Somatotrophs (GH cells) were classified immunoelectron microscopically into three types mainly on the basis of the size of secretory granules in the mouse pituitary of ICR strain. Type I cells contained large secretory granules. Type II cells contained both large secretory granules and small secretory granules. Type III cells contained small secretory granules. All three types of GH cells were found from the neonatal ages to adult. The relative proportion of three types did not change with age, and no sex differences in the relative proportion of the cell types were detected. Type I cells predominate in all age groups observed. In 60-day-old male mice percentages of each type were as follows: type I 93.7 ± 0.1%, type II 5.4 ± 0.8%, and type III 0.9.0 ± 0.4% (n = 5), and in 60-day-old female mice type I 95.2 ± 0.1%, type II 2.7 ± 0.5%, and type III 2.1 ± 0.9% (n = 5). The maximum diameters of the large secretory granules increased from 7 to 60 days of age. The small secretory granules similarly increased in size in female mice, but those in male mice did not change. In the diabetic female mice of the nonobese diabetic (NOD) strains, GH cells in diabetic mice became smaller, and the number and size of secretory granules decreased, indicating diminished GH secretion. However, the relative proportion of each subtype of GH cells did not differ irrespective of the occurrence of diabetes. Copyright (C) 2000 S. Karger AG, Basel.
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