Effect of beta-haloalkylamines and ephedrine on noradrenaline release from the intact spleen of the cat

Abstract

1. The effects of beta-haloalkylamines, phenoxybenzamine (PBZ), N-alpha-naphthyl-methyl-N-ethyl-beta-bromoethylamine (SY28), N-cyclohexyl-methyl-N-ethyl-beta-chloroethylamine (GD131) and ephedrine on noradrenaline (NA) output following nerve stimulation were studied in the intact spleen of the cat. Postganglionic sympathetic nerves were stimulated at frequencies of 10 and 30 Hz for a total of 210 stimuli.2. PBZ and SY28 (10 mg/kg) increased the transmitter output at 10 Hz by nearly 5-10 times.3. Administration of GD131 (10 mg/kg) had no effect on output at either frequency. Phentolamine (3 mg/kg) given after GD131 increased NA output at 10 Hz.4. Ephedrine (0.5 mg/kg) caused no changes in catecholamine output, while higher doses of ephedrine (10-20 mg/kg) increased the amount released at 10 Hz.5. Perfusion of the spleen with Krebs-bicarbonate solution containing either SY28, GD131 or ephedrine (10 mug/ml) increased the recovery of infused NA by 80-90%.6. It is concluded that presynaptic as well as postsynaptic events determine the overflow of NA following stimulation of sympathetic nerves of the spleen.