Site of Action of Antidiuretic Hormone on Mammalian Nephrons

摘要

There are two basic mechanisms by which salt, water and small organic solutes cross epithelial tissues, such as the gut and kidney, from the lumen into the blood. One mechanism is by transcellular transport across the luminal mucosal or apical cell membrane and then through the basolateral or serosal cell membrane. Solutes are transported by membrane carrier molecule pumps which transport the solutes by facilitated or active transport. A second mechanism by which many of the same solutes cross the membrane is through passive, paracellular movement through the tight junctions and the lateral intercellular spaces between the epithelial cells. Peptide hormones can directly affect transcellular movement by binding to the cell membranes at receptor sites and modulating intracellular events which increase or decrease pump activity. These same hormones could have cardiovascular effects which modify transcellular pumping by altering the delivery of O2 to the cells for support of transport energy requirements. Passive, paracellular transport can be altered by hormones acting through cardiovascular effects by changing blood flow and thus the degree of 'washout' of absorbed molecules from the epithelium and by changing capillary and tissue pressures resulting in a change in the magnitude of ultrafiltration across the capillaries and epithelium. The research supported by this grant investigated several aspects of the above mechanisms.