Changes in Regional Blood?Brain Transfer of l-Leucine Elicited by Arginine-Vasopressin

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Abstract
Arginine-vasopressin (AVP), injected into the carotid artery in physiological concentration together with L-leucine, changed kinetic constants of the blood—brain barrier (BBB) transport of this neutral amino acid without changing the cerebral blood flow (CBF). The maximum velocity of transport (Vmax), the half-saturation constant (Km), the nonsaturable transport constant (KD), and CBF were estimated in nine brain regions of male Wistar rats anesthetized with ether. In cerebral hemisphere, Vmax decreased from 21 nmol min−1. g−1 (control) to 7.6 nmol. min−1. g−1 (AVP). Km decreased from 0.11 to 0.029 mM. Regional differences of the kinetic constants were found in controls as well as in AVP-treated animals. In all regions, the calculated constants Vmax and Km of animals coinjected with AVP were significantly decreased when compared to controls. A direct or indirect interaction of AVP with the transport system of large neutral amino acids is suggested.