Abstract
Alpha-adrenoceptor stimulation may induce malignant hyperthermia (MH) in vivo. Consequently, we have investigated the effects of the alpha-adrenoceptor agonist phenylephrine and, for comparison, the effects of the beta-adrenoceptor agonist isoproterenol on inositol-lipid metabolism of malignant hyperthermia susceptible (MHS) and healthy control (MHN) swine. The experiments were performed on electrically stimulated (frequency 0.2 Hz) trabeculae isolated from the right ventricles of the hearts of MHS and MHN animals. After labelling with [3H]inositol for 6 h, different inositol phosphates were measured by high pressure liquid chromatography, including inositol 1-phosphate, inositol 1,4-bisphosphate, inositol 1,3,4-trisphosphate, inositol 1,4,5-trisphosphate (1,4,5-IP3) and inositol 1,3,4,5-tetrakisphosphate. After stimulation with isoproterenol, the inositol phosphate content did not increase or vary between muscle from MHS and MHN animals. In contrast, all inositol phosphates increased after stimulation with phenylephrine in both muscle types, the effects being greater in MHS than in MHN, especially as regards 1,4,5-IP3 content. As 1,4,5-IP3, a presumed second messenger, has been shown to mobilize intracellular calcium, it is concluded that an enhanced alpha-adrenergic response is involved in the development of MH.
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