first messenger
noun
: an extracellular substance (as the hormone epinephrine or the neurotransmitter serotonin) that binds to a cell-surface receptor and initiates intracellular activity compare second messenger
Cite this Entry
“First messenger.” Merriam-Webster.com Medical Dictionary, Merriam-Webster, https://www.merriam-webster.com/medical/first%20messenger. Accessed 3 Nov. 2025.
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