title: An in situ perfused guinea-pig eye model for blood-ocular transport studies: application to amino acids.
abstract: A technique for in situ vascular eye perfusion (VEP) in the guinea-pig has been developed for measurements of the blood-ocular transport kinetics of substrates under controlled conditions of arterial inflow. The blood-aqueous and blood-vitreous barriers remained intact to the vascular space marker [3H]dextran (MW 70 kDa) with the perfusion pressure maintained between 80 and 100 mmHg. Several 3H-, 14C- or 35S-labeled amino acids, and 3H- or 14C-labeled sucrose (extracellular space marker) were used to validate the VEP model for transport kinetic studies. Multiple time-point graphic analysis was used to estimate the compartmental unidirectional blood-ocular transport constants, K(in), within the 20 min period of the VEP experiment. Blood-to-aqueous humor K(in) values for [3H]serine, [14C]N-methyl-alpha-aminoisobutyric acid (MeAIB) and [3H] or ]14C]sucrose were 3.57 +/- 0.38, 1.21 +/- 0.13 and 1.13 +/- 0.17 microliters min-1 g-1, respectively. The respective blood-to-lens K(in) values for labeled serine, MeAIB and sucrose were 1.71 +/- 0.19, 0.09 +/- 0.03 and 0.03 +/- 0.002 microliters min-1 g-1. The uptake of newly secreted amino acids from the aqueous humor in the lens followed the order: [35S]methionine greater than [3H]serine greater than or equal to [35S]cysteine greater than or equal to [3H]alanine greater than [14C]cycloleucine greater than or equal to [14C]MeAIB greater than or equal to [3H] or [14C]sucrose. The data indicate lack of a rapid blood-to-lens uptake of two model amino acids defining the A and L amino acid carriers.(ABSTRACT TRUNCATED AT 250 WORDS)
authors.affiliation: Department of Neurological Surgery, Children's Hospital of Los Angeles, University of Southern California School of Medicine 90033.
authors.forename: B V
authors.initials: BV
authors.lastname: Zlokovic
authors.forename: J B
authors.initials: JB
authors.lastname: Mackic
authors.forename: J G
authors.initials: JG
authors.lastname: McComb
authors.forename: R
authors.initials: R
authors.lastname: Kannan
authors.forename: M H
authors.initials: MH
authors.lastname: Weiss
mesh_terms: D000596:Amino Acids / Q000493:pharmacokinetics*; D000818:Animals; D001082:Aqueous Humor / Q000378:metabolism*; D001693:Biological Transport, Active; D001769:Blood / Q000378:metabolism*; D003911:Dextrans; D005260:Female; D006168:Guinea Pigs; D007908:Lens, Crystalline / Q000378:metabolism*; D008297:Male; D008954:Models, Biological; D010477:Perfusion; D013395:Sucrose / Q000493:pharmacokinetics
chemical_list: D000596:Amino Acids; D003911:Dextrans; D013395:Sucrose