Progesterone secretion and prostaglandin F release in vitro by endometrial and luteal tissue of cyclic pigs

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Abstract
Blood and tissue were collected from 30 pigs on various days of the estrous cycle to compare progesterone [P] in peripheral plasma and P release in vitro with prostaglandin (PG) F release in vitro by endometrial and luteal tissue (.apprx. 100 mg in 5 ml Krebs-Ringer-bicarbonate buffer, pH 7.4, for 2 h with 3 different incubation treatments). Plasma P increased from days 8-12 of the estrous cycle (25.1-42.8 ng/ml, P < 0.05) and decreased from day 14-16 (36.3-5.9 ng/ml, P < 0.05). P release in vitro at 37.degree. C decreased from 18.0-2.7 ng/ml tissue from days 8-16 (P < 0.05). Endometrial PGF release in vitro at 37.degree. C increased slightly from days 8-14, then increased significantly from 43.7-103.5 ng/100 mg tissue between days 14-16 (P < 0.05). The rapid increase in endometrial PGF release coincided with the decrease in plasma P. A small increase in mean luteal PGF release was detected between days 14-16. Apparently luteal PGF-2.alpha. does not play a critical role in the luteolysis process in the pig but there is involvement of endometrial PGF-2.alpha.