New evidence for a presynaptic action of prednisolone at neuromuscular junctions.
The action of prednisolone at the neuromuscular junction was studied in mouse isolated phrenic nerve-diaphragm and rat external popliteal/sciatic nerve-tibialis anterior muscle preparations. Prednisolone (0.03 mM and 0.3 mM) did not alter the twitch-tension in phrenic nerve-diaphragm preparations after 120 min, but increased the frequency (170 +/- 4%) and amplitude (200 +/- 13%) of miniature end-plate potentials. Quantal content was not influenced by the glucocorticoid treatment. Prednisolone (400 microg/kg) did not change the twitch-tension in rat external popliteal/sciatic nerve-tibialis anterior muscle preparations. However, this steroid (0.3 mM) prevented the neuromuscular blockade by d-tubocurarine (1.45 microM) in mouse preparations by 70 +/- 10% (P < 0.05). A similar effect (82 +/- 6% protection, P < 0.05) occurred in rats treated with prednisolone (400 microg/kg) before d-tubocurarine (225 microg/kg). In phrenic nerve-diaphragm preparations, prednisolone (0.3 mM) increased (13 +/- 4%, p < 0.05) the twitch-tension in the presence of beta-bungarotoxin (1 microM), and prevented the blockade produced by this toxin (0.15 microM) in its third phase of action. This presynaptic facilitatory effect may contribute to the usefulness of prednisolone in myasthenia gravis.
Department of Pharmacology, Faculty of Medical Sciences, State University of Campinas (UNICAMP), P.O. Box 6111, CEP 13083-970, Campinas, SP, Brazil.
Cháriston André
CA
Dal Belo
Gildo Bernardo
GB
Leite
Marcos Dias
MD
Fontana
Alexandre Pinto
AP
Corrado
Ana Cristina
AC
Zanandréa Baso
Carmen Sílvia
CS
Moreno Serra
Antonio Carlos
AC
Oliveira
Léa
L
Rodrigues-Simioni
D000818:Animals; D003964:Diaphragm / Q000187:drug effects / Q000294:innervation / Q000502:physiology; D066298:In Vitro Techniques; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D051379:Mice; D018482:Muscle, Skeletal / Q000187:drug effects / Q000502:physiology; D009466:Neuromuscular Blocking Agents / Q000494:pharmacology; D009469:Neuromuscular Junction / Q000187:drug effects* / Q000502:physiology*; D010791:Phrenic Nerve / Q000187:drug effects / Q000502:physiology; D011239:Prednisolone / Q000494:pharmacology*; D017729:Presynaptic Terminals / Q000187:drug effects* / Q000502:physiology*; D051381:Rats; D017208:Rats, Wistar; D012584:Sciatic Nerve / Q000187:drug effects / Q000502:physiology
D009466:Neuromuscular Blocking Agents; D011239:Prednisolone