Abstract

Studies have been made of the potential usefulness of adrenergic blocking 2-halogenoethylamines for labeling time α-receptor. The uptake of ³H-labeled N-(2-bromoethyl)-N-ethyl-N-1-naphthylmethylamine (³H-SY.28) by rabbit vas deferens was shown to be nonspecific and the 2-halogenoethylamine apparently showed little specificity for the α-receptor. In an attempt to obtain greater specificity, rabbit aorta and vas deferens were pretreated with N,N-dimethyl-2-bromo-2-phenylethylamine, a short-lasting irreversible α-receptor antagonist, prior to treatment with ³H-SY.28. Tissues pretreated with the short-lasting antagonist should take up less ³H-SY.28 and the difference between this uptake and that of controls should reflect the concentration of α-receptor material. However, this treatment did not afford any significant protection against the uptake of ³H-SY.28. The possible protective effects of various amines against labeling by ³H-SY.28 were also investigated: no correlation could be found between the protective ability of these amines and their "direct" or "indirect" sympathomimetic activities. An investigation was also made of the finding that trypsin can reverse the blockade of ³H-SY.28. It was concluded that the recovery of response following trypsin is probably unrelated to α-receptor regeneration.

The distribution of ³H-SY.28 and its corresponding alcohol was studied in rats. Our results suggest that the prolonged tissue retention of radioactivity following ³H-SY.28 is probably due to the high binding capacities of tissues for ³H-SY.28 alcohol rather than to the presence of high concentrations of covalently bound ³H-SY.28.