DEMO DEMOIntroduction
The aim of this computer simulation program is to demonstrate the effects of adrenergic drugs and sympathetic nerve stimulation on isolated segments of rabbit jejunum as described by Finkleman (1930)1. The jejunum and attached mesentery, which contains the sympathetic nerve supply, is removed and set up in an organ bath. Rhythmical, pendular contractions may be recorded and the preparation may be used to investigate:
The variable level of spontaneous activity means that it is difficult to quantify drug effects, and it is suggested that qualitative effects are recorded.
Ileum, duodenum or jejunum can be used; all show rhythmic movements though these are sometimes more regular in magnitude in ileum than in duodenum. Duodenum often possesses more inherent tone and shows not only a diminution in the size of the rhythmic contractions when the sympathetic nerves attached to the tissue are stimulated but also a net relaxation and reduction in overall muscle tone.
Sympathetic Innervation of the Small Intestine
The post-ganglionic sympathetic nerves utilise norepinephrine as a transmitter and originate in the paravertebral ganglia (coeliac). They run periarterially (along with the arteries) in the mesentery of the intestine. In the experiment they are usually stimulated by suspending a portion of mesentery containing vein (easily visible), artery and a fatty strip over a hook electrode. Even though the electrodes may be 2 or more cm from the intestine, stimulation is usually entirely post-ganglionic. Occasionally stimulation may produce effects which are not completely blocked by drugs which would be expected to prevent the actions of the sympathetic transmitter norepinephrine, indicating that some other substance may sometimes make a significant contribution as a co-transmitter.
Effects of drugs which mimic or block the response to electrical stimulation (both pre- and post- synaptically) can be demonstrated easily. In addition the preparation contains a variety of other receptors (e.g. muscarinic) and a cholinergic nerve supply (running in the various muscle plexuses, NOT periarterially) which can be affected by appropriate drugs. The action of cholinergic drugs on small intestinal motility may be investigated more effectively in other preparations such as guinea pig ileum and have therefore been omitted from this computer simulation.
