In the mechanism of action of a protein hormone, one of the second messengers is
a. Cyclic AMP
b. Insulin
c. T3
d. Gastrin
The answer is the option (a) Cyclic AMP
Explanation: Hormones which react with membrane-bound receptors and generally do not enter the target cell, but create second messengers (Cyclic AMP, IP3, Ca++, etc.)