Neurokinin A inhibits oxytocin and GABA release from the posterior pituitary by stimulating nitric oxide synthase.
Neurokinin A (NKA) is a tachykinin that participates in the control of neuroendocrine functions. The posterior pituitary lobe (PP) contains abundant nitric oxide synthase (NOS), suggesting that nitric oxide (NO) may play a role in controlling the release of neuropeptides and neurotransmitters. In the present project, we investigated the in vitro effect of NKA on oxytocin release from hypothalamic explants and PP of male rats and the possible involvement of NO in the action of NKA. Since NKA inhibits gamma-aminobutyric acid (GABA) release from PP, we also examined the role of NO in the effect of NKA on basal and K(+)-evoked GABA release. NKA (10(-7)-10(-5) M) significantly decreased oxytocin release from PP, whereas it did not affect its release from hypothalamic explants. The inhibitory effect of NKA on oxytocin release from PP was completely blocked by the NOS inhibitors N(G)-monomethyl-L-arginine (L-NMMA, 0.5 mM) or N(G)-nitro-L-arginine-methyl-ester (L-NAME, 1 mM). Sodium nitroprusside (0.5 mM), an NO releaser, had no effect on basal GABA release but significantly decreased K(+)-evoked GABA release. L-NMMA (0.3 mM) and L-NAME (0.5 mM) increased K(+)-evoked GABA release, indicating that NO plays an inhibitory role in GABA release from PP. The inhibition in both basal and K(+)-evoked GABA release induced by NKA (10(-7) M) was reduced by L-NAME (1 mM). Also, NKA (10(-7) M) increased NO synthesis as measured by [(14)C] citrulline production. Considered all together, our data indicate that NO may mediate the inhibitory effect of NKA on the release of both oxytocin and GABA from PP.
De Laurentiis
A
A
Centro de Investigaciones en Reproducción, Facultad de Medicina, Universidad de Buenos Aires, Buenos Aires, Argentina.
Pisera
D
D
Duvilanski
B
B
Rettori
V
V
Lasaga
M
M
Seilicovich
A
A
D000818:Animals; D006152:Cyclic GMP / Q000031:analogs & derivatives* / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D004791:Enzyme Inhibitors / Q000494:pharmacology; D007031:Hypothalamus / Q000187:drug effects / Q000378:metabolism; D066298:In Vitro Techniques; D008297:Male; D019331:NG-Nitroarginine Methyl Ester / Q000494:pharmacology; D015288:Neurokinin A / Q000494:pharmacology*; D009569:Nitric Oxide / Q000502:physiology; D019001:Nitric Oxide Synthase / Q000187:drug effects* / Q000378:metabolism; D010121:Oxytocin / Q000187:drug effects* / Q000378:metabolism; D010904:Pituitary Gland, Posterior / Q000187:drug effects* / Q000378:metabolism; D011188:Potassium / Q000494:pharmacology; D051381:Rats; D017208:Rats, Wistar; D013873:Thionucleotides / Q000494:pharmacology; D005680:gamma-Aminobutyric Acid / Q000187:drug effects* / Q000378:metabolism; D019323:omega-N-Methylarginine / Q000494:pharmacology
D004791:Enzyme Inhibitors; D013873:Thionucleotides; C083763:8-bromoguanosino-3',5'-cyclic monophosphorothioate; D019323:omega-N-Methylarginine; D009569:Nitric Oxide; D010121:Oxytocin; D005680:gamma-Aminobutyric Acid; D015288:Neurokinin A; D019001:Nitric Oxide Synthase; D006152:Cyclic GMP; D011188:Potassium; D019331:NG-Nitroarginine Methyl Ester