Fig. 2. Regulation of surfactant phosphatidylcholine (PC) secretion by the adrenergic agonist, isoproterenol (100 µmol l^-1) and the cholinergic agonist, carbamylcholine chloride (Carbachol, 100 µmol l^-1), in alveolar type II cells isolated from warm-active and torpid ground squirrels. Both warm-active and torpid cells were assayed at 37°C and 4°C for 0.5 and 1 h. ^*Significant increase above basal secretion for each experimental group (paired t-test, P<0.05). Significant difference in secretion between matching experimental groups measured at the two different assay temperatures, i.e. 0.5 h/torpid/4°C vs 0.5 h/torpid/37°C (t-test, P<0.05). Significant difference in % secretion between warm-active cells assayed at 37°C and torpid cells assayed at 4°C (t-test, P<0.05). Bars represent % of incorporated [³H]choline secreted as phosphatidylcholine (mean ± S.E.M.) for N experiments after 0.5 and 1 h; for warm-active animals, N=4; for torpid animals, N=5. % secretion = % c.p.m. measured in the medium divided by the total cpm (cells + medium)x100 measured for each sample.