Changes of parvalbumin protein levels and immunolocalisation during the postnatal development of the female rat heart were investigated in order to determine if they were correlated with age-related changes in cardiac function. Hearts from newborn, 3-month-old (young), 6-month-old (young adult) and 12-month-old (adult) female Wistar rats were processed for immunohistochemical localization of parvalbumin and for Western blotting assay. Parvalbumin was detected by both methods in all age groups from newborn to 12-month-old rats. In the newborn rat heart, parvalbumin immunoreactivity did not fully fill the sarcoplasm of the cardiac myocytes and the amount of parvalbumin was low compared to the adult levels. In contrast, in 3-12-month-old rats, strong parvalbumin immunoreactivity was detected throughout the sarcoplasm of all cardiac myocytes and the amount of parvalbumin increased with increasing age (from newborn to adult). Our study indicates that an increase of parvalbumin levels in the female rat heart with increasing age may be associated with maintenance of proper relaxation of the cardiac myocytes needed to cope with the increasing workload of the heart during postnatal growth.
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