Evidence for a stimulatory beta-adrenergic component in the release of the ovulatory LH surge in pro-oestrous rats.

The effect on ovulation of intraventricular infusions of noradrenaline, adrenaline and various pharmacological agents acting on the adrenergic receptor subtypes were investigated in cyclic female rats on the day of pro-oestrus. The inhibitory effects on ovulation of the different infusions were monitored by administering the drugs before 11.00 h (several hours before the critical period for the ovulatory LH surge). In experiments designed to show how the drugs under investigation might stimulate ovulation, pentobarbitone sodium (35 mg/kg) was given at 14.30 h; this anaesthetic inhibits ovulation and its effects can be overcome by substances that advance the preovulatory LH surge. Noradrenaline (an alpha-agonist) stimulated ovulation when administered on the morning of pro-oestrus to rats injected with pentobarbitone early in the afternoon of the same day. Phenoxybenzamine and phentolamine (non-selective alpha-antagonists) and clonidine (a selective alpha 2-agonist) all inhibited ovulation when infused on the morning of pro-oestrus. Yohimbine (a moderately selective alpha 2-antagonist) neither stimulated nor inhibited ovulation. Both isoprenaline (a non-selective beta-agonist) and fenoterol (a selective beta 2-agonist) stimulated ovulation in pentobarbitone-treated rats when administered on the morning of pro-oestrus and fenoterol was also able to overcome the pentobarbitone block when infused later in the afternoon. Propranolol (a non-selective beta-antagonist) and metoprolol (a selective beta 1-antagonist) were stimulatory only when administered in the afternoon. Adrenaline (both an alpha- and beta-agonist), prenalterol (a selective beta 1-agonist), atenolol (a selective beta 1-antagonist) and ICI 118,551 (a selective beta 2-antagonist) neither stimulated nor inhibited ovulation.(ABSTRACT TRUNCATED AT 250 WORDS)