Substantial detrusor overactivity in conscious spontaneously hypertensive rats with hyperactive behaviour.

Objective: The spontaneously hypertensive rat (SHR) is a useful model for studying the mechanisms of detrusor overactivity (DO). However, owing to their confounding phenotypic characteristics of hyperactive behaviour, there could be some problems with the interpretation of cystometric data, which is significantly confused by abdominal straining (AS), causing changes in intravesical pressure (IVP).

Material And Methods: IVP and intra-abdominal pressure (IAP) were recorded simultaneously to evaluate true DO in conscious healthy male SHRs and Wistar/ST (Wistar) rats. Intravesical pressure rises (IVPRs), defined as increments that exceeded 2 cmH(2)O from baseline, were counted, and those that were caused by AS or DO were determined according to the presence of simultaneous changes in IAP.

Results: Compared with Wistar rats, SHRs had a shorter filling phase (p<0.01) and greater frequency of IVPRs (p<0.01). SHRs, but not Wistar rats, showed DO. The substantial DO represented up to 76% of total IVPRs, with the remainder caused by AS. The amplitude (p<0.05) but not the frequency of AS (p>0.05), was higher in SHR than Wistar rats.

Conclusion: In conscious SHRs, variations in IAP due to hyperactive behaviour may cause misinterpretation of pressure parameters and result in false reports of DO. Thus, simultaneous registration of IAP and IVP is needed for accurate recording of substantial DO in these animals.