Effects of hydroxocobalamin and haemoglobin on no-mediated relaxations in the rat anococcygeus muscle.
1. The effects of hydroxocobalamin (Vitamin B12a) on relaxations produced by nitric oxide (NO), some NO-donating compounds and nitrergic nerve stimulation in isolated preparations of the rat anococcygeus muscle were compared with the effects of haemoglobin. 2. Hydroxocobalamin (30 mumol/L) significantly reduced relaxations induced by NO (0.1-3 mumol/L) and sodium nitroprusside (SNP; 0.01-0.3 mumol/L) but did not affect relaxations induced by glyceryl trinitrate (GTN; 0.01-1 mumol/L), S-nitrosocysteine (0.1-0.3 mumol/L) or stimulation of nitrergic nerves. A higher concentration of hydroxocobalamin (100 mumol/L) slightly reduced nitrergic nerve stimulation-induced relaxations. 3. Haemoglobin (10 mumol/L) blocked relaxation induced by NO and reduced relaxations induced by SNP, GTN, S-nitrosocysteine and nitrergic nerve stimulation. 4. When nitrergic nerve stimulation-induced relaxations had been partially reduced by the NO synthase inhibitor L-NAME (5-10 mumol/L), hydroxocobalamin had only a weak and transient inhibitory effect. 5. Noradrenergic contractions induced by field stimulation were not affected by hydroxocobalamin (30 mumol/L), but were enhanced by haemoglobin (10 mumol/L). 6. The results suggest that the transmitter released from nitrergic nerves in anococcygeus muscles resembles NO-releasing compounds such as S-nitrosocysteine and GTN but not SNP or free NO.
Li
C G
CG
Department of Pharmacology, University of Melbourne, Parkville, Victoria, Australia.
Rand
M J
MJ
D000818:Animals; D001120:Arginine / Q000031:analogs & derivatives / Q000494:pharmacology; D003545:Cysteine / Q000031:analogs & derivatives / Q000494:pharmacology; D004558:Electric Stimulation; D006454:Hemoglobins / Q000494:pharmacology*; D006879:Hydroxocobalamin / Q000494:pharmacology*; D066298:In Vitro Techniques; D008297:Male; D009126:Muscle Relaxation / Q000187:drug effects; D009130:Muscle, Smooth / Q000187:drug effects* / Q000294:innervation / Q000502:physiology; D019331:NG-Nitroarginine Methyl Ester; D009569:Nitric Oxide / Q000494:pharmacology*; D005996:Nitroglycerin / Q000494:pharmacology; D009599:Nitroprusside / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D026403:S-Nitrosothiols
D006454:Hemoglobins; D026403:S-Nitrosothiols; D009599:Nitroprusside; D009569:Nitric Oxide; C021315:S-nitrosocysteine; D001120:Arginine; D005996:Nitroglycerin; D003545:Cysteine; D006879:Hydroxocobalamin; D019331:NG-Nitroarginine Methyl Ester