Agents: mannitol, sorbitol. Site of action: mainly the proximal tubules. Mode of action: Since NaCl and H2O are reabsorbed together in the proximal tubules, Na+ concentration in the tubular fluid does not change despite the extensive reabsorption of Na+ and H2O. Body cells lack transport mechanisms for polyhy-dric alcohols such as mannitol (structure on p. 171) and sorbitol, which are thus prevented from penetrating cell membranes. Therefore, they need to be given by intravenous infusion. They also cannot be reabsorbed from the tubular fluid after glomerular filtration. These agents bind water osmotically and retain it in the tubular lumen. When Na ions are taken up into the tubule cell, water cannot follow in the usual amount. The fall in urine Na+ concentration reduces Na+ reabsorption, in part because the reduced concentration gradient towards the interior of tubule cells means a reduced driving force for Na+ influx. The result of osmotic diuresis is a large volume of dilute urine.
Was this article helpful?
You are about to discover the "little-known" techniques, tricks and "mind tools" that will show you how to easily "program" your body and mind to produce an instant, rock-hard erection. Learn how to enjoy all of the control, confidence and satisfaction that comes from knowing you can always "rise to the challenge" ... and never have to deal with embarrassment, apologies, shyness or performance anxiety in the bedroom, ever again.