Influence of Synthesis and Membrane Pump Inhibition on the Nerve Impulse Induced Disappearance of Noradrenaline from Rat Salivary Glands

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Abstract
The cervical sympathetic trunk of rats was unilaterally stimulated with 5 imp/s for different time intervals up to 3 h and the contraction response of the lower eye‐lid was recorded. At the end of the stimulation the content of endogenous noradrenaline (NA) and previously administered dl‐3H‐NA was measured in the submaxillary + sublingual glands. For inhibition of the NA synthesis 500 mg/kg DL‐a‐methyl‐p‐tyrosine methylester (H 44/68) was given to one group of rats and for blocking the recapture of NA into the nerve endings protriptyline (initially 10 mg/kg) was administered to some other rats. Also, some rats received both drugs. In untreated rats3H‐NA disappeared faster than endogenous NA following nerve stimulation while after synthesis inhibition no difference in disappearance rate was found between tritiated and endogenous NA. The contraction response of the lower eye‐lid was gradually reduced after synthesis inhibition while it remained essentially unchanged throughout the experiment in the untreated animals. The data suggest that the amount of immediately available transmitter decreases during stimulation after inhibition of the NA synthesis, resulting in a reduced transmitter output per stimulus and hence in a reduced effector response. The retarded disappearance of3H‐NA seen after protriptyline treatment could also be explained by a reduced output per stimulus but other possibilities may also exist.