Azot oksid (NO) i antagonist NMDA receptora u konvulzijama izazvanim pentilenetetrazolom

Abstract

Controversy about proconvulsant and anticonvulsant nitric oxide (NO) effects and the place of oxidative stress in convulsions, are still a matter of research. We investigated the interaction between 2-amino-5-phosphonovaleric acid (APV), a competitive N-methyl-D-aspartate (NMDA) receptor antagonist and Nw-nitro-L-arginine methyl ester (L-NAME), a nonselective nitric oxide synthase (NOS) antagonist, in pentylenetetrazole (PTZ)-induced convulsions. Pentylenetetrazole was applied to adult Wistar rats intraperitoneally (ip) in a single dose of 80 mg/kg, and L-NAME (10 µg/10 µl) or APV (20 µg/10 µl) intracerebroventricularly (icv), 30 and 10 minutes before PTZ, respectively. In the same manner, another group received both antagonists. Control animals were given 0.9% saline. Nw-nitro-L-arginine methyl ester exerted a weak anticonvulsant effect, preventing generalized clonic (GCC) and clonic-tonic convulsions (CTC) in 17% of cases. With APV protection against GCC and CTC was 100%, forelimb dystonia (FLD) was decreased in 33% of cases, and time to onset of all convulsive patterns was prolonged (p<0.05 to 0.01). All effects of APV, except in CTC, were reversed by L-NAME applied prior to APV. In APV-PTZ treated animals, superoxide anion content was increased in the forebrain cortex, striatum and hippocampus, without an overwhelmed antioxidative superoxide dismutase (SOD) defense system in the other treatments. When the APV-PTZ group was treated with L-NAME, both SOD activity and superoxide anion content were additionally decreased indicating that the NOS-NO system was involved in the metabolism of superoxide anions. It is suggested that clinical and biochemical effects of NO strongly depend upon the pretreatment and might lead to a wrong impression of NO contradictory activity.

Kontroverzni nalazi o prokonvulzivnim kao i antikonvulzivnim efektima azot oksida (NO) i značaju oksidativnog stresa u konvulzijama, i dalje su predmet istraživanja. U konvulzijama izazvanim primenom pentilentetrazola (PTZ) ispitivali smo interakciju između 2-amino-5-fosfovalerinske kiseline (APV) kompetitivnog antagoniste N-metil-D-aspartat (NMDA) receptora i Nw-nitro-L-arginin metil estra (L-NAME), neselektivnog antagoniste azot oksid sintaze (NOS). Odraslim pacovima Wistar soja, PTZ je ubrizgavan intraperitonealno (ip) u jednoj dozi od 80 mg/kg. Ostale supstance, L-NAME (10 µg/10 µl) i APV (20 µg/10 µl), primenjivale su se intracerebroventrikularno (icv), i to L-NAME 30, a APV 10 minuta pre PTZ. Po istom vremenskom principu, jedna grupa dobila je oba antagonista, a kontrolna fiziološki rastvor NaCl. Nw-nitro-L-arginin metil estar ispoljio je slabo antikonvulzivno dejstvo, smanjujući incidenciju generalizovanih kloničnih (GCC) i klonično-toničnih konvulzija (CTC) za 17%. Za razliku od L-NAME, APV je sprečila nastanak GCC i CTC kod svih životinja (100%), a incidencija klonusa prednjih nogu (FLD) smanjena je za 33%. Istovremeno primenom APV produženo je vreme od aplikacije PTZ do pojave svih konvulzivnih tipova (p<.05 do 0.01). Primenom L-NAME pre APV, umanjeni su efekti APV, pri čemu je došlo do povećanja incidencije FLD i GCC za 16% odnosno 50%. U kori prednjeg mozga, strijatumu i hipokampusu, životinja koje su dobile APV+PTZ, došlo do povećanja koncentracije superoksidnog anjona. Aktivnost superoksid dizmutaze ne prati ovaj skok. Njen dodatni pad u grupi tretiranoj sa L-NAME pre APV+PTZ, ukazuje da je sistem NOS-NO uključen u metabolizam superoksidnog anjona. Dobijeni rezultati ukazuju da klinički i biohemijski efekti NO u velikoj meri zavise od prethodno primenjenih supstanci i promena izazvanih njima, što može da doprinose sticanju pogrešnog utiska o kontradiktornim dejstvima NO.