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This study was conducted to determine if intrauterine injections of estradiol-17 beta (E2 beta) could maintain luteal function in nonpregnant sows. Eight sows were assigned to surgery on d 8 or 9 of the estrous cycle (first day of estrus = d 0). At surgery, cannulas were inserted bilaterally into the uterine artery (UA) and common utero-ovarian vein (UOV), as well as into the lumen of each isolated uterine horn. Electromagnetic blood flow transducers were placed around the middle uterine artery supplying each horn of four sows. After surgery, sows were assigned randomly to receive either intrauterine injections of vehicle (.9% NaCl) into both uterine horns (control sows) or E2 beta into one uterine horn (375 ng/injection) and vehicle into the other (treated sows) every 6 h from 1200 h on d 11 to 1200 h on d 15. Uterine blood flow (UBF) was quantified, and blood was sampled from the UA and UOV, periodically, from d 11 to 18. On d 18, sows were ovariectomized and corpora lutea (CL) were weighed. Blood plasma was subsequently analyzed for progesterone (P4) and prostaglandin F (PGF) by radioimmunoassay. Control sows had smaller (P less than .05) CL than treated sows on d 18 (3,046 +/- 614 vs 4,451 +/- 324 mg). Progesterone concentrations in UOV blood of treated sows tended to increase from d 11 (469 +/- 110 ng/ml) to 18 (626 +/- 209 ng/ml) while P4 in UOV blood of control sows decreased markedly (P less than .01) from d 11 (579 +/- 79 ng/ml) to 18 (14 +/- 5 ng/ml). In addition, UOV P4 concentrations on the E2-beta-injected side of treated sows were higher (P less than .05) than those on the vehicle-injected side from d 14 to 18. The UBF of two treated sows increased eightfold to 10-fold within 12 h of the first E2 beta injection and remained elevated through d 17, while UBF of two control sows remained constant. Prostaglandin F concentrations in UOV blood of treated sows were lower (P less than .05) than in UOV blood of control sows on d 14 and 15. There was no effect of side of E2 beta injection on PGF concentrations, which were similar in UOV blood draining both uterine horns of treated sows. Thus, the local effect of E2 beta in stimulating P4 secretion by the ipsilateral ovary is not due to reduced PGF concentrations in UOV blood draining the E2 beta-injected horn.

A dramatic 15-fold increase in uterine blood flow in pigs occurs during pregnancy in association with marked increases in uterine arterial (UA) diameter. This study was conducted to determine UA collagen and elastin content, diameter, alpha 1- and alpha 2-adrenergic receptor (AR) numbers, norepinephrine (NE) and in vitro reactivity to phenylephrine on d 0, 20, 50, 80 and 110 of pregnancy in the pig. Uterine arterial collagen content declined progressively throughout pregnancy (P less than .01), whereas the content of elastin remained constant from d 0 to d 80, then increased (P less than .05) from d 80 to d 110. The UA collagen to elastin ratio was correlated with UA diameter (r = -.69; P less than .01), which increased from 4.5 mm on d 0 to 9.0 mm on d 110. Uterine arterial alpha 1-AR numbers remained low and constant throughout pregnancy, consistent with its retained ability to contract in response to phenylephrine. Uterine arterial NE content declined (P less than .05) from d 20 to d 80 before increasing slightly to d 110. Uterine arterial alpha 2-AR numbers remained high from d 0 to d 80 before decreasing (P less than .05) to low values on d 110. These data are consistent with a reduced adrenergic neuronal control and increased elasticity of the UA during pregnancy in the pig.

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