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UBC Theses and Dissertations

Protein synthesis in the ovine fetus Schaefer, Allan Lee


To study the effect of maternal nutrition on fetal protein synthesis, isotopic kinetic studies were undertaken in which indwelling catheters were implanted in the inferior vena cava and saphenous vein of ovine fetuses as well as the jugular vein and femoral artery of ewes at 120-130 days of gestation Following a five day post surgical recovery period an 8h continuous infusion of L-[2,3,5,6-³H] or L-[U-¹⁴ C] tyrosine was made into the fetus and ewe simultaneously. An enzymatic procedure specific for L-tyrosine was used to measure the plateau specific activity in fetal and maternal plasma. Using these values the net placental transfer, endogenous production and net utilization of tyrosine by the fetus were determined employing a two pool kinetic model. For determining the fractional protein synthetic rates in individual tissues the ewes were sacrificed and the fetuses obtained by laparotomy immediately following the continuous infusion of labelled tyrosine. The effect of starvation on tyrosine transfer across the placenta and protein synthesis by the fetus was studied by repeating the above procedures in ewes starved for 48h. Values for the net placental transfer, endogenous production and net utilization of tyrosine were 5.14, 1.29 and 6.42 mmol/d/kg respectively for fetuses of fed ewes, whereas, these values were -0.29, 4.53 and 3.88 mmol/d/kg in fetuses of starved ewes. The plasma concentrations (mg%) of glucose, alpha amino nitrogen and lactate in the fed ewes were 60.18, 10.68 and 5.58 versus 43.66, 7.80 and 7.41 in starved ewes. Glucose, alpha amino nitrogen and lactate values were also seen to change in the fetus from 12.55, 13.38 and 12.98, respectively in the fed versus 8.18, 11.55 and 15.08 in fetuses of starved ewes. The fetal tyrosine net utilization values, corrected for oxidative loss of 5.2%, were used to calculate the whole body protein synthetic values. From an average tyrosine content of carcass protein of 15.71 mmol/kg, the whole body protein synthetic rates were 63 g/d/kg in the fed versus 25 g/d/kg in the starved fetuses. Fetal tissue fractional protein synthetic rates were also affected by maternal starvation. The fractional synthetic rates (%/day) for liver, kidney, lung, heart and skeletal muscle were 78%, 45%, 65%, 14% and 26% for fed versus 12%, 22%, 23%, 11% and 10%/d for the fetuses of starved ewes. The data demonstrate that maternal feed deprivation reduces protein synthesis in the fetus.

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