Plasma catecholamine and cardiovascular responses to morphine and D-ala2-d-leu5-enkephalin in conscious rats
Conway, E.L.; Brown, M.J.; Dollery, C.T.
Archives Internationales de Pharmacodynamie et de Therapie 265(2): 244-258
1983
ISSN/ISBN: 0003-9780 PMID: 6360061 Document Number: 215326
The effects of morphine and DADL on cardiovascular parameters and plasma catecholamine levels were studied in conscious unrestrained rats. Morphine 30 micrograms icv increased blood pressure over the 3 hr recording period, produced an initial bradycardia followed by a tachycardia and increased plasma epinephrine and norepinephrine levels 20- and 2-fold respectively. These responses were not altered by systemic naloxone 0.8 mg/kg ia or naloxone injected icv 110 micrograms. In adrenalectomized rats blood pressure, heart rate and plasma norepinephrine responses were not significantly altered. Lower doses of morphine 1, 3 and 10 micrograms icv produced dose-related increases in plasma catecholamines, in the absence of any signs of respiratory depression, which were antagonized by naloxone 110 micrograms icv. 1m Morphine 10 mg/kg produced effects similar to those of icv morphine and these were readily antagonized by naloxone 0.8 mg/kg ia. DADL 10 micrograms icv also produced effects similar to those of morphine but of a shorter duration, and these were also inhibited by naloxone 0.8 mg/kg ia. The results are consistent with an action of opiates on a specific opiate receptor in the brain mediating an increase in catecholamine release. The rise in blood pressure may in part be a consequence of the increase in circulating catecholamines.