The
cough and
emetic reflexes involve a synchronized firing of motor neurones involved in respiratory control.
Tachykinin NK1 receptor antagonists and
5-HT1A receptor agonists are examples of centrally acting drugs that reduce
cough and
emesis. In the present studies, therefore, we examined the possibility that other classes of drugs known to reducing
cough have
anti-emetic properties to prevent
emesis induced by diverse challenges. We examined the potential of
codeine (1-10 mg/kg),
baclofen (1-10 mg/kg),
scopolamine (0.3-10 mg/kg),
diphenhydramine (1-10 mg/kg),
imperialine (1-30 mg/kg) and
verticine (0.3-3 mg/kg) to inhibit
emesis induced by
nicotine (5 mg/kg, s.c.),
copper sulphate (120 mg/kg, intragastric), and provocative motion (4 cm horizontal displacement, delivered at 1 Hz) in Suncus murinus (house
musk shrew). Only
codeine had broad inhibitory properties (P<0.05) to antagonize
emesis induced by all challenges with ID50 values ranging from 1.2 to 2.3 mg/kg.
Baclofen antagonized
emesis induced by
nicotine (maximum reduction was 44.9%, P<0.05) and motion (maximum reduction was 97.3%, P<0.01), but potentiated
copper sulphate-induced
emesis (maximum potentiation was 73.0%, P<0.05).
Scopolamine antagonized
copper sulphate-induced
emesis (maximum reduction was 61.2%, P<0.05) and
imperialine antagonized
nicotine-induced
emesis (maximum reduction was 30.2%, P<0.01), but
verticine potentiated motion-induced
emesis (maximum potentiation was 60.0%, P<0.05).
Diphenhydramine did not significantly reduce
emesis induced by any of the challenges (P>0.05). In conclusion,
codeine has broad inhibitory
anti-emetic actions but a known ability to reduce coughing does not necessarily predict broad inhibitory
anti-emetic properties.