Effects of corticosteroids on the myoneural junction. A morphometric and electrophysiological study.
The mean size of the synaptic vesicles in the nerve endings of the isolated rat diaphragm was significantly increased after incubation with the glucocorticoids prednisolone (10(-5) mol/l) and dexamethasone (2 X 10(-7) mol/l). The shape of the vesicles was also changed, i.e. they became rounder. Similar increases in the mean size of the diaphragm synaptic vesicles were seen when the rats were injected with prednisolone (i.p., 2 mg/kg) and dexamethasone (i.p., 50 micrograms/kg) 2-4 h previously. The amplitude of the miniature endplate potentials was also significantly increased in diaphragms isolated from rats which had been injected with prednisolone or with dexamethasone. Changes in frequency of the MEPPs were less marked after injection of prednisolone, but a significant increase was seen after injection of dexamethasone. It is concluded that relatively low concentrations of glucocorticoids have direct effects on the motor endplate in rat diaphragm both in vitro and in vivo. We tentatively suggest that presynaptic effects may contribute to the beneficial effect of corticosteroids in deficient neuromuscular transmission, e.g. in myasthenia gravis.
D000109:Acetylcholine / Q000378:metabolism; D000818:Animals; D003907:Dexamethasone / Q000494:pharmacology; D004594:Electrophysiology; D005260:Female; D005938:Glucocorticoids / Q000494:pharmacology*; D009045:Motor Endplate / Q000187:drug effects; D009469:Neuromuscular Junction / Q000187:drug effects* / Q000648:ultrastructure; D011239:Prednisolone / Q000494:pharmacology; D051381:Rats; D013572:Synaptic Vesicles / Q000187:drug effects; D013997:Time Factors
D005938:Glucocorticoids; D003907:Dexamethasone; D011239:Prednisolone; D000109:Acetylcholine