IOSR Journal of Dental and Medical Sciences (IOSR-JDMS) e-ISSN: 2279-0853, p-ISSN: 2279-0861. Volume 10, Issue 4 (Sep.- Oct. 2013), PP 93-97 www.iosrjournals.org www.iosrjournals.org 93 | Page The Effect of Nitric Oxide on the Rat Diaphragm at Different Frequencies of Indirect Electrical Stimulation Rasha Eldeeb 1 *,Hemmat Kholousy 2 , Samah El-Attar 2 1Physiology Department, Dubai Medical College for Girls (DMCG), Dubai, UAE 2Physiology Department, College of Medicine, Cairo University, Egypt Abstract: Introduction: Nitric oxide (NO) is a second messenger that regulates neurotransmitter release at the neuromuscular junction (nmj). Evidences accumulate on its potency as a neuro-modulator in CNS, PNS. This work investigates the effect of NO on (nmj) by adding L-arginine known as NO donor. Material and Methods: 30 albino rats’ diaphragms divided into two groups. Both exposed to L-argnine followed by Bovine Hb and stimulated by indirect electrical stimulation. Gp 1 stimulated at 0.5Hz. Gp 2 stimulated at 100Hz. The amplitude of maximum contraction (AMC) (ΔY), contraction time (ΔX) and half relaxation time (½ Rt) measured. Results: In presence of NO Gp1 showed a significant increase in (AMC) (ΔY) and (ΔX) with a significant decrease in (½ Rt). Gp2 showed a significant increase in (AMC)(ΔY). Conclusion: Nitric oxide (NO) facilitates neuromuscular transmission at presynaptic level. Bovine Hemoglobin reduces Nitric oxide’s induced effects. Key words: Hemoglobin, L-arginine, nitric oxide (NO), rat diaphragm, neuromuscular transmission. I. Introduction Over the last two decades, the image of nitric oxide (NO) has been totally changed as it was found to exhibits diverse vital roles in the brain, arteries, immune system, liver, pancreas, uterus, peripheral nerves, lung and almost every system in the human body. It is now clear that NO participate in the control of vascular tone as an antagonist of the adrenergic regulatory system. It causes smooth muscle relaxation at the vascular wall, gastrointestinal tract and it functions in both the central and peripheral nervous system 1,2 . Intracellular NO production is catalyzed by several isoforms of an enzyme termed, nitric oxide synthase (NOS). Neural NO- synthase is present in the sarcolemmma of type II skeletal muscle fibers 3 . In rats, the nitric oxide (NO) synthase pathway is present in skeletal muscle, vascular smooth muscle and motor nerve terminal 3, 4 . This study aims to investigate the effect of NO in rat neuromuscular preparation (diaphragm) at different frequencies of nerve stimulation and modulation of its effect by hemoglobin as NO scavenger. II. Materials and Methods The Experimental Research Committee of the Physiology Department and the ethics committee of College of Medicine, Cairo University approved all procedures. Male rats were supplied by Animal Care facility of Cairo University. The study was conducted in accordance with World Helsinki declaration. II-I Experimental protocol: The phrenic nerve and the diaphragm muscle of 30 Wistar rats weighing from 100-120 g each, were isolated by the method of Bulbring 5 . Each muscle was immersed in a 20-ml chamber containing Krebs buffer (188 mMNaCl, 4.7 mMKCl, 1.9 mM CaCl 2 , 1.2 mM MgSO 4 , 25 mMNaHCO 3 , 1.2 mM KH 2 PO 4 , and 11 mM glucose) at 37 o C and continuously aerated with a mixture of oxygen (95%) and carbon dioxide (5%).Isometric force was measured with isometric force transducer from which the signals was amplified and displayed simultaneously on Intracept TSC 28611 computer using analysis software phys 4 (Intracel Company). Gp 1 (no: 15) was stimulated by indirect electrical supramaximal stimuli of 0.5 msec duration at a frequency of 0.5Hz. In Gp 2 (no: 15) was stimulated by indirect electrical stimuli of 100Hz frequency. In both groups a square-wave stimulator palmer electronic, England, was used to induce simple muscle twitch and the following parameters were measured ; maximal twitch force (ΔΥ), Contraction time (ΔΧ), Half relaxation time (1/2 RT) . The recordings of both Gp 1 and Gp 2 were done three times with 10 minutes rest in between each recording, the first recording was done in presence of Krebs solution in 50 ml bath then to study the effect of NO, 4.7mM of L- arginine as a NO donor was added to Krebs solution, after a contact time of 3 minutes the second recording was taken. In order to prove that the observed responses were NO mediated, 50 nM of bovine