ONTOGENY OF ANGIOTENSIN-II VASCULAR SMOOTH-MUSCLE RECEPTORS IN OVINE FETAL AORTA AND PLACENTAL AND UTERINE ARTERIES

OBJECTIVE: Our purpose was to determine if differences in angiotensin II vascular smooth muscle receptor binding account for the attenuated fetal placental and systemic responses to infused angiotensin II relat ive to maternal responses and for the differences between umbilical an d fetal systemic responses. STUDY DESIGN: Using plasma membranes prepa red from the medial layer of fetal aorta, fetal placental artery, and maternal uterine artery obtained between 107 and 134 days of ovine ges tation (n = 17), we measured and compared angiotensin II receptor bind ing density (in femtomoles per milligram of protein) and affinity (in nanomoles per liter) in radioligand binding studies with iodine 125-an giotensin II. Maternal and fetal plasma angiotensin II were also compa red. RESULTS: A single class of high-affinity receptor was identified in all arteries. Although the binding density was similar at < 1 00 an d > 130 days for fetal aorta (388 +/- 87 [SE] vs 262 +/- 56), placenta l artery (319 +/- 95 vs 235 +/- 54), and uterine artery (46 +/- 6 vs 5 0 +/- 13), values for fetal arteries exceeded those for uterine arteri es (p less-than-or-equal-to 0.018) in spite of higher fetal plasma ang iotensin II (74 +/- 18 vs 30 +/- 8 pg/ml, p < 0.01). Affinity did not differ between arteries and, except for fetal aorta (1.4 +/- 0.2 vs 2. 1 +/- 0.4, r = 0.49, p = 0.045), was unchanged during late gestation.C ONCLUSION: Differences between fetal and maternal responses and fetal placental and systemic responses to infused angiotensin II in sheep do not reflect alterations in total angiotensin II vascular smooth muscl e receptor binding density or affinity.