New effective gonadotropin releasing hormone antagonists with minimal potency for histamine release in vitro

Abstract

In order to minimize the adverse effect of histamine release in the rat of some gonadotropin releasing hormone (GnRH) antagonists, such as [Ac-D2Nal1,D4FPhe2,DTrp3,DArg6]-GnRH, new structures with modifications at positions 1, 2, 3, 5, 6, 7, and 10 were synthesized and tested in several biological systems. In vitro: the affinity for the pituitary GnRH receptor was measured as was the ability of the analogues to inhibit GnRH-stimulated release of luteinizing hormone (LH) by dispersed anterior pituitary cells in culture and to release histamine from rat mast cells. In vivo: inhibition of ovulation in the cycling rat was determined after subcutaneous (sc) injection of the peptides at noon on the day of proestrus; the duration of action of the peptides was evaluated by measuring LH levels in the castrated male rat after sc injection of some selected analogues. [Ac-D2Nal1,D4ClPhe2,D3Pal3,Arg5,D-4-p-methoxy benzoyl-2-aminobutyric acid6,DAla10]-GnRH was found to be one of the most potent analogues of this series, causing a 100% inhibition of ovulation at 5 micrograms/kg or less. Release of histamine was observed at doses 10-25 times that required for [Ac-D2Nal1,D4FPhe2,DTrp3,DArg6]-GnRH. Thus, introduction of arginine in position 5 with a hydrophobic amino acid in position 6 is compatible with high potency in several biological systems and results in compounds with lowered potency to release histamine compared to homologous peptides with tyrosine in position 5 and D-arginine in position 6.

Atrial natriuretic peptide induces rat peritoneal mast cell activation by cGMP-independent and calcium uptake-dependent mechanism

“…In previous studies, several peptides such as substance P, C3a and C5a, somatostatin are known to promote histamine-dependent plasma extravasation when injected intracutaneously in rats (Pearce, 1986;Rivier et al, 1986;Kowalski et al, 1997). Also ANP has recently been shown to increase dermal vascular permeability of rat in vivo (Forman and Jordan, 1983;Opgenorth et al, 1990).…”

Identification of a second corticotropin-releasing factor receptor gene and characterization of a cDNA expressed in heart.

“…Peptides were synthesized by standard methods (15) and iodinated as reported previously (16). Plasmid DNA corresponding to the full-length CRF-RB in pcDNA1 was prepared by the alkaline-lysis method.…”

Highly potent antagonists of luteinizing hormone-releasing hormone free of edematogenic effects.

“…While repeated administration of LH-RH agonists is required to lower the levels of luteinizing hormone (LH), follicle-stimulating hormone (FSH), and sex steroids, similar effects can be obtained with single administration of LH-RH antagonists (7). Competitive antagonists of LH-RH were developed by multiple modification of the parent molecule, <Glu-His-Trp-Ser-Tyr-Gly-Leu-Arg-ProGly-NH2 (8)(9)(10)(11)(12)(13)(14) (<Glu, pyroglutamic acid). Agonist activity is reduced by substitution of aromatic D amino acids at positions 2 and 3, and receptor affinity is retained when there are replacements at residues 1 and 6, and in some analogs also in position 10.…”

“…In addition, these analogs cause a dose-related whealing response (17), increase histamine levels in rats (16), and elicit histamine release from rat mast cells (18). The anaphylactoid reactions to these antagonists are not invariably associated with their edematogenic potencies (16) , was reported to be 1/10th as potent as I in releasing histamine and showed no edematogenic effect in the rat at the doses tested (0.5-1.0 mg/kg) (14). Antagonist H, which induced edema at the challenge dose of 1.5 mg/kg, was also about 1/10th as potent in histamine release assays as the other hydrophilic antagonists studied (16).…”