Abstract
Summary
The present quantitative results demonstrate that the terminal amino group, phenolic hydroxyl, aromatic ring and basicity in positions, 1-3 and 8, respectively, of the neurohypophyseal hormones are important for optimizing hormone-receptor affinity and intrinsic (contractile) activity on both rat aortas and mesenteric arterioles; basicity in position 8 is, however, definitely not an absolute requirement for vasopressin-induced contractions of blood vessels. The use of 12 synthetic neurohypophyseal hormones and analogues, and direct in vitro and in vivo studies on rat aortas and mesenteric arterioles respectively, indicates many discrepancies between hormone potency obtained through rat-pressor assays versus those obtained through direct studies on peripheral vascular smooth muscle. The present findings thus question the use of rat-pressor assays in assessing structure-activity relationships of neurohypophyseal hormones on rat arterial or arteriolar smooth muscle. In addition, the data supports the notion that a heterogeneity of the vasopressin receptor, which subserves contraction in mammalian vascular muscles, may exist in different types of blood vessels.
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