Physiology of the sphincter of oddi - the present and the future? - part 1

The mechanisms controlling the sphincter of Oddi [SO] have received considerable attention over the past two decades. Progress towards their elucidation has been slow, perhaps because of the sphincter's relative inaccessibility and the different responses of the human "resistor" as compared to the "pumper" observed in several animal models. The list of agent affecting the sphincter grows alarmingly. In this review, divided into two parts, substances have been classified as neurotransmitters, hormones, local factors and pharmacological agents. The first part considers the roles of neurotransmitters. These include [a] vasoactive intestinal polypeptide [VIP] and nitric oxide [NO]. Both cause relaxation. A recent model of their complex interrelationships in smooth muscle is described.[b] Substance P [SP] and enkephalins. These produce contractions. The former can act directly. An indirect effect via cholinergic neurones may be the result of SP release from vagal afferents.[c] Catecholamines, which cause contraction or relaxation via activation of alpha or beta adrenoreceptors, respectively. In the second part attention is focussed on cholecystokinin [CCK] which normally relaxes the SO via neuronal mechanisms.A CCK- sensitive pathway from sensory duodenal neurones to SO ganglia has been described. Reactive oxygen species are among the local factors discussed. Their description as being "the good, the bad and the ugly"seems merited. Pharmacological agents include No donors, octreotide and botulinum toxin [BTX]. Octreotide induces tachyoddia and may impair biliary flow. BTX has exciting potential in the diagnosis of SO abnormalities and as a therapeutic alternative to sphincterotomy. In both past of the review current concepts of different aspects of smooth muscle control are presented. In several instance data regarding the SO is lacking. We discuss [a] the role of interstitial cell of Cajal in the control of slow waves, [b] different pathways contributing to tonic and phasic contractions, [c] the 4 levels of neural control, [d] interrelationships of immune and nervous systems, and [e] links between emotional states and gut functions

physiology of the biliary tree motility of the gallbl bladder-part 1

An incomplete picture has emerged of the complex means by which gallbladder motility is controlled under normal and pathophysiological conditions. In the first part of this review an overall account is presented. The mechanisms of cholecystokinin release, its stimulation by dietary factors and peptides elaborated by both pancreas and small intestine are discussed. The inhibition of cholecystokinin release by bile acids and proteases is also described. In the second part attention is focussed on other peptides affecting motility. These include [a] octreotide, effective for treatment of acromegaly, [b] peptide YY, contributing to a "colonic brake", [c] motilin, associated with interdigestive contractions, analogues of which possibly correct gallbaldder hypomotility, and d] substance P and calcitonin gene- related peptide, which facilitate ganglionic transmission after release from exrinsic sensory neurones and alter gallbladder responses to vagal stimulation. The sympathetic nervous system and diabetes mellitus also influence vagal responses. The former, acting presynaptically, may provide a "brake" to prevent vagal overactivity. The latter could cause hypomotility via autonomic neuropathy, although hyperglycaemia, itself, may play a role. The role of nitric oxide, released from neurones also producing vasoactive intestinal peptide is recognized. Both lengthen muscle, the former producing responses without requiring plasma membrane receptors. Gallbaldder motility also changes during pregnancy and stone formation. Progesterone and cholesterol can limit G protein actions, thus impairing contractions. Inflammation is associated with abnormal motility. The production of reactive Oxygen metabolites, acting directly or releasing prokinetic prostaglandins, may be responsible. It has been proposed that the gastrointestinal tract may be normally in a state of controlled inflamation, primed to react to harmful challenges

Swallowing-induced cardio-respiratory responses in man

Swallowing transiently increases heart rate. One of the authors developed pronounced bradycardia while breath holding, particularly after an expiration. The objective, therefore, was to study his cardiac responses during swallowing as pronounced bradycardia developed. When, after a maximum inspiration [supine], the heart rate slowly fell below 50 beats min-1 well-defined P waves [lead II] disappeared. By swallowing 6 times on command after the P waves disappeared his heart rate increased immediately [68 +/- I beats min-1 n=6]. P waves with similar morphology to those pro-swallowing were recorded 0.7 +/- 0.1 s [n=6] after the first swallow. He continued breath holding after swallowing. P waves again disappeared although at faster heart rates [57 +/- I beats min-1; n=6]. Furthermore, well-defined P waves were observed after the second disappearance at heart rates within the range 30-40 beats min-1 Small amplitude P waves continued to be recorded from lead I with P wave disappearance in lead II, suggesting a pacemaker shift although not to the av node. Autonomic nerves can shift the dominant pacemaker within the sa node. The present report indicates that increased vagal tone may be rapidly reversed by swallowing