Distribution and characterization of rat immunoreactive proadrenomedullin N-terminal 20 peptide (PAMP) and the augmented cardiac PAMP in spontaneously hypertensive rat.

Proadrenomedullin N-terminal 20 peptide (PAMP) is a novel hypotensive peptide processed from an adrenomedullin precursor. In this study, high concentrations of immunoreactive PAMP (ir-PAMP) were detected in rat cardiac atrium and adrenal gland by the radioimmunoassay (RIA) for rat PAMP. The mean plasma concentration of rat ir-PAMP was 3.8 +/- 0.3 fmol/ml. Analysis in atrium, adrenal gland and plasma with high performance liquid chromatographies showed that most ir-PAMP emerged as one major peak at the position exactly identical to that of the authentic rat PAMP. We further investigated the tissue and plasma concentrations of rat ir-PAMP in spontaneously hypertensive rat (SHR) to elucidate the role of PAMP in hypertension. The ir-PAMP concentration in heart tissue of SHR was found to be increased compared with that of the control rat. Especially, the atrial concentration of ir-PAMP of SHR (5.66 +/- 0.78 fmol/mg wet tissue) was significantly higher than that of the control (3.29 +/- 0.22 fmol/mg wet tissue). Cardiac PAMP might have a role for the protection from systemic hypertension.