DOPAMINE D-2-LIKE RECEPTORS IN THE KIDNEY OF SPONTANEOUSLY HYPERTENSIVE RATS - A RADIOLIGAND BINDING ASSAY AND LIGHT-MICROSCOPE AUTORADIOGRAPHY STUDY

1 Dopamine D-2-like receptors were investigated in sections of kidney from male spontaneously hypertensive rats (SHRs) at 6 and 14 weeks of age using radioligand binding assay and autoradiographic techniques wi th [H-3]-spiperone as a ligand. 2 Systolic blood pressure values were slightly higher in 6-week-old SHRs in comparison with age-matched norm otensive Wistar-Kyoto (WKY) rats and considerably higher in 14-week-ol d SHRs in comparison with the other groups investigated. Renal dopamin e levels were higher in SHRs aged 6 and 14 weeks in comparison with ag e-matched WKY rats. Noradrenaline concentrations were similar in 6-wee k-old SHRs and normotensive WKY rats, and increased slightly in SHRs a ged 14 weeks. 3 The density of [H-3]-spiperone binding sites was simil ar in SHRs and WKY rats at 6 weeks of age, and decreased in SHRs at 14 weeks in comparison with age-matched normotensive animals. Light micr oscope autoradiography revealed the accumulation of silver grains in t he tunica adventitia, in the adventitia-media border of intrarenal art eries and within cortical tubules. A few specific silver grains were a lso developed in the glomerular tuft. No changes in the density and pa ttern of silver grains were noticeable between SHRs and WKY rats at 6 weeks of age, whereas a reduction in silver grains largely affecting v ascular binding sites was observed at 14 weeks of age. 4 Renal denerva tion considerably decreased the density of [H-3]-spiperone binding sit es in sections of rat kidney, with an almost complete loss of vascular binding sites. 5 The above findings indicate the occurrence of a decr ease of dopamine D-2-like receptors in the kidney of SHRs with the pro gress of hypertension. Dopamine D-2-like receptors which are mainly pr ejunctional are involved in the modulation of sympathetic neurotransmi ssion in the kidney, The loss of these receptors in SHRs may contribut e to the pathophysiology of hypertension.