second messenger
noun
: an intracellular substance (as cyclic AMP) that mediates cell activity by relaying a signal from an extracellular molecule (as of a hormone or neurotransmitter) bound to the cell's surface compare first messenger
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“Second messenger.” Merriam-Webster.com Medical Dictionary, Merriam-Webster, https://www.merriam-webster.com/medical/second%20messenger. Accessed 3 Nov. 2025.
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