Takeshi Tsujino

Oral taurine supplementation prevents fructose-induced hypertension in rats

Taurine is known to have antihypertensive and lipid-lowering effects in some experimental models and patients. On the other hand, intracellular free calcium and magnesium play important roles in regulating the tonus of blood vessels and insulin sensitivity. We examined the effect of oral taurine supplementation on blood pressure, serum metabolic parameters, and platelet cytosolic free calcium ([Ca2+]i) and magnesium ([Mg2+]i) concentration in fructose-fed Sprague-Dawley rats. Systolic blood pressure and platelet [Ca2+]i were significantly higher in rats fed a 60% fructose diet. Oral taurine supplementation (1% in drinking water) completely prevented the elevation of blood pressure and an increase in platelet [Ca2+]i, but exacerbated hyperinsulinemia, hypertriglyceridemia, and a decrease in platelet [Mg2+]i. In conclusion, taurine may ameliorate fructose-induced hypertension in rats by preventing an increase in intracellular free calcium concentration. The blood pressure-lowering effect of taurine appeared to be independent from its effect on glucose and lipid metabolism in this model.

α-, βII- and γ-subspecies of protein kinase C localized in the monkey hippocampus: pre- and post-synaptic localization of γ-subspecies

Abstract Protein kinase C (PKC) has attracted wide attention as a key enzyme for the expression of long-term potentiation in the hippocampus, a basic model for memory. It is of interest to study the detailed localization of PKC subspecies in the monkey hippocampus. We used immunocytochemistry to examine the localization of PKC subspecies in the hippocampus of the monkey, Macaca mulatta . Subspecies of PKC in the monkey could be separated by hydroxyapatite chromatography and the elution profile proved to be similar to that of the rat. Antibodies against each α, βII and γ-subspecies of the rat specifically reacted with the respective subspecies of monkey PKC. The α-, βII- and γ-subspecies were distinctly distributed in the hippocampus. The βI-subspecies was not evident in the hippocampus. While both the α- and γ-subspecies immunoreactive pyramidal cells were distributed throughout the hippocampus (CA1–CA3), the βII-subspecies immunoreactive cells were scattered only in the CA1 region. The γ-subspecies was found in granule cells and dendrites in the dentate gyrus, in mossy fibers and in their terminals in the CA3 region. The α-subspecies was also present in granule cells and in the dendrites but not in the mossy fibers. Glial cells did not stain with any of the antibodies used. Electron microscopy clearly showed that the γ-subspecies was localized in both presynaptic terminals and post-synaptic dendrites. These observations suggest that subspecies of PKC in the monkey hippocampus may be involved in distinct functions and that the γ-subspecies of PKC may act pre- and post-synaptically in pyramidal cells of the hippocampus.

Expression of Fos-like immunoreactivity by yohimbine and clonidine in the rat brain

To elucidate the role of alpha 2-adrenoceptors in transcriptional control in the rat brain, we localized the Fos-like immunoreactivity (Fos-LI) induced by alpha 2-adrenoceptor agonists and by an antagonist. Injections of yohimbine (5 mg/kg, i.p.) into rats led to the induction of Fos-LI in areas with a dense alpha 2-adrenoceptor binding such as the locus coeruleus, the bed nucleus of stria terminalis, the central nucleus of amygdaloid complex, the paraventricular nucleus, the nucleus tractus solitarius, and ventrolateral medulla oblongata. Clonidine (500 micrograms/kg, i.p.) suppressed the Fos expression by yohimbine in these nuclei, and clonidine (100 micrograms/kg, i.p.) or guanabenz (4 mg/kg, i.p.) induced Fos-LI in oxytocin neurons in the paraventricular and supraoptic nuclei in the hypothalamus. Thus, the alpha 2-adrenoceptor is involved in transcriptional control via Fos expression in neurons related to autonomic and other functions.

Inhibitory effect of insulin on vasopressin-induced intracellular calcium response is blunted in hyperinsulinemic hypertensive patients: role of membrane fatty acid composition.

Impaired insulin-mediated vasodilation has been implicated in hypertension that is associated with the metabolic syndrome. The aim of this study was to determine whether an abnormality in membrane fatty acid composition was related to a weakening of insulins inhibitory effect on agonist-stimulated intracellular free calcium elevation. Mild to moderate hypertensive patients (n = 27) and normotensive controls (n = 11) were studied. Hypertensive patients were divided into normoinsulinemic patients (n = 14) and hyperinsulinemic patients (n = 13) according to the area under the curve of plasma insulin concentrations during a 75-g oral glucose tolerance test. Nonstimulated and arginine-vasopressin (AVP) (1u2009µmol/l)-stimulated intraplatelet free calcium concentrations (p[Ca2+]i) were measured with or without insulin (100u2009µU/ml) preincubation. Platelet membrane fatty acid composition, intraerythrocyte sodium content, and the ouabain-sensitive sodium efflux rate constant (Kos) of erythrocytes were also determined. Insulin preincubation reduced AVP-stimulated p[Ca2+]i elevation in both normotensive controls and hypertensive patients. The inhibitory effect of insulin on AVP-stimulated elevation of p[Ca2+]i (%Inhibition) was significantly (P < 0.05) blunted in hyperinsulinemic hypertensive patients (9.7% ± 2.4%) as compared to normoinsulinemic hypertensive patients (17.4% ± 2.7%) and normotensive controls (16.9% ± 1.7%). In hypertensive patients, the %Inhibition was correlated negatively with saturated fatty acids (SFA) (r = −0.51, P < 0.05) and systolic blood pressure (r = −0.44, P < 0.05), and correlated positively with membrane polyunsaturated fatty acids (PUFA) (r = 0.53, P < 0.01) and Kos (r = 0.53, P < 0.005). Multiple regression analysis showed that SFA, PUFA, and Kos were the significant variables for %Inhibition. These findings indicate that an increase in SFA and a decrease in PUFA may cause insulin insensitivity in cellular calcium and sodium handling in hypertension with hyperinsulinemia.

Immunocytochemical localization of α-, βI-, βII- and γ-subspecies of protein kinase C in the motor and premotor cortices of the rhesus monkey

Abstract We obtained evidence for the localization of α-, βI-, βII- and γ-subspecies of protein kinase C (PKC) in the monkey motor and premotor cortices (Brodmanns areas 4 and 6). In Brodmanns area 4, the immunoreactivity for the α-PKC was present in horizontal and round cells in the layers I and II, and small pyramidal cells in layer III and also in the glial cells in subcortical white matter. The α-PKC immunopositive glial cells contained GFAP-immunoreactive product. The βI-PKC immunoreactivity was present in the round cells in layer I and in the pyramidal cells in the layer V, including Betz cells. The βII-PKC immunoreactivity was observed as small dots in perikarya of the small and medium-sized pyramidal cells in layers II, III, V and VI, but not in layer I. The γ-PKC immunoreactive cell bodies were observed in layers II, III and VI, and most of the immunoreactive cells were pyramidal. Intense γ-PKC immunoreactivity was found in the neuropils of layers I and II. Similar distributions of four PKC subspecies were seen in Brodmanns area 6, except that βI-PKC immunoreactive Betz cells were not present. The unique localization of PKC subspecies suggested that each PKC subspecies was involved in the specific function in motor and premotor cortices of the rhesus monkey.