Gender differences in the effect of age on adrenergic neurotransmission in the heart

In male rats, there is an age-associated decline in the capacity of cardiac sympathetic nerves to release norepinephrine. To investigate whether this phenomenon also occurs in female rats, we examined adrenergic neurochemical transmission in the hearts of female and male Fischer 344 rats. Rats aged 6, 12, and 24 months were employed. Hearts with the right cardiac sympathetic nerve intact were isolated and perfused with Krebs-Ringer solution. Stimulations were performed following the administration of cocaine or metanephrine separately and in combination or following the combination of cocaine, metanephrine, and yohimbine. Cocaine (1 microM) was used to block uptake 1, metanephrine (1 x 10(-5) M) to block uptake 2, and yohimbine (3 microM) to block alpha 2 receptor presynaptically. The nerve was stimulated with frequencies of 2, 6, and 12 Hz, and norepinephrine amount in the effluent was determined by high performance liquid chromatography/electrochemical detection methods. Neither norepinephrine release nor the effects of yohimbine, cocaine, or metanephrine were found to be affected in older female rats (24 month). This suggests that age-related changes in adrenergic neurochemical transmission in the heart of female rats differ from those seen in older male rats.