Activation of Hypertensin and Tyrosine by Subthreshold Amounts of Epinephrine.

Abstract

Hypertensin has no effect on the vessels of the perfused rabbit''s ear. It becomes strongly vasoconstrictive, however, when supplemented with traces of epinephrine and also when fresh plasma is added to the perfusate. None of 20 different amino acids tested in perfusion expts. on the rabbit''s ear had any constrictor effect. When traces of epinephrine were included in the perfusion fluid, tyrosine was the only one of the 20 that exhibited a strong and sustained vasoconstriction. Glycyl-1-tyrosine was inactive with and without epinephrine. 1-Tyrosyl-glycine and tyrosine-amide-acetate both inactive when perfused alone, constricted the vessels if combined with minute amts. of epinephrine. The activity of these 2 compds., however, was definitely less than that of tyrosine. Introduction of I into the tyrosine molecule abolished the constrictor action entirely. It is concluded that constriction of the blood vessels of the rabbit''s ear is dependent to a large degree upon traces of epinephrine and available tyrosine-containing compds.