British journal of pharmacology
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1. The effects of a selective delta-opioid agonist Tyr-D-Ser(Otbu)-Gly-Phe-Leu-Thr (DSTBULET) were examined on the C- and A beta-evoked responses of convergent dorsal horn neurones in the halothane anaesthetized, intact rat. 2. Intrathecal DSTBULET produced selective dose-dependent inhibitions of electrically-evoked C fibre responses of both superficial and deep neurones. ⋯ The same dose of kelatorphan inhibited the formalin response in the present study. 5. From this study it appears that the delta-opioid agonist DSTBULET can produce profound inhibitions of the responses of convergent neurones to nociceptive afferent inputs. Furthermore, activation of delta-opioid receptors either by DSTBULET, or by protection of endogenous enkephalins with kelatorphan, can inhibit a more prolonged chemically-evoked nociceptive input onto these dorsal horn neurones.
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1. Pithed rats were respired at a fixed rate of 54 cycles min-1 and with a ventilation volume of either 20 (control) or 10 ml kg-1. In these two preparations, the dose-response relationships for the systemic blood pressure responses to endothelin-1, administered i.v., were examined. ⋯ Endothelin-1 induced profound vasoconstriction in the mesenteric bed of the pithed rat both in vivo and in situ. The potency of endothelin-1 on this bed in situ was doubled by lowering the ventilation volume. An increase in cardiac contractility and severe gastrointestinal vasoconstriction may be the initial events leading to the eventual toxic effect of endothelin-1 in the hypoxic pithed rat.