We measured the net rates of skeletal muscle glycogen synthesis and glycolysis (conversion of [3-3H]glucose to 3H2O) in healthy overnight-fasted volunteers. Two studies were performed. In study 1, seven subjects participated in two paired infusions under basal conditions of either [2-3H]glucose (H2) or [3-3H]glucose (H3). Total glucose uptake (Rd) and rates of whole body 3H2O formation (3H2O Ra) were measured. With H2, Rd and 3H2O Ra were similar. With H3, 3H2O Ra, equal to glycolysis, was 65% of Rd. In study 2, six different subjects underwent a 3-h, 40 mU.m-2 x min-1 euglycemic insulin clamp. [6,6-2H2]glucose was infused throughout and H3 was infused during the last hour of the study. Open muscle biopsies were obtained at 150 and 180 min. Glycogen synthesis was assessed by three independent means: 1) direct measurement, as 3H disintegrations per minute in isolated muscle glycogen per plasma H3 specific activity; 2) extrapolation from the activity of glycogen synthase assayed in the presence of the concentrations of glucose 6-phosphate and UDP-glucose measured in the biopsy; and 3) the difference between Rd and glycolysis. Despite a wide range in Rd [24.5-58.8 mumol.kg fat-free mass (FFM)-1 x min-1] and glycolysis (14.2-26.1), the three methods yielded similar results of 20.0 +/- 3.9, 22.5 +/- 3.7, and 20.6 +/- 3.7 mumol.kg FFM-1 x min-1 and correlated highly with each other (r2 = 0.92-0.96). Our results (study 1) indicate that the rate of plasma tritiated water formation reflects the intracellular detritiation of tritiated glucose. Under hyperinsulinemic conditions (study 2) the net rate of muscle glycogen synthesis can be accurately estimated from the glycogen synthase activity and from the difference between total glucose uptake and glycolysis. Thus, at high physiological plasma insulin concentrations resulting in submaximal stimulation of muscle glycogen synthesis, the latter can be accurately measured in humans.

Summary. Twenty-three amino acids appeared linearly in oviduct fluid to reach an average concentration 27% of that in the plasma, with glycine and alanine present in greatest amount. In contrast, the concentration of urea in the fluid approached its plasma concentration after 1 h, and remained at this level for the duration of the experiment. The oviduct was unable to bring about the overall uphill transport of amino acids from plasma to oviduct lumen. The amounts of amino acids appearing in the oviduct lumen of rabbits injected 3 days previously with hCG were mostly similar to those of the controls, but the movements of 6 neutral amino acids appeared to be enhanced relative to their plasma concentrations following ovulation.

Pyruvate, lactate and lactate dehydrogenase appeared linearly in 2 ml 0.9% NaCl recirculated through the rabbit oviduct for 4 h in vivo. In oviducts from rabbits injected 3 days previously with 100 i.u. hCG, the rate of appearance of all three constituents was considerably reduced. It is considered unlikely that the lactate dehydrogenase secreted brings about the interconversion of pyruvate and lactate in the oviduct lumen.

Summary. The uterine horns of anaesthetized rats were cannulated and 2\m=.\5ml 0\m=.\9% NaCl at 37\s=deg\C were recirculated for up to 90 min. Glucose appeared in the medium, reaching a concentration of approximately 1 mM. Various aspects of the transport process were examined, and it is suggested that the glucose is mainly derived from the plasma, and probably enters the uterine lumen by a process involving facilitated diffusion.