Sex steroids in follicular fluid and blood plasma during the estrous cycle of pigs.

Concentrations of estrogen (E), progestin (P),and androgen (A) were determined in follicular fluid (FF), and concentrations of E and P were measured in peripheral plasma and perifollicular plasma during the estrous cycle in the pig. Also, concentrations of E, P,and A were determined in the utero-ovarian vein (U-OV) plasma every 2h during estrus period in pigs. It was observed that as follicles increased in size, the concentration of E, P, andA in the FF rises from 13,32 and 1 ng/ml at day 8 of the cycle to 180, 754, and 21 ng/ml at day 20 of the cycle, respectively. Approximately 12 h before ovulation there is a significant (P less than 0.01) drop of E, P, and A in the FF to 27, 120, and 0.77 ng/ml, respectivley. Concentrations of E and P in FF and peripheral plasma do not correlate during the second half of the estrous cycle. At day 20 of the cycle, E and P concentrations in the plasma were 20 pg/ml and 0.4 ng/ml, respectively. Concentration of P in the U-OV plasma started increasing 18 to 24 h after the onset of estrus, which is coincident with the drop of P concentration in the FF. As estrus progressed there was a linear drop of E concentration (r = 0.90) in the U-OV plasma. E and P concentrations in the FF were found to be about 1000 times greater than those in the peripheral blood and 5 times greater than in the blood obtained from the perifollicular capillary network at the end of the cycle.