In intact male rats fed on a normal diet, the subcutaneous administration of progesterone for 4\m=.\5 days resulted in a significant increase in the aldosterone secretion rate and a significant decrease in the corticosterone secretion rate as measured by the secretion of these hormones into adrenal vein blood of anaesthetized animals. In hypophysectomized rats the administration of progesterone for 5\m=.\5 days resulted in a significant increase in aldosterone secretion and a small, non-significant, decrease in the rate of corticosterone secretion. It is concluded that progesterone may influence the rate of secretion of aldosterone in pregnancy and that the mechanism by which this is achieved probably does not involve the pituitary gland.

In animals with one renal artery clip hypertension was associated with a highly significant increase in aldosterone but not corticosterone secretion rate. In unilaterally nephrcctomized animals with a clip on the remaining renal artery, hypertension was not associated with a significant change in the secretion rates of aldosterone or corticosterone. Experiments designed to determine whether this difference in the groups was due to the fact that in the first group the 'clipped' kidney was still in the circulation during blood collection while in the second it was not have yielded essentially negative results. It is concluded that the increase in aldosterone secretion in renal hypertension is related to the response of the untouched kidney to the clamping of the renal artery of the other kidney.

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