The nature of intracrine peptide hormone action

Current theory holds that peptide hormone action results from hormone bindi ng to cell-surface receptors, with the generation of intracellular second m essengers. However, a growing body of evidence suggests that intracellular peptide hormone, either internalized or synthesized in situ, can exert phys iologically relevant effects. These effects are diverse and poorly understo od. I propose that such intracrine action can serve to modulate cellular fu nction over time and thereby play a role in biological memory of various so rts, in the maintenance of hormonal responsiveness, and in cellular differe ntiation.