Chromatin-associated ribonucleases are activated by estradiol in chick oviduct

Mechanisms of hormone action: parallels in receptor-mediated signal propagation for steroid and peptide effectors

The purpose of this contribution is to provide in brief form growing evidence in support of an integrated concept of hormone action that appears to shed fresh light on the information gap between the triggering and the effectuation of outcome of the action of given hormones. In accord with these new concepts there has now arisen a substantial body of data from a wide variety of effectors and target cells that demonstrates an astonishing unity in the actions of hormones of widely dissimilar chemical structure. In a nutshell, it now appears that primary recognition sites for both peptide and steroidal agonists occur at the outer cell surface. For steroid hormones, as exemplified by estradiol-17 beta, these sites possess several of the hallmarks of true receptors. Moreover, capture of this ligand is associated with unmistakable signs of membrane perturbation. And at a still very early stage in the signal propagation sequence, activation of a very limited fraction of the cellular lysosomal population may be identified following the application of steroid, as well as peptide, hormones. In turn, there is mounting evidence for cellular entry and even lysosomal uptake of peptidal effectors, the significance of which is still under debate. Likewise, there occur clear signs of limited reorganization of components of the cellular architecture at the surface, in the cytoplasm, and in the nucleus and its subcompartments, which are consistent with minimal recompartmentation of 'microquanta' of lysosomal constituents. These observations may be made within seconds to minutes following application of tropic hormone of either class to its selective targets, and thus, at times preceding those relatively more distal responses of augmented transcriptional and translational activities.