176 FETAL SHEEP PLASMA INSULIN CONCENTRATION AND UMBILICAL LACTATE UPTAKE

To determine the relationship between fetal and maternal plasma insulin concentrations (If, Im) and umbilical uptake of glucose (Qg) and lactate (Ql) in sheep, 6 ewes of 120-130 days gestation were prepared with indwelling catheters in the umbilical vein, fetal pedal artery and vein, and maternal uterine and femoral arteries. Fed state Qg, Ql, If, and I were determined at intervals from the 2nd to the 11th postoperative day (POD). Qg and Ql were determined by the Fick principle employing steady state diffusion of antipyrine to determine umbilical blood flow. Studies were performed before (control n=15) and after (n=15) the perfusion of the uterine artery with ovine insulin 7.5 mU/kg ewe/30 min. Insulin was measured by radioimmunoassay. Results: Control If and Im in μ U/ml increased with increasing POD as described by the following regression equations: If = 0.76 POD + 3.74, (F ratio, p < .025), and Im = 1.86 POD + 8.61, (p < .05). Uterine artery insulin infusion increased Im but did not affect If or Ql. The postoperative increase in If from 5.5-16.0μ μ U/ml was associated with a decrease in Ql in mM/min/kg fetus: Ql = -0.004 If + 0.072 (p < .025). Qg was unrelated to POD, Ql, or If. Conclusions: These studies (1) confirm the lack of ovine insulin transfer across the ovine placenta in vivo, (2) demonstrate increasing Im and If for as long as 11 days after surgery and resumption of maternal nutrition, and (3) show that umbilical lactate uptake is inversely related to fetal plasma insulin concentration, but is independent of umbilical glucose uptake and of maternal plasma insulin concentration.