In the experiments presented in this article, the effect.,, of four caged analogs of the (~radrenergic agoni~,t phenylcphrm¢ ( PE| on the properties of small ( I(X)--200 p.m outer diameter ~. isolated rat me~,enteric arteries, were compared. The four ca~cd PE anah~g', contained either an unsubstituted (analo~, l and II ~ or arl ~r-carboxy substituted ( analog., III and IV j 2-nitrobcn/yl group attached tt, the phenolic ox~zt2n atom ( ()-linked: analogs II anti IV ) or to tile amino ~roup ( N-linked: analog-, i and Ill ) of PE. The structure of each ca~ed PE analog wa,, conlirmed by UV. IR and q-i NMR spectral analysis. For i~hysiolo~ical cxpcrhnents, photol~,i~, of the caged PE ana[o.~,. ~.~.;.l~, accomplished with a Hi-Tech Scientilic flashlamp, and vascular smooth mw, clc contraction wa~, mea~,ured wnh a computer-based image analy~,i~, system, in some experiments, tile fura--' rat|nine|rio technklu,: ~va~, u~,ed to examine the effect,, of the caged PE analogs on intracellular Ca: ' ieveb,. At cnncentralion < I0 *' M. none of the four analogs displayed measurable |hiring, it va~,oconstricting activity, that is. va~,t~onstrictions ~,.m.' ~n~y ~bserved f~h~wing ~ight ~a~h~. c~nsisten~ with th~ r~as~ ~f fr~ PE. At c~ncectrati~n~ >_ I0 ~ M. howe~er, both ()-Iinkedcomp~mnd~, (analogs II and IV ) and the ,~-carbo~ y ~,ub~,tituted N-linked caged P[-(analog III ) prefaced va~,tx:onstriction prior to photolysis. In contra~,t. no intrinsic vast~:onstricting ;.tcll,,ity ,,.t. as evident with tile un!.,ub~,tituted N-linked caged PE ( analog I | at concentration,, up to 3(X) p.M ( the highest concentration tested ). At concemrations _> I0 p.M. the ()-linked un~,ubstituted caged PE (analog II) also had intrin,,ic ,,a.,,¢Milating activity and markedly attenuated :a~,oconstriction~, and increases in intracellular Ca 2 prt~luced by high KCI. Similar effects were ob~,crved with the N-linked caged PE analogs ( 1 and Ill ) at >_ I(XI p.M. whereas lie measurable relaxation.,, were seen with the ~-carboxy ()-linked caged PE ana.log ( IV ) at concentrations up to 3(X) p.M ! the highest concentration tea, ted ). Taken together, the results pre~,ented heredemonswate that the N-linked unsub,,tituted caged PE an;dog ( l ) can bc used reliably at concentrations, up to I(~0 p.i and is. therefore, the analog tff choice for physiological studies of ~-rcceptor-mediatcd events.