Effect of progestogens and oestrogens on the contractile response of rat detrusor muscle to electrical field stimulation.

1. The effect of oestradiol and progesterone pretreatment on the contractile response of isolated rat detrusor muscle to electrical field stimulation was investigated. The response to direct administration of 2 mumol/l progesterone and 2 mumol/l diethylstilboestrol in the organ bath was also examined. 2. Virgin female Wistar rats were injected subcutaneously with oestradiol benzoate (150 micrograms/kg) for 3 days followed by 1 day of progesterone (160 micrograms/kg). This cycle was repeated once. Control rats received no injections. 3. In controls, progesterone significantly reduced the maximum contractile response of rat detrusor muscle in vitro by 12% (P < 0.01). The EF50 was significantly increased compared with control. When 2 mumol/l diethylstilboestrol, was added, the maximum contractile response was significantly reduced by 42% (P < 0.01) and the frequency-response curve showed a further increase in EF50. 4. Progesterone had no effect on the atropine-resistant component of electrical field stimulation, but progesterone and diethylstilboestrol reduced the atropine-resistant response by 16% (P < 0.01). 5. Detrusor muscle from pretreated rats showed a non-significant increase in maximum contractile response compared with untreated controls. The addition of 2 mumol/l progesterone to the bath chamber had no effect on this response, but the further addition of 2 mumol/l diethylstilboestrol reduced the maximum contraction. 6. Pretreatment with oestradiol and progesterone had no effect on the atropine- or tetrodotoxin-sensitive response to electrical field stimulation. 7. In conclusion, the direct effect of progesterone and diethylstilboestrol inhibited the contractile response of detrusor muscle to electrical field stimulation and the effects of each summated.(ABSTRACT TRUNCATED AT 250 WORDS)