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

Abstract

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.

Acute Effect of Different Types of Exercise on Natriuretic Peptides of Wistar Rats

“…The production of ANP and BNP depends on the integrity and structure of the nuclear membrane of the cardiomyocyte since the nuclear membrane of eukaryotic cells is fundamental in the mechanism of the passage of substances from the nucleus to the cytoplasm and vice-versa. 21 The involvement of this membrane in the regulation of nuclear functions, including transcription and replication, for the production of proteins in the cytoplasm, is fundamental for the production of ANP and BNP in different stress situations to which cells are submitted. 22 Interesting, neither groups presented any alterations in the number of nuclear pores.…”

Effects of Aerobic Training on the Cardiomyocytes of the Right Atrium of Mice

“…Ten electron micrographs per animal obtained by systematic random sampling of quadrants examined with final magnification of x15, 000 were used to obtain: the number of granules per 96 μm 2 , the area of granules (μm 2 ) and the relative volume (%) of endoplasmic reticulum, mitochondria and Golgi complex [10][11][12][13] (Figure 1). The number of granules present in each field was determined and its area measured using an image analysis program (Axio Vision, Zeiss).…”

“…First, aerobic training can have a significant influence on BP and there is a direct relationship between BP and the NP system in experimental animals [6][7][8][9][10] . However, there are no observations of NP system, were aerobic-trained mice were compared with sedentary controls.…”