"Caged" phenylephrine: development and application to probe the mechanism of alpha-receptor-mediated vasoconstriction.
A "caged" analogue of the alpha-adrenergic receptor agonist phenylephrine (PE) was prepared by exploiting the 2-nitrobenzyl protecting group and using a synthetic procedure developed to permit preferential derivatization at the amino group. On isolated adult rat mesenteric arterioles, caged-PE had no measurable effects at concentrations up to 100 microM; 0.5-ms light flashes in the presence of caged-PE, however, produced marked and dose-dependent vasoconstriction. Flash-induced vasoconstrictions were blocked by the alpha-receptor antagonist phentolamine and were unaffected by the beta-receptor antagonist propranolol, indicating that the light-induced responses reflect the selective activation of alpha-adrenergic receptors. After a single flash, a large transient decrease in vessel diameter was recorded, and in most vessels, this was followed by a smaller, sustained constriction. The sustained component of the contraction was selectively eliminated when Ca2+ was removed from the bath, which suggests that different mechanisms underlie the transient and the sustained responses to PE. The responses to single flashes of varying intensities occurred with a mean latency of 460 ms, which is consistent with the intermediacy of several steps between alpha-receptor activation and contraction. We anticipate that it will be possible to extend this approach to develop caged analogues of other neurotransmitters for mechanistic and kinetic studies.
Department of Molecular Biology and Pharmacology, Washington University School of Medicine, St. Louis, MO 63110.
S
S
Muralidharan
G M
GM
Maher
W A
WA
Boyle
J M
JM
Nerbonne
D000818:Animals; D001160:Arterioles / Q000187:drug effects / Q000502:physiology*; D004305:Dose-Response Relationship, Drug; D066298:In Vitro Techniques; D008638:Mesenteric Arteries / Q000187:drug effects / Q000502:physiology; D009131:Muscle, Smooth, Vascular / Q000187:drug effects / Q000502:physiology*; D010646:Phentolamine / Q000494:pharmacology; D010656:Phenylephrine / Q000031:analogs & derivatives* / Q000138:chemical synthesis / Q000494:pharmacology; D010782:Photolysis; D011433:Propranolol / Q000494:pharmacology; D051381:Rats; D011942:Receptors, Adrenergic, alpha / Q000187:drug effects / Q000502:physiology*; D013997:Time Factors; D014661:Vasoconstriction / Q000187:drug effects / Q000502:physiology*
D011942:Receptors, Adrenergic, alpha; C081527:N-2-nitrobenzylphenylephrine; D010656:Phenylephrine; D011433:Propranolol; D010646:Phentolamine