Alterations in Plasma and Tissue Prostaglandin Levels in Rabbits During Luteal Regression1,2

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Abstract
To determine if ovarian as well as uterine prostaglandin [PG] production was associated with luteal regression, tissue and plasma concentrations of PGF, PGE, 6-keto-PGF1.alpha. (6-keto-PGF), and thromboxane B2 (TxB) were measured by radioimmunoassay in uterus, corpora lutea, nonluteal tissue, uterine venous plasma and ovarian venous plasma on Days 8, 12 and 15 of pseudopregnancy in the rabbit. Total prostaglandin levels (PGF + PGE + 6-keto-PGF + TxB) were 4-fold greater in the uterus compared to nonluteal tissue and 8-fold greater than in corpora lutea. Both PGF and PGE levels were increased in uterine tissue on Day 15 compared to Days 8 or 12 (P < 0.01). The ratio of PGF:PGE was also elevated on Day 15 compared to Days 8 or 12 (P < 0.05) which suggests that the luteolytic effect of PGF predominates over the possible luteotropic effect of PGE. There were no significant changes in the concentration of TxB or 6-keto-PGF or the ratio of TxB:6-keto-PGF in uterine tissue on any day studied. In nonluteal tissue, PGE was the only PG to vary significantly; PGE levels were elevated (P < 0.05) on Day 8 of pseudopregnancy compared to Days 12 or 15. Although corpora lutea contain significant quantities of PGF, PGE, TxB and 6-keto-PGF, no alterations in the levels of any of these substances were observed between Days 8, 12 or 15 of pseudopregnancy. There were no significant alterations in the levels of any PG in ovarian venous plasma or in the ratio of either PGF:PGE or TxB:6-keto-PGF in luteal and nonluteal tisse or the ovarian venous plasma. The only PG which was observed to increase with luteal regression in the rabbit was PGF in uterine tissue. These data do not support the concept that intraluteal production of PGF, PGE, TxB or 6-keto-PGF plays a predominant role in regulating luteal function during pseudopregnancy in the rabbit.