Hypertrophy of the ACTH-Producing Cell Following Adrenalectomy: A Quantitative Electron Microscopic Study

Abstract

For an electron microscopic analysis of the response of the ACTH-cell to adrenalectomy, pituitaries were taken from normal controls and from rats 24 hr after adrenalectomy and at additional intervals up to 3 weeks. Electron micrographs of ACTH-cells that had been sampled by an objective, blind procedure were measured by planimetry and the measurements submitted to statistical analysis. The ACTH-cell undergoes a significant increase of 30% in cell size by 24 hr after adrenalectomy; a 100% increase in cell size is reached as early as 5 days, and then cell size plateaus through 21 days. The size of the nucleus of the ACTH-cell shows a significant increase by the fifth postoperative day and then remains constant to 21 days. The nucleoli of ACTH-cells are significantly enlarged 24 hr postadrenalectomy, and heterochromatin also shows a transformation to euchromatin at this early interval. Secretory granulation of the ACTH-cells is strikingly reduced at 24 hr, then gradually increases at the later intervals. These results are consistent with the known response of the pituitary in the synthesis, storage, and secretion of ACTH following adrenalectomy. In addition, acute cortisol blockade of ACTH secretion was applied to a group of normal rats and to rats 14 days after adrenalectomy. It did not affect cell size, but resulted in the marked accumulation of secretory granules previously reported for normal and 7 day postoperative rats. This finding confirms our earlier suggestion that the initial effect of cortisol blockage is on release of ACTH from the cell, and only later does it inhibit ACTH synthesis, and/or interfere with elaboration of ACTH-granules. (Endocrinology93: 1257, 1973)