"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.
Muralidharan
S
S
Department of Molecular Biology and Pharmacology, Washington University School of Medicine, St. Louis, MO 63110.
Maher
G M
GM
Boyle
W A
WA
Nerbonne
J M
JM
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