6533b837fe1ef96bd12a33ef

RESEARCH PRODUCT

Nicotine receptors do not modulate the 3H-noradrenaline release from the isolated rat heart evoked by sympathetic nerve stimulation.

subject

description

Isolated rat hearts with the right sympathetic nerves attached were perfused at a constant flow rate of 7 ml/min with Tyrode's solution. (-)-3H-Noradrenaline (final concentration 10–13.9 nM) was infused for 10 min to label the noradrenaline stores. After wash-out the sympathetic nerves were stimulated electrically (3 Hz, 180 impulses, 1 ms, 20–30 mA) three times (S1–S3) at intervals of 15 min. 3H-Noradrenaline and its metabolites were determined by liquid scintillation counting according to Graefe et al. (1973). Both, nicotine 50 μM and p-aminophenethyltrimethylammonium (PAPETA) 30 μM, enhanced the 3H-noradrenaline overflow in the absence of nerve stimulation. The effect of PAPETA was biphasic and was still observed in the presence of N-methylatropine 0.1 μM. Hexamethonium 10 μM abolished the first phase only, but cocaine 10 μM antagonized both phases. The decline of the stimulation-evoked overflow of 3H-noradrenaline from the first to the third stimulation period was similar in the absence and in the presence of cocaine 10 μM starting before S1 and perfused throughout. Cocaine 10 μM added before S2, however, enhanced the evoked overflow by 77%. PAPETA 30 μM increased the stimulation-evoked overflow by 67% in the absence, and by 73% of the respective control in the presence, of hexamethonium 10 μM. PAPETA 30 μM failed to enhance the evoked overflow in the presence of cocaine. Hexamethonium (added before S2) did not modify the effectiveness of nerve stimulation. Nicotine, neither when perfused from 6 min before S2, nor when added to the perfusion fluid simultaneously with the onset of nerve stimulation, caused changes in the 3H-noradrenaline output upon S2. Upon stimulation a rather discrete increase in 3H-DOPEG overflow was observed. This increase was abolished by cocaine and/or PAPETA. It is concluded that nicotine and PAPETA stimulate the output of 3H-noradrenaline from the rat heart sympathetic nerves by activation of nicotine receptors. However, the amount of transmitter released is small. Neither drug appeared to modulate the output of 3H-noradrenaline upon electrical nerve stimulation via nicotine receptors. PAPETA, like cocaine, appears to block the reuptake of released transmittsrs thereby enhancing the 3H-noradrenaline overflow and reducing the overflow of 3H-DOPEG (formed intraneuronally from recaptured noradrenaline after nerve stimulation).