The effects of highly selective opioid receptor antagonists on the release of arginine vasotocin induced by hyperosmotic stimulation and angiotensin II injection

The effects of highly selective antagonists to μ-, δ-, and κ-opioid receptor subtypes on hyperosmotic- or angiotensin II (AII)-induced arginine vasotocin (AVT) release were investigated in chicks. Plasma levels of AVT increased about 1.5-fold after the administration of 1.5 M NaCl (200 μl, ip) or 100 ng AII (5 μl, icv). The administration of the μ-antagonist naloxonazine and the κ-antagonist nor-Binaltorphimine further elevated plasma levels of AVT stimulated by hypertonic NaCl or AII. These effects of μ- and κ-opioid receptor antagonists on AVT release were dose dependent. Nor-Binahorphimine enhanced hyperosmotically stimulated plasma levels of AVT at a lower dose than that of naloxonazine. Conversely, the δ-selective antagonist naltrindole did not significantly affect AVT secretion. None of the opioid receptor antagonists influenced basal plasma levels of AVT. Therefore, these results suggest that μ- and δ-opioid receptors are involved in hyperosmotic- and AII-induced AVT release, and the effect of the κ-opioid receptor antagonist in the AVT release stimulated by hyperosmolality is strong compared to that of the μ-opioid receptor antagonist, (C) 2000 Academic Press.