Competitive Analog Antagonists of Bradykinin in the Canine Hindlimb

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Abstract
Six structural analogs of bradykinin were tested to determine whether they antagonize the vasodilator response to bradykinin. The dog hindlimb preparation was used as a bioassay. Mongrel dogs were anesthetized and the femoral arteries were isolated and fitted with a noncannulating electromagnetic flow probe. An indwelling catheter was also placed for administration of saline, bradykinin, or the various analogs. The vasodilatory responses of the hindlimb circulation to bolus doses of bradykinin from 1 of 20 ng were tested during vehicle or analog administration at 1 and 10 .mu.g/min. Bradykinin analogs which were characterized by amino acid replacement by .beta.-(2-thienyl)-L-alanine (Thi) at positions 5 and 8, D-phenylalanine (D-Phe) at position 7, and an additional replacement of hydroxyproline at position 2 or 3 were effective antagonists of bradykinin. The decapeptide bradykinin analog (BKA06) D-Arg-(Hyp3-Thi5-D-Phe7-Thi)-BK was the most potent analog tested, producing a full log dose shift in the dose-response curve to bradykinin at the 10 .mu.g/min (4 nmole/min) infusion rate. None of the analogs we tested produced vasodilation or had any effect upon systemic blood pressure at the concentrations tested. Our results suggest that these structural analogs of bradykinin may be effective pharmacologic tools to study the role of endogenous kinins in the control of vascular resistance and circulatory homeostasis.

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