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E Rebas

Publications and source records attributed to E Rebas.

13 recordsLinked to original sources
PubMed2005

Estradiol modulates the synapsins phosphorylation by various protein kinases in the rat brain under in vitro and in vivo conditions.

Synapsins are the neuronal phosphoproteins which play very important role in processes of synaptic neurotransmission. They are physiological substrates for Ser/Thr protein kinases. The reversible phosphorylation of synapsins may be modified by several compounds including steroid hormones. The aim of our study was to investigate, if the one of neuroactive steroid--17beta-estradiol--could modulate the phosphorylation of synapsins by PKA, CaM-PK and PKC in rat brain and what type of mechanism of their action is possible. The activity of kinases was evaluated as phosphorylation of synapsin in cerebral cortex and hippocampus in vivo and in vitro conditions. We conclude that 17E2 has inhibitory effect on synapsins phosphorylation by all tested kinases in vitro and in vivo conditions. The lack of nuclei in synaptosomal membrane fraction and short time of hormone exposure can be evidence of direct, non-genomic mechanism of estradiol action.

Animals↗
PubMed2004

Angiotensin IV stimulates the activity of tyrosine kinases in rat anterior pituitary gland acting via AT1-like receptors?

Angiotensin II (Ang II) is known to modulate tyrosine kinases (PTKs) activity in pituitary tumor cells. It is known that AngII is acting via AT1 receptors in many tissues. The aim of this study was to see whether 3-8 fragment of AngII, called angiotensin IV (AngIV) has a similar effect on tyrosine kinase activity in normal pituitary gland and what type of angiotensin receptor is involved in this process. The homogenates of normal rat pituitaries was a source of enzymes. The PTKs activity was determined using the synthetic substrate poly GluTyr and gamma-(32)P-ATP. Ang IV was found to increase the PTK activity in the rat anterior pituitary tissue, with the maximal effect at concentration of 10(-10) M. AngII was ineffective at all concentrations studied. Losartan, a selective AT1 receptor blocker, added together with Ang IV abolished the effect of the latter, however losartan diminished also the PTK activity when applied together with Ang II, but only when it was added immediately before, but not after, the addition of Ang II. The involvement of a non-classic AT1-like receptor is suggested.

Angiotensin II↗
PubMed2001

Pregnenolone sulfate modulates angiotensin II-induced inositol 1,4,5-trisphosphate changes in the anterior pituitary of female rat.

The present study was designed to test whether pregnenolone sulfate can influence the angiotensin II (AngII) action in the anterior pituitary. Female rats were ovariectomized and 10 days after operation were treated with either 50 or 250 microg per animal in one of the following substances: oil (control), pregnenolone sulfate (PREG-S), estradiol benzoate (E(2),) progesterone (P), or dehydroepiandrosterone sulfate (DHEA-S), given in single intraperitoneal injection. Because AngII is known to act in the anterior pituitary through the phosphatidiloinositol breakdown, thus increasing the level of inositol-1,4,5-trisphosphate (IP(3)), the IP(3) concentration was determined 24 h after the injection in the anterior pituitary homogenate after in vitro exposure to AngII. Among the tested steroids only PREG-S enhanced the basal (without AngII) and AngII-induced level of IP(3) in both doses used. There was no difference between the effect of a high and low dose of PREG-S. These results show that PREG-S may modulate AngII action in the anterior pituitary, regardless of the presence of ovary.

Adjuvants, Immunologic↗
PubMed2000

Effect of 17-beta-estradiol and progesterone on angiotensin II-induced changes in inositol-1,4,5-trisphosphate content and protein kinase C activity in anterior pituitary.

Angiotensin II (AngII) is known to act in the anteriorpituitary through phosphatidiloinositol breakdown, increasing the level of inositol-1,4,5-trisphosphate (IP(3)) and diacyloglycerol (DAG), a potential activator of protein kinase C (PKC). We examined the effect of estradiol and progesterone treatment in vivo on IP(3) levels and activity of PKC under the influence of AngII. Three groups of intact female rats received in vivo injections of 17-beta-estradiol, progesterone, and oil (control) for five days, and then the in vitro effect of AngII was examined using homogenate of the anterior pituitary. AngII increased either the IP(3) concentration or the synapsin I phosphorylation catalyzed by PKC. Estradiol enhanced the basal (without AngII) IP(3) level and PKC activity induced by AngII. Progesterone did not change the basal and AngII-induced IP(3) concentrations. On the other hand, it decreased the basal PKC activity and blocked the effect of AngII. Our data suggest that ovarian steroids can modulate the effect of AngII on the anterior pituitary gland.

Angiotensin II↗
PubMed1995

Neuroactive steroids modulate in vivo the Mg2+/Ca(2+)-ATPase activity in rat cortical and cerebellar synaptosomal membranes.

Estradiol and pregnenolone sulfate administered in vivo inhibited the Mg2+/Ca(2+)-ATPase activity in synaptosomal membranes from rat cortex by 20% and 30%, respectively. In cerebellum, estradiol decreased the activity up to 43%. The calmodulin-stimulated activity declined in cortex after treatment with estradiol and pregnenolone sulfate, but significantly increased in cerebellar membranes. Dehydroepiandrosterone sulfate had influence neither on enzyme activity, nor on stimulation by calmodulin in both examined rat brain regions.

Animals↗
PubMed1995

Estradiol and pregnenolone sulfate could modulate PMA-stimulated and Ca2+/calmodulin-dependent synaptosomal membrane protein phosphorylation from rat brain in vivo.

We have examined the effect of two steroids, pregnenolone sulfate and 17-beta-estradiol, on the activity of two protein kinases: protein kinase C and Ca2+/calmodulin-dependent protein kinase. The activity of the kinases was evaluated as phosphorylation of two synapsins Ia and Ib in cerebral cortex and hippocampus of the rat brain. Both steroids decreased phosphorylation of both synapsins to a great extent; however, in hippocampus neither pregnenolone nor estradiol influenced the reaction catalyzed by Ca2+/calmodulin-protein kinase. In the remaining areas of the brain estradiol decreased the activity of both studied kinases to a greater degree than pregnenolone sulfate. Our study suggests that pregnenolone sulfate and 17-beta-estradiol could modulate directly Ca2+/calmodulin-dependent protein kinase and protein kinase C and thus directly influence processes of neurotransmission.

Animals↗
PubMedDate not supplied

Effects of somatostatin and its analogues on tyrosine kinase activity in rodent tumors.

The effects of native somatostatin-14 (SS-14) and of its two analogues, octreotide and CH-275, on the activity of tyrosine kinases (TK) in two rodent tumors (rat pituitary tumor and murine colonic cancer) were studied in vitro. The activity of TK was measured in tissue homogenates using gamma[(32)P]ATP as the donor of the phosphoryl group and poly(Glu(80), Tyr(20)) as a substrate. It was found that native SS-14 inhibited TK activity in both investigated tumors. Octreotide, which acts preferentially via somatostatin receptor subtype 2 (SSTR2), was very effective in inhibiting TK activity in the rat pituitary tumor, but it is a rather weak inhibitor of TK activity in murine colonic cancer. CH-275, a selective ligand of the SSTR1 subtype of SS receptors, suppressed TK activity in the pituitary tumor but was ineffective in the colonic cancer. It is hypothesized that the effect of neuropeptide somatostatin (SS-14) on murine colonic cancer is exerted via the subtype of receptor which does not interact with CH-275 and has no or low affinity for octreotide (SSTR 4, 3 or 5?).

Animals↗
PubMedDate not supplied

Angiotensin II changes inositol-1,4,5-trisphosphate content in the pituitary and hypothalamus but not in cerebral cortex of the rat brain.

The present study was undertaken to investigate the effect of angiotensin II (AngII) on the concentration of inositol-1,4,5-trisphosphate (IP3) and the modulation of AngII action by estradiol in the brain. Our studies were conducted in male rat anterior pituiary, hypothalamus and cerebral cortex with and without previous estradiol treatment. In the cerebral cortex, there were no changes in IP3 content after exposure to AngII. In the anterior pituitary, AngII increased the IP3 concentration at all doses studied. However, in the hypothalamus, AngII decreased the IP3 concentration and its effect was also time dependent. Prior treatment with estradiol intensified the effects of AngII action on IP3 concentrations, in both the pituitary (increase) and hypothalamus (decrease). These results indicate that in the male rat anterior pituitary, AngII increases phosphatidiloinositol hydrolysis, leading to the increased production of the intracellular messenger, IP3. The decrease of IP3 concentration observed in the hypothalamus suggests a different site of AngII action in this region. We also suggest that estrogens can modulate AngII action in the brain.

Analysis of Variance↗
PubMedDate not supplied

The activity of protein tyrosine kinases of rat heart after ischemia and reperfusion.

BACKGROUND: Protein phosphorylation plays a very important role in the modulation of signal transduction in many tissues including heart. The activities of protein tyrosine kinases (PTKs) of the heart are rather low but PTKs in cardiac myocytes could be involved in many processes including necrosis, apoptosis, and inflammation. All of them lead to heart failure and are the result of such conditions as ischemia and reperfusion. The aim of our study was to investigate if the ischemia and reperfusion could change the protein tyrosine kinases activities in rat cardiac myocytes. MATERIAL AND METHODS: The specific activities of PTKs were defined as (3)2P incorporation into exogenous poly(Glu, Tyr)--known as an artificial substrate for all types of protein tyrosine kinases. RESULTS: The activity of tyrosine kinases in ischemic heart was lower than in control-intact heart and amounted to 50-60% of control values. In the heart after ischemia and following reperfusion the activities of PTKs increased to 135% of control. CONCLUSIONS: Ischemia and reperfusion changed activity of PTKs. There were no differences in protein tyrosine activity between the left and right ventricles.

Animals↗