Effects of catecholaminergic blockade by haloperidol or propranolol at different stages of the oestrous cycle on ovulation and gonadotrophin levels in the rat.

Rats with a 4-day oestrous cycle were injected with 2.5 mg haloperidol/kg, a dopaminergic blocker, or with 2.0 mg propranolol/kg, a beta 1- and beta 2-receptor blocker, at 13.00 h on oestrus, dioestrous day 1, dioestrous day 2 or pro-oestrus. Animals were autopsied on the next expected day of oestrus. Haloperidol blocked ovulation when injected on oestrus, dioestrous day 1 or pro-oestrus and was less effective when injected on dioestrous day 2. Propranolol caused a decrease in the number of ova shed when injected on dioestrous day 2 or pro-oestrus. Serum concentrations of FSH at oestrus were below the control values in those animals in which ovulation was blocked by haloperidol. No significant changes in serum concentrations of LH were observed. The normal gonadotrophin peak which occurs during the afternoon of pro-oestrus was blocked by administration of haloperidol on oestrus or dioestrous day 1. Administration of gonadotrophin-releasing hormone (GnRH) to haloperidol-treated animals on oestrus or dioestrous day 1 did not restore ovulation or increase serum FSH levels. When the same dose of GnRH was given to rats treated with haloperidol on pro-oestrus, they all ovulated and their FSH levels rose normally. Treatment with both FSH and LH of rats given haloperidol at oestrus restored ovulation in 50% of the animals, whereas it was ineffective in animals treated on dioestrous day 1. Fifty per cent of the animals treated with haloperidol on oestrus or dioestrous day 1 ovulated when oestradiol benzoate was injected on dioestrous day 2.(ABSTRACT TRUNCATED AT 250 WORDS)