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Department of Physiology, Asahikawa Medical College, Japan.

1. The influence of prolonged exposure to a low ambient temperature on the pancreatic exocrine function was investigated in rats. Amylase concentration in acini prepared from rats housed at 5 degrees C for 2 weeks was specifically and dramatically reduced. The enzyme activity relative to acinar DNA concentration was only 48% of that of control acini obtained from rats reared at the thermoneutral temperature of 25 degrees C. Amylase content relative to acinar protein concentration also decreased by 35%. In contrast, acinar trypsinogen content relative to protein concentration increased to 161% of that of control acini. No comparable change was found in the parotid glands. 2. In acini from cold-exposed rats, amylase release in response to cholecystokinin octapeptide or carbamylcholine was simultaneously reduced when expressed relative to acinar DNA or protein concentration and the dose-response curve shifted downward. However, when the secretory responsiveness of amylase was represented as a percentage of initial acinar enzyme content, the observed decrease disappeared and the dose-response curve was unaffected by cold exposure. 3. Secretagogue-stimulated trypsinogen release was augmented in acini from cold-exposed rats when expressed per acinar protein concentration. Conversely, its percentage release was slightly lowered but the release per acinar DNA concentration remained unaltered. 4. Pancreatic insulin concentration normalized to tissue wet weight or protein concentration was unaffected by prolonged cold exposure but the plasma insulin concentration significantly decreased by 45% as compared with that of thermoneutral rats. 5. Chronically administered exogenous insulin partially restored the decreased acinar amylase concentration in cold-exposed rats. The dose-response curve for amylase normalized by acinar DNA or protein content also tended to be shifted upward by insulin treatment. Acinar trypsinogen concentration in these rats was not significantly altered from that in cold-exposed, non-insulin-treated rats. Percentage release of each enzyme was decreased by exogenous insulin. 6. Cold-induced suppression of pancreatic acinar amylase concentration, resulting in a proportional decrease in secretory responsiveness, was confirmed at the cellular level. Insulin deficiency at a low ambient temperature is likely to be a major cause of cold-induced suppression of amylase biosynthesis and its release via an insulin-pancreatic acinar axis.