In congestive heart failure (CHF), endogenous compounds with ouabainlike activity (OLA) may contribute to the maintenance of the circulatory homeostasis by peripheral as well as central effects. In the present study, we assessed changes in peripheral (plasma and left ventricle) and central (pituitary, hypothalamus, pons, and cortex) OLA in two animal models of CHF and determined whether brain OLA mediates sympathetic hyperactivity in CHF. Cardiomyopathic hamsters with their controls were studied at 9 months of age for tissue OLA. Rats were studied 4 weeks after acute coronary artery ligation for tissue OLA and sympathetic activity. In both models, left ventricular end-diastolic pressure was markedly increased. CHF was associated with significant increases in both plasma and tissue OLA in both models. In the brain, the most marked (twofold to threefold) increases occurred in the hypothalamus. In vitro, all OLA measured could be blocked by antibody Fab fragments (Digibind). Conscious rats with CHF showed elevated plasma catecholamines and enhanced responses of mean arterial pressure (MAP), heart rate (HR), and renal sympathetic nerve activity (RSNA) to air stress and to intracerebroventricular (ICV) injection of the alpha 2-adrenergic receptor agonist guanabenz compared with sham-operated rats. ICV administration of the Fab fragments did not change resting RSNA or responses to air stress at 1 hour. However, 18 hours after injection of the Fab fragments, resting RSNA levels had significantly decreased compared with the control values, and plasma catecholamine levels had decreased to control values.(ABSTRACT TRUNCATED AT 250 WORDS)

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To assess the possible contribution of brain ouabain-like activity (OLA) to the pressor effects of high-sodium intake in Dahl salt-sensitive (Dahl S) rats, we assessed the effects of high (8%) on blood pressure (BP) and peripheral and brain OLA in Dahl on blood pressure (BP) and peripheral and brain OLA in Dahl S and Dahl salt-resistant (Dahl R) rats. On regular sodium intake, Dahl S and R had similar BP; however, by 7 wk of age adrenal and plasma OLA were 15-30% higher in Dahl S vs. R, whereas central OLA remained similar. On high-sodium intake, in Dahl S both peripheral and central OLA increased within 1 wk with additional increases after 3 wk. These increases preceded the rise in BP. In Dahl R rats, high sodium did not increase BP. However, 3 wk of high sodium did increase peripheral as well as central OLA, the latter to a lesser extent compared with Dahl S and not in the hypothalamus. These results are consistent with the concept that central OLA may be involved in the pressor responses to high sodium in Dahl S. Circulating OLA may play a role in the regulation of renal function to excrete excess sodium in both strains.

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