Exogenous L‐arginine administration improves uterine vascular perfusion, uteroplacental thickness, steroid concentrations and nitric oxide levels in pregnant buffaloes under subtropical conditions

Heat stress (HS) during pregnancy adversely affects uterine vascular perfusion and foetal development. L-arginine (L-Arg), a nitric oxide (NO) precursor, has been proven to enhance an organ's vascular perfusion. Therefore, this study aimed to examine the effect of L-Arg administration on the pregnant buffaloes' uterine haemodynamics and uteroplacental thickness under environmental HS conditions. For this purpose, pluriparous (n = 12) HS-pregnant buffaloes (mid-gestation, 180-190 days; temperature humidity index >85) were haphazardly assigned into two groups, either administered a single intravenous (IV) bolus of 5 mg/kg BW of L-Arg Hcl (n = 6; ARG) or received normal saline (0.9%; IV; 25 ml) that served as a control group (n = 6; CON). Combined uteroplacental thickness (CUPT, mm), middle uterine arteries' (MUA) diameter (mm) and uterine Doppler haemodynamics (ipsilateral and contralateral to the pregnant horn) were examined utilizing B-mode and colour Doppler ultrasonography, respectively. The serum levels of progesterone (P4), estradiol 17β (E2), nitric oxide (NO) and total antioxidant capacity (TAC) were assayed using commercial kits. The experimental time points were - 1, 0, 2, 4, 24, 48, 72, 96 and 120 h post-L-Arg administration. The ARG group showed higher (p < .05) CUPT and MUA diameter values starting at 24 h post-treatment and onward than the control buffalo cows. In addition, there were improvements (p < .05) in the blood flow parameters in the ipsilateral MUA after L-Arg treatment evidenced by lower values of pulsatility and resistive indices starting at 48 and 4 h, respectively and onward, and higher values of peak systolic velocity, coloured areas towards the pregnant uterine horn (both 24-72 h). Increases in the NO levels were found during the period between 4 and 120 h in the ARG group compared to the CON group. Moreover, significant increases in the E2 and P4 means were noted in the ARG group, especially at 24 h onward, respectively compared to the CON group. Concerning the TAC status, neither the administration nor the hours affected serum TAC levels in the HS pregnant buffaloes (CON and ARG). In conclusion, L-Arg administration improved uteroplacental thickness and enhanced uterine haemodynamics, NO levels, and steroids production in mid-pregnant buffalo cows under environmental heat stress conditions which could improve foetal growth and development.