African Journal of Biotechnology Vol. 5 (25), pp. 2534-2539, 29 December 2006   

ISSN 1684–5315 © 2006 Academic Journals        

Review

Atrial natriuretic peptide (ANP)-granules: ultrastructure, morphometry and function

Eliane Florencio Gama and Romeu Rodrigues de Souza*

Universidade São Judas Tadeu, Departamento de Anatomia Humana, São Paulo, Brasil.

*Corresponding Authors E-mail: souzarrd@uol.com.br. Tel: 551138899196

Accepted 6 December, 2006

The atrial granules containing the peptide hormone, Atrial natriuretic peptide (ANP) are present in the four regions of the atrial-auricular complex (two atria and two auricles). ANP-immunoreactivity was detected in all granules from the four regions. Ultrastructurally, atrial myocytes show the presence of very electron dense granules, with sparsely granular and homogeneous content, coated with a double membrane. The number of granules is greatest in the right atrium followed by the left atrium and left auricle and right auricle, in this order. The diameter of granules in the cardiocytes is significantly largest in the right atrium and reduced via the left auricle to the left atrium and right auricle. These data lead to suppose that the right atrium is the one that most synthesizes and stores the ANP. The number of ANP-granules is influenced by several physiological conditions: temperature, dehydration and nutritional condition. The main physiological stimulus for increased ANP release is the atrial muscle stretch, which normally occurs when extra cellular fluid volume or blood volume is elevated. The ANP is eliminated through the atrial myocytes, via exocytosis. Granule content is released into the extra-cellular space (extrusion). The ANP causes diuresis, natriuresis, vasodilatation and depression of blood pressure. It is also involved in the modification of the water-electrolyte balance.

Key words: ANP-granules, ultrastructure, morphometry.