Evaluation of changes in secretory granules of atrial myocytes: a morphometric approach.

OBJECTIVE

To evaluate the sensitivity and applicability of stereologic analysis for estimating changes in the secretory granule content of atrial myocytes.

STUDY DESIGN

The content of secretory granules in the right atrial myocytes of Sprague-Dawley (SD) and Lewis (LW) rats was assessed using a stereologic analysis of electron microscopic images under control conditions and in response to forced wheel running.

RESULTS

Volume density analysis revealed significant heterogeneity in the granule content of different strains of rats. The content of the dark secretory granules was significantly lower in control LW compared with control SD rats. The difference in pale granule content was opposite but less pronounced. Forced wheel running did not elicit statistically significant changes in the granule volume density. However, it changed significantly the number of dark granules in each rat strain, albeit in opposite directions, most likely due to changes in the number of small dark granules. No change was observed in the case of pale granules. This suggests higher sensitivity of dark granules to enhanced physical load.

CONCLUSION

Both the volume and the number of secretory granules should be estimated in parallel to reveal responses of the atrial secretory system to different internal or external stimuli.