Fat-tailed dunnarts, Sminthopsis crassicaudata, survive dramatic changes in body temperature during torpor without experiencing surfactant dysfunction. Adrenergic factors regulate surfactant secretion through beta(2)-adrenergic receptors on alveolar type II cells. Temperature has no effect on the secretory response of dunnart type II cells to adrenergic stimulation. We hypothesise that during torpor, dunnart type II cells up-regulate the number of adrenergic receptors present on type II cells to enable stimulation at lower concentrations of agonist. Here, we isolated type II cells from warm-active (35 degreesC) and torpid (15 degreesC) dunnarts and examined the effects of an in vitro temperature change on the number and activity of adrenergic receptors. Torpor did not affect the beta-adrenergic receptor number. However, we observed a significant decrease in adrenergic receptor number when cells from warm-active animals were incubated at 15 degreesC and when cells from torpid animals were incubated at 37 degreesC. cAMP production was significantly higher in type II cells from torpid durmarts than warm-active durmarts and this may contribute, in part, to the temperature insensitivity we have previously observed in the adrenergic regulation of surfactant secretion. (C) 2003 Elsevier Inc. All rights reserved.