Organic osmolyte distribution and levels in the mammalian urinary bladder in diuresis and antidiuresis

Inositol, sorbitol, glycerophosphocholine (GPC), and betaine are organic osmolytes that are accumulated by renal medullary cells in response to hyperosmotic stress. Previous screening studies, using nuclear magnetic resonance spectroscopy, have shown some of these same compounds to be present in extracts of whole urinary bladder from rabbits and rats. In the present study, we used highperformance liquid chromatography to quantify levels of these compounds in the separated epithelium and muscle of bladders taken from normal rabbits as well as diuretic and thirsted rats. We find that 1) high concentrations of organic osmolytes, namely inositol, GPC, and sorbitol, are present in urinary bladder; 2) levels of these osmolytes in the bladder epithelium are higher than in the muscle; 3) increased urinary osmolality due to antidiuresis is associated with a 2.4-fold increase in total osmolyte levels in rat bladder epithelium and a lesser (1.5-fold) increase in the muscle, compared with corresponding levels in tissues from diuretic animals; and 4) these increases in total osmolyte amounts in the epithelium are due to increased levels of GPC, sorbitol, and perhaps inositol (P = 0.07), whereas only GPC increases in the bladder muscle.