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4-point angiotensin assays risk interaction bias; leaves open standardization of dose-response methods in cardiovascular pharmacology.
Specific pressor activity of Asp1-Val5-antiotensins I and II was determined by a 4-point assay in rats against various synthetic angiotensins. Specific pressor activity of various angiotensins was also obtained from the dose-blood pressure-response (DR) curve, using a single angiotensin sample per rat. Comparison of two values showed that two angiotensins interacted in the 4-point assay, yielding a potentiation factor of 0.465-1.373. Therefore, specific pressor activity from DR curve is more reliable, because two angiotensins are not able to interact. Potency ratio on a molar basis of Asp1-IIe5-angiotensin I, Asp1-Val5-angiotensins I and II, Asn1-Val5-angiotensin II (Ciba Lot-094691), and Asp1-Val5-Ser9-angiotensin I against Asp1-IIe5-angiotensin II were 0.76, 0.91, 2.02, 0.50, and 1.39, respectively. Asp1-Val5-angiotensin II had twice the pressor activity of Asp1-IIe5-angiotensin II. Lyophylized Asp1-IIe5-angiotensins I and II kept desiccated at --20 degrees C, were stable for 27 months. Solutions of 100, 10, and 0.8 microng/ml were stable for 12, 8, and 6 months at--20 degrees C, respectively.
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Watanabe et al. (1977) studied this question.
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