Histological and immunohistochemical study on the possible cardioprotective role of acetylcysteine in oral formalin myocardial toxicity in adult albino rats

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Forty percent solution of formaldehyde in water is known as formalin. Formalin is added to milk in the production of cheese and dairy products as an antimicrobial agent. It is a very reactive compound, reacting with cellular proteins and nucleic acids; thus, safety evaluation of formalin as an additive to milk and dairy products (cheese and yoghurt) must be thoroughly considered.

Aim of the study

This study was conducted to investigate the effects of oral formalin ingestion on the histological structure of the myocardium of adult albino rats and the possible cardioprotective effects of the formalin antidote ‘acetylcysteine’.

Materials and methods

Thirty adult albino rats were used. They were classified into three main groups as follows: group I: served as a control. Group II: rats received formalin orally. Group III: rats received formalin in addition to the specific formalin antidote ‘acetylcysteine’. Myocardial sections were stained with H&E, MT stain, and immunohistochemical staining for endothelial nitric oxide synthase (eNOS) antigen.


It was found that oral formalin consumption induced myocardial abnormalities in the form of disruption, vacuolation, and wide separation of cardiac muscle fibers. Such abnormalities were, to a huge extent, prevented with the use of the antidote acetylcysteine. eNOS immunoreactivity, in ventricles of formalin-exposed rats, showed a significant decrease compared with the control group and then showed a highly significant increase in group III compared with group II and the control group.


Oral formalin consumption was shown to induce deleterious morphological changes on the myocardium, most of which were prevented with the use of acetylcysteine. The study highlights the importance of eNOS in healthy cardiovascular cells and suggests that the decrease in eNOS that occurs in formalin toxicity may lead to altered vascular reactivity and possibly impaired cardiac function.

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