The highly selective CRF2 receptor antagonist K41498 binds to presynaptic CRF2 receptors in rat brain

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Abstract
Novel analogues of antisauvagine-30 (aSvg-30), a selective antagonist for CRF2 receptors, have been synthesized and characterized in vitro and in vivo. The analogues were tested for their ability to compete for [125I-Tyr0]Svg binding and to inhibit Svg-stimulated adenylate cyclase activity in human embryonic kidney (HEK) 293 cells, permanently transfected with cDNA coding for the human CRF1 (hCRF1), hCRF2α and hCRF2β receptor. One analogue [D-Phe11, His12, Nle17]Svg(11-40), named K41498, showed high affinity binding to hCRF2α (Ki=0.66±0.03 nM) and hCRF2β (Ki=0.62±0.01 nM) but not the hCRF1 receptor (ki=425+50 nM) and decreased Svg-stimulated cAMP accumulation in hCRF2 expressing cells. In conscious Wistar-Kyoto rats, K41498 (1.84 μg, i.v.) antagonized the hypotensive response to systemic urocortin (1.4 μg, i.v.), but did not block the pressor response to centrally administered urocortin (2.35 μg, i.c.v.). K41498 was subsequently radio-iodinated, and in autoradiographic studies, specific (sensitive to rat urocortin, astressin and aSvg30, but insensitive to antalarmin) binding of 125I-K41498 (100 pM) was detected in the heart and in selected brain regions including the nucleus tractus solitarius (NTS), spinal trigeminal nucleus, lateral septum and around the anterior and middle cerebral arteries. Following unilateral nodose ganglionectomy, binding of 125I-K41498 was reduced by 65% in the ipsilateral NTS, indicative of presynaptic CRF2 receptors on vagal afferent terminals. These data demonstrate that K41498 is a useful tool to study native CRF2 receptors in the brain and periphery. British Journal of Pharmacology (2002) 136, 896–904. doi:10.1038/sj.bjp.0704783