second messenger

https://doi.org/10.1351/goldbook.ST06842
Intracellular @E01901@ substance increasing or decreasing as a response to the stimulation of a @RT06841@ by an @A00186@, considered as the 'first messenger'.
Source:
PAC, 2004, 76, 1033. (Glossary of terms used in toxicokinetics (IUPAC Recommendations 2003)) on page 1070 [Terms] [Paper]