SUMMARY

The ability of three new beta adrenergic blocking agents, dl-1-(2-nitrophenyl)-1-hydroxy-2-isopropylaminoethane (2-INPEA), dl- 1- (3-nitrophenyl)-1-hydroxy-2-isopro-pylaminoethane (3-INPEA), and dl- 1- (4-nitrophenyl)-1-hydroxy-2-isopropylaminoeth-ane (4-INPEA) to antagonize norepinephrine-induced lipolysis was investigated utilizing an isolated fat cell preparation. All three isomers were capable of blocking norcpinephrine competitively. The pA10 values for 2-INPEA, 3-INPEA, and 4-INPEA were determined and concentration-inhibition curves were plotted. 4-INPEA wa found to be approximately ten times as potent as 2-INPEA and 3-INPEA, the latter two being equipotent. The results are discussed in relation to the classification of the adrenergi’ receptor in adipose tissue