Elsevier

Peptides

Volume 19, Issue 1, 1998, Pages 119-131
Peptides

Article
Structural Requirements and Mechanism of the Pressor Activity of Leu-Val-Val-hemorphin-7, a Fragment of Hemoglobin β-chain in Rats

https://doi.org/10.1016/S0196-9781(97)00273-8Get rights and content

Abstract

Moisan, S., N. Harvey, G. Beaudry, P. Forzani, K. E. Burhop, G. Drapeau, and F. Rioux. Structural requirements and mechanism of the pressor activity of Leu-Val-Val-hemorphin-7, a fragment of hemoglobin β-chain in rats. Peptides 19(1) 119–131, 1998.—A rat blood pressure assay was used to perform a structure-activity relationship study (SAR) of Leu-Val-Val-hemorphin-7 (LVV-H7), a fragment of hemoglobin (Hb) β-chain, elucidate the mechanisms of its cardiovascular effects, and test its potential involvement in the pressor activity of diaspirin crosslinked Hb (DCLHb), a recently developed Hb-based oxygen carrier. The SAR study revealed that the C-terminal-Arg-Phe-amino acid sequence of LVV-H7 contained the main determinants of the pressor activity of this peptide. Drug interaction studies using various inhibitory drugs (e.g., phentolamine, clonidine, etc.) and LVV-H7 showed that the pressor effect and tachycardia elicited by LVV-H7 involved the activation of the sympathetic nervous system (SNS). Additional studies using phenytoin (sodium channel blocker), [Tic7]H7(5-7)-NH2 (putative antagonist of receptors for LVV-H7) and H7(5-7)-NH2, an amidated C-terminal fragment of LVV-H7, suggested that LVV-H7 activated the SNS by interacting with specific receptors functionally coupled with phenytoin-sensitive sodium channels. The pressor effect and tachycardia caused by LVV-H7 were potentiated by captopril, suggesting that the angiotensin converting enzyme may contribute to the inactivation of LVV-H7 in rats. The pressor activity of DCLHb, in contrast to that elicited by LVV-H7, was not affected by animal pretreatment with LVV-H7 fragments shown to inhibit the pressor effect of LVV-H7. We conclude that: 1) LVV-H7 is unlikely to mediate the pressor activity of DCLHb in rats; 2) the pressor and tachycardic activities of LVV-H7 are mediated by the SNS; 3) the C-terminal-Arg-Phe-amino acid sequence of LVV-H7 contains the chemical groups responsible for the pressor effect of this peptide in rats; 4) LVV-H7 and FMRF amide-related peptides may share the same mechanism of pressor activity in rats.

Section snippets

The Rat Blood Pressure Assay

All experiments were performed using male Sprague-Dawley rats (400–500 g) purchased from Charles River Canada Inc., St-Constant, Québec, Canada. The animals were housed 2–3 per cage, given rat purina chow and tap water ad libitum, and kept under stable environmental conditions for a few days before use. Experiments were conducted in accordance with the principles and guidelines of the Canadian Council on Animal Care and approved by the local Institutional Committee on Animal Care.

The animals

Pressor Activity of LVV-H7, Its Fragments and Analogs

IV injections of 38, 76, 152 and 228 nmoles/kg of LVV-H7 in anesthetized, vagotomized rats elicited pressor effects (ΔMABP: 9 ± 2, 17 ± 2, 36 ± 3 and 37 ± 2 mmHg, respectively) and tachycardia (▵HR: 2 ± 1, 10 ± 2, 21 ± 3 and 25 ± 3 beat/min, respectively) (n = 45). Peak BP and HR responses to 152 nmoles/kg of LVV-H7 occurred at 14 ± 2 sec (n = 13) and 20 ± 2 sec (n = 11) after injection, respectively. Both the pressor effect and tachycardia elicited by LVV-H7 (152 nmoles/kg) were short-lasting

Structure–Pressor Activity Relationships of LVV-H7

Studies with Ala-containing derivatives of LVV-H7 were quite informative, despite the fact that replacement of the normal constituents of LVV-H7 with Ala gives equal weight to all positions in the peptide chain, without considering their presumably unequal importance for the pressor activity of LVV-H7 as a whole. Replacement of Phe7, Arg6 or Trp3 by Ala abolished partially (LVV-[Ala3]H7) or completely (LVV-[Ala7]H7 and LVV-[Ala6]H7) the pressor activity of LVV-H7, whereas replacement of all

Acknowledgements

The authors wish to thank Mrs. Elisabeth Lemay for typing this manuscript, and Baxter Healthcare Corporation for their financial support (contract no. 2A-S-0153).

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