Quantitative cytological analysis of functional changes in adrenomedullary chromaffin cells in normal, sham-operated, and pinealectomized rats in relation to time of day: III. Nuclear density.

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The sizes of adrenaline (A) and noradrenaline (N) cells in the adrenal medulla of nonoperated (NO), sham-operated (SPX), and pinealectomized (PX) male rats (n = 126) were investigated by quantitative light microscopy. Animals were killed at eight time points during a standardized 24-h, light-dark (12:12) cycle 14 days after surgery. Nuclear densities were measured in semithin sections of epon-embedded specimens, initially fixed with glutaraldehyde and OsO4. Major findings are as follows. 1) The mean size of adrenomedullary A cells throughout 24 h (P less than 0.001), especially in the dark phase (P less than 0.001) but not in the light phase, was larger in PX animals than in NO and SPX animals. There were no statistically significant differences in the size of N cells among the three experimental groups in either the dark phase or the light phase. 2) The sizes of A and N cells showed time-of-day changes in the NO and the SPX animals but not in the PX animals. The temporal relationship of 24-h changes in the cell size tended to be different between A and N cells in the NO and the SPX animals but not in the PX animals. 3) The cell size was apparently larger in A cells than in N cells in each experimental group. Pinealectomy thus caused hypertrophy of A cells, especially in the dark phase, but not apparently hypertrophy of N cells. Concerning the pinealectomy effects in relation to the time of day, the results support the hypothesis of pineal action being phase-tuning and coordinating of at least some circadian systems.