reduced vasoconstrictive effect in old SHR is due to a reduced densit y of V-1a receptors. Copyright <(c)> 2001 S. Karger AG, Basel.