On the peptidergic hypothesis for non-adrenergic non-cholinergic innervation in the rat duodenum

1. The nature of the non-adrenergic, non-cholinergic (NANC) transmitter was studied in vitro in the rat duodenum, by use of an isometric-isovolumic preparation. 2. Electrical field stimulation (EFS) induced a tetrodotoxin (TTX)-sensitive fall both in luminal pressure and in isometric tension. 3. Neurotensin (NT) induced TTX-insensitive inhibitory responses similar to those induced by EFS. Vasoactive intestinal peptide (VIP) caused a delayed, slow, concentration-dependent, TTX-insensitive inhibitory effect, detected only by a change in luminal pressure. 4. alpha-chymotrypsin prevented the NT- and VIP-induced inhibitory effects and antagonized the response to EFS. 5. Apamin antagonized the EFS- and NT-induced effects, but failed to affect the relaxation in response to exogenous VIP. 6. Desensitization of NT receptors by exposure to NT (10 nM) for 30 min did not affect the EFS-induced relaxation. 7. These findings provide support for the involvement of a peptide in the NANC relaxation in rat duodenum. However, there is no evidence that NT or VIP are neurotransmitters released from the NANC system in this preparation.

Neurotensin: dual effect on the motor activity of rat duodenum

The effects of neurotensin on mechanical activity of rat duodenum were investigated using an isometric-isovolumic preparation. Neurotensin (1 pM to 10 nM) induced a concentration-dependent, tetrodotoxin (TTX)-insensitive fall in both endoluminal pressure and isometric tension. At higher concentrations of neurotensin (1 nM to 1 microM) the relaxation was followed by a concentration-dependent TTX-insensitive contraction, detected only by an increase in endoluminal pressure. Different concentrations of neurotensin were required to desensitize the relaxant and the contractile actions of the neuropeptide. The relaxation was antagonized by apamin, while the contractile response was blocked by nifedipine. Neurotensin, when tested separately on longitudinal and circular muscular strips, caused relaxation of the longitudinal strips. Circular strips showed contractions in response to neurotensin, following an inhibitory phase, if the strips were spontaneously or pharmacologically activated. The results suggest the presence of two sets of neurotensin receptors with a differential localization between the two muscular layers in rat duodenum.

Non-adrenergic, non-cholinergic inhibitory responses to nerve stimulation in rat colonic circular muscle

The nerve-mediated response to electrical field stimulation (EFS) in rat colonic circular muscle was investigated using the single sucrose-gap technique. EFS with a single pulse (0.4 ms, supramaximal voltage) elicited transient TTX-sensitive hyperpolarization (IJP) often followed by an 'off' depolarization associated with muscular contraction. No relaxation associated with the IJP could be seen unless tone was pharmacologically induced by carbachol (10(-6) M). IJPs were due to non-adrenergic, non-cholinergic (NANC) nerve activation since they were not affected by atropine (10(-7) M) or guanethidine (10(-6) M) superfusion. The mechanism underlying the IJP was presumably an increase in K+ conductance, and the NANC neurotransmitter might open largely apamin-sensitive, Ca(2+)-dependent K+ channels. Purines or vasoactive intestinal polypeptide (VIP) did not mimic the effects of NANC nerve stimulation. Therefore, the NANC inhibitory system, producing IJPs, in rat colonic circular muscle is not purinergic or VIPergic in nature.

The avian oesophageal motor function and its nervous control: some physiological, pharmacological and comparative aspects

1. This paper deals with the avian oesophageal motor function and it attempts to draw some comparative aspects between neural regulation of the avian and mammalian oesophagus. 2. Different from the mammalian oesophagus, the avian oesophagus, presents at rest electrical activity associated to spontaneous contractions. 3. Swallowing elicits peristaltic contraction, characterized by an inhibitory and an excitatory component. 4. Non-adrenergic, non-cholinergic neurons are responsible for the inhibitory component. 5. Contrarily to what observed in mammals, where the peripheral mechanism are important for the peristaltic sequence, the primary peristaltism of birds seems to be entirely mediated by extrinsic nervous system.

Evidence that adenosine is not involved in the non-adrenergic non-cholinergic relaxation in the rat duodenum

In rat isolated duodenal segments, adenosine induced, in the presence of atropine and guanethidine, a dose-dependent, long-lasting (about 20 s), tetrodotoxin (TTX)-resistant relaxation both in endoluminal pressure and in isometric tension. Electrical field stimulation (EFS) induced, in the presence of atropine and guanethidine, a TTX-sensitive short-lasting (about 6 s) relaxation followed by a sustained rebound contraction. Theophylline, a P1 receptor antagonist, at the concentration of 100 microM caused a marked inhibition of the adenosine-induced relaxation, while the EFS-induced relaxation was not modified. Our results suggest that adenosine induces relaxation of the rat duodenal smooth muscle acting on P1 receptors localized at muscular level. However, differences in the morphology and in the sensitivity to theophylline between adenosine- and EFS-induced relaxation ruled out adenosine as neurotransmitter of the non-adrenergic, non-cholinergic inhibitory system.

Evidence against purines being neurotransmitters of non-adrenergic, non-cholinergic nerves in rat duodenum

The possible involvement of purines in the non-adrenergic non-cholinergic (NANC) relaxation of rat duodenum was studied using an isometric-isovolumic preparation. Purines (adenosine, AMP, ADP, ATP) induced a concentration-dependent, tetrodotoxin (TTX)-insensitive, fall in both endoluminal pressure and isometric tension. The relaxation induced by adenosine and by 2-chloroadenosine was selectively antagonized by 8-phenyltheophylline (1, 10 nM, 0.5 microM) and the ATP-induced relaxation was opposed by alpha, beta-methylene ATP (10 microM) and by reactive blue 2 (10 microM). Electrical field stimulation (EFS) caused TTX-sensitive inhibitory effects similar to those induced by ATP. None of the purinergic antagonists used were capable of affecting the EFS-induced relaxation. Our results indicate that both P1 and P2 purinoreceptors are present in muscle of the rat duodenum and are not involved in the NANC relaxation.

On the purinergic system in rat duodenum: existence of P1 and P2 receptors on the smooth muscle

In rat duodenum, in vitro, in the presence of atropine and guanethidine, ATP administration caused a tetrodotoxin-insensitive relaxation followed by a rebound contraction. A similar response was obtained also after electrical field stimulation (EFS) of non-adrenergic, non-cholinergic (NANC) nerves. alpha, beta-methylene-TP and theophylline antagonized the response to ATP, but they failed to affect the noradrenaline- and EFS-induced relaxation. These results suggest that P1 and P2 receptors are present in rat duodenum, but their activation is not responsible for the inhibitor effects due to the NANC nerves.

Excitatory effects of opiates on the spontaneous EMG activity in pigeon oesophagus

The effects and the mechanism of action of morphine, methionine-enkephalin and leucine-enkephalin were examined in transverse muscular strips from pigeon oesophagus. All the opiates produced a concentration-dependent excitatory effect on the spontaneous EMG activity, characterized mainly by an increase in the spike burst frequency. The maximal excitatory response to morphine and opioid peptides was fully antagonized by naloxone and tetrodotoxin, significantly reduced by atropine and it was not affected by guanethidine pretreatment. Treatment of pigeons with reserpine abolished the excitatory effects induced by opiates. The above results suggest the existence of specific opioid receptors in pigeon oesophagus. Opiates have no direct action on smooth muscle cells, increasing the EMG activity via excitatory both cholinergic and non-adrenergic non-cholinergic neurons. The hypothesis of a possible involvement of serotonergic interneurons might be advanced.

Inhibitory influences of vagal afferences on the oesophageal EMG peristaltic pattern

The influence of vagal afferents on the EMG peristaltic pattern was studied in pigeon oesophagus. Bilateral vagotomy did not abolish the primary peristalsis, but induced significant modifications of the peristaltic pattern parameters. Vagal afferent stimulation induced an inhibitory effect consisting of a temporary break or definitive block of the EMG peristaltic activity already in progress. Vagal afferent stimulation also induced a reduction of the spontaneous EMG activity and this effect was abolished either by glossopharyngeal bilateral section or ganglionic block. Likewise vagal afferent stimulation, the crop distension caused inhibitory effects on EMG peristaltic pattern. This effect was abolished by bilateral vagotomy. These results indicate that vagal afferents, originating from the crop, could influence the central neurons responsible for the peristaltic motor programme.

Role of glossopharyngeal nerve on the control of pigeon cervical esophagus motility

The effects of i) glossopharyngeal section on the occurrence of the primary peristalsis and ii) electrical efferent stimulation of glossopharyngeal nerve on the EMG activity were studied in the pigeon cervical esophagus. The results pointed out that glossopharyngeal nerve is an indispensable requirement for the primary peristalsis occurrence and that motor sequence is centrally programmed.

[Esophageal EMG activity in the pigeon (Columbia livia) in vivo]

The pigeon esophageal smooth muscle shows "spontaneous" rhythmic bursts of spikes with increasing discharge frequency from pharynx to crop. There are no slow waves. The changes of the electric pattern induced by pharmacological administrations of atropine, prostigmine, hexamethonium and by asphyxia suggest that the electric activity is myogenic in origin. The innervation plays a role in the control of this activity and it is essential for the functional polarization.

The biosynthesis of hemoglobin G San Josè (beta 7(A4) Glu replaced by Gly)

This report is concerned with the evaluation of hematological parameters and the percentage level of the abnormal hemoglobin (Hb) G San Josè as found in 4 heterozygous carriers from a family of Sicilian origin. Biosynthetic studies and in vitro recombination experiments strongly indicate that abnormal beta chains are synthesized at lower rate than beta A chains and exhibit a minor affinity (relative to beta A chains) for complementary chains in a condition of relative aA chain deficiency. The possibility that the low affinity of beta G chains for a chains may play a decisive role in controlling the level of the abnormal Hb in the peripheral blood of the present non-a-thalassemic abnormal Hb carriers is therefore discussed.