AIMS OF STUDY.
Current methods used in the evaluation of isometric bladder contraction involve the suspension of a strip of bladder into a chamber, tying one end of the tissue to a fixed point and the other to a force transducer. In the present study we introduce a new instrument for the measurement of bladder contraction obviating the need to tie the tissue. This instrument was used in the evaluation of bladder stiffness, produced by cholinergic stimulation of the rat bladder. The tissues used for these experiments were obtained from ovariectomized (OVX) and estrogen-treated (OVX+E) rats.

METHODS.
The stiffness biosensor was made up of a piezoelectric crystal (PZT) having 1mm in diameter and supported by a micromanipulator. The crystal was electrically driven at its resonance frequency by an oscillator. Upon contact with the tissue the resonance frequency of the PZT shifted in accord with tissue stiffness. This frequency shift, Df, was calibrated to represent tissue stiffness in gm/cm. Tissue segments, 50 mg in weight and approximately 5x5 mm2 in size, were dissected from the bladder domes of 6 OVX and 6 OVX+E rats. The tissues were placed on a cotton gauze, soaked in Krebs solution, and placed under the biosensor so that three consecutive measurements could be taken. These initial measurements represent baseline stiffness. The response of the bladder was measured when high [K+] and increasing doses of Carbachol 2,20,200 ng/kg were directly applied onto the surface of the tissues. Three measurements were taken after the addition of each dose. Dose response curves were generated for the stiffness of the OVX and OVX+E groups.

RESULTS
The results show that the biosensor was able to produce consistent and reliable measurements of bladder stiffness under control conditions. Figure 1 shows a dose response curve of the relationship of bladder stiffness to Carbachol concentration. As indicated stiffness is shown to increase significantly following the addition of Carbachol. The response to increasing doses of the stimulant was markedly different between the two groups of rats, indicating that the biosensor possesses sufficient sensitivity for detecting variations in tissue stiffness.

CONCLUSIONS AND DISCUSSION
The stiffness dose response curves obtained using the PZT biosensor method were similar to those using the conventional tissue bath isometric techniques(1). While contractility has been measured under in vitro conditions using tissue strips which are stretched and suspended in a bathing solution, there has not been to date an equally feasible approach which allows for the determination of un-stretched bladder stiffness. Using this method it is concluded that ovariectomy significantly increases bladder stiffness in response to low doses of cholinergic stimulation in comparison to the estrogen supplemented rats. The results obtained from this study using the PZT transducer demonstrate the potential of Estrogen manipulation in modulating the mechanical charactristics of the bladder. We project that by using this alternative method of assesing the effect of pharmacologic stimulation on the bladder the influence of hormones on the bladder as well as the prostate can be objectively evaluated. Finally we expect that this approach, which uses smaller amounts tissue than isometric recordings may prove appropriate in the evaluation of tissue segments obtained from biopshies. 1 Life Sciences 64(23)279-289