Additional signals from VPAC/PAC family receptors.

The receptors for the neuropeptides vasoactive intestinal polypeptide and pituitary adenylate cyclase-activating polypeptide are strong activators of adenylate cyclase, but recent evidence suggests that they can elicit a number of additional intracellular signals. Some of these are likely to be downstream of the conventional adenylate cyclase pathway, but it is now clear that others reflect novel primary coupling events of the receptors.

ADP-ribosylation factor-dependent phospholipase D activation by VPAC receptors and a PAC(1) receptor splice variant.

The VPAC(1) and VPAC(2) receptors for vasoactive intestinal polypeptide and the PAC(1) receptor for pituitary adenylate cyclase-activating polypeptide are members of a subfamily of G protein-coupled receptors (GPCRs). We recently reported that phospholipase D (PLD) activation by members of the rhodopsin group of GPCRs occurs by at least two routes, one of which seems to involve the small G protein ADP-ribosylation factor (ARF) and its physical association with GPCRs. Here we report that rat VPAC and PAC(1) receptors can also stimulate PLD (albeit less potently than adenylate cyclase) in transfected cells and also in cells where they are natively expressed. PLD responses of the VPAC receptors and the hop1 spice variant of the PAC(1) receptor but not its null form are sensitive to brefeldin A (BFA), an inhibitor of GTP exchange at ARF. The presence of the hop1 cassette in the rat PAC(1) receptor facilitates PLD activation in the absence of marked changes in ligand binding, receptor internalization, and adenylate cyclase activation, with some reduction in phospholipase C activation. Both VPAC(2) and PAC(1-hop1) (but not PAC(1-null)) receptors were shown to associate with immunoprecipitates directed against native or epitope-tagged ARF. A chimeric construct of the VPAC(2) receptor body with intracellular loop 3 (i3) of the PAC(1-null) receptor mediated BFA-insensitive activation of PLD, whereas the response of the corresponding PAC(1-hop1) construct was BFA-sensitive. Motifs in i3 of the PAC(1-hop1) receptor may act as critical determinants of coupling to ARF-dependent PLD activation by contributing to the GPCR:ARF interface.

Differential activation of phospholipase D by VPAC and PAC1 receptors.

To investigate the phospholipase D (PLD) responses of the VIP/PACAP receptors, VPAC1 and VPAC2, and the PACAP-specific PAC1 receptors (short and "hop" intracellular loop 3 (i3) splice variants), stable CHO cell lines expressing similar levels of each wildtype receptor were generated (except for the VPAC1 receptor clone which showed considerably lower expression and lesser responses in signalling assays). All clones caused activation of PLD in response to agonists, as monitored by [3H]phosphatidylbutanol production. The PLD responses of the PAC1 "hop", but not the "null" receptor, were sensitive to the ARF inhibitor, brefeldin A (BFA) (as were VPAC1 and VPAC2 responses). Chimeric constructs of VPAC2 receptors containing i3 of either PAC1 hop or PAC1 null receptors were transiently expressed in COS 7 cells and PLD responses were measured. Only the PLD response of the hop construct was sensitive to BFA. This suggests that i3 motifs in certain Group II GPCRs may play a key role in determining their linkage to ARF-dependent PLD activation.

Use of the laryngeal mask airway as an alternative to the tracheal tube during ambulatory anesthesia.

UNLABELLED: We designed a prospective, randomized, multicenter study to compare anesthetic requirements, recovery times, and postoperative side effects when a laryngeal mask airway (LMA) was used as an alternative to the tracheal tube (TT) during ambulatory anesthesia. After induction of anesthesia with midazolam 2 mg, fentanyl 1 microg/kg, and propofol 2 mg/kg, 381 patients were randomly assigned to receive either an LMA (n = 207) or TT (n = 174) for airway management. In patients assigned to the TT group, succinylcholine 1 mg/kg or a nondepolarizing muscle relaxant was administered to facilitate tracheal intubation. Anesthesia was maintained with volatile anesthetics in combination with nitrous oxide 60% and oxygen. The average time to placement of the two airway devices (5 min) and the failure rates (1%) were similar in the two groups. Although there was a significant decrease in the intraoperative fentanyl requirement in the LMA group, the difference was of little clinical significance. Furthermore, there were no differences in the volatile anesthetic requirements. The time from end of surgery to removal of the airway device (5 min) was also similar in the two study groups. Although duration of the postanesthesia care unit stay and time to ambulation were significantly shorter in the LMA group, there were no differences in the times to "home readiness." The incidence of nausea and vomiting and the need for rescue antiemetic treatments in the postoperative period were similar in the two airway management groups. However, the incidence of postoperative sore throat was significantly greater in patients receiving the TT (versus the LMA). In conclusion, this study suggests that the LMA is a useful alternative to the TT for airway management during ambulatory anesthesia. IMPLICATIONS: Use of the laryngeal mask airway can obviate the need for insertion of a tracheal tube for many ambulatory surgery procedures, and thereby decrease the incidence of postoperative sore throats.

Effect of antagonism of mivacurium-induced neuromuscular block on postoperative emesis in children.

The routine use of cholinesterase inhibitors to antagonize residual neuromuscular block may be associated with increased postoperative emesis. Rapid spontaneous recovery from mivacurium may obviate the need for these drugs. In this randomized, double-blind, placebo-controlled study of 113 healthy children who had received mivacurium as part of a standardized anesthetic regimen, we compared the incidence of postoperative complications after spontaneous recovery and after the use of neostigmine-glycopyrrolate or edrophonium-atropine. The anesthetic regimen consisted of halothane, nitrous oxide, fentanyl, 2 micrograms/kg intravenous (i.v.), mivacurium in an initial dose of 0.2 mg/kg, followed by an infusion, adjusted to maintain > or = 1 evoked contraction response to a supramaximum train-of-four stimulus. At the end of the procedure, patients received by random assignment one of three drug combinations: 1) neostigmine 70 micrograms/kg + glycopyrrolate 10 micrograms/kg, i.v., 2) edrophonium 1 mg/kg + atropine 10 micrograms/kg, i.v., and 3) saline. The trachea was extubated when evoked responses to peripheral nerve stimulation and clinical signs of adequate neuromuscular recovery were present. Postoperative pain was treated with morphine and emesis with metoclopramide. There were no significant differences between the three groups with respect to age, surgery, intraoperative fentanyl, and mivacurium use, time from the end of surgery to tracheal extubation, postanesthesia care unit (PACU) arrival and discharge, or in postoperative oxygen saturation values and analgesic requirements. Compared to the placebo group, emesis occurred more often in the PACU in patients receiving the neostigmine-glycopyrrolate combination, but not after edrophonium-atropine.(ABSTRACT TRUNCATED AT 250 WORDS)