Involvement of opiate system in the α₂-adrenergic depressor and bradycardiac effects evoked by microinjection of norepinephrine into the CNTS of rabbits

Abstract

In mongrel rabbits microinjection of norepinephrine (NE; 30 nmol) into the subnucleus commissuralis of nucleus tractus solitarii (CNTS) evoked a decrease of blood pressure and a slow-down of heart rate. Preinjection of yohimbin, prazosin or propranolol respectively in the same dose (0.3 nmol) into the CNTS did not have any effect on blood pressure and heart rate, but yohimbin could totally antagonize or even reverse the depresssor and bradycardiac effects of NE, while prazosin or propranolol could not. Microinjection of opiate receptor antagonist naloxone 3 nmol into CNTS did not itself affect the level of blood pressure and heart rate, but could markedly attenuate the cardiovascular effects of NE in CNTS.

Microinjection of morphine 10 μg into CNTS resulted in reduction of blood pressure and heart rate. Administration of 3 nmol of NE into the CNTS did not have any effect on blood pressure and heart rate, but could significantly enhance the cardiovascular effects of morphine in the CNTS.

The results indicated that at least part of the α₂-adrenergic cardiovascular effects in the CNTS is mediated by the opiate system.

Keywords

norepinephrine / subnucleus commissuralis of nucleus tractus solitarii of rabbit / blood pressure / heart rate

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