Methylene blue inhibits stimulatory effect of sodium nitroprusside but not of 3-morpholino sydnonimine on prolactin secretion in freely moving male rats.
Previously we reported that intracerebroventricular (i.c.v.) administration of nitric oxide (NO) donors, sodium nitroprusside (SNP) (1-10 microg), and 3-morpholino-sydnonimine (SIN-1) (10-100 microg), induced dose-dependent increases in plasma prolactin levels of freely moving male rats, suggesting a role of NO in the control of prolactin secretion. The present results show that i.c.v. pretreatment with methylene blue (MB) (30 microg), a guanylyl cyclase inhibitor, significantly reduced the effects of microinjections of SNP (3 and 5 microg), however, this did not modify the stimulatory action of SIN-1 (30 microg) on plasma prolactin levels of conscious male rats. Alone, MB did not modify basal prolactin levels. These results suggest different mechanisms of action of SNP and SIN-1 to stimulate prolactin secretion in vivo. Activation of soluble guanylyl cyclase seems to mediate the neuroendocrine action of NO released from SNP but not of SIN-1. Different cellular distribution of NO generating activity from these donors as well as the possible generation of other radicals simultaneously with NO from SIN-1 could explain these differences.
Department of Physiology, School of Medicine, University of La Laguna, Tenerife, Spain. mglezh@ull.es
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González
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Llorente
D000818:Animals; D004305:Dose-Response Relationship, Drug; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D006162:Guanylate Cyclase / Q000037:antagonists & inhibitors; D007276:Injections, Intraventricular; D008297:Male; D008751:Methylene Blue / Q000494:pharmacology*; D008981:Molsidomine / Q000031:analogs & derivatives* / Q000494:pharmacology; D009599:Nitroprusside / Q000494:pharmacology*; D011388:Prolactin / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley
D004791:Enzyme Inhibitors; D009599:Nitroprusside; C002385:linsidomine; D011388:Prolactin; D008981:Molsidomine; D006162:Guanylate Cyclase; D008751:Methylene Blue