Induction of cardiac natriuretic peptide gene expression in rats trained in hypobaric hypoxic conditions.

Adaptation of cardiac muscle to prolonged hypobaric hypoxia (770-740 mbar, 2,250-2,550 m), endurance training, and their combination was studied in rats by investigating the gene expression of atrial natriuretic peptide (ANP) and B-type natriuretic peptide (BNP) in atria and ventricles. Rats were assigned into the following groups according to the barometric conditions and physical activity; normobaric sedentary (NS), normobaric training, hypobaric sedentary (HS), and hypobaric training (HT). Experimental periods were 10, 21, and 56 days; the groups at 91 days served as recovery groups from exposure to and training in normobaric and hypobaric conditions for 56 days. The right ventricular hypertrophy in HT rats at 10 days and 56 days was associated with elevated BNP mRNA levels (2.1- and 1.7-fold, P < 0.05, respectively), whereas hypobaric exposure without training was not sufficient to significantly increase ventricular BNP gene expression, although it lead to hypertrophy of the right ventricle. Right and left atrial BNP mRNA levels were also increased (up to 3.9-fold, P < 0.01) in 10-day HS and 10-day HT groups. ANP mRNA levels in right ventricle and left ventricular epicardium were over twofold higher (P < 0.05-0.01) in 10-day HS and 10-day HT groups in comparison to 10-day NS group. Plasma immunoreactive ANP concentration was increased (P < 0.05) in both hypobaric groups up to 21 days. The results show that exposure to hypobaric hypoxia itself and endurance training in hypobaric, hypoxic conditions lead to a marked early increase in ventricular and atrial ANP and BNP mRNA levels. The adaptational response to hypoxia was more pronounced when the oxygen availability was lowered additionally by endurance training carried out in hypobaric hypoxic conditions.