EMERGING DIVERSITIES IN THE MECHANISM OF ACTION OF STEROID-HORMONES

The classical genomic action of steroid hormones acting through intrac elluar receptors is well recognized. within this concept of action, qu estions regarding the ultimate fate of the hormone and lack of a tight correlation between tissue uptake and biological activity with recept or binding remain unanswered. Evidence has accumulated that steroid ho rmones can exert non-classical action that is characterized by rapid e ffect of short duration. In most of these cases, the hormone effect oc curs at the membrane level and is not associated with entry into the c ell. The possible mechanisms for these non-classical actions are: (a) changes in membrane fluidity; (b) steroid hormone acting on receptors on plasma membranes; (c) steroid hormones regulating GABA(A) receptors on plasma membranes; and (d) activation of steroid receptors by facto rs such as EGF, IGF-1 and dopamine. Data have also been obtained indic ating that receptor-mediated insertion of steroid hormones into DNA ma y take place with the steroid acting as a transcription factor. These new proposed mechanisms of action of steroid hormones should not be vi ewed as a challenge to the classical mechanism. These diverse modes of action provide for an integrated action of hormones which may be rapi d and of short duration or prolonged to address the physiological need s of the individual.