Steroid concentrations in uterine lymph: possible mediators of uterine and ovarian blood flow during the estrous cycle and early pregnancy in the pig
Uterine lymphatic vessels, which lie in close linear apposition to the uterine and ovarian arteries, may transport steroids to the utero-ovarian periarterial vasoconstrictor nerves controlling blood flow to reproductive organs. Concentrations of estrone (E(,1)), estradiol-17(beta) (E(,2)(beta)) and progesterone (P(,4)) in uterine lymph (UL) were compared to those in systemic blood (SB) during the estrous cycle (EC) and early pregnancy (EP) and subsequently contrasted to patterns of ovarian blood flow (OBF). Experiment I: Uterine lymphatic catheters were implanted chronically into Yorkshire gilts on Days 0 or 1 (n = 5), 5 (n = 4), 11 (n = 5) or 15 (n = 4) of the EC, and UL and SB were sampled daily. Concentrations of E(,1), E(,2)(beta) and P(,4) in UL were positively correlated (P < 0.01) with the concentrations of these same steroids in SB throughout the EC. The E(,1) + E(,2)(beta)/P(,4) (E/P(,4)) ratio was greater (P < 0.01) during the follicular phase than the luteal phase of the EC in both UL and SB; however, concentrations of estrogens were greater (p < 0.01) and P(,4) was lower (p < 0.01) in UL than SB. Experiment II: UL and SB were sampled at surgery on Days 11 (n = 4), 13 (n = 4) or 15 (n = 4) of the EC or EP. Although E(,1), E(,2)(beta) and P(,4) in SB were similar on these days of the EC and EP, E(,1) and E(,2)(beta) concentrations were greater (P < 0.01) in UL of pregnant vs. nonpregnant gilts. Regardless of pregnancy status, and in agreement with data in experiment I, UL had greater (P < 0.01) concentrations of E(,1), E(,2)(beta), and less (P < 0.01) P(,4) than SB resulting in higher E/P(,4) ratios in UL. Experiment III: OBF and SB concentrations of E(,1), E(,2)(beta) and P(,4) were quantified in 4 sows throughout the EC and first 21 days of pregnancy. OBF was positively correlated (P < 0.01) with P(,4) concentrations during the EC and EP. During the EC, OBF and P(,4) concentrations were lowest at estrus, highest during the luteal phase and declined precipitously after Day 14. OBF during EP was similar to the EC until Day 12. Between Days 12 and 15 of EP, but not the EC, OBF and P(,4) concentrations increased transiently by 26% (P < 0.01) and 20% (P < 0.05), respectively. P(,4) concentrations were maintained in the pregnant sows through Day 21. Thus, patterns of E(,1), E(,2)(beta), and P(,4) in UL and SB were similar throughout the EC. Estrogens were elevated in UL of pregnant gilts compared to nonpregnant gilts between Days 11-15, in association with a dilatation of the uterine and ovarian vascular beds and luteal maintenance. Steroids in UL may control dynamic changes in uterine and OBF, due to their close proximity to the periarterial nerves of the utero-ovarian vasculature.