BACKGROUND: This study aimed to determine amino acid (AA), ammonia and urea concentrations in human ovarian follicular fluid and to compare these concentrations with those in the circulation. METHODS: Samples of pre-ovulatory follicular fluid and peripheral venous blood were obtained from 14 IVF patients. High-performance liquid chromatography (HPLC) measurements of 25 AAs were the main outcome measures. RESULTS: There was a significant gradient of most AAs from plasma to follicular fluid, with the exception of glutamate, which demonstrated a three-fold increase in follicular fluid concentration (70.0 +/- 3.80 mu M) compared with plasma (23.18 +/- 2.20 mu M; P < 0.001). The plasma-to-follicular fluid concentration difference for glutamine (81.83 +/- 9.2 mu M) was greatest among all AAs. Among essential AAs, this difference was greatest for the branched-chain AAs, isoleucine, leucine and valine. Ammonia concentrations in follicular fluid and blood were 38.87 +/- 2.23 and 22.11 +/- 1.96 mu M, respectively (P < 0.001). Urea concentration in follicular fluid was 3.37 +/- 0.18 mM, a value not significantly different from plasma concentration (3.36 +/- 0.22 mM; P = 0.911). CONCLUSIONS: These plasma-follicular fluid differences may reflect both the utilization of AAs and the transport characteristics of the follicular cells. There is accumulation of glutamate and ammonia in pre-ovulatory follicular fluid. The data for urea are consistent with transport by passive diffusion, with no evidence of an active urea cycle in the cells of the follicle.
