Monoamine Oxidase and Semicarbazide-Sensitive Amine Oxidase Activities in Isolated Cardiomyocytes of Spontaneously Hypertensive Rats

In the isolated cardiomyocytes of spontaneously hypertensive rats (SHR, 3 months old) MAO A and B activities were significantly increased compared to the myocytes in the hearts of age-matched Wistar–Kyoto rats. This increase was not associated with cardiac hypertrophy in these young animals, but might represent an early event in the development of hypertrophy. A semicarbazide-sensitive amine oxidase (SSAO) activity was found in cardiomyocytes. This activity showed a high affinity for benzylamine (K_m5–6 μM) and was not inhibited by 10⁻⁴M pargyline and 10⁻⁵M deprenyl, but was largely inhibited by 10⁻⁴M B₂₄(3,5-diethoxy-4-aminomethylpyridine), a specific inhibitor of semicarbazide-sensitive amine oxidase with high affinity for benzylamine. The SSAO enzyme of rat cardiomyocytes is a copper-amine oxidase and has a cross-reactivity with the antibodies raised against pure pig plasma benzylamine oxidase. In the cardiomyocytes of 3-month-old SHR rats the level of this enzymic activity is not significantly increased.