The action of ANS-related drugs on smooth muscle
In the following experiment, the key objective is to compare the mechanical changes in tonic force by longitudinal smooth muscle after the addition of different concentrations of the drugs noradrenaline and acetylcholine. Peristalsis is the wave of muscle contractions that allow circular muscles to constrict the gut and longitudinal muscles to shorten it in an attempt to move the food bolus towards the rectum. A series of dilutions were prepared for both drugs to deduce the effect this would have on the contractions of the mammalian gut. These were added, in turn, to Ringers solution containing the gut (a solution resembling blood serum in its salt constituents used for bathing and culturing animal cells1). Both drugs caused various changes in parameters: tension in the gut and rhythmic contractions. A kymograph helped us measure these parameters in order to draw conclusions to differentiate between the effects of the two drugs at different concentrations on the motility of the gut. Smooth muscle activity is controlled by the autonomic nervous system where the sympathetic and parasympathetic divisions work against each other, thus this experiment allowed us to deduce how one division slows the digestive system and the other accelerates it.
Fig. 1(on separate sheet) portrays the trace from the kymograph. It is a graphical representation of the mechanical rhythm both before acetylcholine was added and immediately after it was added. It displays a rhythm lasting for 120 seconds necessary to produce its maximal effect.
There is a decrease in amplitude after acetylcholine with concentration 10-5 was added. The amplitude is much smaller in height than before the drug was added. However, the baseline increases by 4.5cm which demonstrates that the overall tonic tension in the gut increased too. This graphical representation allows us to observe how tonic force (tension being exerted upon the smooth muscle in the gut) is different to before any drug is added.
Therefore, to calculate tonic force:
Mass x acceleration is used
3.5cm = 9.8newtons
1mm = 9.8/35mm = 0.28 mN
0.28 x baseline movement (mm) = tonic force
Table of results:
|Concentration of drug/M |Final concentration in |Baseline movement/mm |Δ tonic force/mN |Increase/decrease in tonic force | | |organ/M | | | | |1 x 10-6 |1 x 10-8 |+1 |+0.28 |Increase | |1 x 10-5 |1 x 10-7 |+8 |+2.24 |Increase | |1 x 10-4 |1 x 10-6 |+29 |+8.12 |Increase | |1 x 10-3 |1 x 10-5 |+45 |+12.60 |Increase |
|Concentration of drug/M |Final concentration in |Baseline movement/mm |Δ tonic force/mN |Increase/decrease in tonic force | | |organ/M | | | | |1 x 10-6 |1 x 10-8 |No change |0 |No change | |1 x 10-5 |1 x 10-7 |No change |0 |No change | |1 x 10-4 |1 x 10-6 |-1 |-0.28 |Decrease | |1 x 10-3 |1 x 10-5 |-5 |-1.4...
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