BACKGROUND AND OBJECTIVE: Serum level of digitalis-like factors or sodium pump inhibitors increase under numerous pathogenic circumstances. Diminution of sodium pump activity was reported to be secondary to beta-amyloid oligomers, though the mechanism involved remains inconclusive. Therefore, this study was conducted to evaluate the alteration in serum levels of endogenous ouabain and cerebrospinal fluid (CSF) sodium in an animal model of Alzheimer’s disease, induced by intracerebroventricular injection of streptozotocin (ICV-STZ).

METHODS: In this empirical study, 48 male rats were randomly divided into six groups of saline and STZ. Alzheimer’s model was induced by ICV injection of STZ (3 mg/kg) on the first and third days. CSF samples were drawn from cisterna magna, and blood samples were collected from caudal vein. Thereafter, serum levels of ouabain and CSF sodium were evaluated 2, 7, and 14 days after STZ/saline injection in the test groups. Cresyl violet and Congo red stains were applied to study neuronal morphology and presence of amyloid plaques.

FINDINGS: The mean serum levels of ouabain in the STZ groups were 0.2±0.05 ng/mL vs. 0.54±0.04 ng/mL on the second day, 0.3±0.02 ng/mL vs. 0.59±0.06 ng/mL on the seventh day, and 0.2±0.07 ng/mL vs. 0.65±0.08 ng/mL on the fourteenth day. These results indicated a significant increase of endogenous ouabain in the experimental groups compared to the saline groups (p<0.05). On the second day, CSF sodium concentration in the STZ groups was significantly higher than the saline groups (142.6±2.9 vs. 150.6±3.2; p<05.0). However, despite the increasing trend, in the STZ groups there were no significant differences between the 7- and 14-day STZ groups.

CONCLUSION: In this study, elevated serum level of endogenous ouabain is a sign of early pathological changes in sodium pump activity and can be recommended as a potential therapeutic target