Hormones and high pulse rate are connected?

I have a question is hormones are connected with high pulse rate. I know that caffeine increases pulse rate because caffeine increases the strength and frequency of heartbeats. Since this info does not mean anything to me, I would like an explanation. One friend of mine told me this is connected with hormones so I wish to hear could it be true. Can you tell me more about effects of caffeine and hormones to pulse rate?

As you probably already know, a cell's activity is often regulated by various hormones that we can find in human organism. One of the ways that hormones can affect a cell's activity is by binding to specific hormone receptors. They are activating G-proteins, which then go on to activate other enzymes that direct the cell to function. One such hormone that activates G-proteins is epinephrine. Other name for this important hormone, and maybe widely spread name is Adrenalin. When epinephrine or Adrenalin binds the ß- adrenergic receptor, this activates a G-protein. This one turns activates an enzyme called adenylate cyclase that converts ATP into cAMP. There are many related mechanisms, which caffeine causes on cAMP levels. For example, by inhibiting this adenosine receptor, caffeine removes this check, such that adenylate cyclase activity becomes even more sensitive to hormone binding, which is connected with pulse rate. That is why, by preventing various enzymes from binding to molecules containing adenine, caffeine can yield the same physiological effects as epinephrine, though less intense.