Comparison of the effects of oestrogen deficiency and old age on primary bladder afferent activity and voiding behaviour in the ageing female rat

OBJECTIVE To determine if a decrease in oestrogen (E) levels increases activity in bladder afferent nerves, by investigating the effects of E loss on afferent nerve activity in ovariectomized (OVX) rats, and making comparisons with findings in ageing female rats. MATERIALS AND METHODS Female Sprague-Dawley rats were divided into four groups: ageing; OVX + E; OVX + vehicle (V); and sham-operated (SHAM) + V. The E (250 mu g/kg) or V (cottonseed oil) was injected s.c. once a week for 8 weeks. Frequency-volume recordings were performed with the rats in metabolic cages, and single A delta- or C-fibre activities from the bladder were measured. After measurements, the blood serum was collected and the estradiol (E2) level was measured. RESULTS The C-fibre activity of OVX + V rats was significantly lower than in the other groups. A delta-fibre activity was unchanged. Despite low E2 levels, ageing rats showed high afferent activity and voiding frequency. CONCLUSION Although a low E level may affect storage function, it is unlikely that it is the main cause of the high afferent activity and voiding frequency observed in the ageing female rat.