Autoradiographic detection of kinin receptors in the human medulla of control, hypertensive, and diabetic donors

Abstract

Kinins have been elected to the status of central neuromediators. Their effects are mediated through the activation of two G-protein-coupled receptors, denoted B-1 and B-2. Functional and binding studies suggested that B-1 and B-2 receptors are upregulated in the medulla and spinal cord of hypertensive and diabetic rats. the aim of this study was to localize and quantify kinin receptors in post-mortem human medulla obtained from normotensive, hypertensive, and diabetic subjects, using in vitro receptor autoradiography with the radioligands [I-125]HPP-HOE140 (B-2 receptor) and [I-125]HPP[des-Arg(10)]-HOE140 (B-1 receptor). Data showed specific binding sites for B-2 receptor (0.4-1.5 fmol/mg tissue) in 11 medullary nuclei from 4 control specimens (paratrigeminal > ambiguus > cuneate, gelatinous layer of the caudal spinal trigeminal nucleus > caudal and interpolar spinal trigeminal, external cuneate, solitary tract > hypoglossal > gracile > inferior olivary nuclei). Increased density of B-2 receptor binding sites was observed in seven medullary nuclei of four hypertensive specimens (paratrigeminal > external cuneate > interpolar and caudal spinal trigeminal, gracile, inferior olivary > hypoglossal nuclei). B-2 receptor binding sites were seemingly increased in the same medullary nuclei of two diabetic specimens. Specific binding sites for B-1 receptor (1.05 and 1.36 fmol/mg tissue) were seen only in the inferior olivary nucleus in two out of the ten studied specimens. the present results support a putative role for kinins in the regulation of autonomic, nociceptive, and motor functions at the level of the human medulla. Evidence is also provided that B-2 receptors are upregulated in medullary cardiovascular centers of subjects afflicted of cardiovascular diseases.