Blood Flow Steroid Secretion and Nutrient Uptake of the Gravid Bovine Uterus

An experiment was conducted with mature Hereford cows to quantitate blood flow, steroid secretion and nutrient uptake of the bovine uterus at various stages of gestation. Electromagnetic blood flow probes were placed around the middle uterine artery supplying the gravid horn at about 30 (n=5), 80 (n=4), 140 (n=4), 180 (n=4), 210 (n=5) and 240 (n=4) days postmating. In addition, indwelling catheters were placed in an artery and vein on the surface of the gravid horn. Beginning on the second day after surgery, blood flow was monitored daily for 15 minutes. Uterine arterial (A) and venous (V) blood samples were collected immediately after blood flow through the middle uterine artery was monitored. Plasma was obtained, frozen and later assayed for progesterone, estrone, estradiol, glucose, α-amino nitrogen, urea nitrogen and selected amino acids. Blood flow to the gravid horn (milliliters/minute) was 119 ± 18 (n=3), 205 (n=l), 1,966 ± 626 (n=3), 3,212 ± 428 (n=3), 3,896 ± 459 (n=3) and 3,155 ± 195 (n=3) at 31 to 45, 77 to 92, 139 to 155, 178 to 199, 202 to 224 and 230 to 258 days postmating, respectively. Progesterone in uterine arterial blood increased throughout pregnancy and averaged 1.44 ± .69, 2.57 ± .79, 4.31 ± .98, 5.77 ± 1.92, 6.57 ± .75 and 9.92 ± 1.04 ng/ml at 33, 83, 140, 182, 207 and 245 days postmating. Estradiol in arterial blood averaged 20.8 ± 10.0, 59.4 ± 40.5, 802.9 ± 484.1, 45.0 ± 7.2, 60.5 ± 18.9 and 65.6 ± 11.4 pg/ml on the same respective days post-mating. No A-V differences were observed in concentrations of progesterone or estradiol on any of the days examined. Plasma estrone followed a pattern silimar to that of estradiol, but uterine V concentrations were higher than A concentrations. These results indicated a nonuterine source of progesterone and estradiol but suggested that estrone was produced by tissue within the gravid uterus. The A-V difference in glucose, α-amino nitrogen and urea nitrogen did not change with days postmating. The mean A-V difference (n=20) for these metabolites was 5.6 ± .5, .72 ± .15 and −.37 ± .09 mg/ml respectively. The A-V difference of specific amino acids did not change with days postmating. These results suggest that the increased nutrient uptake by the bovine uterus during the course of gestation was a result of increased blood flow to the uterus.