Serdar Uma

Evidence of relaxant effect of omeprazole in rabbit corpus cavernosum in vitro

The present experiments were designed to investigate the effects of omeprazole, a H(+)-K+ ATPase inhibitor, on corporal smooth muscle tone in vitro. All spontaneous contractile activity in the corpus cavernosum was blocked following omeprazole (0.1 mM-1 mM) administration. However atropine (1 microM), Nw-nitro L-arginine methyl ester (L-NAME, 30 microM) or indomethacin (10 microM) did not affect the spontaneous contraction. Omeprazole (10 microM-1 mM) concentration-dependently induced relaxation in corporal smooth muscle precontracted with 10 microM phenylephrine or 80 mM KCl. Pretreatment of corporal tissue with L-NAME (30 microM), indomethacin (10 microM), ammonium chloride (7.5 mM), sodium acetate (7.5 mM), tetraethyl ammonium chloride (0.5 mM) or glibenclamide (1 microM) had no effect on the omeprazole induced relaxant responses. Nimodipine, an L-type Ca++ channel blocker, relaxed corporal strips precontracted with 80 mM KCl. Collectively, these results indicate that the inhibition of spontaneous contraction and the relaxation of precontracted corporal smooth muscle by omeprazole is probably mediated by the blockade of calcium channels. Further work is needed to determine the cellular mechanism(s) of action by which omeprazole acts on corpus cavernosum smooth muscle.

Omeprazole-induced relaxation in rat aorta is partly dependent on endothelium.

We investigated the effect of omeprazole (1 x 10(-5)-3 x 10(-4)M), an inhibitor of H(+),K(+)-ATPase, on rat aortic rings pre-contracted with phenylephrine (10(-6)M). Omeprazole relaxed the tissue in a concentration-dependent manner. Either removal of the endothelium or incubation with nitric oxide (NO) synthase inhibitor N(G)-nitro-L-arginine methyl ester (L-NAME, 3 x 10(-5)M) significantly attenuated the relaxations. Pre-treatment with L-arginine (10(-3)M), but not with D-arginine, reversed the inhibitory action of L-NAME. Indomethacin (10(-6)M) and tetraethylammonium (TEA, 10(-2)M) did not affect the relaxant responses to omeprazole indicating the lack of involvement of cyclooxygenase products and K(+) channels, respectively. These results suggest a role of NO in the mechanism of action of omeprazole.

Effects of Atorvastatin and L-Arginine Treatments on Electrical Field Stimulation-mediated Relaxations in Pulmonary Arterial Rings of Monocrotaline-Induced Pulmonary Hypertensive Rats

This study aimed to examine the effect of monocrotaline (MCT)-induced pulmonary hypertension on electrical field stimulation (EFS)-mediated relaxation in rings of rat main pulmonary artery and to see whether treatment with atorvastatin or l-arginine would prevent the action of MCT. Rats were killed 21 days after MCT injection (60 mg/kg), and the main pulmonary arteries were isolated. EFS (40 V, 0.2 milliseconds, 5 seconds, 10 Hz)-induced relaxations in vessels precontracted with phenylephrine (10−6 to 3 × 10−6 M) were abolished in MCT-injected group compared with control group. Treatment of MCT group with atorvastatin (10 mg/kg, orally) completely, whereas treatment with l-arginine (500 mg/kg, intraperitoneally) partially but significantly prevented the inhibition. Similarly, acetylcholine (10−9 to 3 × 10−5 M)-evoked relaxations that were markedly inhibited in MCT-group were also protected from inhibition after pretreatment with atorvastatin or l-arginine. Responses to endothelium-independent relaxants sodium nitroprusside (10−9 to 10−5 M), pinacidil (10−10 to 10−4 M), and papaverine (10−8 to 10−4 M) were unaltered in MCT-induced pulmonary hypertensive rats. The present findings suggest that MCT-induced pulmonary hypertension inhibits the EFS-mediated relaxation through suppression of endothelial NO production. Reversal of this inhibition by atorvastatin treatment presumably results from stimulation of endothelial nitric oxide synthase expression. Relatively weak protection elicited by l-arginine might be secondary to impaired endothelial nitric oxide synthase activity caused by MCT-induced pulmonary hypertension.

Does endothelium-derived hyperpolarizing factor play a role in endothelium-dependent component of electrical field stimulation-induced vasorelaxation of rat mesenteric arterial rings?

Electrical field stimulation (EFS)-induced, nonadrenergic, noncholinergic vasodilation was investigated in rat mesenteric arterial rings. Tetrodotoxin (10−6M), capsaicin (10−5M), or l-NAME (10−4M) failed to change the EFS-induced relaxations, whereas they were increased with indomethacin (10−5M). Removal of the endothelium caused approximately 20% reduction in the maximum response, whereas precontraction with 40 mM KCI abolished the relaxations at all frequencies. Iberiotoxin (3 × 10−7M) attenuated the relaxations in endothelium-intact tissues but blocked completely those in endothelium-denuded arteries. Combination of TRAM-34 (10−5M) with apamin (5 × 10−7M) and single administrations of NiCI2 (5 × 10−4M), ruthenium red (3 × 10−5M), and 18α-glycyrrhetinic acid (10−4M) significantly reduced the responses only in endothelium-intact tissues. These data indicate that in rat mesenteric arteries, EFS leads to vasodilation through both endothelium-dependent and endothelium-independent mechanisms. The major component of the relaxation is endothelium independent and seems to occur via BKCa channels, whereas endothelium-dependent component is likely to be mediated by endothelium-derived hyperpolarizing factor rather than nitric oxide, prostacyclin, or a neural substance. We propose that Ca2+ entry into endothelial cells via nonspecific cation channels in response to EFS induces hyperpolarization by activating endothelial IKCa and SKCa channels, which is spread to the smooth muscle via gap junctions to produce relaxation.

TWO NEW NITRIC OXIDE SYNTHASE INHIBITORS: PYRIDOXAL AMINOGUANIDINE AND 8-QUINOLINECARBOXYLIC HYDRAZIDE SELECTIVELY INHIBIT BASAL BUT NOT AGONIST-STIMULATED RELEASE OF NITRIC OXIDE IN RAT AORTA

Structural modification at one of the guanidine nitrogens of L-arginine has led to the development of a number of compounds N(G)-monomethyl-L-arginine (L-NMMA), N(G)-nitro-L-arginine (L-NOARG), N(G)-nitro-L-arginine methyl ester (L-NAME) that competitively inhibit nitric oxide synthase (NOS). It was reported that another chemically related compound known as a glycation inhibitor, aminoguanidine also inhibits NOS. Recently, two new glycation inhibitors, structurally related to aminoguanidine (AG), pyridoxal aminoguanidine (PLAG) and 8-quinoline carboxylic hydrazide (8Q) were synthesized. In this study, the effects of these two inhibitors on responses mediated by constitutive nitric oxide (NO) were investigated in vitro. For this purpose, in the present study vascular responses to phenylephrine and acetylcholine in isolated aortas were evaluated. Incubation (15 min) with PLAG and 8Q (10(-4)M for each) induced potentiation of phenylephrine-induced contraction in endothelium intact but not in endothelium denuded rings of rat aorta. The ability of PLAG or 8Q to augment phenylephrine-induced tone in endothelium containing rings was completely prevented by preincubation with L-arginine (1mM), but not with D-arginine. Both compounds (PLAG, 8Q) did not affect acetylcholine-induced relaxation. These results suggest that both of the new compounds produced a selective inhibition of basal but not agonist stimulated production of nitric oxide in rat aorta.

Electrical field stimulation (EFS)-induced relaxations turn into contractions upon removal of extracellular calcium in rat mesenteric artery.

In the present study, we aimed to examine the effect of blockade of L-type Ca(2+) channels (LTCC) and in addition the removal of extracellular Ca(2+), on EFS-induced relaxations in rings of rat mesenteric artery. EFS applied to the tissues precontracted with phenylephrine caused relaxations which were markedly inhibited by nifedipine (10(-7)M) and tetraethylammonium (TEA) (1mM). Addition of LTCC opener BAY K 8644 (10(-7)M) failed to enhance the relaxations. Upon removal of Ca(2+), EFS with the same stimulation parameters produced frequency-dependent transient contractions. Tetrodotoxin (10(-6)M), capsaicin (10(-5)M) and removal of endothelium did not alter these contractions suggesting that they were not neural in origin and endothelium-derived contracting factors were unlikely to be involved. However, they were increased by nearly 40% in response to BAY K 8644 (10(-7)M) and were inhibited by nifedipine (10(-7)M), indicating that activation of the LTCCs was essential. Inositol triphosphate (InsP3) receptor antagonist 2-APB (10(-4)M) significantly reduced, and high concentration of caffeine (20mM) almost totally suppressed the contractions. These results suggest that in the absence of extracellular Ca(2+) EFS through membrane depolarization, evokes the opening of the LTCCs which subsequently leads to the release of Ca(2+) from internal stores via InsP3 receptors, a phenomenon known as Ca(2+) channel-induced Ca(2+) release (CCICR), to trigger vasoconstriction. That activation of LTCCs causes arterial relaxation or contraction depending on the Ca(2+) status apparently exemplifies how the same messenger fulfils opposing physiological functions in a given cell.

Absence of desensitization to the relaxant activity of streptozotocin in isosorbide dinitrate‐tolerant rat aorta

Abstract— The effect of in‐vitro isosorbide dinitrate (ISDN)‐induced tolerance on the vasodilatory actions of streptozotocin, a nitric oxide containing compound, and papaverine was studied in rat aortic strips precontracted by phenylephrine. Aortas made tolerant to ISDN remained fully responsive to streptozotocin but exhibited a greater response to low concentrations of papaverine compared with control strips. Methylene blue produced parallel displacement to the right of the relaxant concentration‐effect curves of both ISDN and streptozotocin, whereas responses to only low concentrations of papaverine were significantly antagonized. These results indicate that the relaxant activity of streptozotocin is due to the stimulation of guanylate cyclase and impaired activity of this enzyme is not likely to be the operating mechanism for nitrate tolerance. It is also suggested that the vasodilating action of papaverine is partly dependent on the tissue cGMP level.

Lack of insulin results in reduced seladin-1 expression in primary cultured neurons and in cerebral cortex of STZ-induced diabetic rats.

Several studies demonstrated that Diabetes mellitus (DM) enhances the risk for Alzheimers disease (AD). Although hyperglycemia and perturbed function of insulin signaling have been proposed to contribute to AD pathogenesis, the molecular mechanisms behind this association is not clear yet. Seladin-1 is an enzyme catalyzing the last step in cholesterol biosynthesis converting desmosterol to cholesterol. The neuroprotective function of seladin-1 has gained interest in AD research recently. Seladin-1 has anti-apoptotic properties and regulates the expression of β-secretase (BACE-1). Here we measured seladin-1 mRNA and protein expressions in rat primary cultured neurons under diabetic conditions and also in the brains of rats with streptozotocine (STZ)-induced diabetes. We show that constant lack of insulin for 5days decreased seladin-1 levels in cultured rat primary neurons. Similarly, a decrease in seladin-1 was found in the brains of rats with STZ-induced diabetes. However, if the lack of insulin and/or high glucose treatment was intermittent, neuronal seladin-1 levels were not affected in vitro. On the other hand, treatment of neurons with metformin resulted in a significant increase in seladin-1. Constant lack of insulin for 5days, as well as high glucose treatment, increased the neuronal expression of BACE-1 in vitro, but not in the in vivo model. Our study defines insulin as a regulator of seladin-1 expression for the first time. The relevance of these findings for the association of DM with AD is discussed.

β-Adrenoceptor stimulating effects of phenylephrine and noradrenaline in the rat pulmonary vascular bed

Abstract— The effects of phenylephrine and noradrenaline have been investigated on the perfusion pressure of the rat isolated lung. Both drugs (0.3–30 μg) produced a dose‐dependent decrease in perfusion pressure elevated by 20 mM KCl, which was reversed to a dose‐dependent increase after addition of propranolol (1 × 10−7 M) to the perfusion fluid. Increments due to both agonists in the presence of propranolol were antagonized by prazosin (1 × 10−6 M). Propranolol, but not prazosin, elevated the basal perfusion pressure. The results indicate that phenylephrine and noradrenaline are more effective in stimulating β‐adrenoceptors than α‐adrenoceptors in the rat pulmonary vascular bed and that β‐adrenoceptors may regulate the vascular tone of the rat pulmonary circulation.

Insulin deprivation decreases insulin degrading enzyme levels in primary cultured cortical neurons and in the cerebral cortex of rats with streptozotocin-induced diabetes

BACKGROUND Many studies have indicated a relationship between diabetes and Alzheimers disease (AD). However, the molecular mechanism underlying this association has not been clarified. Among several factors, insulin degrading enzyme (IDE), which plays roles in the degradation of both insulin and amyloid β (Aβ), has gained interest as a potential target in efforts to solve this puzzle. This study sought to examine the effects of varying insulin and/or glucose concentrations on IDE expression. METHODS Experiments were performed on primary cultured rat neurons and cortices of rats with streptozotocin (STZ)-induced diabetes. IDE protein and mRNA expression levels were measured by western blot and RT-PCR, respectively. RESULTS In primary cultured cortical neurons, removal of insulin for 5days reduced the expression of IDE. A five-day treatment with a high concentration of glucose in insulin-free media reduced IDE levels, while a high concentration of glucose in the presence of insulin had no effect. In groups treated with glucose or insulin intermittently, the reduction in IDE levels was observed only in neurons exposed to high glucose together with no insulin for 5days. Shorter incubation periods (48h), either continuously or intermittently, did not affect IDE levels. IDE expression in the cortex of rats with STZ-induced diabetes was found to be decreased. CONCLUSION Our data suggest that insulin deprivation, rather than high glucose, is a significant determinant of IDE regulation. As evidence indicates potential roles for IDE in diabetes and AD, understanding the mechanisms regulating IDE expression may be important in developing new treatment strategies.