DIVERSE MODES OF ACTION OF PROGESTERONE AND ITS METABOLITES

Progesterone and its metabolites have a variety of diverse effects in the brain, uterus, smooth muscle, sperm and the oocyte. The effects in clude changes in electrophysiological excitability, induction of anest hesia, regulation of gonadotropin secretion, regulation of estrogen re ceptors, modulation of uterine contractility and induction of acrosome reaction and oocyte maturation. The latency of the effects vary from several seconds to several hours. Thus, it is not surprising that mult iple mechanisms of action are involved. The classical mechanism of ste roid hormone action of intracellular receptor binding has been supplem ented by the possibility of the steroid acting as a transcription fact or after the binding of the receptor protein to DNA. Other mechanisms include influence of the steroids on membrane fluidity and acting thro ugh other cell signalling systems, membrane receptors and GABA(A) rece ptors. Of particular interest are multiple mechanisms for the same typ es of action. For example the effect of progesterone on gondadotropin release is largely exerted via the classical intracellular receptor as well as membrane receptors, whereas 3 alpha,5 alpha-tetrahydroprogest erone-induced LH release occurs via the GABA(A) receptor system. The i nhibition of uterine contractility by progesterone is regulated by pro gesterone receptors while the action of 3 alpha,5 alpha-tetrahydroprog esterone on uterine contractility is regulated by GABA(A) receptors. T he regulation of the differences in the pattern of progesterone effect s on estrogen receptor dynamics in the anterior pituitary and the uter us in the same animal are also of considerable interest.