The bioassay is an experiment that measures the response of a particular chemical substance on the living organism of a tissue . Bioassays can therefore aid in the research and development of drugs especially in the pharmaceutical industry. In this bioassay the influence of two drugs (antagonists) on Acetylcholine mediated contractions on smooth muscle were measured . Acetylcholine is a neurotransmitter that when bound to a particular receptor is involved in the contraction and relaxation phases of muscles . Skeletal muscles in comparison to smooth muscles share the same agonist or ligand that binds to a receptor in order for a contraction to occur, they differ in receptor and the method of activation on muscle contractions. In skeletal muscles Acetylcholine is released at the post synaptic terminals at the neuromuscular junction of the skeletal muscle fibre , which then binds to Nicotinic Acetylcholine receptors, causing a action potential that will ultimately results in a contraction . In contract Smooth muscles contain Muscarinic Acetylcholine receptors . These are acetylcholine receptors which have G protein receptor complexes their intracellular signalling mechanism in neuron cells. Acetylcholine is the ligand for Muscarinic receptors , hence when bound an intracellular cascade of events occur such as muscle contraction.
Specifically it is the M3 receptor that is found in smooth muscle , when the agonist (Acetylcholine) is bound to the M3 receptor, contraction of the smooth muscle occurs. When Nitric Oxide (NO) binds to the M3 receptor the smooth muscle relaxes. An Agonist is a substance that binds to a receptor and causes the response that is similar to the naturally occurring substance  (for example the same response that Acetylcholine has on the Muscarinic Receptor). In contrast however, an antagonist is a substance or drug that binds to the same receptor yet inhibits or minimises the agonist or naturally occurring response. The two most common types of antagonists are competitive and non competitive. Competitive antagonists bind at the same site that the ligand or agonist would, however non competitive antagonists binds to another site on the receptor causing a change in the shape of the active site. In this experiment differences in the responses of the two drugs A and B in comparison to the baseline response of Acetylcholine concentration in smooth muscle contraction were measured . The response without the antagonists can be observed in the Acetylcholine plot. It is expected that the % maximal responses of Drugs A and B when compared to the naturally occurring response of Acetylcholine in muscle contraction and relaxation would be lower, as antagonists inhibit or decrease the response of the agonist. Methods
Refer to Introduction to Bioassay. PC2001: Molecular Basis of Therapeutics 2 / BC2024 Cell Regulation. 2010. Pages 3-4. Materials In this experiment smooth muscle from the intestine of a rat was used. It is vital that the choice of gender, strain and choice of anaesthetic agent be taken into consideration in accordance to the variable being tested.
The gender of the animal must be carefully considered as males and femals differ physiologically in reproductive systems, and in their body mass as males tend to have higher body masses than females. In this particular experiment where there is involvement at the intracellular and hormonal level, gender plays an important role as to whether hormone levels in the animal will affect both the normal activity of ligand to receptor binding, and drug interactions with the receptor. In addition it is known that certain female hormones level will fluctuate due to the menstrual cycle and that males may have higher levels of particular hormones (such as testosterone). In both cases levels and interactions of other hormones such as Acetylcholine may be different in one gender when compared to the