Magnesium fluxes in ventricular fibrillation and defibrillation in untreated and dibenzepine HC1 pretreated cats.

Serum magnesium concentration (S-Mg) was estimated in 12 anesthetized cats before and after central thoracotomy, during an electrically induced ventricular fibrillation (VF) and after defibrillation (DEF), and again, in the same experimental animals, after the administration of 3 mg/kg of dibenzepine HC1--a tricyclic antidepressant reported to facilitate spontaneous DEF--as well as during a subsequently induced VF and after the spontaneous DEF which followed. In the first part of the experiment, the surgery and the induction of VF caused no significant change of mean serum magnesium concentration (S-Mg) or serum calcium concentration (S-Ca), whereas the DEF was accompanied by Mg efflux (a significant increase of mean S-Mg from 0.824 mmol/l, SD 0.182, n = 12 to 0.991 mmol/l, SD 0.182, n = 12; P less than 0.05). In the second part of the experiment, following the administration of dibenzepine HCl there was Mg influx (a lowering of mean S-Mg to 0.891 mmol/l, SD 0.160, n = 12; P less than 0.05). During VF in the pretreated cats, S-Mg remained unchanged, while S-Ca decreased significantly (P less than 0.05), followed by a rebound Ca++ efflux (a systematic rise of S-Ca) as the animals defibrilated spontaneously. Concomitantly, there was Mg efflux (a systematic rise of S-MG), the mean S-Mg rising from 0.879 mmol/l, SD 0.143, n = 9 to 1.083 mmol/l, SD 0.257, n = 7, ie to virtually the same value as that obtained after electrically induced DEF.(ABSTRACT TRUNCATED AT 250 WORDS)