Final answer:
The activation of alpha 1 receptors by sympathetic nerve varicosities results in increased vasoconstriction due to the contraction of smooth muscle caused by a rise in intracellular calcium.
Step-by-step explanation:
The activation of post-synaptic adrenergic alpha 1 receptors by sympathetic nerve varicosities primarily results in the contraction of smooth muscle. When adrenaline or noradrenaline binds to alpha 1 receptors, which couple to Gq proteins, there is an increase in intracellular calcium. This increase in calcium leads to smooth muscle contraction, which in the case of blood vessels, results in vasoconstriction. Therefore, the correct answer is C. Increased vasoconstriction.
Specifically, the alpha 1 adrenergic receptors are involved in vasoconstriction of various vessels including the skin, gastrointestinal system, kidney (renal artery), and brain. Moreover, these receptors facilitate smooth muscle contraction in other body parts such as the ureter, vas deferens, and are involved in mechanisms like glycogenolysis and gluconeogenesis.