Uncompetitive character of inhibition by prostaglandin E2 of the enhancing effect of alpha-adrenoceptor blocking drug on noradrenaline secretion in isolated guinea-pig vas deferens

Some mechanism which may modulate noradrenaline release in guinea-pig isolated ileum

Guinea-pig isolated ileum pre-incubated with [3H]noradrenaline, released 3H-label during coaxial stimulation at 3.2-12.8 Hz. This evoked 3H-overflow seems due to nerve stimulation, and may be frequency-dependent. The 3H-overflow evoked by coaxial stimulation was increased with 2.6 muM phentolamine, reduced at threshold stimulation by 0.56 muM prostaglandin E1, but the tendency for 2.8 muM indomethacin to increase the evoked 3H-overflow was not statistically significant. The results indicate that the release of noradrenaline from guinea-pig ileum may be modulated by activation of presynaptic alpha-adrenoceptors, whereas prostaglandins act mainly at a postsynaptic site to modulate the sympathetic response.

Some physiological and pharmalogical characteristics of the stimulus induced release of norepinephrine from the rabbit superior cervical ganglion

The cervical sympathetic nerve stimulated release of norepinephrine (NE) from the rabbit superior cervical ganglion (SCG) was characterized. The quantity of NE released per impulse declined with increasing stimulation frequency over the range of 3/sec to 15/sec. Nerve stimulated NE release was potentiated by 1 micromolar desmethylimipramine and 25 micromolar phenoxylbenzamine and inhibited by 1 micromolar bretylium, 25 micromolar methoxamine and 1 micromolar prostaglandin E1. These results suggest that nerve stimulated NE release in the rabbit SCG occurs from sympathetic fibers which are subject to the same neurosecretory control mechanisms as sympathetic fibers elsewhere in the autonomic nervous system.