CHANGES IN BLOOD AND RED-CELL VOLUME IN THE NEONATAL LAMB AND THE EFFECT OF INSULIN-LIKE GROWTH-FACTOR-I

1. Blood volume was measured weekly using [Cr-51]-labelled red cells i n 10 lambs from 3 to 10 weeks of age, Red cell and plasma volumes were calculated using the measured blood volume and haematocrit. Other par ameters, including plasma erythropoietin, urea, creatinine and glucose , were measured twice weekly, The results were compared to a group of five lambs that received an infusion of insulin-like growth factor I ( IGF-I). 2, In control lambs, plasma volume increased linearly by 47 +/ - 7 mL/week over the experimental period, Red cell volume only increas ed by 10 +/- 2 mL/week during weeks 3-7, but then increased by 25 +/- 2 mL/week over weeks 7-10, Haematocrit declined from 28,0 +/- 1.6 to 2 4.7 +/- 1.7% over weeks 3-7 and then increased to 30.7 +/- 1.1% by wee k 10, 3, In 10 control lambs infused for 8 days (starting at 22-26 day s of age) with 10 mmol/L HCl, there was a decrease in plasma IGF-I con centrations, 3 days after the start of infusion. In five lambs infused for 8 days with IGF-I (6 mu g/kg per h) plasma IGF-I concentration wa s maintained significantly (P < 0.01) higher than that of the controls , 4. There was no significant difference in haematocrit, red cell or p lasma volumes between the treatment groups and no reticulocytosis was observed, Plasma erythropoietin concentrations did not change over the infusion period in either group, 5, Serum urea decreased significantl y in the IGF-I infused group but serum creatinine did not change in ei ther group during the infusion period. In both the groups, there was a significant decrease in glucose, urea and creatinine over weeks 3-10 after birth, There was no difference in growth rates between the two g roups. 6. Thus, it appears that the observed changes in haematocrit ar e due to a constant increase in plasma volume with varying rates of re d cell volume increases. 7. IGF-I infused at a dose that maintains phy siological concentrations and alters protein metabolism does not resul t in increased erythropoietin or erythropoiesis during the neonatal pe riod of the lamb.