Atrial natriuretic peptide detected by immunocytochemistry in peripheral organs of Tupaia belangeri

Chronic atriopeptin regulation of arterial pressure in conscious hypertensive rats

Acute coadministrations of an inhibitor of endopeptidase 24.11 (thiorphan) and a ligand (SC-46542) selective for the non-guanylate cyclase-linked atriopeptin binding sites increases urinary sodium excretion to a greater degree in conscious spontaneously hypertensive rats than in normotensive Wistar-Kyoto rats. In the present study, we examined the effects of chronic 10-day intravenous infusions of SC-46542 (des[Phe106,Gly107,Ala115,Gln116] atriopeptin-(103-126] (0.1 mg/kg/hr), thiorphan (1.5 mg/kg/hr), and atriopeptin-(103-126) (100 ng/hr) alone or in combination on direct recording of mean arterial pressure in conscious spontaneously hypertensive rats. During an 11-day time-control infusion of isotonic saline vehicle (100 microliters/hr), mean arterial pressure remained stable. Chronic infusion of atriopeptin-(103-126) decreased mean arterial pressure progressively over the first 3 days; then mean arterial pressure progressively rose to control level over the following 3 days and remained at control level for the remainder of the experiment. Similarly, coinfusions of atriopeptin-(103-126) and SC-46542 or thiorphan, SC-46542 and thiorphan, or the triple infusion of atriopeptin-(103-126), SC-46542, and thiorphan had only transient effects on mean arterial pressure during 10-day infusions. SC-46542 alone had no effect on mean arterial pressure. Similarly, thiorphan alone had no effect on mean arterial pressure except at doses that blocked the acute pressor response to angiotensin I. Chronic infusions of atriopeptin-(103-126), SC-46542, and thiorphan alone or in combination are not effective long-term treatments for hypertension in spontaneously hypertensive rats.

Isolation and structural analysis of "urodilatin", a new peptide of the cardiodilatin-(ANP)-family, extracted from human urine

Two major forms of cardiac peptides have been established in the last few years: (a) a prohormone of 126 amino acids (CDD/ANP-1-126) in the endocrine heart and (b) the circulating CDD/ANP-99-126 (= alpha ANP) in blood plasma. The method we applied earlier to isolate the circulating form of cardiodilatin from human blood was used to detect and analyze the biologically active, predominant form of the same polypeptide family excreted by the kidneys. Each step of the isolation procedure was followed up by a bioassay using an in vitro vascular smooth muscle relaxation test and a highly specific RIA against cardiodilatin (CDD-99-126) for the initial purification steps. The polypeptides excreted in 1000 l of normal human urine were adsorbed to 2.5 kg of alginic acid, and after elution and lyophilization processed on a G-25 Sephadex column. The obtained crude polypeptide fractions were applied to ion-exchange chromatography. Thereafter four steps of HPLC were carried out to purify the polypeptide which was the suggested form of cardiodilatin (CDD) in human urine. The amino acid analysis and gas phase sequence analysis showed that the main form of urinary cardiodilatin is a 32 amino acid residue containing molecule, cardiodilatin-95-126. The molecule is N-terminally extended compared to the circulating CDD-99-126. This suggests that the analyzed urinary peptide is not the residual plasma form, filtrated and renally cleared from blood, but probably a polypeptide produced and processed in the kidney tubules and cleaved by a different postranslational process. Therefore, this vasorelaxant polypeptide is called urodilatin.

Urodilatin (CDD/ANP-95-126) is not biologically inactivated by a peptidase from dog kidney cortex membranes in contrast to atrial natriuretic peptide/cardiodilatin (alpha-hANP/CDD-99-126)

Atrial natriuretic peptide (CDD/ANP-99-126) is rapidly inactivated by a membrane preparations from dog kidney cortex. Inactivation occurs by cleavage of the ring structure in the position between Cys-105 and Phe-106. A unique proteolytic product separated by HPLC on reverse-phase column appears as a single peak which elutes prior the intact peptide. In contrast, CDD/ANP-95-126 (urodilatin) which is released from the kidney is not destroyed by proteolysis using an identical membrane preparation.