Myometrial responses in situ to nicergoline, acebutolol, phentolamine and noradrenaline of the rat in proestrus

Inhibition of prostaglandin synthetase alters uterine response to adrenoceptor agonists in pregnant and post-partum rats

1. The involvement of intramurally generated prostaglandins in uterine response to adrenoceptor agonists has been investigated in rats during late pregnancy and post partum. 2. Both adrenaline and salbutamol (10(-9)-3 x 10(-7) M) produced concentration-dependent inhibition of acetylcholine-induced tone in preparations from 20-day pregnant and 1-day post-partum rats. 3. Inhibition of prostaglandin synthetase with flurbiprofen enhanced uterine response to these agonists in late pregnancy and post partum. 4. In endometrium-free preparations, flurbiprofen treatment had no significant effect on myometrial responses to adrenaline and salbutamol, suggesting a role for the endometrium in the interaction between adrenoceptor agonists and the prostaglandin synthetase pathway. 5. The above results provide pharmacological evidence for the involvement of prostaglandins in rat uterine response to adrenoceptor agonists during pregnancy and post partum.

Involvement of alpha-adrenoceptors in myometrial responses in the pro-oestral rat

1. Myometrial responses to different agents acting on adrenoceptors were examined in vivo in the pro-oestrous rat. Changes in spontaneous uterine mechanical activity were recorded isometrically and evaluated in terms of amplitude and duration of uterine contractions. 2. Phenylephrine (10 micrograms kg-1) markedly increased the amplitude and duration of contractions and 40 micrograms kg-1 gave rise to tetanic contractions. 3. Administration of either nicergoline (400 micrograms kg-1) or phentolamine (1000 micrograms kg-1) to phenylephrine-primed rat uterus reduced the strength of contractions and phentolamine abolished the phenylephrine-induced uterine contracture. 4. Following blockade of alpha 2-adrenoceptors by yohimbine (1000 micrograms kg-1) and beta-adrenoceptors by propranolol (2400 micrograms kg-1), a single injection of phenylephrine (100 micrograms kg-1) increased the amplitude of uterine contractions by 30%. 5. Noradrenaline reduced the amplitude of contractions and caused elevation of the baseline level. The response of myometrium to the combination of both propranolol and noradrenaline was the establishment of uterine contracture with subsequent increase of the duration of contractions. 6. These results clearly demonstrate the involvement of alpha-adrenoceptors in the myometrial activity of the rat in vivo during pro-oestrus.