Jv. Rabadan et al., CHANGES IN RIGHT ATRIAL CATECHOLAMINE CONTENT IN NATIVE RATS AND AFTER NALOXONE-INDUCED WITHDRAWAL, British Journal of Anaesthesia, 80(3), 1998, pp. 354-359
In this study, we determined if changes in heart catecholamine content
during naloxone-induced withdrawal correlated with modifications in h
eart rate. In addition, we determined plasma concentrations of cortico
sterone as an index of the hypothalamo-pituitary-adrenal (HPA) axis. T
he effects of naloxone on norepinephrine, epinephrine or dopamine cont
ent and turnover, plasma concentrations of corticosterone and the mech
anical response of the right atria of the rat were studied. Male rats
were implanted with placebo or morphine pellets for 7 days. On the day
of sacrifice, animals were injected with saline or naloxone 1 mg kg(-
1) s.c. to precipitate a withdrawal syndrome. Administration of naloxo
ne to morphine-treated (tolerant) animals induced a decrease in atrial
content of norepinephrine, epinephrine and dopamine (290.2 (11.9) ng
g(-1), 15.6 (2.1) ng g(-1) and 9.52 (0.5) ng g(-1), respectively) and
an increase (1.38 (0.2) ng g(-1) in the dihydroxy phenyl acetic acid/d
opamine (DOPAC/DA) ratio. Administration of naloxone to morphine-treat
ed animals enhanced plasma concentrations of corticosterone (435.8 (27
.6) ng ml(-1)). In the isolated right atria, L-naloxone induced an inc
rease in atrial rate in preparations from morphine-treated rats wherea
s in placebo-pelleted (naive) rats, L-naloxone induced a decrease. In
contrast, administration of D-naloxone (inactive isomer) produced a de
crease in atrial rate in preparations from placebo or morphine-treated
rats. We conclude that this study has provided evidence that naloxone
-induced withdrawal was characterized by activation of catecholaminerg
ic neurones in the heart that was accompanied by an increase in atrial
rate.