[Antagonistic effects of angiotensin II and morphine on synaptosomal calcium uptake].
Behavioral observations have repeatedly shown that the analgesic effect of morphine can be antagonized by intracerebroventricular injection of angiotensin I (A I), although mechanisms underlying the action were obscure. Since a prevention of Ca2+ uptake into the nerve terminals was considered as one of the mechanisms for morphine analgesia, we examined the effect of A I and morphine on the 45Ca uptake by rat brain synaptosomal preparations. Morphine of 10(-8)-10(-6) mol/L produced a dose-related suppression on synaptosomal 45Ca uptake, which was completely reversed by the opioid antagonist naloxone of 10(-6) mol/L. A I of 10(-8)-10(-6) mol/L, on the contrary, enhanced 45Ca uptake. This effect was totally abolished by saralasin, a A I antagonist, at 10(-6) mol/L. When synaptosomal preparations were incubated in a mixture of morphine (10(-6) mol/L) and A I (10(-8)-10(-6) mol/L), the effect of morphine was almost completely reversed. The results suggest that the distinct effect of A I may account for, at least in part, the antagonistic effect of A I on morphine analgesia.
Wang
X M
XM
Wang
X J
XJ
Han
J S
JS
D000804:Angiotensin II / Q000494:pharmacology*; D000818:Animals; D001921:Brain / Q000378:metabolism; D002118:Calcium / Q000493:pharmacokinetics*; D005260:Female; D008297:Male; D009020:Morphine / Q000037:antagonists & inhibitors*; D051381:Rats; D011919:Rats, Inbred Strains; D013574:Synaptosomes / Q000378:metabolism*
D000804:Angiotensin II; D009020:Morphine; D002118:Calcium