CENEXA—Centro de Endocrinología Experimentaly Aplicada, CONICET—Universidad Nacional de La Plata, Facultad de Ciencias Médicas, Calle 60 y 120, 1900 La Plata, Argentina
(Received 10 March 1978)
Circadian variations in the serum concentration of immunoreactive insulin in the mouse (Gagliardino & Hernández, 1971) and the effect of fasting and feeding on this rhythm (Pessacq, Rebolledo, Mercer & Gagliardino, 1976) have already been described. However, no information is available on circadian variations in the level of glucagon in the blood of experimental animals and the present experiments were performed to investigate changes in the concentrations of glucagon in the plasma and glycogen and cyclic AMP in the liver of the female mouse over a 24 h period.
Female mice (C3HS strain), 19–21 weeks old, were kept at a constant temperature (25 ± 1·0 °C) under a schedule of 12 h light : 12 h darkness (lights on 06.00–18.00 h) and allowed free