1 To determine the identity of an unknown drug you will obse

1. To determine the identity of an unknown drug, you will observe the response of the ileum to the application of the unknown drug, both alone and in combination. Your unknown agent could be any of the following: Acetylcholine (mACh agonist) Pilocarpine (mACh agonist) Atropine (mACh antagonist) Eserine (anti-AChesterase) DMPP (nACh agonist) Hexamethonium (nACh antagonist) lsopreteronol (beta agonist) Propanolol (beta antagonist) Phenylepherine (alpha agonist) Phentolamine (alpha antagonist) Epinephrine (adrenergic agonist, Beta have higher affinity for Epi) Norepinephrine (adrenergic agonist, Alpha have higher affinity for NE) Histamine 2. You will first add the unknown to the ileum bath, and observe the response. Does the ileum contract, relax, or do nothing? Thus, your flow-chart will begin using these 3 possible responses.

Solution

Answers:

(1 and 2 ) The ileum may contract or relax depending upon the drug, the probable individual effects of which have been discuused below:

Acetylcholine causes smooth muscles to contract.

Pilocarpine acts on ciliary muscles and causes it to contract.

Atropine blocks contraction of the circular pupillary sphincter muscle.

Eserine induces contraction of guineapig distal colon.

DMPP induces longitudinal muscle contractions.

Hexamethonium acts as antagonist at the nicotinic acetylcholine receptors, so does not induce contraction of muscles.

Isoproterenol induces contraction of cultured rat ventricular cells.

Propranolol also reduces the force of contraction of heart muscle and thereby lowers blood pressure.

Phenylepherine induces contraction of single vascular smooth muscle cells.

Phentolamine reduces contraction of muscle.

Epinephrine induces contraction of the smooth muscle in arterioles.

Non epinephrine induces constriction of smooth muscles.

Histamine allows contraction of muscles.

(3) and (4)

The drug can be any of the above except atropine, hexamethonium and propanolol which acts against contraction of muscles.

The potent drugs other than acetylcholine are pilocarpene (mAch agonist) and DMPP (nAch agonist).

The action of DMPP is blocked by hexamethonium, but the ileum contracts even after addition of hexamethonium in case of acetylcholine and pilocarpine. Thus, the drug should be pilocarpine or acetylcholine.

5. Eserine prevents the hydrolysis of acetylcholine by acetylcholinesterase at the transmitted sites of acetylcholine and stimulates both nicotinic and muscarinic acetlycholine receptors. Pilocarpine and eserine does not have any additive effect, but pilocarpine has been seen to reduce the activity of eserine.

So, the unknown drug is probably acetylcholine.