Steroids regulate differentiation, growth and functioning of many tissues via a nuclear receptor gene activation mechanism. Molecular biology has opened the way for more detailed investigation of the complex set of intracellular interactions contributing to organ-selective actions of steroids and steroid-like compounds such as vitamin D. In this volume leading experts address basic molecular mechanisms of tissue specificity and related issue, with the goal of attaining a better understanding of the underlying mechanisms of organ selective actions of steroids. Discussed is the extent to which tissue specificity might selectively be modified by chemical modification of the hormones and how this may be applied towards improved therapies by taking advantage of tissue selectivity.

Studies on the colon not only serve medical interest or clinical purposes, but are also a highly interesting subject of comparative physiology, from which we can learn much about the basic principles in physiology. Presented here are examples of research on colonic ion transport of each vertebrate group, including the classical models of epithelia, rat and rabbit, and also on the special and unique features in fish, amphibians, reptiles, birds, and selected mammals such as the guinea pig. Physiology and pathophysiology of ion transport in the human large intestine are as well covered as the use of colonic cell cultures as model systems for crypt cell properties.