CIRCADIAN-RHYTHMS OF RAT PANCREATIC ACINAR-CELLS

On the basis of the circadian oscillations of the rat's exocrine pancr eatic function and previous reports on concomitant ultrastructural cha nges in the pancreatic tissue, we analysed stereologically the circadi an rhythmicity in the structure of this organ. Twenty-four male Wistar rats, four and a half months old, were singly housed two months befor e the experiment in a lighting regimen LD=12:12, constant environmenta l temperature and relative humidity, with food and water ad libitum. T he experiment was performed in winter. The rats were randomly divided into 6 balanced groups and killed under ether anesthesia at 6 equidist ant time points in 24 hours. The pancreatic tissue was fixed in glutar aldehyde and osmium and embedded in Epon. 1 mu m thick sections were e xamined by light microscopy for the evaluation by stereological method s of: a) volume fractions of the different parenchymal components of t he exocrine pancreas; b) surface fractions of acinar cell faces; c) si ze distribution of acinar cell nuclei, their number per unit tissue vo lume and their mean diameter. Single cosinor method analysis of the da ta demonstrated statistically significant circadian rhythms for the vo lume fraction of the cytoplasm of acinar cells and the volume fraction s of pancreatic acini and acinar cells. The volume fraction of the cyt oplasm of the rat pancreatic acinar cells undergoes circadian oscillat ions with the highest values at the end of the light span; this rise p recedes the well-known physiological nocturnal surge of pancreatic dig estive enzymes. Our findings further support the hypothesis of a close relationship between pancreatic cell structure and its function.