Metoprolol, but not atenolol, reduces stress induced neuropeptide Y release in pigs.

Objectives: To explore if β-adrenergic receptors in the brain are involved in acute and delayed cardiovascular responses to a brief emotional stress, by comparing the effects of the β1-blockers metoprolol (lipophilic) and atenolol (hydrophilic).

Design: Male dominant pigs, singleliving, freely moving, with telemetric recordings of intra-arterial pressure and ECG and assay of plasma levels of the adrenergic cotransmitter neuropeptide Y (NPY), were confronted with four alien pigs for three minutes at weekly intervals. Weeks 1 and 4 were controls, in weeks 2 and 3 randomized crossover treatment with metoprolol or atenolol were given.

Results: The confrontation caused instant and transient tachycardia and more prolonged effects in terms of increased plasma NPY levels, increased arterial pressure and reduced cardiac vagal activation. The two β-blockers inhibited the tachycardia equally, but only metoprolol reduced the prolonged effects.

Conclusions: Emotionally induced sympathetic activation involves peripheral release of NPY causing a prolonged increase of arterial pressure and a reduction of cardiac vagal activity. These effects are prevented by central nervous β-adrenoceptor blockade.