Which hormone among the following utilizes cAMP as its secondary messenger?

Explanation

Parathyroid hormone (PTH) signals through the cAMP pathway, activating adenylate cyclase to increase intracellular cAMP levels. Insulin primarily uses tyrosine kinase receptors, vasopressin acts via different receptor subtypes (V1 uses IP3/DAG, V2 uses cAMP in kidneys), and adrenaline can activate multiple pathways including cAMP depending on receptor type.