CYCLIC GUANOSINE-MONOPHOSPHATE RESPONSES TO ATRIAL-NATRIURETIC-FACTOR, BRAIN NATRIURETIC PEPTIDE, BUT NOT C-TYPE NATRIURETIC PEPTIDE, AND THE CHARACTERIZATION OF THEIR RECEPTORS IN RAT MEDULLARY THICK ASCENDING LIMB

The effects of atrial natriuretic factor (ANF), brain natriuretic pept ide (BNP), and C-type natriuretic peptide (CNP) on renal medullary thi ck ascending limb (mTAL) have not been fully understood. The aim of th is study is to examine the second-messenger responses of rat mTAL to A NF, BNP, and CNP. Characterizations of the ANF, BNP, and CNP receptors in mTAL were also performed by radioligand studies. Results showed th at ANF and BNP were both capable of eliciting cyclic guanosine monopho sphate (cGMP) responses in mTAL. Conversely, no cGMP response was obse rved upon stimulation by CNP in mTAL. The presence of ANF receptors wa s demonstrated by radioligand studies. One receptor site was found, an d the Kd and maximum binding capacity were 4.0 +/- 0.45 nmol/L and 277 .8 +/- 47.7 fmol/mg protein, respectively. BNP receptors were also fou nd in mTAL, and ANF and BNP were sharing the same receptor. On the con trary, no CNP receptor could be shown by radioligand studies. These re sults suggest that guanylyl cyclase-coupled receptors (atrial natriure tic peptide receptor-A [ANPR-A]) specific for ANF and BNP are present in rat mTAL, while those for CNP (ANPR-B) are absent. ANF and BNP but not Chip act on mTAL to control water excretion. Copyright (C) 1994 by W.B. Saunders Company