Effect of progesterone on monoamine turnover in the brain of the estrogen-primed rat.

The effect of progesterone (P) on monoamine levels and turnover was evaluated in 8 brain nuclei in estrogen-primed rats. Animals were subcutaneously (SC) injected with P or vehicle 21 hours after SC treatment with 5 micrograms of estradiol benzoate (EB). EB-primed animals treated with P showed high levels of lordosis behavior and an LH surge three hours later. Initial concentrations of norepinephrine (NE), dopamine (DA), serotonin (5HT) and 5-hydroxyindole acetic acid were determined in EB-saline treated controls 3 hours after P or vehicle. NE and DA turnover was estimated from the exponential decline of these amines 2 hours after IP injection of alpha-methyl-p-tyrosine (5 hours after P or vehicle). The accumulation of 5HT 20 min following IP injection of pargyline was used as an index of 5HT turnover. P did not affect the initial NE, 5HT or 5HIAA concentrations in any of the brain nuclei studied, but decreased DA content in the arcuate-median eminence region (Ar-ME). The DA rate constant was elevated in the nucleus of the diagonal band of Broca and the DA turnover rate was decreased in the Ar-ME. In the periventricular region (PVE, anterior hypothalamic level) the NE turnover rate (K, pg/microgram protein/hr) and rate constant (k, hr-1) decreased following P treatment. Progesterone treatment decreased the accumulation of 5HT in the ventromedial hypothalamus (VMN, pars lateralis) and the dorsal midbrain central grey (MCG). Progesterone effects on monoamine turnover were not found in the lateral septal, medial preoptic, anterior hypothalamic or dorsal raphe nuclei.(ABSTRACT TRUNCATED AT 250 WORDS)