STRUCTURE OF THE GOLGI-APPARATUS IN STIMULATED AND NONSTIMULATED ACINAR-CELLS OF MAMMARY-GLANDS OF THE RAT

The structural features of the Golgi apparatus of acinar cells of mamm ary glands were examined with the electron microscope in 3 groups of r ats: (1) in lactating female animals at 8 days postpartum, which serve d as controls; (2) in female rats sacrificed at various intervals from 2 to 30 hours following separation from their 8-day old pups; and (3) in females separated from their 8-day-old pups for a period of 12 hou rs and returned to their litters for durations of 1, 2, 4, and 8 hours . In animals of group 2, the Golgi stacks remained identical to that o f controls between 2 and 8 hours. At 12 hours and later, the Golgi sta cks decreased progressively in size, but the number of elements compos ing the stacks remained similar to that of lactating females and all c ontained casein submicelles. At 24 and 30 hours, typical secretory gra nules containing casein micelles disappeared from the trans aspect of the stacks. The earliest and most striking changes observed in the Gol gi apparatus of the rats of group 2 took place at 12 hours. At this ti me, the prosecretory and secretory granules decreased considerably in volume and lost most of their electron-lucent content. This indicated that the delivery of small molecules, i.e., lactose and H2O, to these structures was soon altered following arrest of the sucking stimulus. In animals of group 3, the size of prosecretory and secretory granules and the amount of their electron-lucent content reverted to normal at 4 hours. Thus the influx of lactose and H2O into these structures app ears to be rapidly restored after returning the pups to their mothers. The decrease in size of the Golgi stacks noted at 12, 18, and 24 hour s following arrest of lactation (group 2), was accompanied by an incre ase in number of small vesicles that formed clusters next to the Golgi stacks and in ''wells.'' Thus in these regressing Golgi stacks, many of the associated small vesicles appear to arise by vesiculation of th e saccules. (C) 1993 Wiley-Liss, Inc.