Modulation of Melatonin Receptors Regulates Reproductive Physiology: The Impact of Agomelatine on the Estrus Cycle, Gestation, Offspring, and Uterine Contractions in Rats.

Agomelatine is a pharmaceutical compound that functions as an agonist for melatonin receptors, with a particular affinity for the MT1 and MT2 receptor subtypes. Its mode of action is integral to the regulation of diverse physiological processes, encompassing the orchestration of circadian rhythms, sleep-wake cycles, and mood modulation. In the present study, we delve into the intricate interplay between agomelatine and the modulation of estrus cycles, gestation periods, offspring numbers, and uterine contractions, shedding light on their collective impact on reproductive physiology. Both in vivo and in vitro experiments were performed. Wistar Albino rats, divided into four groups: two non-pregnant groups (D1 and D2) and two pregnant groups (G1 and G2). The D1 and G1 groups served as control groups, while the D2 and G2 groups received chronic agomelatine administration (10 mg/kg). Uterine contractions were assessed in vitro using myometrial strips. Luzindole, a melatonin receptor antagonist, was employed to investigate the pathway mediating agomelatine's effects on uterine contractions. In in vivo studies, chronic agomelatine administration extended the diestrus phase (p<0.05) in non-pregnant rats, prolonged the gestational period (p<0.01), and increased the fetal count (p<0.01) in pregnant rats. Additionally, agomelatine reduced plasma oxytocin and prostoglandin-E levels (p<0.01) during pregnancy. In vitro experiments showed that agomelatine dose-dependently inhibited spontaneous and oxytocin-induced myometrial contractions. Luzindole (2 µM) reverse the agomelatine-induced inhibition of myometrial contractions. These findings suggest that agomelatine holds the potential to modulate diverse reproductive parameters during the gestational period, influencing estrus cycling, gestational progression, offspring development, and the orchestration of uterine contractions.

Effects of treadmill exercise on sexual behavior and reproductive parameters in chronically stressed-male rats.

Exposure to chronic stress stimulates the hypothalamic-pituitary-adrenal (HPA) axis and then simultaneously inhibits hypothalamic-pituitary-gonadal axis (HPG) axis activity. The inhibition formed by the HPA axis is the main mechanism of action of stress on reproductive function. HPG axis activity is known to be changed by various factors, including exercise. Exercise has been found to have a number of positive effects on sexual behavior, reproductive hormones, and sperm parameters in studies with animal models for many years. The main aim of this study is to investigate the effects of chronic treadmill exercise on chronically stressed-male rats' sexual behavior, reproductive hormones, and sperm parameters. A total of 40 sexually adult male rats were randomly and equally divided into four groups as control, stress, exercise, and stress+exercise. Animals in the exercise group were subjected to the chronic treadmill exercise (moderate intensity) for 33 days with a periodic increase in speed and duration. Animals in the stress group were exposed to restraint stress for 1 h, 2 h, and 3 h during the first, second and third 15 days respectively. Sexual behavior parameters, hormone measurements, and sperm parameters were evaluated. The main effects of chronic exercise on sexual behavior were centered on a significant increase in the ejaculation frequency (EF) in the stress+exercise group. Also, sperm concentration and motility in the stress group significantly decreased, and then sperm motility was improved by exercise in the stress+exercise group. In sum, our results show that chronic treadmill exercise may improve the adverse effects of chronic stress on sexual behavior and sperm parameters in male rats in terms of some parameters.

Orexins activates protein kinase C-mediated Ca(2+) signaling in isolated rat primary sensory neurons.

Previous results have suggested that orexins causes a rise of intracellular free calcium ([Ca(2+)](i)) in cultured rat dorsal root ganglion (DRG) neurons, implicating a role in nociception, but the underlying mechanism is unknown. Hence, the aim of the present study was to investigate whether the orexins-mediated signaling involves the PKC pathways in these sensory neurons. Cultured DRG neurons were loaded with 1 micromol Fura-2 AM and [Ca(2+)](i) responses were quantified by the changes in 340/380 ratio using fluorescence imaging system. The orexin-1 receptor antagonist SB-334867-A (1 microM) inhibited the calcium responses to orexin-A and orexin-B (59.1+/-5.1 % vs. 200 nM orexin-A, n=8, and 67+/-3.8 % vs. 200 nM orexin-B, n=12, respectively). The PKC inhibitor chelerythrine (10 and 100 microM) significantly decreased the orexin-A (200 nM)-induced [Ca(2+)](i) increase (59.4+/-4.8 % P<0.01, n=10 and 4.9+/-1.6 %, P<0.01, n=9) versus response to orexin-A). It was also found that chelerythrine dose-dependently inhibited the [Ca(2+)](i) response to 200 nM orexin-B. In conclusion, our results suggest that orexins activate intracellular calcium signaling in cultured rat sensory neurons through PKC-dependent pathway, which may have important implications for nociceptive modulation and pain.

Effects of different weight loss protocols on serum leptin levels in obese females.

We investigated the effects of different weight loss protocols on leptin levels in obese females with the aim of addressing the leptin resistance which has been found to be an aggravating factor in obesity. Twenty-four obese females enrolled to one of three 12-week weight loss protocols: orlistat-induced weight loss (OWL, n=8), exercise-induced weight loss (EWL, n=8) and orlistat plus exercise-induced weight loss (OEWL, n=8). Serum leptin levels were measured in duplicate by radioimmunoassay. There were significant reductions (P<0.01) in body weight and fat mass after the 12 week period in all groups: -11.4+/-0.5 kg and -9.8+/-0.5 kg (OEWL), -8.3+/-0.8 kg and -5.7+/-0.9 kg (OWL), -8.9+/-1.2 kg and -7.4+/-1.2 kg (EWL), respectively. Serum leptin levels were also decreased markedly in all groups: -59.2 % (OEWL1), -37.8 % (OWL) and -48.6 % (EWL) (P<0.01 all). In addition, there were marked decreases in leptin levels for each kilogram of fat mass after the 12 week period: -48.2+/-7.2 % (OEWL), -27.8+/-4.8 % (OWL) and -39.3+/-4.3 % (EWL) (P<0.01 all). Decreases in serum leptin levels expressed per kilogram of fat mass were significantly higher in the OEWL group compared to the OWL group (P=0.03). Consequently, an exercise training program in adjunct to pharmacotherapy provides higher weight reduction and fat mass loss in obesity treatment. It also seems to have further beneficial effects on leptin resistance, as indicated by decreases in leptin levels expressed per kilogram of fat mass.

Pinealectomy aggravates and melatonin administration attenuates brain damage in focal ischemia.

Large infarcts develop in pinealectomized rats subjected to middle cerebral artery occlusion, which was attributed to loss of antioxidant action of melatonin. However, melatonin also has vascular actions, and pinealectomy may induce hypertension. The authors investigated (1) whether hemodynamic factors contribute to infarct development in pinealectomized rats, (2) whether melatonin administration can reverse the unfavorable effect of pinealectomy on infarct formation, and (3) whether melatonin can reduce the infarct volume in nonpinealectomized rats subjected to focal transient ischemia (2 hours middle cerebral artery occlusion, 22 hours reperfusion). Rats were pinealectomized 3 months before ischemia to eliminate any possible action of pinealectomy-induced hypertension on stroke. Blood pressure and regional CBF values during ischemia and reperfusion were not significantly different between pinealectomized and sham-operated rats, suggesting that pinealectomy-induced increase in infarct was not related to hemodynamic factors. The infarct volume resumed to the level of sham-operated rats on melatonin administration. Injection of melatonin (4 mg/kg) before both ischemia and reperfusion reduced infarct volume by 40% and significantly improved neurologic deficit scores in pinealectomized as well as sham-operated rats subjected to middle cerebral artery occlusion. These data suggest that physiologic melatonin release as well as exogenously given melatonin has a neuroprotective action in focal cerebral ischemia.

The influence of reproductive status on vasopressin release in the rat.

It has been shown that surgical ovariectomy of the rat results in a fall in plasma vasopressin concentrations suggesting that ovarian steroids may influence hormone release. To determine whether a similar fall is found on suppression of the oestrous cycle, vasopressin concentrations were monitored after treatment with the antioestrogen preparation tamoxifen or a long-acting analogue of LH-releasing hormone (LHRH) which suppresses ovarian function. Treatment with either agent was found to result in a fall in circulating vasopressin concentrations, with little effect on fluid balance. To determine whether the ovary could influence the vasopressin release in response to known stimuli, hormone concentrations were measured in ovariectomized animals during extracellular fluid hypertonicity produced by an i.p. injection of hypertonic saline and hypovolaemia produced by an i.p. injection of polyethylene glycol. It was found that after ovariectomy or treatment with tamoxifen, the response to hypertonicity was unaffected but that to hypovolaemia was attenuated. Treatment with LHRH affected the response to both hypovolaemia and hypertonicity.

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.

Melatonin inhibits high voltage activated calcium currents in cultured rat dorsal root ganglion neurones.

The actions of melatonin on high-voltage activated calcium channels (HVACC) and intracellular free Ca(2+) concentration in cultured dorsal root ganglion (DRG) neurones from neonatal rats were investigated using the whole-cell patch clamp and the fura-2 fluorescence ratio Ca(2+)-imaging techniques. HVACC were pharmacologically and biophysically isolated and the effects of melatonin were investigated. Extracellular application of melatonin inhibited HVACC in a dose dependent manner. In calcium imaging experiments, application of extracellular recording medium containing 30 mM KCl evoked increases in intracellular free Ca(2+) that were dependent upon external Ca(2+) ions. This increase was prevented by both low (10 microM) and high dose (100 microM) of melatonin pre-treatment. The results of this study indicate that the pineal hormone melatonin has inhibitory actions on voltage dependent calcium entry in cultured rat DRG neurones.

Effects of acute hypoxia on the determination of anaerobic threshold using the heart rate-work rate relationships during incremental exercise tests.

Anaerobic threshold which describes the onset of systematic increase in blood lactate concentration is a widely used concept in clinical and sports medicine. A deflection point between heart rate-work rate has been introduced to determine the anaerobic threshold non-invasively. However, some researchers have consistently reported a heart rate deflection at higher work rates, while others have not. The present study was designed to investigate whether the heart rate deflection point accurately predicts the anaerobic threshold under the condition of acute hypoxia. Eight untrained males performed two incremental exercise tests using an electromagnetically braked cycle ergometer: one breathing room air and one breathing 12 % O2. The anaerobic threshold was estimated using the V-slope method and determined from the increase in blood lactate and the decrease in standard bicarbonate concentration. This threshold was also estimated by in the heart rate-work rate relationship. Not all subjects exhibited a heart rate deflection. Only two subjects in the control and four subjects in the hypoxia groups showed a heart rate deflection. Additionally, the heart rate deflection point overestimated the anaerobic threshold. In conclusion, the heart rate deflection point was not an accurate predictor of anaerobic threshold and acute hypoxia did not systematically affect the heart rate-work rate relationships.

Effects of acute hypoxia on the estimation of lactate threshold from ventilatory gas exchange indices during an incremental exercise test.

The purpose of this study was to investigate the validity of non-invasive lactate threshold estimation using ventilatory and pulmonary gas exchange indices under condition of acute hypoxia. Seven untrained males (21.4+/-1.2 years) performed two incremental exercise tests using an electromagnetically braked cycle ergometer: one breathing room air and other breathing 12 % O2. The lactate threshold was estimated using the following parameters: increase of ventilatory equivalent for O2 (VE/VO2) without increase of ventilatory equivalent for CO2 (VE/VCO2). It was also determined from the increase in blood lactate and decrease in standard bicarbonate. The VE/VO2 and lactate increase methods yielded the respective values for lactate threshold: 1.91+/-0.10 l/min (for the VE/VO2) vs. 1.89+/-0.1 l/min (for the lactate). However, in hypoxic condition, VE/VO2 started to increase prior to the actual threshold as determined from blood lactate response: 1.67+/-0.1 l/min (for the lactate) vs. 1.37+/-0.09 l/min (for the VE/VO2) (P=0.0001), i.e. resulted in pseudo-threshold behavior. In conclusion, the ventilatory and gas exchange indices provide an accurate lactate threshold. Although the potential for pseudo-threshold behavior of the standard ventilatory and gas exchange indices of the lactate threshold must be concerned if an incremental test is performed under hypoxic conditions in which carotid body chemosensitivity is increased.

The inhibitory effects of dantrolene on action potential-induced calcium transients in cultured rat dorsal root ganglion neurons.

We investigated the actions of dantrolene Ca(2+)-induced on Ca(2+)-release (CICR) evoked by action potentials in cultured rat sensory neurons. The effect of dantrolene on action potential after-depolarization and voltage-activated calcium currents was studied in cultured neonatal rat dorsal root ganglion cells (DRG) using the whole-cell patch-clamp technique. Depolarizing current injection evoked action potentials and depolarizing after-potentials, which are activated as a result of CICR following a single action potential in some cells. The type of after-potentials was determined by inducing action potentials from the resting membrane potential. Extracellular application of dantrolene (10 microM) abolished after-depolarizations without affecting action potential properties. Furthermore, dantrolene significantly reduced repetitive action potentials after depolarizing current injection into these neurons, but had no significant effect on the steady-state current voltage relationship of calcium currents in these neurons. We conclude that dantrolene inhibits the induction of action potential after depolarizations by inhibiting CICR in cultured rat sensory neurons.

Effects of body mass index on maximal work production capacity and aerobic fitness during incremental exercise.

The aim of this study was to investigate the relationship between cardiopulmonary fitness as indicated by maximal work rate (Wmax) production and aerobic capacities (WAT), body mass index (BMI) and heart rate reserve. A total of 60 sedentary subjects (30 males, 30 females, aged 18-25 years) were enrolled in the study. Each subject performed an incremental exercise test (15 W/min) to the limit of tolerance on an electromagnetically-braked cycle ergometer. There was a negative correlation between increased BMI to Wmax capacity per kilogram body weight in male (r=-0.846, P=0.0001) and in female (r=-0.896, P=0.0001) subjects. In addition, W(AT) for each kilogram body weight also negatively correlated with increased BMI in male (r=-0.870, P=0.0001) and in females (r=-0.807, P=0.0001). The heart rate reserve correlated negatively with increasing BMI: r=-0.699, P=0.0001 (males) and r=-0.655, P=0.0001 (females). The results of the present study have suggested that, due to the inverse correlation between BMI, Wmax capacity, aerobic fitness and heart rate reserve, it may be useful to consider BMI in establishing cardiopulmonary fitness in various subjects.

Pinealectomy increases and exogenous melatonin decreases leptin production in rat anterior pituitary cells: an immunohistochemical study.

Melatonin, the main hormone of the pineal gland, informs the body about the environmental light and darkness regimen, which in turn contributes to the photoperiodic adaptation of several physiological functions. Leptin, the hormone secreted mainly by adipocytes and some other tissues including the pituitary, informs the brain about the mass of adipose tissue, which plays an important role in energy homeostasis. Melatonin has been shown to decrease circulating leptin levels. It is currently not known whether melatonin has an effect on leptin synthesis in the pituitary. The aim of this study was to immunohistochemically examine the effects of pinealectomy and administration of melatonin on leptin production in the rat anterior pituitary. The pituitary samples obtained from 18 male Wistar rats including sham-pinealectomized, pinealectomized and melatonin-injected pinealectomized groups were immunohistochemically evaluated. Immunostaining of leptin was moderate (3+) in sham-pinealectomized rats, heavy (5+) in pinealectomized rats and low (1+) in melatonin-treated pinealectomized rats, respectively. The present results indicate that pinealectomy induces leptin secretion in anterior pituitary cells, and this increase of leptin synthesis can be prevented by administration of melatonin. Thus, melatonin seems to have both physiological and pharmacological effects on leptin production in the anterior pituitary of male rats.

Melatonin inhibits spontaneous and oxytocin-induced contractions of rat myometrium in vitro.

OBJECTIVE: The aim of this study was to investigate the effects of melatonin on spontaneous and oxytocin-induced contractility of pregnant and non-pregnant rat myometrium in vitro. DESIGN: Myometrial strips were removed from virgin or late pregnant (21 days gestation) Wistar rats following decapitation and placed in an organ bath containing Krebs' solution at 37 degrees C and pH 7.4, constantly bubbled with 95% oxygen-5% carbon dioxide and isometric contractions were recorded. Effects of cumulative concentrations of melatonin (0.1 to 10 microM) on spontaneous and oxytocin-induced contractions were studied. Possible involvement of Ca(2+)-activated K (+) channels in inhibitory actions of melatonin was investigated by using apamin (100 nM). RESULTS: Melatonin inhibited spontaneous and oxytocin-induced contractions of myometrium from both virgin and late pregnant rats in a dose-dependent manner. After inhibition of oxytocin-induced contractions by melatonin, application of prostaglandin F (2alpha) (1 microM) but not high KCl (30 mM) containing solution initiated contractile activity. Inhibitory response induced by melatonin (13 microM) was not affected by apamin (100 nM). CONCLUSIONS: Data from this study demonstrates that melatonin inhibits spontaneous and oxytocin-induced contractions of myometrium from pregnant and non-pregnant rats. Although the exact mechanism is not clear, melatonin-induced inhibition of myometrial contractions may results from its interactions with Ca(2+) channels.

Effects of pinealectomy on the circadian release pattern of leptin in male rat.

OBJECTIVES: Exogenous and endogenous melatonin decrease leptin release. It is not known whether melatonin also has an effect on circadian release pattern of leptin. So, this study was planned to investigate the possible changes in the circadian release of leptin following pinealectomy. METHODS: A group of rats were surgically pinealectomized while some others were exposed to sham operation. The animals were decapitated at 13.30 p.m. and 01.30 a.m. Serum leptin levels were measured by radioimmunoassay. RESULTS: Serum leptin levels at 13.30 p.m. were lower than the values at 01.30 a.m. in both pinealectomized (P<0.002) and sham rats P<0.001). Serum leptin levels measured at 13.30 p.m. and 01.30 a.m. were significantly elevated (P<0.05 and P<0.01, respectively) in the pinealectomized rats in comparison to sham animals. CONCLUSION: The circadian release of leptin does not seem to be regulated by melatonin release from the pineal gland whereas melatonin, physiologically released, may have a decreasing effect on leptin release.

Effects of eight weeks of exercise training and orlistat therapy on body composition and maximal exercise capacity in obese females.

A comparative assessment was made of the short-term effects of orlistat therapy and exercise training on body composition and aerobic fitness in obese females. A total of 24 obese patients were enrolled in to the study; 12 received orlistat therapy (DO) and 12 participated in a regular aerobic exercise-training programme (DE). All patients were on hypocaloric diets. Each patient performed three incremental ramp exercise tests (one at Week 0, one at the end of Week 4 and one at the end of Week 8) to exhaustion using an electromagnetically braked cycle ergometer to determine their anaerobic threshold and maximal exercise (Wmax) capacity. Patients in the DE group performed continuous exercise at a work rate that corresponded to the anaerobic threshold. Weight loss and loss of fat mass after 8 weeks were -6.4% (P=0.002) and -13.4% (DE) vs -5.8% (P=0.002) and -6.4% (P=0.008) (DO), respectively. Wmax capacity was 90.8+/-5 W (basal) vs 92.9+/-5 W (Week 4, P=0.1) and 100.4+/-6 W (Week 8, 10.5%, P=0.04) in the DO group, and 96.2+/-6 W (basal) vs 129.1+/-4 W (Week 4, 34.1%, P=0.002) and 137.5+/-5 W(Week 8, 42.9%, P=0.002) in the DE group. Despite similar decreases in body weight in both groups, patients in the DE group achieved a markedly higher level of Wmax, reflecting a better improvement in cardiopulmonary fitness, compared with patients in the DO group. Considering the improvement of aerobic fitness in the short term, an aerobic exercise-training programme should be considered for sedentary obese patients to improve their aerobic fitness and thereby reduce the negative outcomes of obesity.

Immunohistochemical, histological and ultrastructural evaluation of the effects of leptin on testes in mice.

This study was undertaken to examine the effects of leptin on testes in mice. For this purpose, 12 male mice were divided into two groups. Animals in Group I were designated as control. Mice in Group II were injected daily with leptin for 5 days. All animals were decapitated at the end of the experiment. The testes were removed and weighed out. Testicular tissue specimens were processed for light and electron microscopic examination and semi-quantitative evaluation of immunohistochemical testosterone staining. Intensity of immunostaining was determined on a scale between 0 (no staining) and 5 (heavy staining). For morphometric comparison, diameters of seminiferous tubules from each group were measured. In the leptin injected group, testicular weights and diameters of seminiferous tubules were significantly increased in comparison to control values. In light microscopic examination, an increase in secretory granules in the cytoplasm of Leydig cells was observed after leptin treatment. In the same group, distinct changes indicative of increased cell activation were seen in the ultrastructure of Leydig cells. Amount of mitochondria, lysosomes and cytoplasmic secretory granules were increased. Furthermore, an increase in extensiveness of rough endoplasmic reticulum was noted in this group. Immunohistochemical testosterone staining of the cytoplasm of Leydig cells was heavy (5+) in the leptin treated mice compared to mild score (2+) in the control mice. Additionally, heavy immunostaining of testosterone was also observed in the interstitial space after injection of leptin. The present findings indicate that testicular functions and synthesis of testosterone increase after administration of leptin.

The role of the pineal in the control of the daily patterns of neurohypophysial hormone secretion.

Plasma concentrations of neurohypophysial hormones show clear rhythms over 24 hr which can be suppressed by exposure to constant light, an observation consistent with pineal involvement. A study has therefore been performed on the changes in the hormone levels in the hypothalamus, posterior pituitary, and plasma over 24 hr in control, pinealectomised, and sham pinealectomised animals to determine if the pineal could play a role. Water intake, urine excretion, packed cell volume, plasma osmolality, and electrolytes were also monitored. Pinealectomy had little effect on fluid balance, but after 8 weeks for oxytocin and 2 weeks for vasopressin the morning values (0700-0800) for the circulating concentrations of the hormones were significantly higher in the pinealectomized group compared with the combined sham operated and unoperated groups (pineal intact). By contrast, the pituitary vasopressin was significantly lower in the pinealectomised group. The increase in plasma oxytocin and vasopressin seen over the hours of daylight and accompanying fall in plasma osmolality seen in the pineal intact group were absent in the pinealectomised group. Similarly, the evening fall in pituitary hormone concentrations and increase in hypothalamic hormone content were absent in the pinealectomised animals. After 10 days of exposure to constant light, the fall in plasma osmolality in the pineal-intact animals over the day was no longer significant; instead a significant increase in plasma osmolality and sodium was seen in the pinealectomised group. Exposure to constant light, while altering the patterns of neurohypophysial activity in the pineal intact group, had little effect on the pinealectomised animals.

Release of vasopressin in response to altered plasma volume and sodium concentrations following pinealectomy in the rat.

Pinealectomy has been shown to alter daily rhythms of neurohypophysial hormone release, with plasma hormone concentrations being elevated in the morning, as compared to intact rats. To determine whether pineal removal also altered the response to known stimuli of hormone release, vasopressin concentrations were measured in control, sham-operated, and pinealectomized animals during extracellular fluid hypertonicity produced by an intraperitoneal (i.p.) injection of hypertonic saline or hypovolaemia produced by an i.p. injections of polyethylene glycol. In the combined sham-operated and unoperated groups, injection of hypertonic saline produced a marked increase in plasma vasopressin concentrations from 2.18 +/- 0.28 to 7.2 +/- 1.24 pmol/liter, but the response was attenuated in pinealectomized animals, concentrations increasing to only 3.4 +/- 1.2 pmol/liter. Similarly, following infusion of hypertonic saline, the increase in plasma vasopressin per unit increase in plasma sodium was lower in pinealectomized animals than the pineal intact controls. The response to hypovolaemia was also attenuated, plasma hormone concentrations following reduction in blood volume of approximately 10% increasing to only 3.6 +/- 0.6 pmol/liter as compared to 7.3 +/- 2.2 pmol/liter in the control groups. There were no significant differences in pituitary vasopressin content in any of the groups studied. Thus, the pineal may influence the vasopressin response to physiological stimuli.

Effects of paint thinner exposure on serum LH, FSH and testosterone levels and hypothalamic catecholamine contents in the male rat.

We have investigated the effects of thinner inhalation on serum LH, FSH and testosterone levels together with changes in hypothalamic catecholaminergic system in the male rat. A control group inhaled normal air ventilation. The remaining animals were divided into two groups and exposed to paint thinner in a glassy cage for 15 or 30 d. Toluene concentration (the largest constituent in thinner, 66%) was set at 3000 ppm in the inhalation air. At the end, all animals were decapitated and blood samples obtained. Serum LH and FSH levels were measured by RIA and testosterone by enzyme immunoassay. Following removal of brains on dry ice, medial preoptic area, suprachiasmatic nucleus, median eminence and arcuate nucleus were isolated by micropunch technique. Noradrenaline, 3,4-dihydroxyphenylglycol (DHPG) and dopamine concentrations of these hypothalamic areas were determined by HPLC-ECD. Fifteen-day thinner inhalation significantly suppressed serum LH and testosterone levels in parallel (p<0.001) compared to control group values (LH: 0.77+/-0.07; testosterone: 2.67+/-0.39). Thirty-day exposure markedly decreased LH levels (p<0.001), but surprisingly had no significant effect on testosterone. Serum FSH levels were not significantly altered in either group. Thinner inhalation for 15 or 30 d did not cause any significant change in noradrenaline, DHPG or dopamine concentrations in the hypothalamic regions examined (except in the arcuate nucleus). These results suggest that paint thinner has an anti-gonadotropic effect and may cause long-term endocrine disturbances in the male. It is thought that the hypothalamic catecholaminergic system is not involved in thinner inhibition of LH and testosterone secretion.