Role of conceptus-induced vasodilation in controlling utero-ovarian function of ewes, cows and sows
During early pregnancy, estrogens (E) and (or) prostaglandin E(,2) (PGE(,2)), secreted from the gravid uterus, may reduce the function of periarterial sympathetic vasoconstrictor nerves (PSVN), resulting in transient increases in uterine and overian blood flow (BF) previously observed on days critical for maintenance of corpora lutea (CL) in cows and sows. Experiment I: Uterine arteries (UA) were collected from follicular phase (FP; Days 19-21; n = 8) or luteal phase (LP; Day 13; n = 7) nonpregnant (NP) gilts and from pregnant (P; Day 13; n = 7) gilts. Although UA from FP and P gilts ahd reduced (P < 0.01) vasoconstriction in vitro compared with UA from LP gilts, (alpha)-adrenergic receptor levels were reduced (P < 0.05) only for UA from FP and not P gilts compared with LP gilts. Experiment II: As observed for UA in experiment I, vasoconstriction of the ovarian vascular bed was reduced (P < 0.01) for FP (Days 20 to +1; n = 5) and P (Day 13; n = 5) compared with LP (Days 11 to 13; n = 4) gilts, and was significantly correlated (r = -0.99; P < 0.01) with the E:P(,4) ratio in systemic blood in NP (FP and LP) but not P gilts. Experiment III: For NP ewes (5/day), blood flow (BF) did not differ between uterine horns (UH) and was constant across Days 9, 11, 13 and 15. During the subsequent pregnancy of these ewes, BF was elevated (P < 0.01) only for UH ipsilateral to a CL-bearing ovary on Days 11, 13 and 15. Although increased BF of ipsilateral UH was not associated with increased estradiol-17(beta) (E(,2)(beta)) in UA or uterine venous blood, E(,2)(beta) in uterine flushings of P ewes was greater (P < 0.05) than for NP ewes across all days. Experiment IV: Sixteen NP heifers (4/group) received intrauterine infusions of vehicle (VEH), E(,2)(beta) (150 ng), PGE(,2) (250 (mu)g) or E(,2)(beta) + PGE(,2) every 6 hr from Day 13 to Day 21. Ten of 12 VEH-, E(,2)(beta)- and PGE(,2)-treated heifers, but none of the E(,2)(beta) + PGE(,2)-treated heifers, returned to estrus by Day 21. Systemic P(,4) levels of E(,2)(beta)-treated heifers were elevated (P < 0.05) for 3 days beyond those of VEH- or PGE(,2)-treated heifers, but were basal (< 1 ng/ml) by Day 19. Systemic P(,4) of E(,2)(beta) + PGE(,2)-treated heifers remained elevated (P < 0.05) until Day 21. Estrogens of conceptus origin may increase uterine and ovarian BF, but the function of PSVN is not reduced during early pregnancy. Increases in uterine and ovarian BF may enhance transport of a conceptus-induced luteotropin, such as PGE(,2), to the CL-bearing ovary during early pregnancy in ewes, cows and sows.