Pancreatic alpha cell function in the fetal foal during late gestation

Plasma glucagon concentrations were measured in chronically catheterized fe tal ponies and their mothers between 260 days of gestation and term (approx imate to 335 days). Fetal alpha cell responses to arginine and variations i n fetal glycaemia were also examined during late gestation. Immunoreactive glucagon was present in fetal plasma at 260 days of gestation and its conce ntration in utero increased after 320 days and then again at birth. Materna l plasma glucagon concentrations were higher after 300 days than earlier in gestation but were lower than the corresponding fetal value throughout the period of gestation studied. Fetal alpha cells responded rapidly to intrav enous arginine infusion but not to changes in the fetal glucose level induc ed by maternal fasting for 36 h or by intrafetal infusion of glucose. The m aximal increment in fetal plasma glucagon in response to arginine occurred at the end of the 5 min infusion and was positively correlated to the basal preinfusion plasma glucagon concentrations. Fetal plasma glucagon concentr ations were unaffected by either hyper- or hypoglycaemia. In contrast, mate rnal plasma glucagon levels were significantly increased by fasting. These observations indicate that equine pancreatic alpha cells are functional in utero but that they are unresponsive to variations in glycaemia until after birth.