Release of endogenous noradrenaline from the vascularly perfused rat stomach in vitro: modulation by pre- and postsynaptic adrenoceptors.

We developed an experimental in vitro model to detect a very small amount of endogenous noradrenaline (NA) released from the rat gastric sympathetic nerve terminals. The stomach was perfused via celiac artery with modified Krebs-Ringer solution containing 10 mM pargyline and 0.1% bovine serum albumin at a constant flow of 4 ml/min. The right greater splanchnic (SPL) nerve (preganglionic nerve of the gastric sympathetic nerve) was stimulated electrically with square-wave pulses of 2 msec duration and supramaximal intensity (5 mA) for 1 min. The rat stomach contained about 750 ng of NA and spontaneous overflow was about 0.05% of tissue content per 2 min. The NA overflow induced by SPL nerve stimulation at 5 Hz was abolished by tetrodotoxin (3 x 10(-7) M) and by Ca(++)-free medium containing 2 mM ethylene glycol bis(beta-aminoethyl ether)-N,N'-tetraacetic acid. Hexamethonium (5 x 10(-4) M) significantly decreased the NA overflow induced by SPL nerve stimulation at 5 Hz. Yohimbine (10(-7) and 10(-6) M) and prazosin (10(-7) and 10(-6) M) dose-dependently enhanced the NA overflow induced by SPL nerve stimulation at 5 Hz. Clonidine (10(-7) and 10(-6) M) and methoxamine (10(-5) M) significantly decreased the NA overflow induced by SPL nerve stimulation at 1 Hz and this methoxamine-induced inhibition was abolished by 8-(p-sulfophenyl)-theophylline (5 x 10(-5) M).(ABSTRACT TRUNCATED AT 250 WORDS)