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Blood Flow, Steroid Secretion and Nutrient Uptake of the Gravid Bovine Uterus and Fetus^1,2,3,

US Department of Agriculture, Clay Center, NE 68933 and and Iowa State University, Ames 50011

Abstract

A study was conducted with mature Hereford cows to quantitate blood flow, steroid secretion and nutrient uptake of the gravid uterus and fetus. Surgery was performed on cows at 163 to 166 (stage 1, N = 5) and 173 to 176 (stage 2, N = 11) d postmating. The uterus of each cow was exposed by midventral laparotomy and catheters were placed in a major branch of an artery (UA) and vein (UV) of the gravid uterine horn, an umbilical vein (UMV) and a fetal femoral artery (FA) and vein (FV). Samples were taken daily from the UA, UV, UMV and FA catheters. Plasma was frozen and later assayed for -amino N (AN), urea N (UN), glucose (G), estrone (E₁), estradiol-17β (E₂β) and progesterone (P₄). Blood flow was estimated by the steady state diffusion method using antipyrine as the test substance on about d 7 postsurgery. Antipyrine, G, lactate (L) and O₂ concentrations were determined in blood collected during this procedure. Concentrations of E₁ and E₂β were greater (P<.05) in UV than in UA plasma, but these differences were reduced from stage 1 to stage 2. The UA and UV plasma concentrations of E₁ were greater (P<.05) than those of E₂β across both stages of gestation (31 ± 3 vs l6 ± l and 72 ± 11 vs 25 ± 4 pg/ml, respectively). In contrast, E₂β concentrations were greater (P<.05) than E₁ in UMV and FA plasma (20 ± 3 vs 12 ± 2 and 22 ± 2 vs 12 ± 1 pg/ml, respectively). Concentrations of E₁. and E₂β in UMV plasma were equal to or greater than in FA plasma of stage 1 cows (14 ± 4 and 27 ± 3 vs 11 ± 2 and 20 ± 3 pg/ml, respectively). Stage 2 cows, however, had greater (P<.05) E₂β concentrations in FA than UMV plasma (23 ± 3 vs 13 ± 2 pg/ml) while E₁ concentrations in FA plasma were similar to those in UMV plasma (12 ± l vs 9 ± l pg/ml). Regardless of stage of gestation, P₄ concentrations in UA were greater (P<.05) than in UV plasma (7.01 ± .94 vs 4.38 ± .42 ng/ml) while concentrations of P₄ in UMV (.21 ± .04 ng/ml) and FA plasma (.18 ± .05 ng/ml) approached the lower limits of assay sensitivity. These data suggest the bovine fetus maintained constant levels of E₂β despite decreased E₂β concentrations in UMV plasma. Mean uterine and umbilical blood flows were 5,954 ± 518 and 1,107 ± 44 ml/min, respectively. Net uptake of AN, UN, G, L and O₂ by the gravid uterus was 1.17 ± .11 meq/min, —.408 ± .037 meq/min, .748 ± .093 mmol/min, —.186 ± .017 mmol/min and 4.04 ± .19 mmol/min, respectively. Net fetal uptake of each of these metabolites was .184 ± .007 meq/min, —.099 ± .004 meq/min, .130 ± .022 :nmol/min, .192 ± .048 mmol/min and 1.158 ± .087 mmol/min, respectively. These data indicated a net uptake of AN, G and O₂, and a net loss of UN by the fetus and gravid uterus, and indicated a net flux of lactate from the utero-placental unit to both the maternal and fetal circulations.

¹ Cooperation of the Nebraska Agr. Exp. Sta., Univ. of Nebraska, Lincoln, is acknowledged.

² The authors wish to thank Fred Philips, Leroy Hassler, Bill McDonald, Kathy Sorensen, Ronda Williams and Julie Jacobson for their able assistance.

³ Mention of trade name, proprietary product or specific equipment does not constitute a guarantee or warranty by the USDA and does not imply approval to the exclusion of other products that may be suitable.

⁴ USDA, SE, ARS, Roman L. Hruska U.S. Meat Animal Research Center, Clay Center, NE 68933.

⁵ Dept. of Anim. Sci., Iowa State Univ., Ames 50011. Journal Paper J-10758 of the Iowa Agr. and Home Econ. Exp. Sta., Ames. Proj. 1994, 2443 and 2444.

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