Caffeine is a stimulant present in tea, coffee, cola beverages, analgesic drugs, and agents used to increase alertness. The cardiovascular effects are extensive and can help with headaches, migraines, or other types of pain in certain circumstances. Caffeine is mainly studied using coffee which has other chemicals present in it. This means that much of the research is not well understood, and there is much conflicting data on caffeine. Caffeine antagonizes the adenosine A2A receptor in blood vessels in the neck and head. The adenosine A2A receptors likely have a higher affinity for caffeine in the head and neck. The adenosine A2A receptor activates adenylate cyclase which catalyzes ATP into cAMP. cAMP inhibits myosin light chain kinase (MLCK), therefore the low concentration of cAMP allows MLCK to be activated by calcium activated calmodulin so it can phosphorylate myosin light chain and cause muscle contraction. The contraction of the muscle in the blood vessel causes vasoconstriction. Adenosine A2a receptors in the head and neck also stimulate the production of nitric oxide which causes vasodilation as seen in another part of this pathway, therefore, the antagonism of these receptors further leads to vasoconstriction in the head and neck. The vasoconstriction in the head and neck helps with migraines and headaches which are causes by vasodilation, but the understanding of this isn't well studied, and caffeine has also been found to cause headaches as well. Chronic caffeine intake leads to an adaptation to the vasoconstritive effects. The opposite effects of caffeine is called the coffee-effect and based on the population of receptors in that area of the body, as well as their affinity for caffeine. This causes vasodilation in the majority of the human body, but vasoconstriction in the head and neck.

Caffeine Adrenergic A1 vasoconstriction Pathway References