Effect of three angiotensin II antagonists, [Sar1, Thr8]-, [Sar1, Ile8]-and [Sar1, Ala8]angiotensin II on blood pressure and endocrine factors in normal subjects

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Abstract
The biological effects of 1-Sarcosine, 8-Threonine angiotensin II ([Sar1, Thr8]ANG II) on blood pressure, plasma aldosterone concentration (PAC) and plasma renin activity (PRA) were investigated in six normal subjects on an unrestricted diet, and compared with those of 1-Sarcosine, 8-Isoleucine ANG II ([Sar1, Ile8]ANG II) and 1-Sarcosine, 8-Alanine ANG II ([Sar1, Ala8]ANG II). All three ANG II analogues (A II A) showed agonistic pressor activity, that of [Sar1, Ile8]ANG II being greater than that of [Sar1, Thr8]ANG II or [Sar1, Ala8]ANG II. The antagonistic effect of [Sar1, Thr8]ANG II on blood pressure was less than [Sar1, Ile8]ANG II or [Sar1, Ala8]ANG II. Both [Sar1, Ile8]ANG II and [Sar1, Ala8]ANG II increased PAC and blocked the steroidogenic action of ANG II, while [Sar1, Thr8]ANG II showed little effect on PAC. All three A II A caused similar suppression of PRA and showed no inhibitory effect on the decrease in PRA produced by ANG II. These results indicate that [Sar1, Thr8] ANG II is an A II A with weak agonistic pressor action and that it has vascular selective properties. It is also suggested that ANG II receptors in a variety of target organs are heterogeneous.