d-Tubocurarine as a dopaminergic antagonist in the rabbit ear artery

31P NMR and freeze fracture studies of sarcoplasmic reticulum membranes from normal and malignant hyperthermic pigs: effect of halothane and dantrolene

The effects of halothane and dantrolene on sarcoplasmic reticulum membranes isolated from normal and malignant hyperthermia pig muscle have been investigated using 31P NMR and freeze fracture electron microscopy. The dynamical and structural changes are estimated from the second moment, as calculated from 31P NMR spectra. For both membranes, addition of halothane induces a similar decrease in the spectral second moment. At high concentration of halothane, freeze fracture replicas show small unilamellar vesicles or mixed micelles, uniformly sprayed in the case of malignant hyperthermia membranes but mainly aggregated for the normal ones. The effect of halothane on both membranes is partially inhibited by adding dantrolene. These results suggest that (i) the malignant hyperthermia syndrome is not directly related to the polar heads of phospholipids and (ii) dantrolene counteracts unspecifically the disturbing effect of halothane at the lipid level.

Dopamine receptors: structure-activity relationship of d-tubocurarine analogues

d-Tubocurarine (dTC) and d-tubocurine acted as antagonists of the dopamine-induced inhibition of adrenergic neurotransmission in the isolated, perfused rabbit ear artery. N-Methyl-dTC and O,O,N-trimethyl-dTC (metocurine) did not exhibit dopaminergic antagonist activity. dTC contains one tertiary (3 degrees) nitrogen and one quaternary (4 degrees) nitrogen and d-tubocurine contains two 3 degrees nitrogens; whereas, both N-methyl-dTC and O,O,N-trimethyl-dTC have two 4 degrees nitrogens. The results suggest that a dTC analogue (e.g., metocurine) which lacks a 3 degrees nitrogen should be considered for use in patients treated with dopamine.