Epinephrine initiates a signal transduction pathways that produces cyclic AMP (cAMP) and leads to the breakdown of glycogen to glucose, a major source of energy for cells. Glycogen breakdown is only part of the flight-or-fight response that epinephrine brings about because the overall effect on the body includes an increase in heart rate and alertness, as well as a burst of energy. Given that caffeine blocks the activity of cAMP phosphodiesterase, this suggests that caffeine blocks the epinephrine pathway that was just described.

Propose a mechanism by which caffeine ingestion leads to heightened alertness and sleeplessness.

The ability of caffeine to inhibit adenosine receptors, plays a very important role in heightened alertness and sleeplessness.

Explanation:

"Caffeine" (1,3,7-trimethylxanthine) is an alkaloid obtained from plants. It has a chemical formula of C8H10N4O2.

Caffeine is generally hydrophillic but sufficiently lipophilic to pass through all biological membranes and readily cross the blood-brain barrier.

Therefore can bind with the adenosine receptors. Due to the blocking of adenosine inhibitory effects through its receptors held by paraxanthine and caffeine, it indirectly affects the release of norepinephrine, dopamine, acetylcholine, serotonin, glutamate e.t.c.

The release of the above-mentioned hormones have a great impact on the heightened alertness of the body, especially dopamine and serotonin.