Opium alkaloids pharmacological action

Opium is the milky exudate obtained by incising the unripe seed capsule of the poppy plant Papaver somniferum and morphine is the most important alkaloid of opium. Morphine produces analgesia through action in the brain and spinal cord, that contain peptides possessing opioid like pharmacological action. These endogenous substances are known as endogenous opioid peptides (earlier known as endorphin now known as P-endorphin). 

The pharmacological effects of this complex mixture of alkaloids in opium may, in some respects, be more beneficial than the effects of an individual alkaloid. The effect of opium in the treatment of diarrhoea is better than that of either morphine or codeine given individually. It is possible to calm the gastrointestinal tract with a dose which contains only half of the dose which would be necessary for morphine alone. The combination of the increase in stretch reflex caused by morphine and the inhibition of increased peristaltic action by papaverine leads to a better therapeutic effect. The increase in muscle tone due to morphine is reduced by papaverine, and other benzylisoquinolines also participate in this tranquillisation of the g.i. tract. In the normal 50 mg dosage of opium used for the treatment of diarrhoea there is about 5 mg of morphine, 0.5 mg of papaverine and 3 mg of nos-capine which contrasts markedly with a dose of 100—200 mg of papaverine if this were given alone. The analgaesic activity of opium is due mainly to the morphine present, as the levels of codeine, neopine and papaverine are relatively small. The respiratory depression effect of opium is also due to the morphine content and the antagonistic effects of noscapine and narcotoline are not so pronounced. Thus the main use of opium in medicine is for the treatment of diarrhoea. 

---