ONTOGENY OF OVINE FETAL RENAL ATRIAL-NATRIURETIC-FACTOR RECEPTORS

Ovine fetal renal responses to ANF decrease during the last third of g estation, although circulating fetal plasma atrial natriuretic factor (ANF) levels are higher than in the maternal circulation, and do not c hange with gestation. This study examined whether previously reported maturational changes in fetal renal responses to ANF are due to change s in renal ANF receptor numbers and/or affinity during gestation. ANF receptor numbers (Bmax) and dissociation constants (Kd) were measured in isolated renal glomeruli from early (95 and 110 day; mean 103+/-2) and late gestation (131 and 145 day; mean 138+/-2) fetal and maternal sheep. Fetal renal ANF receptor Bmax values significantly increased be tween 103 and 138 days gestation (13+/-3 to 29+/-4 fmol/mg protein) bu t were significantly lower than maternal values (60+/-13 fmol/mg prote in). Fetal ANF receptor Kd values also increased significantly (245+/- 34 to 37+/-36 pM), with early gestation values significantly lower tha n maternal values (470+/-69 pM). Thus, the blunted fetal renal respons e to ANF in late as compared to early gestation is not due to reduced ANF receptor numbers. Rather, an increased proportion of ANF clearance receptors, reduced post-receptor function and/or altered intrarenal h emodynamics may contribute.