Selim Kutlu

Inhibitory effects of melatonin on neural lipid peroxidation induced by intracerebroventricularly administered homocysteine

Abstract: Melatonin, the main secretory product of the pineal gland, has been shown to be potentially effective in prevention of numerous types of neurodegenerative disorders in which free radical processes are involved. Homocysteine (Hcy), an independent risk factor for atherosclerosis, undergoes auto‐oxidation and generates reactive oxygen species. The purpose of this study was to test whether intracerebroventricular (ICV) injection of Hcy leads to neural lipid peroxidation and also to investigate the protective effects of melatonin on the brain tissue from oxidative stress of Hcy. Adult male Wistar rats under anaesthesia were injected ICV with Hcy at a dose of 143 μg/kg. Melatonin was administered intraperitoneally to a group of rats for three consecutive days before Hcy injection. The rats were decapitated and brain tissues were removed and hippocampus, cortex and cerebellum were dissected. There was a significant development of oxidative stress as indicated by an increase in malondialdehyde in hippocampus, cortex and cerebellum of rats injected with Hcy, whereas melatonin prevented the elevation of lipid peroxidation. Furthermore, melatonin significantly increased glutathione levels and glutathione peroxidase activity in all brain regions. The present study demonstrates that Hcy, in high levels, may be a causal factor in generation of free radicals in the brain and it may be one of the mechanisms which cause neurodegeneration in elderly people. It also shows that melatonin could potentially be beneficial in prevention of neurodegeneration caused by hyperhomocysteinemia.

Effects of pinealectomy and exogenous melatonin on serum leptin levels in male rat

The effects of pinealectomy and exogenous melatonin (N-acetyl-5-methoxytryptamine) on serum leptin levels were investigated in rats. Exogenous administration of melatonin to intact rats resulted in significant decreases in serum leptin levels (P < 0.05) compared to those of the intact control group. Serum leptin levels were significantly elevated in the pinealectomised rats in comparison to the sham-pinealectomised animals (P < 0.001) and were significantly suppressed by exogenous administration of melatonin compared to those of non-treated pinealectomised rats (P < 0.001). Hormone concentrations in the melatonin-treated pinealectomised group were found to be similar to those seen in the sham-pinealectomised group. These results suggest that pineal gland has an effect on leptin release.

Effects of raloxifene, hormone therapy, and soy isoflavone on serum high-sensitive C-reactive protein in postmenopausal women

Objective: To compare the effects of raloxifene, estradiol valerate plus dienogest, and soy isoflavones (genistein) on serum concentrations of high‐sensitive C‐reactive protein in healthy postmenopausal women. Methods: The 80 healthy postmenopausal women enrolled in the study were randomly allocated to receive 60 mg of raloxifene, 2 mg of estradiol valerate plus dienogest, 40 mg of genistein, or placebo (n = 20 in each group). Blood samples were collected at the start of the study and at 3 and 6 months. Lipid profile was also determined. Results: Only the group receiving estradiol valerate plus dienogest showed an increase in serum levels of high‐sensitive C‐reactive protein compared with baseline values and values in the control and other groups. All 3 treatments resulted in an increase in high‐density lipoprotein cholesterol levels and a decrease in total, low‐density, and very‐low‐density lipoprotein cholesterol levels. Conclusions: Estradiol valerate plus dienogest, but not raloxifene and genistein, increase serum high‐sensitive C‐reactive protein levels. All 3 treatments, however, have an estrogen‐like effect on serum lipid profile.

INFLUENCE OF CHRONIC MORPHINE EXPOSURE ON SERUM LH, FSH, TESTOSTERONE LEVELS, AND BODY AND TESTICULAR WEIGHTS IN THE DEVELOPING MALE RAT

Opiate abuse has been a matter of serious concern in male adolescents. This study investigates the effects of chronic morphine administration on serum luteinizing hormone (LH), follicle-stimulating hormone (FSH), testosterone levels, testicular histology, and body and testes weight in developing male rats. Animals were subcutaneously injected with morphine (5 mg/kg) or saline (1 mL/kg) twice daily for 30 days. Body weight determinations and injections were carried out under light ether anesthesia. At the end of the experiments, the rats were decapitated and blood samples were collected. Serum levels of LH and FSH were measured. Chronic morphine administration significantly decreased decreased serum testosterone (p < .02) and LH (p < .01) levels, but not FSH release compared to controls. Morphine exposure reduced body weight (p < .01), but had no significant effect on the testicular weight. When the testicular tissue was histologically examined, structural features of the seminiferous tubules and Leydig cells were similar in both saline and morphine-treated animals. The results suggest that opiates affect testosterone release through the hypothalamo-hypophyseal-gonadal axis rather than by a local testicular mechanism. Chronic morphine exposure during sexual maturation may have long-term endocrine disturbances in male rats.

Antinociceptive efficacy of levetiracetam in a mice model for painful diabetic neuropathy.

Background and Objective: Despite important advances in available knowledge, management of neuropathic pain remains incomplete, and results from experimental and clinical studies indicate that some anticonvulsants show promise for treating neuropathic pain. The aim of this study was to assess the antinociceptive efficacy of levetiracetam (LEV, ucb L059) in a mice model for painful diabetic neuropathy using the in vivo nociceptive behavioral ‘hot‐plate test.’

Mu opioid modulation of oxytocin secretion in late pregnant and parturient rats: Involvement of noradrenergic neurotransmission

We have investigated effects of µ- and ĸ-opioid agonists and antagonists on plasma oxytocin levels and noradrenaline content in the supraoptic nucleus (SON) and paraventricular nucleus (PVN) of 20-day pregnant rats. β-Endorphin, oxytocin, estrogen and progesterone profiles in late pregnant and parturient rats were also sought. Stage of estrous cycle was monitored by vaginal smear, and pro-estrous animals were left overnight with male. In the first set of experiments, pregnant rats were monitored and decapitated on days 20 and 21 and after the delivery of second pup. In the second set, 20-day pregnant rats were intracerebroventricularly infused with morphine (50 µg/10 µl), U50,488H (ĸ-agonist; 50 µg/10 µl), clocinnamox (µ-antagonist; 50 µg/10 µl) and norbinaltorphimine (ĸ-antagonist; 50 µg/10 µl). Controls received saline alone. Serum estrogen and progesterone levels were measured by enzyme immunoassay, and plasma oxytocin and β-endorphin by radioimmunoassay. Noradrenaline and its metabolite (3,4-dihydroxyphenylglycol) were determined in micropunched hypothalamic nuclei by HPLC-ECD. In parturient rats, oxytocin levels were increased (p < 0.05) and β-endorphin decreased (p < 0.01) compared to 20-day pregnant animals. Serum progesterone concentrations progressively declined towards parturition (p < 0.001). Clocinnamox raised oxytocin levels (p < 0.01) while U50,488H caused decreases (p < 0.05). Noradrenaline content was elevated by clocinnamox in the SON (p < 0.01) and PVN (p < 0.05) compared to control values. Other agonists and antagonists had no significant effect on the noradrenergic neurotransmission or oxytocin secretion. We suggest that noradrenaline may mediate the inhibitory effects of µ-opioids on oxytocin release. Our findings have also shown that ĸ-opioid receptors are not involved in modulation of oxytocin neurons in late pregnant rats.

Leptin modulates noradrenaline release in the paraventricular nucleus and plasma oxytocin levels in female rats: a microdialysis study.

The neural control and mutual interrelationships among individual factors involved in the regulation of food intake and simultaneously related to reproduction are far from being understood. We have suggested that at least some of the effects of orexigenic and anorexigenic peptides might be mediated via noradrenaline release in the paraventricular nucleus (PVN). The main hypothesis was that leptin has an inhibitory action on oxytocin secretion and hypothalamic release of noradrenaline. Non-pregnant female rats in their diestrus were subjected to cannulation of the carotid artery and a microdialysis procedure with the probes in the hypothalamic PVN. Intra-arterial administration of cholecystokinin-8 (CCK) at the dose of 50 mg/kg was used to induce oxytocin and noradrenaline release. Leptin (10 mg/5 ml) was intracerebroventricularly injected in addition to CCK. Blood and microdialysis samples were collected at 20-min intervals for 80 min. Central administration of leptin significantly reduced both plasma oxytocin and hypothalamic noradrenaline responses to CCK at 20 min following the treatments. In conclusion, leptin may inhibit oxytocin secretion by lowering noradrenergic neurotransmission in the PVN. The modulator effect of leptin on noradrenaline release in the PVN may be related to feeding behavior.

Effects of levobupivacaine and bupivacaine on intracellular calcium signaling in cultured rat dorsal root ganglion neurons

Bupivacaine and levobupivacaine have been shown to be effective in the treatment of pain as local anesthetics, although the mechanisms mediating their antinociceptive actions are still not well understood. The aim of this study was to investigate the effects of bupivacaine and levobupivacaine on intracellular calcium ([Ca2+]i) signaling in cultured rat dorsal root ganglion (DRG) neurons. DRG neuronal cultures loaded with 5 μM Fura-2/AM and [Ca2+]i transients for stimulation with 30 mM KCl (Hi K+) were assessed by using fluorescent ratiometry. DRGs were excited at 340 and 380 nm, emission was recorded at 510 nm, and responses were determined from the change in the 340/380 ratio (basal-peak) for individual DRG neurons. Data were analyzed by using Student’s t-test. Levobupivacaine and bupivacaine attenuated the KCl-evoked [Ca2+]i transients in a reversible manner. [Ca2+]i increase evoked by Hi K+ was significantly reduced to 99.9 ± 5.1% (n = 18) and 62.5 ± 4.2% (n = 15, P < 0.05) after the application of 5 and 50 µM levobupivacaine, respectively. Bupivacaine also inhibited Hi K+-induced [Ca2+]i responses, reduced to 98.7 ± 4.8% (n = 10) and 69.5 ± 4.5% (n = 9, P < 0.05) inhibition of fluorescence ratio values of Hi K+-induced responses at 5 and 50 μM, respectively. Our results indicate that bupivacaine and levobupivacaine, with no significant differences between both agents, attenuated KCl-evoked calcium transients in a reversible manner. The inhibition of calcium signals in DRG neurons by levobupivacaine and bupivacaine might contribute to the antinociceptive effects of these local anesthetics.

Effects of letrozole on bone biomarkers and femur fracture in female rats.

We aimed to investigate the effects of the aromatase inhibitor letrozole on femur fracture and serum levels of alkaline phosphatase (ALP), calcium and phosphate in female rats. Intact 32 Sprague-Dawley female rats were divided into four groups (n=8): control, letrozole 0.2 , letrozole 1 (treatment of 0.2 and 1 mg/kg for six weeks) and recovery (letrozole-treated 1 mg/kg for six weeks then allowed to recover for two weeks). Besides, 24 ovariectomized rats were divided into three groups (n=8): ovariectomized+control, ovariectomized+letrozole and ovariectomized+letrozole+ estradiol (10 μg/rat). After experimental period, rats’ femur bones were removed for biomechanical studies following decapitation. Serum ALP, calcium and phosphate were measured. Biomechanical values, ALP and phosphate significantly increased by letrozole in a dose-dependent manner (p<0.05) while calcium levels and net bone area decreased (p<0.05). Ultimate strength was positively correlated with ALP and phosphate and negatively correlated with calcium. The results indicate that letrozole may increase risk of bone fracture and affect bone biomarkers such as ALP, calcium and phosphate in both intact and ovariectomized rats.

Combined Use of Melatonin and Terazosin Restores Bladder Contractility in Rabbits With Partial Outlet Obstruction

OBJECTIVES To investigate the effects of terazosin and melatonin on isolated rabbit bladder strips after partial bladder outlet obstruction and determine responses to agonist-induced contractility and changes in oxidant-antioxidant system. METHODS We created partial bladder outlet obstruction in 5 groups of rabbits, each containing 8. Rabbits with sham operation (group 1) received no drug treatment. Similarly, animals in group 2 underwent partial bladder outlet obstruction and received no drug treatment. Rabbits in groups 3 were administered 5 mg/day oral terazosin, and rabbits in group 4 received 10 mg/kg/day melatonin intraperitoneally. Animals in group 5 received both terazosin and melatonin. We removed their bladders and performed histopathological and biochemical measurements. We assessed tissue malondialdehyde and antioxidant enzyme activity levels and recorded in vitro contractility response to KCl in isolated organ baths. RESULTS The thickness of muscularis propria was significantly increased in group 2 compared with all other groups. KCl-evoked contractions after partial outlet obstruction were significantly impaired in group 3 and 4 animals receiving terazosin and melatonin, respectively. However, combined use of melatonin and terazosin in group 5 showed contractility responses similar to sham-operated animals (P <0.05). Melatonin administration to groups 4 and 5 showed decreased levels of lipid peroxidation. Similarly, animals receiving melatonin and melatonin plus terazosin showed statistically significant increase in antioxidant enzyme activities. CONCLUSIONS In the present study, we showed that oxidative stress induced by partial bladder outlet obstruction can be successfully antagonized by the potent antioxidant melatonin, and its combined use with an alpha-antagonist such as terazosin may restore in vitro contractility.