MEASUREMENT OF CHANGES IN CEREBRAL BLOOD-VOLUME IN SPONTANEOUSLY HYPERTENSIVE RATS FOLLOWING L-ARGININE INFUSION USING DYNAMIC SUSCEPTIBILITY CONTRAST MRI

To understand whether the NO-dependent vasodilator L-arginine was effe ctive upon a chronically hypertensive cerebral capillary endothelium, dynamic susceptibility contrast MRI was used to measure the relative c erebral blood volume (rCBV) changes in nonischemic spontaneously hyper tensive rats (SHRs), rCBV was measured in 11 rats at 4.7 T using fast gradient echo imaging with intravenous injection of Gd-DTPA, Images we re acquired before, immediately after, and up to 90 min after the infu sion of 300 mg/kg L-arginine (n = 7) or of an equivalent volume of sal ine (n = 4), L-arginine increased rCBV in cortex beginning 10 min afte r infusion and reached significance after 30 min (P < 0.01), reached a peak of 1.24 +/- 0.06 (mean +/- SEM) times pre-injection level after 50 min, and was sustained throughout the 90 min observation period. In contrast, the rCBV in the deeper gray matter (striatum) showed no sta tistically significant change over the 90 min observation period, Whil e this is consistent with previous studies showing that L-arginine inf usion can directly modulate vascular tone and cerebral hemodynamics, i t demonstrates that the effect is present only in cortex, and that it can occur also in the setting of a disturbed capillary endothelium.