Gut Motility Practical assessment - Essay Example

EFFECT OF FIELD STIMULATION ON ILEUM CONTRACTION Paper Lecturer November 5 Describe and explain the effect of field stimulation on ileum contraction? Field stimulation involves the use of acetylcholine or transmural stimulation. Drugs whose roles are tested in the experiment include atropine and morphine drugs. The stimulants are applied exogenously. At the initial stage of the transmural stimulation, a pulse of 0.1 Hz and a frequency width of 0.5 ms are used. The pulse is thereafter amplified until a recordable contraction can be achieved (The Journal of Biological Chemistry, 2009).

The ileum is reactive on transmural stimulation due to the activity of the enteric nervous system lining (US National Library of Medicine National Institutes of Health, 1986). The stimuilation causes a reaction on the membrane. It becomes depolarized. Permeability to calcium ions is also increased. The calcium ions concentration in is increased as a result of the voltage gated calcium-ions channel. From the synaptic cleft ACh is released to fuse with the muscuranic receptors as a result. The Gs protein then activates PLC after phosphoinositides activation.

Diacylglycerol and inositol-1,4,5-triphosphate are generated inducing phosphorylation and leading to the regulation of the calcium ion concentration, Burnstock (1972). This is the initialization of the ileum contraction. Diacylglycerol triggers protein kinase C, phosphorylating the target proteins leading to increased Ca+2 instigating contraction. 2. Draw the following graphs from the experiment and provide detailed figure legendsi. Molar concentration morphine v contractile response of field stimulated tissue (in mN)ii.

The logarithm of the molar concentration morphine v contractile response of field stimulated tissue (in mN)iii. Molar concentration morphine v % relaxation of stimulated tissue iv. Molar concentration acetylcholine v contractile response in unstimulated tissue (in mN)v. The logarithm of the molar concentration acetylcholine v contractile response in unstimulated tissue (in mN)3. Explain the cellular mechanisms of action of morphine and atropine on field stimulated-induced contractions and how/why this is affected by naloxone, using the data collected from BOTH the field stimulated and the direct ACH-induced contraction of ileumAs illustrated from the graphs, it is evident that morphine has no much variance with field stimulated contraction.

Atropine however recorded a substantial effect on the ACh-induced contraction. Atropine at concentration levels of between 10-9 and 10−8 M antagonized the contractile response of the tissues causing relaxation of the ileum described by Brenda et.al (1983). Morphine, through Gi-protein, restrains the formation of cAMP (Gracious et.al, 2008). Ca+2 concentrations are increased. Endogenous ACh release is effected. However, for ACh-induced contractions, M3 receptors are exogenously occupied by ACh.

This initiates the ileum contraction. This indicates that morphine has minimal effect on ACh action. It restricts about 0.35mm only.Atropine is an inhibitor to ACh action. It is faster than ACh in occupying the muscarinic receptors. It therefore inhibits the contraction of the ileum due to its antagonistic properties.Naloxone does not exploit Muscarinic receptors. According to Gillan & Pollock (1980), it behaves like an opioid receptor antagonist. It has insignificant effect on ACh-induced contraction.

Naloxone restricts morphine (morphine functions on the opioid receptor) action causing higher concentration of ACh within the synaptic region. This causes noticeable contraction.As illustrated in the graph, at 0.1nM morphine concentration, there is no notable effect. As the concentration is increased, the ileum contraction level decreases followed by abrupt decrease at concentrations of 100nM onwards. Stabilization is however achieved at 300nM onwards. The morphine drug opioid receptors get activated.

Adenyly cyclase is inhibited causing lower formation of cAMP. The Ca+2 channels get closed causing reduced contraction of the muscles and consequential lower ACh release, US National Library of Medicine National Institutes of Health (1992). Naloxone reverses the effect of morphine. It frees the opioid receptors by replacing morphine. It also reduces the unfilled receptors limiting morphine actions. The response increases with the concentration increase from 190nM to about 2500nM. For the atropine on the other hand, it is an antagonist on the ACh receptors and therefore occupies M3 receptors causing lower ileum contractions.

List of referencesBrenda C., Robert, J., Naylor & Connie C. (1983) Field stimulation-induced responses of circular smooth muscle from guinea-pig stomach. Naunyn-Schmiedebergs Archives of Pharmacology Volume 323, Issue 2, pp 155-161Burnstock, G. (1972) Purinergic nerves. Pharmacol Rev 24:509–581Gillan,MG. & Pollock, D. (1980) Acute effects of morphine and opioid peptides on the motility and responses of rat colon to electrical stimulation.Br J Pharmacol 68(3): 381–392.Gracious, RR., Bichoy HG, William LD.

, & Hamid IA. (2008) Morphine Tolerance in the Mouse Ileum and Colon. The Journal of Biological Chemistry (2009) Signaling Processes for Initiating Smooth Muscle Contraction upon Neural Stimulation [online] available from [5 November 2013]US National Library of Medicine National Institutes of Health. (1992) Involvement of opioid mechanisms in peripheral motor control of detrusor muscle [online] available from [5 November 2013]US National Library of Medicine National Institutes of Health. (1986) Effects of verapamil on acetylcholine and field stimulation induced contraction in postnatal development of guinea-pig ileum [online] available from [5 November 2013]