About Mannitol A polyol (Sugar alcohol), Low molecular weight non electrolyte, Osmotic diuretic. Mechanism of Action of Mannitol It is a non electrolyte of low molecular weight which limit the tubular water and electrolyte reabsorption in a variety of ways such as: - 1. Expanding extra cellular fluid volume and increase glomerular filtration rate and inhibits renin release. 2. Increases renal blood flow especially to the medulla hence medullary hyper tonicity is reduced and corticomedullary osmotic gradient is dissipated and thus passive salt reabsorption is reduced. 3. Retains water isoosmotically in proximal tubule and thus dilutes luminal fluid which opposes sodium chloride reabsorption. 4. Inhibits transport process in the thick ascending loop of Henle which ultimately leads to diuresis and enhanced excretion of all cations and anions. It also decongestant the eye by osmotic action.