Final answer:
Activation of α1-adrenergic receptors by sympathetic nerves leads to increased vasoconstriction due to the triggering of smooth muscle contraction.
Step-by-step explanation:
Activation of post-synaptic adrenergic receptors (α1) by sympathetic nerve varicosities commonly results in vasoconstriction. The binding of ligands such as noradrenaline or adrenaline to these α1-adrenergic receptors, which couple to Gq proteins, leads to an increase in intracellular calcium (Ca²+). This increased Ca²+ concentration causes smooth muscle contraction, which in turn results in the vasoconstriction of arteries and veins. Thus, the specific effect of activating α1-adrenergic receptors by sympathetic nerve action is Increased vasoconstriction (A).