Insulin sensitivity was increased in rats treated for 21 days with mebanazine, 10mg./kg., phenelzine, 30mg./kg., or tranylcypromine, 10 mg./kg. but not in rats treated with isonicotinic acid hydrazide, 10 mg./kg., for 21 days or in animals treated with a single injection of mebanazine, 10 mg./kg. Pargyline, 14 mg./kg., given for 21 days produced 83% inhibition of hepatic monoamineoxidase and had a hypoglycaemic action when compared with 0·15 mg. mebanazine/kg., a dose just less than that required to inhibit monoamineoxidase. Increased insulin sensitivity seemed to be related to chronic inhibition of monoamineoxidase rather than to administration of hydrazine derivatives.
There was a tendency to anorexia during the drug treatment, but rats treated with monoamineoxidase inhibitors gained less weight than pair-fed control animals. This could be due to the previously reported reduction in growth hormone activity during treatment with monoamineoxidase inhibitors; nevertheless, any explanation for the increase in insulin sensitivity should be based upon the monoamineoxidase-inhibiting action of these drugs.