title: Developmental change in magnesium sulfate-induced relaxation of rabbit pulmonary arteries.
abstract: Magnesium causes a variety of vascular smooth muscle to relax. The present study was designed to determine whether there is a developmental change in the magnesium-induced response of pulmonary vasculature. Isolated pulmonary arteries (PA) of newborn (1- to 3-day-old) and juvenile (4- to 6-wk-old) rabbits were suspended in organ chambers filled with modified Krebs-Ringer bicarbonate solution (95% O(2)-5% CO(2), 37.0 degrees C), and their isometric tension was recorded. In arteries preconstricted with endothelin-1 to a similar tension level, MgSO(4) caused greater relaxation of juvenile rabbit PA than that of the newborn rabbit PA. Verapamil, a voltage-dependent Ca(2+) channel blocker, attenuated magnesium-induced relaxation in juvenile rabbit PA but not in newborn PA. The uptake of Ca(2+) of juvenile rabbit PA was inhibited by MgSO(4), and the inhibition was attenuated by verapamil. The uptake of Ca(2+) of newborn rabbit PA was smaller than that of the juvenile PA and was not significantly affected by MgSO(4) and verapamil. These results demonstrate that there is a developmental increase in the dilator effect of MgSO(4) in rabbit PA. In newborn rabbit PA, an incomplete maturation of the voltage-dependent Ca(2+) channels may contribute to the smaller vasodilation induced by MgSO(4).
authors.affiliation: Department of Pediatrics, Harbor-UCLA Medical Center, University of California, Los Angeles, School of Medicine, Torrance, California 90502, USA. Jean-Francois.Tolsa@chuv.hospvd.ch
authors.forename: J F
authors.initials: JF
authors.lastname: Tolsa
authors.forename: Y
authors.initials: Y
authors.lastname: Gao
authors.forename: J U
authors.initials: JU
authors.lastname: Raj
mesh_terms: D000818:Animals; D000831:Animals, Newborn; D002118:Calcium / Q000378:metabolism; D002121:Calcium Channel Blockers / Q000494:pharmacology; D015220:Calcium Channels / Q000187:drug effects; D005260:Female; D066298:In Vitro Techniques; D008278:Magnesium Sulfate / Q000494:pharmacology*; D008297:Male; D009126:Muscle Relaxation / Q000187:drug effects; D009131:Muscle, Smooth, Vascular / Q000166:cytology / Q000187:drug effects*; D011189:Potassium Chloride / Q000494:pharmacology; D011453:Prostaglandins / Q000494:pharmacology; D011651:Pulmonary Artery / Q000187:drug effects*; D011817:Rabbits; D014700:Verapamil / Q000494:pharmacology
chemical_list: D002121:Calcium Channel Blockers; D015220:Calcium Channels; D011453:Prostaglandins; D011189:Potassium Chloride; D008278:Magnesium Sulfate; D014700:Verapamil; D002118:Calcium