Focal hypoxia of the obstructed rabbit bladder wall correlates with intermediate decompensation.

Abstract

We showed that partial obstruction of the rabbit bladder outlet caused decreases in detrusor blood flow that were directly proportional to the level of decompensation present. Bladder decompensation is characterized by decreases in detrusor contractility, mitochondrial function, and sarco/endoplasmic reticulum calcium ATPase (SERCA) activity in obstructed rabbits. The current study was designed to create bladder decompensation and to relate its characteristic dysfunctions to the presence or absence of hypoxia in the obstructed rabbit bladder wall. Tissue hypoxia was visualized immunohistochemically after administration of a hypoxia probe in vivo. Twelve New Zealand White rabbits were separated into two groups. The rabbits in group 1 received sham operations; the rabbits in group 2 received partial outlet obstructions by standard methods. Four weeks after surgery, each rabbit received an intraperitoneal injection of aqueous Hypoxyprobe-1, which forms protein adducts in cells having O(2) concentrations less than 14 microM. Two hours after injection, the rabbit was anesthetized and the bladder exposed through a midline incision. One full-thickness bladder strip was cut and immediately placed in fixative for immunohistochemical recognition and visualization of Hypoxyprobe-1-protein adducts. The remaining bladder was then excised, and three additional strips were cut for contractility studies. The remainder of the bladder was frozen for biochemical and slot-blot analyses. Bladder weight was increased fourfold after obstruction, and significant contractile and biochemical dysfunctions were observed that indicated an intermediate level of decompensation. Immunohistochemical visualization revealed focal areas of moderate to severe hypoxia in the detrusor smooth muscle (SM) and subserosal regions of these bladders. No hypoxia was observed in the obstructed bladder mucosa, consistent with the absence of biochemical dysfunction in this compartment, or in unobstructed bladders. Slot-blot analyses confirmed the presence of significant Hypoxyprobe-1-protein adducts in the detrusor of the obstructed bladder, whereas none were present in the control bladder detrusors. Partial outlet obstruction of rabbit bladders resulted in focal areas of moderate to severe hypoxia in the detrusor SM and subserosal regions concomitant with increased bladder mass, decreased contractile function, and selective metabolic dysfunctions of the SM consistent with an intermediate stage of decompensation. The metabolic characteristics of the normoxic mucosa were normal a were those of unobstructed bladders.