A comparison of rates of depletion and recovery of noradrenaline stores of peripheral and central noradrenergic neurones after reserpine administration: importance of neuronal activity.

1 The noradrenaline (NA) content of various peripheral sympathetic neuroeffector organs and brain was measured at various times after different doses of reserpine administered to the rat.2 About a 25% reduction in the NA content of the heart was observed 24 h after 0.005 mg/kg reserpine. Two to ten times more reserpine was needed to obtain an approximately similar degree of depletion in the salivary gland and vas deferens; 0.1 mg/kg produced almost complete depletion in the heart and salivary gland, whereas 5 mg/kg was needed to deplete the vas deferens of its NA content.3 The NA content of the brain and superior cervical ganglion was lowered by 20 to 30% in 24 h only when the reserpine dose was raised to 0.1 mg/kg, and 5 to 10 mg/kg was required to obtain over 95% depletion.4 The rates of recovery of cardiac and salivary gland NA stores, after about 80 to 100% depletion by low and high doses of reserpine, were almost identical. About 50% restoration occurred in 7 to 15 days after a single dose of 0.1 mg/kg reserpine.5 The superior cervical ganglion, the NA content of which was fully depleted by 10 mg/kg, showed almost complete recovery in about 7 days.6 Transmural stimulation of the left atrium of the guinea-pig for 30 min (5 Hz for 30 s/min), or exposure of the atrium to reserpine (5 mug/ml) for 30 min, caused modest but statistically insignificant reduction in tissue NA content. However, stimulation in the presence of reserpine 5 mug/ml for 30 min produced about 50% depletion of NA.7In vitro reduction in NA content caused by reserpine plus transmural stimulation, was even more pronounced after treatment of the isolated vas deferens of the rat with tetraethylammonium.8 It is suggested that different rates of depletion following in vivo administration of reserpine are mainly due to variation in neuronal activity of different sympathetic neuroeffector organs.