Failure of chronic administration of the angiotensin I-converting enzyme inhibitor, Teprotide (SQ 20881), to affect the ultrastructure of the adrenal cortex and the aldosterone secretion in the rat.

: Administration of Teprotide (SQ 20881), an angiotensin I-converting enzyme inhibitor for up to 10 weeks at a dose of 3 mg. per kg., subcutaneously, twice a day in the rat, effected no change in the ultrastructure of the adrenal cortex nor in the concentration of serum aldosterone. A significant increase (p less than 0.05) in renin granulation indices which was already apparent after 3 weeks of treatment with Teprotide was even more definitive after 10 weeks (p less than 0.01). Moderate renal hypertrophy was present in rats receiving the drug for 3 weeks. Findings pertaining to aldosterone production differed from those reported following acute administration of Teprotide wherein a decrease in the production of serum aldosterone and an increase in plasma renin activity was observed. It has been suggested that decreased aldosterone production following acute administration of Teprotide is a consequence of decreased stimulus of the zona glomerulosa due to diminished synthesis of angiotensin II. If this is the case, mechanisms other than angiotensin II stimulation of the zona glomerulosa must control aldosterone synthesis, perhaps through hormones of the adrenal cortex. Another possibility could be that angiotensin II synthesis may be obtained, after an interval, through an alternative pathway.