title: Characterization of the rat isolated retractor penis muscle as a model for the study of nitrergic transmission.
abstract: BACKGROUND
  The anococcygeus and retractor penis muscles are part of the erectile machinery in male rodents. The rat anococcygeus muscle is a widely used smooth muscle preparation for the study of the effects of test substances on adrenergic, nitrergic, and cholinergic transmission. There is, however, little information available on the process of autonomic transmission in the rat retractor penis muscle, although its autonomic innervation has generally been assumed to be similar to that of the anococcygeus muscle because of the contiguous nature of the two muscles. The present study investigated the involvement of nitrergic transmission in mediating relaxant responses of the rat retractor penis muscle to electrical field stimulation.
  
  
  METHODS
  The retractor penis muscle was isolated from Sprague-Dawley rats and mounted in Krebs solution. Phentolamine (5 microM) was added to the bath to block the adrenergic responses of the muscle, which was then precontracted with carbachol (10 microM).
  
  
  RESULTS
  Electrical field stimulation (20-30 V, 1 ms pulse width, at 0.5-20 Hz for 10 s) of the carbachol precontracted muscle elicited frequency-dependent relaxant responses (0.9-68%). Tetrodotoxin (1 microM), N(G)-nitro-L-arginine (L-NOARG) (50 microM), N(G)-nitro-L-arginine methylester (L-NAME) (100 microM), and haemoglobin (100 microM) inhibited these relaxant responses by 99.3%, 93.9%, 86.9%, and 77.5%, respectively. L-Arginine (250 microM) (but not its D-isomer) reversed the blockade produced by L-NOARG (72.7%) and L-NAME (81.5%).
  
  
  CONCLUSIONS
  Our results provide clear evidence that the inhibitory (relaxant) responses of the rat retractor penis muscle to electrical field stimulation are mediated by nitric oxide involving the L-arginine-nitric oxide synthase-nitric oxide pathway. The rat retractor penis muscle is a versatile preparation that can replace the cumbersome preparations from the pig, ox, and horse, hitherto used as pharmacological models for the study of the retractor penis muscle.
authors.affiliation: Department of Pharmacology, Faculty of Medicine, National University of Singapore, 10 Kent Ridge Crescent, 119260 Singapore, Singapore.
authors.forename: Li-Sam
authors.initials: LS
authors.lastname: Cheah
authors.forename: Matthew C E
authors.initials: MC
authors.lastname: Gwee
authors.forename: Selvanayagam
authors.initials: S
authors.lastname: Nirthanan
mesh_terms: D000818:Animals; D001120:Arginine / Q000494:pharmacology; D002217:Carbachol / Q000494:pharmacology; D004558:Electric Stimulation; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006454:Hemoglobins / Q000494:pharmacology; D066298:In Vitro Techniques; D008297:Male; D023421:Models, Animal; D009119:Muscle Contraction / Q000187:drug effects; D018482:Muscle, Skeletal / Q000187:drug effects / Q000294:innervation* / Q000502:physiology*; D019331:NG-Nitroarginine Methyl Ester / Q000494:pharmacology; D026602:Nitrergic Neurons / Q000187:drug effects / Q000502:physiology*; D009569:Nitric Oxide / Q000378:metabolism; D019001:Nitric Oxide Synthase / Q000037:antagonists & inhibitors / Q000378:metabolism; D019335:Nitroarginine / Q000494:pharmacology; D010413:Penis / Q000033:anatomy & histology* / Q000294:innervation / Q000502:physiology; D051381:Rats; D017207:Rats, Sprague-Dawley; D013779:Tetrodotoxin / Q000494:pharmacology
chemical_list: D004791:Enzyme Inhibitors; D006454:Hemoglobins; D019335:Nitroarginine; D009569:Nitric Oxide; D013779:Tetrodotoxin; D002217:Carbachol; D001120:Arginine; D019001:Nitric Oxide Synthase; D019331:NG-Nitroarginine Methyl Ester