Inhibition of sympathetic neurotransmission via NEM-sensitive H3-receptors in the guinea pig vas deferens.

The influence of N-ethylmaleimide (NEM) on sympathetic neurotransmission induced by field stimulation on the isolated guinea pig vas deferens was studied. Application of (R)-alpha-methylhistamine (0.1 mcmol/l) significantly inhibited the sympathetic response by 26.0%, while thioperamide facilitated the sympathetic contraction of vas deferens evoked by field pulses by 221.1%. Pretreatment of vas deferens with NEM (60 mcmol/l) for 15 min abolished both the inhibitory and facilitatory effects. Attenuation of thioperamide facilitatory effect by NEM was not significantly altered when the H3-receptors were occupied by thioperamide prior to and during NEM treatment. The results suggest that effects mediated by H3-receptors in the guinea pig vas deferens were NEM-sensitive and possibly transmitted by Gi or Go proteins.