Urinary bladder function in conscious rat pups: a developmental study

Abstract

Cystometric studies of bladder function in anesthetized neonatal rats have suggested specific changes in urodynamic parameters that coincide with the development of a mature bladder-to-bladder micturition reflex. Here, we used a conscious cystometry model that avoids the potentially confounding effects of anesthesia to characterize voiding patterns and urodynamic parameters during early postnatal development in healthy rat pups. Cystometry was performed on postnatal day (P)0, 3, 7, 14, and 21 rats with continuous intravesical instillation of NaCl via a bladder catheter. Micturition cycles were analyzed with respect to voiding pattern, nonvoiding contractions, infused volume, and basal, filling, threshold, and micturition pressures. Reproducible micturition patterns were obtained from all age groups. The time from stimulation to contraction was significantly longer (P ≤ 0.001) in ≤1-wk-old rats (∼10 s) than that in older rats (∼3 s). An interrupted voiding pattern was observed in ≤10-day-old subgroups. Micturition pressure progressively increased with age (from 21.77 ± 1.92 cmH(2)O at P0 to 35.47 ± 1.28 cmH(2)O at P21, P ≤ 0.001), as did bladder capacity. Nonvoiding contractions were prominent in the P3 age group (amplitude: 4.6 ± 1.3 cmH(2)O, frequency: ∼4.0 events/100 s). At P7, the pattern of spontaneous contractions became altered, acquiring a volume-related character that persisted in a less prominent manner through P21. Bladder compliance increased with age, i.e., maturation. In conclusion, conscious cystometry in rat pups resulted in reproducible micturition cycles that yielded consistent data. Our results revealed immature voiding and prolonged micturition contractions during the first 10 neonatal days and provide evidence for age-related changes in urodynamic parameters.

Fig. 1.

Representative cystometrogram illustrating unsuccessful stimulation at low bladder volume (arrowhead) and the pattern of interrupted voiding (arrows) characteristic of young rat pups. Note the continuing increases in the amplitude of myogenic contractions throughout the filling phase (volume-related pattern) uninterrupted by incomplete bladder emptying. The tracing represents one micturition cycle measured in a rat pup at postnatal day (P)8. Top: intravesical bladder pressure; bottom: infused volume.

Fig. 2.

Urodynamic parameters. Changes in basal (BP), filling (FP), threshold (TP), and micturition pressure (MP) during early postnatal development in rat pups are shown. The magnitude of the micturition contraction in younger groups was significantly lower compared with older groups. **P ≤ 0.001, P0 and P3 vs. P21; *P ≤ 0.05, P7 vs. P21.

Fig. 3.

Age-related changes in the micturition-contraction profile and peak micturition pressure. Each recording was obtained from a different animal.

Fig. 4.

Representative tracings from one micturition cycle at P0 (A) and P3 (B) illustrating cystometric findings obtained in response to a continuous infusion of saline. Top: intravesical bladder pressure; bottom: infused volume.

Fig. 5.

Representative tracings from one micturition cycle at P14 (A) and P21 (B) illustrating cystometric findings obtained in response to a continuous infusion of saline. Top: intravesical bladder pressure; bottom: infused volume.