Tachyphylaxis and angiotensin receptors

Angiotensin tachyphylaxis was studied in the isolated guinea pig ileum under isometric conditions. 2. In tachyphylactic organs, the initial phasic response to angiotensin was abolished, while the tonic component of the response became faster in its onset and in its reversal (relaxation). 3. The relaxation of non-tachyphylactic organs after angiotensin washout was significantly slower than with bradykinin, des-amino-angiotensin and hexanoyl-angiotensin. This difference did not occur in tachyphylactic organs. 4. There was no correlation between production of tachyphylaxis or rate of relaxation after washout and the partition coefficient of the four peptides in an organic:aqueous solvent system. 5. It is suggested that tachyphylaxis depends on a slowly reversible alteration of a calcium translocation step in the stimulus-response coupling.