Fig. (3).

Schematic of the postulated mechanism of intracellular actions of adrenergic agonists. Alpha-adrenoceptor agonists (α-agonists) bind to α-receptors on vascular smooth muscle and induce smooth contraction and vasoconstriction, thus mimicking the effects of sympathetic adrenergic nerve activation to the blood vessels. The α-adrenergic receptor, activates a different regulatory G protein (Gq), which acts through the IP₃ signal transduction pathway activates the release of calcium from the sarcoplasmic reticulum(SR) which by itself and through the calcium–calmodulin dependent protein kinases(CaMKII) influences cellular processes, which in vascular smooth muscle leads to vasoconstriction.