Urodilatin: A Natriuretic Peptide of Renal Origin

The Natriuretic Peptide System: A Single Entity, Pleiotropic Effects

In the modern scientific landscape, natriuretic peptides are a complex and interesting network of molecules playing pleiotropic effects on many organs and tissues, ensuring the maintenance of homeostasis mainly in the cardiovascular system and regulating the water-salt balance. The characterization of their receptors, the understanding of the molecular mechanisms through which they exert their action, and the discovery of new peptides in the last period have made it possible to increasingly feature the physiological and pathophysiological role of the members of this family, also allowing to hypothesize the possible settings for using these molecules for therapeutic purposes. This literature review traces the history of the discovery and characterization of the key players among the natriuretic peptides, the scientific trials performed to ascertain their physiological role, and the applications of this knowledge in the clinical field, leaving a glimpse of new and exciting possibilities for their use in the treatment of diseases.

Natriuresis after cardiopulmonary bypass: relationship to urodilatin, atrial natriuretic factor, antidiuretic hormone, and aldosterone

OBJECTIVE

Recent studies suggest that urodilatin from the kidneys rather than atrial natriuretic factor from the heart is the more important member of the family of natriuretic peptides involved in the normal regulation of renal sodium and water excretion. We thus examined the relationship between natriuresis, urodilatin, and atrial natriuretic factor in patients after cardiopulmonary bypass, a procedure known to increase levels of atrial natriuretic factor significantly.

METHODS

Excretion rates of sodium and water were correlated with the excretion of urodilatin and with circulating levels of atrial natriuretic factor, antidiuretic hormone, aldosterone, and plasma renin activity during a period of 16 hours in 12 patients having had coronary artery bypass operations and with approximately a 400% elevation in levels of atrial natriuretic factor.

RESULTS

Natriuresis did not correlate with atrial natriuretic factor, antidiuretic hormone, aldosterone, or plasma renin activity. Excretion rates of urodilatin, however, correlated significantly with excretion rates of sodium (r = 0.74, p = 0.03), urine flow (r = 0.83, p = 0.01), and with levels of serum sodium (r = 0.82, p = 0.01).

CONCLUSION

These results suggest an important role for urodilatin, greater than that of atrial natriuretic factor, in the regulation of renal excretion of sodium and water after cardiopulmonary bypass surgery.

Hydrolysis of iodine labelled urodilatin and ANP by recombinant neutral endopeptidase EC. 3.4.24.11

1. Urodilatin is a 32 amino-acid peptide of similar sequence to atrial natriuretic peptide (ANP), with four additional amino-acids at the N-terminus. Although ANP and urodilatin bind to the same receptors with similar affinities, urodilatin is more active than ANP as a natriuretic agent. Previous studies, using neutral endopeptidase EC 3.4.24.11 (NEP) derived from crude membrane preparations, were inconclusive, but suggested that urodilatin was more resistant than ANP to degradation by this enzyme. In the present study, we compared the degradation rates of [125I]-urodilatin and [125I]-ANP by pure recombinant NEP (rNEP). 2. Incubation of radioactively labelled ANP with rNEP resulted in a much more rapid degradation of the peptide than that for labelled urodilatin. 3. Both phosphoramidon and SQ-28,603, potent inhibitors of NEP, completely protected both peptides from metabolism by rNEP. 4. The circular dichroism spectra of the two peptides indicate that they are very similar and exist largely in unordered or flexible conformations. 5. These results support the relative resistance of urodilatin to NEP, and indicate that urodilatin may be of use as a therapeutic agent, in conditions in which ANP is ineffective.