Effect of atrial natriuretic factor and 8-bromo cyclic guanosine 3':5'-monophosphate on [3H]acetylcholine outflow from myenteric-plexus longitudinal muscle of the guinea pig.

We report that atrial natriuretic factor (ANF) inhibits electrically induced cholinergic twitches of longitudinal muscle in whole intestinal segments and myenteric-plexus longitudinal muscle (MPLM) strips from the guinea pig ileum. To elucidate the possible presynaptic mechanism of ANF's action, we studied spontaneous and stimulation-evoked radiolabeled acetylcholine (ACh) outflow from MPLM after incubation with [3H]choline. We developed a method of mounting and treating MPLM preparations, which allowed us, at the same time, to record isometric contractions and to determine [3H]ACh outflow upon electrical stimulation by a train of three pulses.

Inhibitory action of atrial natriuretic factor on cholinergic and nonadrenergic, noncholinergic neurotransmission in guinea pig small intestine.

We studied the effect of synthetic rat atrial natriuretic factor (ANF) (Ser 99-Tyr 126) on the isolated guinea pig proximal ileum. This preparation contained about one-third of the endogenous tissue ANF content which, for the most part, comes from the blood. ANF inhibited, in a dose-dependent manner, cholinergic twitch contractions (EC50 = 4.

Calcitonin gene-related peptide action on intestinal circular muscle.

Isolated segments of the guinea pig small intestine were used to examine the effect of calcitonin gene-related peptide (CGRP) on the motor activity of the circular muscle. CGRP (0.3-30 nM) initiated phasic contractions of the circular muscle due to stimulation of cholinergic neurons.

Action of histamine on nerve mediated responses of the guinea-pig ileum.

The effect of histamine on the responses of the guinea-pig ileum to stimulation of intramural nerves and to some potential nonadrenergic, noncholinergic (NANC) neurotransmitters was analysed. During sustained tonic histamine contraction, electrical stimulation of all intramural nerves elicited a biphasic response (contraction followed by after-relaxation) and application of ATP and bradykinin caused relaxation of the ileum in contrast to their contractile effect on basal tension. Histamine reduced contractile and augmented relaxatory NANC responses, and prevented capsaicin from producing any contractile effect and from significantly influencing the NANC contractions.

The effect of local anaesthetics on noncholinergic-nonadrenergic (NCNA) responses of the gut.

The newly synthesized carbamate local anaesthetics (heptacaine and BK-141) affected the NCNA responses of different segments of the guinea-pig small (jejunum, ileum) and large (colon, taenia coli) intestine in a similar manner to the classic local anaesthetics (procaine and trimecaine). The sensitivity of NCNA responses to the action of local anaesthetics was, in order: primary contraction greater than rebound contraction greater than primary relaxation. The action of the carbamate local anaesthetics resembled that of trimecaine more than that of procaine.