...........

Epinephrine, norepinephrine, and histamine
act directly and very rapidly. Peptide hormones
such as insulin or adrenocorticotropic hormone
(ACTH) initially occur as precursor polypeptides,
which are split by specific proteases to
form active molecules. Some peptide hormones
are coded for by a common gene; differential
RNA splicing of the transcript of this gene produces
different precursors for translation.
(Abbreviations used: ACTH, adrenocorticotropic
hormone; FSH, follicle-stimulating
hormone; LH, leutinizing hormone; TSH, thyroid-
stimulating hormone.) (Figure data after
Lodish et al., 2000.)