2. Endocrines and Populations 201 



depressed the fascicular aliesterase activity (Allen, 1957). The results of 

 the foregoing experiments provide convincing evidence in support of the 

 hypothesis of Greep and his co-workers that the zona glomerulosa secretes 

 the electrolyte-active, and the fasciculata the carbohydrate-active, corti- 

 coids (Greep and Deane, 1947, 1949b; Deane et at., 1948). This hypothesis 

 was based on observations that (1) increased sodium intake or injections 

 of deoxycorticosterone produced histochemical changes indicative of de- 

 creased activity in the zona glomerulosa of the adrenals of rats, and that 

 (2) a reduction in sodium or increase in potassium produced cytological 

 changes indicative of increased activity of the zona glomerulosa. There is 

 little doubt that the glomerulosa is responsible primarily for the secretion of 

 aldosterone and that the carbohydrate-active corticoids are secreted by 

 the zona fasciculata and possibly by the zona reticularis. Convincing evi- 

 dence of a functional separation between the zonae fasciculata and reticu- 

 laris is not available, but the reticularis generally is not believed to be as 

 active a secretory zone as the fasciculata. 



The chief action of aldosterone is on sodium-potassium transport in the 

 tubular cells of the renal nephron, and it is relatively more effective in pro- 

 moting sodium retention than in promoting potassium excretion or water 

 retention (Gaunt et al, 1955; Bartter, 1956; Jones, 1957; Gross and 

 Lichtlen, 1958; Stanbury et al., 1958). It apparently stimulates the ionic 

 exchange between potassium and sodium ions in the renal tubular cells 

 (Bartter, 1956; Stanbury et al., 1958), although an overdosage of aldoste- 

 rone will not produce excessive sodium retention and the animal therefore 

 stays in sodium balance (Bartter, 1956; Gross and Lichtlen, 1958). In 

 general the sodium-retaining corticoids act on the nephric tubular cells to 

 promote an ionic exchange between sodium and potassium; so that sodium 

 is retained and potassium is excreted (Bartter, 1956, 1957). Water is re- 

 absorbed with the sodium or independently under the action of neurohy- 

 pophyseal antidiuretic hormone (ADH) (Bartter, 1957). Proper fluid and 

 electrolyte balance is mamtauied by these homeostatic endocrine activities 

 acting in concert with water and salt intake and with hemodynamic and 

 neural factors which affect fluid volume, blood pressure, and renal glomeru- 

 lar filtration. The apparent anomaly of overdosages of aldosterone failing 

 to produce excessive sodium retention depends on the fact that the blood 

 pressure is raised and therefore the glomerular filtration rate is increased 

 and sodium is lost accordingly (Stanbury et al, 1958) . Proper fluid and 

 electrolyte balance is vital to any animal, and adrenalectomized animals 

 can be maintained with injected deoxycorticosterone or aldosterone, al- 

 though they cannot adapt to added stress (Gaunt et al, 1955) . The adrenal- 

 ectomized laboratory rat or mouse also can be maintained alive by sup- 

 plying W( sodium chloride in its drinking water to replace the sodium loss 



