Yukiko Minatogawa

Effects of anticonvulsants and gamma-aminobutyric acid (GABA) -mimetic drugs on immunoreactive somatostatin and GABA contents in the rat brain

Immunoreactive somatostatin (IR-SRIF) and gamma-aminobutyric acid (GABA) contents in the rat brain were investigated to study chronic effects of the treatment with anticonvulsants, carbamazepine (CBZ), valproic acid (VPA) and phenytoin (PHT). Decreased IR-SRIF levels were found in several brain regions after chronic treatment with VPA and CBZ. GABA concentrations were found to be increased significantly in chronic CBZ and VPA treatment in the rat brain, especially in limbic structures. PHT had no effect on both IR-SRIF and GABA contents in the rat brain. Effects of several GABA-mimetic drugs also were studied on IR-SRIF contents in the rat brain. Aminooxyacetic acid an inhibitor of GABA transaminase, induced a decrease in IR-SRIF concentration in the pyriform and entorhinal cortex, whereas ethanolamine-o-sulfate, another GABA-transaminase inhibitor and muscimol, a GABA receptor agonist had no effect on brain IR-SRIF after acute administration. The present results suggest that endogenous somatostatin has an important role for anticonvulsant properties of CBZ and VPA, but not of PHT. The relationship between the changes in IR-SRIF and the GABA transmitter system in the anticonvulsant action of CBZ and VPA remains to be clarified.

Effects of carbamazepine and valproic acid on brain immunoreactive somatostatin and γ-aminobutyric acid in amygdaloid-kindled rats

Somatostatin and gamma-aminobutyric acid (GABA) concentrations were evaluated in the brain of kindled rats treated chronically with carbamazepine and valproic acid. Kindled seizures were almost completely blocked by treatment with carbamazepine, whereas the effect of valproic acid was partial, suppressing only generalized seizures. The duration of after-discharge in amygdala was suppressed by carbamazepine not by valproic acid. Carbamazepine induced a decrease in immunoreactive somatostatin concentration and an increase in GABA concentration in the temporal cortex of kindled rats. Valproic acid induced only an increase in GABA concentration. The results suggest that somatostatin may be associated with the suppression of focal seizure in amygdala and GABA may have a role in the suppression of generalized seizures.

The role of vasopressin, somatostatin and GABA in febrile convulsion in rat pups.

In order to further elucidate a possible role of neuropeptides and GABA in the pathogenesis of febrile convulsions, we studied changes of immunoreactive-arginine vasopressin (IR-AVP), IR-somatostatin (IR-SRIF) and gamma-aminobutyric acid (GABA) in the rat brain after febrile convulsions induced by ultra-red light (UR). Male Wistar rats at 16 days of age irradiated with UR developed generalized convulsions after 4.9 +/- 0.5 min irradiation. Six rats were killed by microwave irradiation 3 min after UR irradiation prior to convulsion development, and 29 rats were killed either 0 min, 2 h, 6 h, 24 h or 48 h after febrile convulsions. Non-irradiated rats served as controls. The rat brain was dissected into 4 regions; amygdala, hypothalamus, cortex and hippocampus, and subjected to radioimmunoassays. IR-AVP levels in hypothalamus were increased 3 min after UR and decreased at 2 h and 6 h after the convulsions. IR-SRIF levels were increased in cortex and hippocampus at 3 min after UR and 0 min after the convulsions. The GABA content increased in all regions tested at 2 h and 6 h after the convulsions. These results suggest that AVP, SRIF and GABA may be involved in the pathogenesis of febrile convulsions in different ways.

Time-course of hepatic cytochrome P450 subfamily induction by chronic carbamazepine treatment in rats

Recent studies indicate that carbamazepine (CBZ) induces hepatic cytochrome p450 (CYP) protein subfamilies. The present study examines the time-course of the appearance of hepatic CYP subfamilies (2B, 3A) and serum levels of CBZ and its metabolite, CBZ epoxide (CBZE), induced by CBZ treatment in rats. Male Wistar rats were given 5 g of CBZ (CBZ-treated) per 1 kg of feed for 3, 7, 14, 28 and 42 d or feed without CBZ (control). Serum levels of CBZ and CBZE were evaluated by HPLC. Induction ratios of CYP2B and CYP3A were evaluated by Western blotting. Serum levels of CBZ and CBZE became maximal after 14 and 7 d, respectively, after CBZ treatment. Both levels gradually, then significantly decreased after 42 d CBZ compared with maximal levels. The induction ratio of CYP2B did not differ between 3, 7, 14, 28 and 42 d CBZ treatment. The induction ratio of CYP3A reached a maximum after 14 d CBZ, then significantly decreased after 28 and 42 d CBZ compared to the maximal rate. The difference between CYP2B and CYP3A induction by CBZ chronic treatment is a novel finding.

Sensitive determination of deuterated and non-deuterated phenylalanine and tyrosine in human plasma by combined capillary gas chromatography—negative ion chemical ionization mass spectrometry

Abstract A combined capillary gas chromatography—negative ion chemical ionization mass spectrometric method for the determination of deuterated and non-deuterated phenylalanine and tyrosine in plasma was developed. Phenylalanine and tyrosine were converted to pentafluorobenzyl—trifluoroacetyl (PFB—TFA) and PFB—TFA—trimethylsilyl (TMS) derivatives, respectively, after prepurification with a Bio-Rad AG 50W-X2 cation-exchange column. These derivatives showed good gas chromatographic separation properties and provided intense (M  PFB) − ions. These ions were ideal for the specific and sensitive determination of deuterated and non-deuterated phenylalanine and tyrosine by selected ion monitoring assay. [2,2′,3,3,3′,4′,5′,6′- 2 H 8 ] l -Phenylalanine and [2,2′,3,3,3′,5′,6′- 2 H 7 ] l -tyrosine were used as internal standards. This method was used to determine the plasma levels of deuterated and non-deuterated phenylalanine and tyrosine, after oral administration of [2′,3′,4′,5′,6′- 2 H 5 ] l -phenylalanine to a healthy person.