Color-Doppler signals of blood flow in the corpus luteum and vascular perfusion index for ovarian and uterine arteries during expansion of the allantochorion in Bos taurus heifers

- Function of CL increases in early pregnancy.
- Increased blood flow in adjacent uterine artery occurs during increased CL function.
- Vascular perfusion of each main uterine artery increases as allantochorion expands.

Hemodynamics of the CL and each main uterine artery during expansion of the allantochorion from the ipsilateral side (CL side) to the contralateral side were studied in heifers (n = 8 nonbred, 9 pregnant). Progesterone concentration, vascular perfusion index for each uterine artery (by spectral ultrasonography), extent of blood flow in the CL (percentage of CL tissue with color-Doppler signals of blood flow), and intrauterine location of the expanding allantochorion (by gray-scale ultrasonic imaging) were determined daily from Days 14-60 (Day 0 = ovulation). In the pregnant group, but not in the nonbred group, the percentage of CL tissue with blood-flow signals increased (P < 0.003) from Days 16 (66.7 ± 4.2%) to 23 (79.4 ± 2.5) and then more slowly increased (P < 0.02) from Days 24 (76.7 ± 2.9%) to 50 (85.0 ± 2.0%). The volume of CL increased (P < 0.0001) progressively from Days 26 (6.1 ± 0.4 cm3) to 60 (7.3 ± 0.7 cm3). The vascular perfusion index in the ipsilateral uterine artery did not change in the nonbred group and progressively increased in the pregnant group beginning on Day 17 in approximate temporal association with the increase in luteal blood-flow signals. Functional increases in the CL during early pregnancy were attributed to the greater uterine arterial blood flow on the ipsilateral or CL side and the reported prominent anastomosis from a branch of the uterine artery to the ovarian artery that supplies the CL ovary. After an initial significant decrease in vascular perfusion index in each uterine artery in the pregnant group, the index began to increase on Day 17 in the ipsilateral artery and on Day 18 in the contralateral artery. The perfusion continued in the ipsilateral artery but discontinued in the contralateral artery on Day 21. Perfusion and diameter of the uterine artery were greater for the ipsilateral side until the vesicle entered the contralateral horn on Day 33 and increased for the contralateral horn between vesicle entry and filling of the horn on Day 44. During Days 35-60, the perfusion index (P < 0.04) and artery diameter (P < 0.001) were lower in the contralateral than in the ipsilateral artery. Results supported the hypotheses that (1) CL function increases during early pregnancy in temporal association with an increase in blood flow in the ipsilateral uterine artery and (2) blood flow in each of the ipsilateral and contralateral uterine arteries increases as the allantochorion expands in each uterine horn.