Endogenous digitalis compounds and adrenal gland activity

: Endogenous inhibitors of the Na+,K+-pump have been postulated to participate in Na+ and water homeostasis. When present in high amounts, they have been proposed to induce a rise in blood pressure. There is no general agreement concerning their chemical structure and their possible tissue origin has not been well defined. In an attempt to identify a tissue source, (i) the digitalis-like contents of various organs (cross reactivity with digoxin antibodies and inhibition of ouabain binding to the Na+ pump) were determined and (ii) the circulating digitalis-like activity was analyzed under various conditions known to alter the activity of the putative source organs. High levels of digitalis-like compounds were present in the adrenal and pituitary glands (4.1 +/- 0.1, n = 15 and 3.7 +/- 0.4, n = 13 ng digoxin equivalents/g) or 328 +/- 66, n = 6 and 460 +/- 76, n = 6 ng ouabain equivalents/g) respectively. Much lower levels were found in heart, kidney, brain and hypothalamus. Plasma digitalis-like activity was measured in 5 groups of rats: control, ACTH treated, hypophysectomised, and in DOCA-salt treated animals with and without bilateral adrenalectomy. Changes in the plasma digitalis-like activity measured by the crossreactivity with anti-digoxin antibodies or by the inhibition of ouabain binding followed the same pattern. When compared to the control values, the plasma digitalis-like activity was partially decreased after hypophysectomy, markedly decreased after adrenalectomy and enhanced in ACTH-treated animals. These results suggest that the pituitary-adrenal axis plays a major role in the control of the circulating "digitalis-like" activity.