Fine structure of atrial natriuretic peptide (ANP)-granules in the atrial cardiocytes in the hamster, guinea pig, rabbit, cat and dog

Effects of aging on the secretory apparatus in the right atrial cardiomyocytes of rats

The cardiac atria secrets polypeptide hormones usually called natriuretic peptides (NPs). These substances play a relevant role in the blood pressure regulation. The objective of the study was to estimate the effects of aging on the secretory apparatus of NPs in cardiomyocytes of the right atrium. Twenty male Wistar rats were studied: 10 young animals aged 3 months old (237 ± 27 g; mean ± SD) and 10 old animals aged 20 months old (450 ± 68 g; mean ± SD). The systolic blood pressure was verified instants before the moment of the euthanasia. Electron micrographs were prepared to quantify the area and density of the NP granules and the relative volumes of the endoplasmic reticulum, Golgi complex, and mitochondria. In addition, the number of pores per 10 μm of karyotheca was another variable evaluated. The significance of the results between the two groups evaluated was analyzed by the Student's t test (p < 0.05). The cardiomyocytes obtained from animals of the old group showed decreased in sectional area and density of secretory granules of NP and lower relative volume of endoplasmic reticulum, Golgi complex, and mitochondria compared with the young rats. Moreover, the quantitative density of nuclear pores was significantly lower compared with the youngers. CONCLUSION: Aging causes hypotrophy of the cardiomyocytes of right atrium, similar to what occurs in ventricular cardiomyocytes.

Effects of ovariectomy on the secretory apparatus in the right atrial cardiomyocytes of middle-aged mice

OBJECTIVE

The aim of the present study was to evaluate the effects of ovariectomy on the secretory apparatus of natriuretic peptides in right atrial cardiomyocytes.

METHODS

Nine-month-old mice underwent bilateral ovariectomy or sham surgery. The blood exam of the ovariectomized mice showed results consistent with castrated females. Systolic blood pressure was measured after ovariectomy (9 mo of age) and at the moment of sacrifice (12 mo of age). Fragments of the right atrium were collected and prepared for electron microscopy examination. The following variables were quantified: the quantitative density and area of the natriuretic peptide granules, the relative volume of euchromatin in the nucleus, the number of pores per 10 μm of the nuclear membrane and the relative volumes of the mitochondria and Golgi complex.

RESULTS

The cardiomyocytes obtained from ovariectomized mice indicated that the quantitative density and the area of secretory granules of natriuretic peptides were significantly lower compared with the sham-operated mice. Furthermore, there was a decrease in the relative volume of euchromatin, a lower density of nuclear pores, and lower relative volumes of the mitochondria and Golgi complex in the ovariectomized mice compared with the sham-operated mice. These findings suggest a pool with a low turnover rate, i.e., low synthesis and elimination of natriuretic peptides.

CONCLUSION

A lack of estrogen caused hypotrophy of the secretory apparatus in right atrial cardiomyocytes that could explain the weak synthesis of natriuretic peptides in mice. Furthermore, one of the mechanisms of blood pressure control was lost, which may explain, in part, the elevated blood pressure in ovariectomized mice.

Genomic sequence and cardiac expression of atrial natriuretic peptide in cats

OBJECTIVE

To determine the nucleotide and amino acid sequence of atrial natriuretic peptide (ANP) in cats and its typical regions of cardiac expression.

ANIMALS

5 healthy adult mixed-breed cats.

PROCEDURE

Total RNA was extracted from samples obtained from the left and right atrium, left and right ventricle, and interventricular septum of each cat. The RNA was used to produce cDNA for sequencing and northern blot analysis. Genomic DNA was extracted from feline blood samples. Polymerase chain reaction primers designed from consensus sequences of other species were used to clone and sequence the feline ANP gene.

RESULTS

The feline ANP gene consists of 1,072 nucleotides. It consists of 3 exons (123, 327, and 12 nucleotides) separated by 2 introns (101 and 509 nucleotides). It has several typical features of eukaryotic genes and a putative steroid-response element located within the second intron. Preprohormone ANP consists of 153 amino acids. The amino acid sequence of the active form of feline ANP (ANP-30) is identical to that of equine, bovine, and ovine ANP-30 and differs from that of human, canine, and porcine ANP-28 only by 2 carboxy-terminal arginine residues. The ANP mRNA was detected only in the left and right atria.

CONCLUSIONS AND CLINICAL RELEVANCE

The genetic and protein structure and principal regions of cardiac expression of feline ANP are similar to those of other species. Results of this study should be helpful in future studies on the natriuretic response in cats to diseases that affect cardiovascular function.

Distribution of immunoreactive atrial and brain natriuretic peptides in the heart of the chicken, quail, snake and frog

The distribution of atrial natriuretic peptide (ANP)- and brain natriuretic peptide (BNP)-granules was examined immunohistochemically and ultrastructurally in the hearts of the chicken, Japanese quail, Japanese rat snake and bull-frog. Moreover, natriuretic peptide (NP)-granules in the cardiocytes were analyzed by ultrastructural morphometry. Immunohistochemically, ANP-immunoreactivity (IR) was not detected in any cardiocytes, but BNP-IR was detectable in most atrial and ventricular cardiocytes of both chicken and quail. In the snake, ANP-IR was seen in most atrial and ventricular cardiocytes, which showed traces and negative in BNP-IR, respectively. Both ANP- and BNP-IR were detected in the atrial and ventricular cardiocytes in the frog. Ultrastructurally, most of NP-granules were found in the perinuclear region in the chicken, quail and snake atrium, but the frog atrial cardiocytes had granules generally dispersing widely in the cell. By ultrastructural morphometry, the number of granules in the atrial cardiocyte was greatest in the frog, followed by the snake, and chicken or quail, in this order. The diameter of granules in the atrial cardiocyte was largest in the snake and reduced via the frog to the chicken or quail. In the ventricular cardiocytes of all species, the number and size of granules were significantly less than that in the atrial ones. These results indicated that the hearts of the chicken and quail contain only BNP, and that there are two different natriuretic peptides, ANP and BNP, in the snake and frog hearts.