Adenohypophysial cell-types in the pituitary gland of the soft-shelled turtle, Trionyx sinensis. I. Seasonal cycles.

By using various staining techniques, two acidophilic and three basophilic cell-types have been distinguished in the pars distalis of Trionyx sinensis. Seasonal fluctuations in their cytoplasmic granulation, cell and nuclear size have been compared with seasonal patterns of activity in the gonads, adrenals and thyroid. On the basis of the results, specific functions have been ascribed to each cell-type. Basophils 1 activity closely parallels the seasonal thyroid cycle. Basophils 2 are probably FSH-secreting gonadotropes and their activity correlates with the seasonal cycle of spermatogenesis in the seminiferous tubules. The functional activity of the testicular interstitial cells correlates with the secretory pattern of the basophils 3. That these are LH-secreting cells is also suggested by the epididymidal cycle, which indicates a high level of androgen secretion coincident with the rapid degranulation of these cells, at a time of no spermatogenetic activity. Adrenal activity shows no relationship with the basophils 3 cycle, and chromophobic cells may be the locus of ACTH secretion. Acidophils 2 remain stable throughout the year and are probably somatotropes, but acidophils 1 increase their activity in autumn and are likely to be lactotropes.