Effect of partial outflow obstruction on the distribution of free fatty acids and phospholipids in the rabbit bladder

The urinary bladder is separated into two distinct components, the mucosal epithelium (urothelium) and the underlying detrusor smooth muscle. Specific bladder dysfunctions such as partial outlet obstruction may contribute to the breakdown and damage of cell membranes. The major component of cell mem branes is phospholipids, and the release of free fatty acids (FFA) from mem brane phospholipids is suggestive of degradative lipase activity. The curre nt investigation is concerned with the effect of partial outlet obstruction on the subcellular distribution of free fatty acids and phospholipids (PL) in rabbit bladder muscle and mucosa. Partial outlet obstructions were surg ically created in mature male New Zealand White rabbits by standard methodo logy. At 2 weeks following surgery, rabbits were euthanized and the bladder s, removed and separated into smooth muscle and mucosa. Muscle and mucosa w ere homogenized and separated by differential centrifugation to obtain sepa rate subcellular fractions including plasma membranes, mitochondria, micros omes, and cytosol. The homogenate and supernatant fraction, free of membran es, were also saved. The free-fatty-acid (FFA) and choline-containing phosp holipid (PL) content and the rate of generation of FFA were quantitated usi ng in vitro enzymatic colorimetric methods. Relative to controls there was a significant increase in the FFA content of the obstructed smooth muscle a nd an increase in the PL content of the obstructed mucosa. There was an inc rease in FFA content in the mitochondrial fraction and a decrease in the su pernatant of the obstructed smooth muscle. The PL content was reduced in th e obstructed smooth muscle microsomal and supernatant fi-actions and was in creased in the supernatant fraction of the mucosa. Endogenous lipase activi ty among control bladders was more than 10-fold greater in mucosa than in m uscle. The FFA generation of the smooth muscle was significantly reduced by partial outlet obstruction. In conclusion, partial outlet obstruction caus es bladder dysfunction due to activation of enzymes that hydrolyze cellular and subcellular membranes. The increase in endogenous lipase activity and generation of FFA among obstructed bladders indicates that the pathological state affects the membrane structure needed for normal bladder function.