Receptors for steroid hormones: membrane-associated and nuclear forms.

Steroid hormones are now recognized to act through both nuclear and membrane-associated receptors. In this review we focus on receptors for estrogen and the vitamin D metabolite 1,25-dihydroxyvitamin D(3). While the nuclear receptors are part of a 'superfamily' with common structural elements, membrane receptors are more diverse, ranging from variants of the nuclear forms to unrelated proteins. We conclude that both rapid (membrane-initiated) actions, as well as regulation of gene transcription, are necessary to explain the complex actions of steroid hormones on target cells.