Arginine supplementation between 41 and 146 days of pregnancy reduces uterine blood flow in dairy heifers.

We hypothesized that arginine (Arg) supplementation during early pregnancy could foster placental vascularization. The objective of this study was to evaluate the effects of Arg supplementation on uterine artery hemodynamics between 40 and 140 days of gestation. At 41 days of gestation, 17 Holstein heifers (448 ± 73.9 kg) were surgically fitted with a catheter in the peritoneal cavity. After surgery, nine heifers received a daily intraperitoneal infusion of 40 mg of Arg/kg of body weight (BW; ARG), whereas the remaining eight heifers received a daily intraperitoneal infusion of saline solution at equivalent volumes as ARG heifers relative to BW (CTRL). Daily infusions took place every 12 hours until heifers reached 146 days of pregnancy. At 41, 62, 83, 104, 125, and 146 days of pregnancy, all heifers were body weighed, bled, and uterine blood flow volume (FV) and other hemodynamics were determined using Doppler ultrasonography. The measurements included heart rate, FV, pulsatility index, and resistance index. Plasma concentrations of amino acids (AAs), nitric oxide, glucose, insulin growth factor, progesterone (P4), growth hormone, and prolactin were analyzed. In a second experiment, we evaluated Arg metabolism when infused either intravenously or intraperitoneally. Overall, FV did not differ between the treatments, but it increased (P < 0.001) with pregnancy day. Uterine blood FV evolved differently between the treatments, with CTRL heifers having a greater (P < 0.05) FV (1104 ± 65.42 mL/min) at 146 days of pregnancy than in ARG heifers (806 ± 65.32 mL/min). Pulsatility index and resistance index decreased throughout pregnancy but did not differ between the treatments. Heart rate was decreased (P < 0.05) in ARG (74 ± 1.4 beats/min) compared with CTRL heifers (81 ± 1.5 beats/min). Plasma concentrations of Arg tended (P < 0.09) to be greater in ARG than those in CTRL heifers, but carnitine, valine, isoleucine, leucine, phenylalanine, and tryptophan were lower (P < 0.05) in ARG than those in CTRL heifers. The proportion of essential AAs (with respect to total AAs) in plasma was greater (P < 0.05) in CTRL (73 ± 2.4%) than that in ARG heifers (65 ± 2.3%). No differences between the treatments were found in plasma prolactin (P = 0.43), insulin growth factor (P = 0.97), glucose (P = 0.45), growth hormone (P = 0.39), or nitric oxide (P = 0.89) concentrations. However, plasma P4 concentration was greater (P < 0.05) in ARG than in CTRL heifers. Contrary to our hypothesis, Arg supplementation did not increase blood flow to the uterus but did change other parameters that could influence placental and fetal growth such as heart rate, maternal concentration of plasma AAs, or P4 synthesis. Furthermore, infusion sites (blood vs. peritoneum) of Arg render different metabolic responses.