ABSTRACT. To determine the effects of fetal 8-2 agonist fetal lambs results in increased serum glucose levels with elevaexposure on fetal hepatic glycogen metabolism, we infused tion of serum lactate and pyruvate concentrations, and attributed ritodrine at a rate of 1.3 f 0.4 pg/kg/min (mean f SD) for these effects to increased glycolysis. 24 h into six chronically catheterized twin fetal lambs Hepatic glycogen deposition and mobilization are regulated starting between 128 and 134 days gestation. The control by the relative activities of glycogen synthase and glycogen twins received 0.9% saline at 1.2 f 0.12 mllkglh. In phosphorylase, which are in turn regulated by phosphorylase addition, 15 uncatheterized fetuses were killed between kinase and protein phosphatase-1 (7). Phosphorylation of glyco-115 and 148 days gestation as unoperated controls. Rito-gen phosphorylase by phosphorylase kinase activates glycogen drine infusion produced a 1.7-fold elevation in fetal serum phosphorylase, thereby increasing the rate of biodegradation of glucose level, from 23 f 5 to 42 f 15 mgldl, and a 2-fold glycogen. In contrast, phosphorylation of glycogen synthase by elevation in serum insulin level, from 16 f 5 to 34 f 8 mg/ phosphorylase kinase deactivates glycogen synthase, thereby deml, p < 0.01. Hepatic glycogen content increased 7-fold in creasing the rate of glycogen biosynthesis. Protein phosphatasethe uncatheterized controls between 115 and 148 days 1 dephosphorylates glycogen phosphorylase and glycogen syngestation (r = 0.9, p < 0.001). Ritodrine infusion reduced thase, respectively, decreasing and increasing enzyme activity.hepatic glycogen content by 50% from 179 f 19 pglmg inThe purpose of our study was to determine the effects of fetal twin controls to 90 f 25 pglmg in the ritodrine-infused ritodrine exposure on hepatic glycogen metabolism. twins, p < 0.001. Hepatic glycogen phosphorylase kinase activity was elevated 1.3-fold from 0.149 + 0.100 mU/mg protein in control twins to 0.186 f 0.007 mU/mg protein MATERIALS AND METHODS in the ritodrine infused twins, P < 0.001. Glycogen ~h o s -Animalpreparation. Between 120 and 124 days gestation (term ~h o r~l a s e a activity was also increased 1.4-fold from 8-60 is 148 days), six time-dated pregnant ewes were operated on 0.76 nM NADPH/minlmg protein in twins under epidural anesthesia as described previously in detail (8). 11.85 f 0.68 nM NADPHIminlmg protein in the ritodrine Catheters were placed in a fetal carotid artery, jugular vein, and infused twins, p < 0.001. There were no significant differ-the trachea. After the operation the fetuses received 200,000 U ences in hepatic total glycogen phosphorylase (a + b, of penicillin and 10 mg kanamycin intravenously every day, and activity, active (I) or total I + D) glycogen s~nthase activity, the ewes received 1.2 million U of procaine penicillin and 1 g of rotei in, or DNA content between the ritodrine treated and kanamycin intramuscularly daily for 5 days. The fetuses were control twins or between the control twins an...