Effect of 6-hydroxydopamine and alpha-methyltyrosine on brown adipose tissue of infant rats.

A single-dose administration of 6-hydroxydopamine (50 mg/kg body weight, sc) to infant rats resulted in an enlargement, higher fresh weight, markedly elevated lipid content, and higher total protein content of their interscapular and cervical brown adipose tissue. The protein kinase (EC 2.7.1.37) activation ratio in the tissue was decreased as was the phosphoenolpyruvate carboxykinase (EC 4.1.1.32) activity. Fatty acid synthetase, on the other hand, showed an increased activity. These changes commenced as soon as 24 h after the administration of the drug, were fully developed 2-4 days later, and persisted for at least 14 days. The results are in line with the assumption that 6-hydroxydopamine administration causes chemical sympathectomy of brown adipose tissue. This is further supported by the fact that treatment with alpha-methyltyrosine, which is known to competively inhibit norepinephrine systhesis, results in similar changes in brown fat of infant rats. Hence it seems that 6-hydroxydopamine administration offers a simple and inexpensive experimental model for studies of the role norepinephrine-mediated sympathetic nervous system in brown tissue function and development.