Design and Synthesis of the First Selective Agonists for the Rat Vasopressin V_1bReceptor:  Based on Modifications of Deamino-[Cys]arginine Vasopressin at Positions 4 and 8

Abstract

The neurohypophyseal peptides arginine vasopressin (AVP) and oxytocin (OT) mediate a wide variety of peripheral and central physiological and behavioral effects by acting on four different G-protein coupled receptors, termed V1a (vascular), V1b (pituitary), V2 (renal), and OT (uterine). We recently reported that d[Cha4]AVP (A), d[Leu4]AVP (B), d[Orn4]AVP (C), and d[Arg4]AVP (D) have high affinity and are selective agonists for the human V1b receptor. However, peptides A-D were subsequently shown to be potent antidiuretic agonists in the rat and are, thus, not selective V1b agonists in the rat. Peptides A-D served as leads for the studies reported here. They were modified at position 8 by Lys, ornithine (Orn), diaminobutyric acid (Dab), and diaminopropionic acid (Dap) to give d[Cha4,Lys8]VP (1), d[Cha4,Orn8]VP (2), d[Cha4,Dab8]VP (3), d[Cha4,Dap8]VP (4), d[Leu4,Lys8]VP (5), d[Leu4,Orn8]VP (6), d[Leu4,Dab8]VP (7), d[Leu4,Dap8]VP (8), d[Orn4,Lys8]VP (9), d[Orn4,Orn8]VP (10), d[Arg4,Lys8]VP (11), d[Arg4,Orn8]VP (12), and d[Arg4,Dab8]VP (13). All peptides were synthesized by the Merrifield solid-phase method. Their binding and functional properties were evaluated in rat AVP V1a, V1b, and V2 receptors and on the rat OT receptor expressed either in native tissues or in stably transfected cells. They were also examined in rat vasopressor, antidiuretic, and in in vitro (no Mg++) oxytocic assays. Functional studies performed on chinese hamster ovary cells expressing the different AVP/OT receptors confirm that d[Cha4,Lys8]VP (1), d[Cha4,Dab8]VP (3), d[Leu4,Lys8]VP (5), and d[Leu4,Dap8]VP (8) are the first selective agonists for the rat V1b receptor. These selective V1b agonists are promising new tools for studies of the role of the V1b receptor in the rat.

New, Potent, Selective, and Short-Acting Peptidic V1a Receptor Agonists

“…We designed and synthesized new short acting V 1a R selective analogues of general structure [Xaa 2 (68)) were tested by intravenous bolus in rats for duration of vasopressive action. Analogues 31,34,45,and 49 were as short-acting as AVP. Compound 45, FE 202158, is currently undergoing clinical trials in septic shock.…”

“…While no obvious SAR rules for the duration of action in vivo could be identified, compounds 20 and 68, which contain a cyclic aliphatic Cha residue in position 2, had considerably long duration of action. Compounds 31,34,45, and 49 displayed the most favorable overall pharmacological profile, and analogue 45 was selected for further evaluation as a potential treatment in critical care medicine. The differences in vasopressive duration of action in vivo for compounds 1, 2, and 45 are presented in Figure 3.…”

Design, Synthesis, and Pharmacological Characterization of Fluorescent Peptides for Imaging Human V1b Vasopressin or Oxytocin Receptors

“…A selective V1b agonist was produced by replacement in AVP of the glutamine residue in position 4 by a leucine 18 and made highly resistant to degradation by deamination at the Cys 1 position. The subsequent replacement of Arg 8 by a Lys 8 , leading to the V1b agonist A 3,19,20 , did not modify its V1b selectivity. This allowed the covalent addition of a fluorophore to the free epsilon NH 2 group of the Lys residue at position 8 in A, thus making possible the synthesis of new fluorescent V1b agonists.…”

“…We used d[Leu 4 , Lys 8 ]VP (Peptide A in Fig 1, Tables I, II and III) as the parent molecule for designing fluorescent V1b analogues, since we had previously shown that this peptide is a V1b selective agonist both for rat and human VP/OT receptors 3,18,19 . First, we carried out the addition of an hydroxyl (OH) group at the N terminal position of d[Leu 4 ,Lys 8 ]VP to give [1-L-(−)-2-hydroxy-3-thiopropanoic acid, 4-leucine, 8-lysine]vasopressin ([HO 1 ][Leu 4 ,Lys 8 ]VP) (Peptide B in Tables I and II).…”

Somatodendritic dynorphin release: orchestrating activity patterns of vasopressin neurons

“…Hence, it is possible that, under stimulated conditions, enough vasopressin is released into the supraoptic (and paraventricular) nucleus to increase the likelihood that any single vasopressin neuron will adopt phasic firing and so it will be important to determine the effects of vasopressin V 1a , V 1b and V 2 receptor antagonists on the activity of vasopressin neurons under such conditions. Vasopressin receptors have nanomolar affinity for vasopressin [40] and so hypothalamic vasopressin concentrations must be subnanomolar under basal conditions (otherwise all vasopressin neurons would be driven into phasic activity under basal conditions). Based on this observation, we can calculate the maximal secretion rate of vasopressin that must be evident under basal conditions.…”