MANIFESTATIONS OF ACUTE OPIATE WITHDRAWAL CONTRACTURE IN RABBIT JEJUNUM AFTER MU-RECEPTOR, KAPPA-RECEPTOR AND DELTA-RECEPTOR AGONIST EXPOSURE

1 Following a 5 min in vitro exposure to morphine (1.3 X 10(-7) M), U-50,488H (2.5 X 10(-8) M) and deltorphin (1.6 X 10(-8) - 6.5 X 10(-9) M), the rabbit isolated jejunum exhibited a precipitated contracture after the addition of naloxone (2.75 X 10(-7) M). 2 The precipitated responses to U-50,488H and deltorphin but not to morphine were reproducible in the same tissue. 3 The precipitated contractures were blocked completely by tetrodotoxin (3 X 10(-7) M), partially by atropine (1.5 X 10(-7) M) and not affected by hexamethonium (1.4 X 10(-5) M). 4 Naloxone administration (2.75 X 10(-7) M) before the agonist prevented the development of the adaptive response to morphine and U-50,488H but not to deltorphin. 5 The selective antagonists norbinaltorphimine (2.7 X 10(-8) -2.7 X 10(-9) M) and naltrindole (1.1 X 10(-7) M) prevented the adaptive response development only to the respective agonists. 6 The opioid agonists partially inhibited the spontaneous activity of the tissue. This study has shown that independent activation of mu-, kappa- and delta-opioid receptors can induce dependence in this isolated tissue. Rabbit jejunum is a suitable tissue for studying the acute effects of opioids on the adaptative processes determined by their administration.