Atilla Dikmen

Effects of vitamin E and sodium selenate on neurogenic and endothelial relaxation of corpus cavernosum in the diabetic mouse

We studied the effect of vitamin E and sodium selenate treatment on the neurogenic and endothelium-dependent relaxation of isolated corpus cavernosum obtained from streptozotocin-induced diabetic mice. Relaxant responses of corpus cavernosum precontracted by phenylephrine to electrical field stimulation and to acetylcholine were significantly decreased in diabetic mice. There was no significant difference between diabetic and non-diabetic groups for the relaxant response of corpus cavernosum to sodium nitroprusside and papaverine. Treatment with sodium selenate, but not vitamin E, partially prevented the impairment of the neurogenic relaxation, whereas both had a significant, partial restorative action on endothelial dysfunction in corpus cavernosum obtained from diabetic groups. Neither agent exhibited a significant action on the relaxant responses of corpus cavernosum obtained from non-diabetic mice. A decrease in the sensitivity of the neurogenic impairment to antioxidant action may develop more rapidly than that of endothelial dysfunction in streptozotocin-induced diabetic mice.

An in vitro study of nonadrenergic-noncholinergic activity on the cavernous tissue of mouse

The relaxant effects of electrical field stimulation (EFS) and exogenously applied acetylcholine (ACh) or acidified NaNO2 (a-NaNO2) were investigated in the isolated mouse corpus cavernosum precontracted with phenylephrine hydrochloride (PE). Tetrodotoxin (TTX) blocked the relaxant effects of EFS completely, whereas it had no effect on the responses to ACh or a-NaNO2. Guanethidine and indomethacin failed to affect the electrically or ACh-induced relaxations. Atropine completely blocked the effect of ACh; however, it caused a slight reduction in the relaxation evoked by EFS.NG- Nitro-l-arginine (l-NOARG) reduced the effects of EFS and ACh significantly, but it was ineffective on the relaxations induced by a-NaNO2. The inhibitory action ofl-NOARG was partly restored byl-arginine, but not byd-arginine. Methylene blue (MB) and hydroxocobalamin (HC) exhibited significant inhibition on the relaxations evoked by EFS, ACh and a-NaNO2. Hydroquinone (HQ) reduced relaxation due to a-NaNO2, but did not affect that of EFS and ACh. Our findings suggest that EFS-induced relaxations of mouse cavernosal tissue are mediated by a transmitter which probably resembles an organic nitrate.

Protective Effect of L-Arginine Intake on the Impaired Renal Vascular Responses in the Gentamicin-Treated Rats

The purpose of this study was to investigate the effect of gentamicin (100 mg/kg/day, i.p.) treatment on endothelium-dependent and -independent vasodilation in isolated perfused rat kidney, and the effect of amino acid L-arginine (in the drinking water, 2.25 g/l) on renal dysfunction induced by gentamicin. When gentamicin-treated groups were compared with the control group, it was observed that BUN and creatinine levels increased significantly. Also, the relaxant responses induced by acetylcholine, sodium nitroprusside and pinacidil decreased. Histopathological examination indicated acute tubular necrosis in this group. In animals treated with gentamicin together with L-arginine, there was a significant amelioration in the BUN and creatinine levels. The vasodilator responses were similar to those of the control group. Histopathological examination indicated only hydropic degeneration in tubular epithelium of kidney. Co-administration of L-NG-nitroarginine methyl ester (L-NAME) (112.5 mg/l), an inhibitor of nitric oxide synthase, and L-arginine to rats treated with gentamicin did not change the protective effect of L-arginine. In rats receiving L-NAME alone, the level of BUN and creatinine and vasodilation to acetylcholine were not significantly different when compared to those of the control group, while relaxant responses to sodium nitroprusside and pinacidil were increased. These results suggest that gentamicin leads to an impairment in vascular smooth muscle relaxation in addition to acute tubular necrosis in the rat kidney. Supplementation of L-arginine has an important protective effect on gentamicin-induced nephropathy.

A possible role of S-nitrosothiols at the nitrergic relaxations in the mouse corpus cavernosum

Relaxations induced by electrical field stimulation and acetylcholine were compared with those induced by acidified sodium nitrite, sodium nitroprusside, S-nitrosoglutathione and S-nitroso-N-acetyl-D,L-penicillamine in the mouse corpus cavernosum precontracted with phenylephrine. NG-nitro-L-arginine inhibited electrical field stimulation- or acetylcholine-induced relaxation, but was ineffective on relaxations caused by the other stimuli. Hydroquinone and pyrogallol had no inhibitory action on the relaxations caused by any stimulus except acidified sodium nitrite. Incubation of the tissue with diethyldithiocarbamic acid significantly inhibited the relaxations induced by all stimuli except papaverine. In the tissues pre-treated with diethyldithiocarbamic acid, superoxide dismutase, hydroquinone and pyrogallol failed to yield restore or further inhibit the relaxations in response to electrical field stimulation or acetylcholine. LY 83583 (6-anilino-5,8-quinolinedione) and hydroxocobalamin clearly inhibited the relaxant responses to electrical field stimulation, acetylcholine, S-nitrosoglutathione and acidified sodium nitrite whereas there was significant enhancement of the relaxation produced by S-nitroso-N-acetyl-D,L-penicillamine. These findings suggest that the relaxant factor released from non-adrenergic non-cholinergic nerves or endothelial cells in mouse cavernosal tissue may be a superoxide anion-resistant nitric oxide-containing molecule and that S-nitrosoglutathione rather than S-nitroso-N-acetyl-D,L-penicillamine could be a suitable candidate for this.

Effect of tempol (4‐hydroxy tempo) on gentamicin‐induced nephrotoxicity in rats

We investigated the effects of tempol (4‐hydroxy tempo), a membrane‐permeable radical scavenger, on gentamicin‐induced renal failure in rats. The rats were given gentamicin (100 mg/kg/day, i.p., once a day); and gentamicin (100 mg/kg/day, i.p.) and tempol (3.5, 7 or 14 mg/kg/day, i.p., once a day). At the end of 7 days, the gentamicin group produced the remarkable nephrotoxicity, characterized by a significantly decreased creatinine clearance and increased serum creatinine, blood urea nitrogen (BUN) and daily urine volume when compared with controls. In control the BUN value was 21.2 ± 0.07 (mg/100 mL); in comparison, it was 96.9 ± 6.03 in gentamicin group (P < 0.05). Renal histopathologic examination confirmed acute tubular necrosis in this group. In rats treated with gentamicin and tempol a partial improvement in biochemical and histologic parameters was observed. BUN values were 96.9 ± 6.03 and 36.3 ± 2.39 in gentamicin, and gentamicin plus tempol (14 mg/kg) treated groups, respectively (P < 0.05). These results suggest that the administration of tempol may have a protective effect on gentamicin‐induced nephrotoxicity in rats.

Effect of neocuproine, a selective Cu(I) chelator, on nitrergic relaxations in the mouse corpus cavernosum

The effects of neocuproine and bathocuproine, Cu(I) and Cu(II) chelators, respectively, were studied on relaxations in response to electrical field stimulation, acetylcholine, S-nitrosoglutathione, acidified sodium nitrite and sodium nitroprusside in the mouse corpus cavernosum precontracted with phenylephrine. Neocuproine significantly inhibited relaxations induced by electrical field stimulation, acetylcholine and S-nitrosoglutathione, but not by acidified sodium nitrite and sodium nitroprusside. The pre-prepared neocuproine-Cu(I) complex was ineffective on the responses. The discrepancy between the shape of relaxations in response to electrical field stimulation or to acetylcholine and S-nitrosoglutathione was abolished by adding CuCl(2) into the bathing medium. The copper action was blocked by neocuproine but not by bathocuproine. However, the pre-prepared bathocuproine-Cu(II) complex did not accelerate the relaxations affected by CuCl(2). These findings suggest that a Cu(I)-dependent mechanism may play a role in the relaxation induced by the endogenous relaxant factor as well as by S-nitrosoglutathione in mouse cavernosal tissue.

Restorative effects of zinc and selenium on nitrergic relaxations impaired by cadmium in the mouse corpus cavernosum.

We investigated whether Cd2+ intake (in drinking water, 15 ppm) for 30 days can affect the nitrergic relaxations of the mouse corpus cavernosum (CC) and whether Zn2+ (25 mg kg(-1) via a stomach tube at 48-h intervals) or sodium selenate (8 microg kg(-1) day(-1) intraperitoneally) has a restorative action on the impairment in the response. Relaxant responses of the CC obtained from Cd2+-treated mice to electrical field stimulation (neurogenic) or acetylcholine (endothelium dependent) were significantly inhibited. A partial restoration was observed in the nitrergic relaxation of the CC obtained from Zn2+- or sodium selenate-co-treated animals. Neither agent exhibited any significant action on the responses of the tissue from control mice. There was no significant difference between Cd2+-treated and control mice in respect of the relaxation amplitude induced by sodium nitroprusside or papaverine. These results suggest that Cd2+ intake may impair the nitrergic relaxation of the mouse CC, and, co-treatment with Zn2+ or sodium selenate may partially improve the nitrergic mechanisms in the tissue.

The influence of nitric oxide donors on the responses to nitrergic nerve stimulation in the mouse duodenum.

We investigated whether exogenous nitric oxide (NO) donors have a prejunctional and/or postjunctional inhibitory effect on the nitrergic responses and whether this inhibitory effect was mediated by NO itself and in part, by cyclic GMP in mouse duodenal strips. N(omega)-nitro-L-arginine inhibited relaxations induced by electrical field stimulation of nitrergic nerves, but not those with acidified NaNO2. Furthermore, 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ) inhibited both types of relaxations while 2-amino-5,6-dihydro-6-methyl-4H-1,3-thiazine (AMT) and N-ethylmaleimide were ineffective. NO donors, nitroglycerin and sodium nitroprusside, inhibited relaxations induced by nitrergic nerve stimulation, but not those with acidified NaNO2. Hemoglobin, exogenous Cu(2+)/Zn(2+) superoxide dismutase, diethyldithiocarbamic acid and pyrogallol did not influence the relaxation with nitrergic nerve stimulation. However, hemoglobin, diethyldithiocarbamic acid, pyrogallol and diethyldithiocarbamic acid plus pyrogallol attenuated the inhibitory effect of NO donors on relaxation with nitrergic nerve stimulation, and exogenous superoxide dismutase potentiated this inhibitory effect. Moreover, nitrergic nerve-mediated relaxations were inhibited by 8-bromo-cyclic GMP, but not by 8-bromo-cyclic AMP. These results suggest that exogenous NO donors have a prejunctional inhibitory effect on the nerve-mediated nitrergic relaxation and that the inhibitory effects of nitroglycerin and sodium nitroprusside are NO-dependent, but not related to NO metabolites such as peroxynitrite or a nitrosothiol intermediate. However, a contribution of S-nitrosothiol formed intracellularly cannot be entirely ruled out. Also, this prejunctional inhibition is mediated, at least in part, by the cyclic GMP, but not the cyclic AMP, pathway.

A possible effect of sulfhydryl reagents on the contractile activity of the rat detrusor muscle.

We aimed to investigate the effect of sulfhydryl (SH) inactivating agents, ethacrynic acid and N-ethylmaleimide, on the contractile activity of rat detrusor muscle. Wistar Kyoto rats weighing 150-250 g were anaesthetized with ketamine and bled to death. The urinary bladders were surgically removed and detrusor strips were mounted under 0.5 g tension in organ baths. The responses were recorded with isotonic transducers on polygraph paper. After an equilibrium period, the tissues were contracted by electrical field stimulation, acetylcholine, ethacrynic acid or N-ethylmaleimide and the effects of L-cysteine, glutathione, verapamil, Ca(2+)-free solution, sodium nitroprusside or atropine were then examined on these contractions. Verapamil, Ca(2+)-free solution or atropine significantly reduced the contractions elicited by electrical field stimulation and acetylcholine whereas L-cysteine, glutathione or sodium nitroprusside had no effect on the contractions in response to these stimuli. L-Cysteine, glutathione, verapamil or Ca(2+)-free solution significantly inhibited the contractions induced by ethacrynic acid or N-ethylmaleimide. Sodium nitroprusside slightly inhibited only the contraction induced by ethacrynic acid but not that with N-ethylmaleimide. Atropine has no action on the contractions in response to these SH reagents. These findings suggest that SH reagents may play a role in the contractile activity of rat detrusor muscle and this action seems to be related to the gating of Ca(2+) channels. Further experiments are needed to determine the cellular mechanism(s) of action by which these SH reagents act on the detrusor smooth muscle.

Effects of melatonin on impaired neurogenic and endothelial relaxations by bacterial lipopolysaccharide in the mouse corpus cavernosum.

We investigated whether bacterial lipopolysaccharide treatment causes any neuronal and vascular hyporeactivity in mouse cavernous tissue and also whether melatonin has any restorative effect on this possible neuronal and vascular hyporesponsiveness. Lipopolysaccharide treatment attenuated contractions in response to phenylephrine. Treatment with the inducible nitric oxide synthase inhibitor aminoguanidine or melatonin restored the hypocontractility of the cavernous smooth muscle to phenylephrine. Relaxant responses of corpus cavernosum precontracted by phenylephrine to acetylcholine or electrical field stimulation were significantly impaired in mice treated with bacterial lipopolysaccharide. Treatment with aminoguanidine or melatonin could prevent the impairment of the neuronal and endothelial relaxations. There was no significant difference between control and lipopolysaccharide-treated groups in the contractile response to high-dose KCl and in the relaxant response to papaverine. In conclusion, bacterial lipopolysaccharide treatment caused a neuronal and endothelial dysfunction in the mouse corpus cavernosum. A possible increased oxidative activity in the cavernous tissue may be a major reason for the impairment of relaxant responses and hypocontracility of tissue. The restorative effects of melatonin on this hyporeactivity may depend on its antioxidant properties and partly on its inhibitory action on the inducible nitric oxide synthase production.