Changes in ovarian norepinephrine synthesis throughout the follicular and luteal phases

The aims of this study were to determine norepinephrine (NE) synthesis in follicle-dominated and luteal-dominated ovaries as compared to oviducts, and to correlate NE synthesis with NE content and turnover rates. Rats were injected with pregnant mare's serum gonadotropin (PMSG) on Day 28. Ovaries and oviducts were removed during the follicular (Days 28-30) and luteal (Days 31-40) phases and incubated for 2 h with [3H] tyrosine. Tritiated and endogenous NE were determined by high-performance liquid chromatography. Ovarian NE synthesis from [3H] tyrosine was reduced by more than 50% within 24 h after PMSG injection, with a second 50% reduction on Day 30, concomitant with the endogenous gonadotropin surge. The lowest NE synthesis (15% of control values) was observed in the luteinized ovary on Day 33. Ovarian NE synthesis from [3H] L-dihydroxyphenylalanine (DOPA) was similar in control and PMSG-injected rats on selected days during the follicular and luteal phases. Oviductal NE synthesis decreased after PMSG injection, but was similar to control values during the luteal phase. Ovarian NE content was modestly reduced between Days 30 and 35, whereas oviductal NE content was not altered. After an injection of alpha-methyl-p-tyrosine on Day 33, ovarian and oviductal NE content decreased exponentially over a period of 10 h. The NE turnover rates were similar in control and PMSG-injected rats in both tissues. The following conclusions were reached: Circulating gonadotropins appear to suppress ovarian NE synthesis during the follicular phase. The low NE synthesis by the luteinized ovary is consistent with previous reports that follicles, but not corpora lutea (CL), contain catecholamine elements.(ABSTRACT TRUNCATED AT 250 WORDS)