Inhibition of rat testicular androgenesis by a polychlorinated biphenyl mixture aroclor 1248

Polychlorinated biphenyls (PCBs) are complex mixtures of congeners that exhibit carcinogenic and toxicant activities in a variety of mammalian tissues. Here, we studied the acute in vivo and in vitro effects of a commercially used PCB product, Aroclor 1248 (A1248), a mixture of tri-, tetra-, and pentachloro congeners. Single intraperitoneal (i.p.) or bilateral intratesticular (i.t.) injections of A1248 decreased serum androgen levels in both groups 24 h after injection. Chorionic gonadotropin-stimulated androgen production by acute testicular cultures from both groups was also reduced, and progesterone production was attenuated in cultures from i.t.-treated animals. The capacity of the postmitochondrial fractions from testes of i.t.-treated animals to convert pregnenolone to progesterone and progesterone to testosterone was reduced as well. In vitro studies revealed that a 10- to 15-min exposure of postmitochondrial testicular fractions and intact interstitial cells from normal animals to A1248 in a subnanomolar concentration range was sufficient to attenuate the conversion of pregnenolone to progesterone and progesterone to testosterone. At micromolar concentrations, A1248 added in vitro also inhibited the conversion of Delta(4)-androstendione to testosterone without affecting the viability of interstitial cells. These results indicate that A1248 down-regulates the testicular androgenesis by an acute inhibition of 3beta-hydroxysteroid dehydrogenase, 17alpha-hydroxylase/lyase, and 17beta-hydroxysteroid dehydrogenase activities.     

Effects of zinc and melatonin deficiency on testicular tissue of rats

The present study was designed to investigate the effects of zinc and/or melatonin deficiency on rat testes. A total of 24 adult male Sprague-Dawley rats were used in this study. The rats were divided into four groups of six rats each, as follows: (I) controls, (II) zinc deficient, (III) pinealectomized, zinc normal, and (IV) pinealectomized, zinc deficient. The plasma zinc levels in the control group were higher than in all the other groups (p<0.01), and those of the zinc-deficient groups II and IV were significantly lower than for group III (p<0.01). The melatonin levels in the controls were also significantly higher than for all other groups (p<0.01) There was no significant difference in sperm production between the controls and the group of animals that had no epiphysis. A significant suppression was observed in the spermatogenetic activity of the zinc-deficient groups (p<0.01). The suppression was higher in group II than in group IV. These results indicate that testicular damage caused by zinc deficiency may be reduced by melatonin deficiency.     

Nocturnal urinary melatonin levels and urine biochemistry in microwave-irradiated rats

The aim of this study was to explore whether, during the course of a 15 days-lasting experiment, a two hours per day and five days per week, 2.45 GHz microwave whole-body irradiation may substantially and therefore provably affect rats’ nocturnal urinary 6-hydroxy-melatonin sulphate (aMT6s) excretion and urinalysis parameters. The average whole-body specific absorption rate (SAR) equalled to 1.25 (± 0.36 SE) W/kg. To collect nocturnal urine samples, animals were held in individual metabolic cages every experimental night from 7:00 PM till 7:00 AM next day. The concentration of aMT6s in rat urine samples was determined by a direct radioimmunoassay. Bilirubin, ketones, and urine protein content have been determined via multiple-use reagent strips. In comparison to the sham-exposed group, no significant changes in body temperature and food or water intake were observed in the exposed group. A decline in aMT6s, determined in the exposed rats, was observed from day 8 to day 11 of the experiment (P < 0.05). The aMT6s level remained consistently low until the end of the experiment, but not significantly lower than the control values. The results of the urine samples biochemical workup failed to reveal any significant differences between the exposed and the control animal groups. The results of this study suggest that, under the above described experimental conditions, repeated 2.45 GHz irradiation could act as a stressor and therefore influence the melatonine balance in rat.     

Inhibition of planarian regeneration by melatonin

Melatonin, which is a substance produced by the pineal body in vertebrates, inhibited regeneration in the planarian Dugesia japonica japonica Ichikawa et Kawakatsu. When decapitated planarians were maintained in a 1 mmol dm^–3 solution of melatonin, formation of the head was retarded; formation of the eyes, however, was not disturbed. Similarly in animals from which the tail was cut, regeneration of the tail was retarded if the animals were kept in melatonin solution of 1 mmol dm^–3. The effect was reversible once the melatonin was removed. Retardation of regeneration did not occur with similar application of three melatonin derivatives, serotonin hydrochloride, N-acetylserotonin, and 6-hydroxymelatonin. Melatonin endogenous to the planarian could be demonstrated by means of radio-immunoassay and was more abundant in the head region than other regions of the body. Melatonin, thus, appears to play a role in regulating regeneration in planarians and conceivably provides positional information in that process.     

The protective action of melatonin on indomethacin-induced gastric and testicular oxidative stress in rats

Reactive oxygen species and lipid peroxidation play a role in the pathogenesis induced by the non-steroidal anti-inflammatory drug indomethacin. Melatonin (MLT) protection against indomethacin-induced oxidative tissue injury was investigated in gastric mucosa and testis of rats. MLT was administered intragastrically (i.g.) 30 min before the administration to fasted rats of 20 mg indomethacin/kg rat given i.g.. The area of gastric lesion as well as thiobarbituric acid reactive substances (TBARS) and lactate dehydrogenase (LDH) activity were found to be significantly increased 4 h after administration of indomethacin in rat gastric mucosa and testis indicating acute oxidative injury. MLT pretreatment reduced gastric lesion area to 80% of the indomethacin-treated rats and reduced the rise in TBARS concentration. MLT treatment reduced the LDH activity increase in testis but not in gastric mucosa. In indomethacin-treated rats, both the cytosolic Cu,Zn superoxide dismutase (Cu,Zn-SOD) and mitochondrial Mn-SOD activities were significantly diminished in gastric mucosa as well as the total SOD activity in testis. In addition, glutathione (GSH) content in both tissues was markedly decreased following indomethacin treatment. Pretreatment with MLT significantly ameliorated both the inhibition of SOD activity and the decreased GSH content in both tissues. Thus, these results show the effective antiperoxidative and preventive actions of MLT against indomethacin-induced gastric mucosal damage and testicular oxidative injury and we propose that this action might be relevant for its use with other free radical generating drugs.     

Inhibition of testosterone secretion by digitoxin in rat testicular interstitial cells.

Both in vivo and in vitro experiments were conducted to determined the effects of digitoxin on the secretion of testosterone, and its underlying mechanisms including testicular adenosine 3':5'-cyclic monophosphate (cAMP), and the activities of steroidogenic enzymes. Male rats were injected with digitoxin, human chorionic gonadotropin (hCG), or hCG plus digitoxin via a jugular catheter. Blood samples were collected immediately before and at 30 and 60 min after the challenge, and analyzed for testosterone by radioimmunoassay. In an in vitro study, rat testicular interstitial cells were isolated and incubated with digitoxin, hCG, 8-bromo-cAMP (8-Br-cAMP), digitoxin plus hCG, or digitoxin plus 8-Br-cAMP at 34 degrees C for 1 h. The media were collected and analyzed for testosterone. For studying cAMP accumulation, testicular interstitial cells were incubated for 1 h in the medium containing isobutyl-1-methylxanthine (IBMX) and different doses of digitoxin with the absence or presence of hCG. After incubation, cells were processed for determining cAMP content. Intravenous injection of digitoxin decreased hCG-stimulated, but not basal, plasma testosterone levels. Administration of digitoxin in vitro resulted in an inhibition of both basal and hCG- as well as 8-Br-cAMP-stimulated release of testosterone. In addition, digitoxin diminished hCG-stimulated cAMP accumulation in rat testicular interstitial cells. Furthermore, digitoxin inhibited the activity of cytochrome P450 side chain cleavage enzyme (P450scc) but failed to affect the activities of other steroidogenic enzymes. Taken together, these results suggest that the acute inhibitory effect of digitoxin on the testosterone production in testicular interstitial cells involves, at least partly, an inefficiency of post-cAMP events, and a decrease of P450scc activity.     

Inhibition of renal gluconeogenesis in rats by ochratoxin.

In kidney-cortex slices from rats fed on 2.0 mg of ochratoxin A/kg per day for 2 days, gluconeogenesis from pyruvate is decreased by 26%, and renal phosphoenolpyruvate carboxykinase activity is lowered by about 55%. Gluconeogenesis from 10 mM-lactate or 20 mM-malate or -glutamine is also significantly decreased. Hepatic phosphoenolpyruvate carboxykinase is unchanged or increased, and hexokinase activity in kidney and liver remains unaffected. We conclude that ochratoxin A in vivo is an inhibitor of renal phosphoenolpyruvate carboxykinase activity, which is responsible, at least in part, for the block in renal gluconeogenesis.     

Suppression of testicular androgenesis by D-tryptophan-6-luteinizing hormone-releasing hormone does not affect TSH secretion in male subjects

Basal and TRH-stimulated TSH secretion was evaluated in six patients suffering from prostatic cancer, before and after antiandrogenic treatment performed using a long-acting LHRH analogue, D-Trp-6-LHRH. Although serum testosterone values dropped to minimal levels after treatment, TSH secretion remained unchanged. Observed results suggest that pharmacological castration does not affect the regulatory mechanisms involved in the control of TSH secretion.     

Influence of melatonin on the testicular regression induced by subcutaneous testosterone pellets in male rats kept in long or short photoperiod

Daily afternoon injections of 25 micrograms melatonin for 12 weeks had no effect on testicular weights of male rats kept in long photoperiod (14L:10D); similarly, exposure of rats to short photoperiod (2L:22D) had no effect on gonadal weight. However, rats maintained in a long or short photoperiod and implanted every 2 weeks with a 15 mm Silastic pellet containing testosterone showed a significant reduction in testicular weight; this effect was more pronounced in rats exposed to a short photoperiod. Melatonin injections in testosterone-treated rats in a long photoperiod exacerbated the inhibitory effects of testosterone alone. Subcutaneous 2-weekly implants of a beeswax pellet containing 1 mg melatonin reversed the effects of the melatonin injections on relative testicular weights but not those due to short photoperiod exposure. Testosterone implants significantly reduced pituitary LH values in long and short photoperiod-exposed animals, more particularly in those exposed to short photoperiod. Melatonin injections alone or in combination with melatonin pellets did not further exaggerate the depression in pituitary LH due to testosterone alone in long photoperiod-exposed animals; similarly melatonin pellets did not reverse the depression in pituitary LH observed. No significant differences in plasma prolactin concentrations or in thyroxine concentrations or free thyroxine index were observed after any combination of treatments. We therefore suggest that the effects observed with short photoperiod may be due to melatonin.     

Inhibition of rat testicular microsomal steroidogenesis by oxytocin and metyrapone

Capillary gas chromatographic 'steroid profiling' has been utilised to separate and quantify the metabolites (derivatized as methyloximes and/or trimethylsilyl ethers) formed from pregnenolone after incubation with rat testicular microsomes. A wide range of steroid metabolites was found, indicating that both the 5-ene and 4-ene pathways of testosterone biosynthesis were operating, as well as 16 alpha-hydroxylation, 20 beta-reduction and the formation of several C19 steroids (the 16-androstenes). At the concentration used, Metyrapone markedly inhibited 16 alpha- and 17-hydroxylation and side-chain cleavage of 17-hydroxylated C21 steroids. 16-Androstene production was also markedly inhibited and the formation of other metabolites was affected to lesser extents. Oxytocin abolished the formation of all C21 and C19 metabolites of pregnenolone.     

Inhibition of decidual induction in rats by clomiphene and tamoxifen.

The objective of this study was to characterize the estrogen action that confers endometrial sensitization to nontraumatic deciduogenic stimuli by use of antiestrogens. Tamoxifen, ethamoxytriphetol, and clomiphene and its two component enantiomers inhibited decidual induction in pseudopregnant rats when administered 17 h before pyrathiazine. Unexpectedly, clomiphene (250 micrograms/rat) and tamoxifen (25 micrograms/rat) proved inhibitory at all times up to and including the time of induction. Clomiphene, administered in the hours preceding decidual induction, inhibited the increase of ornithine decarboxylase activity, which normally marks the end of the induction phase. Clomiphene had no inhibitory effect on the availability or receptor binding of progesterone. Clomiphene also inhibited implantation of blastocysts when administered at the time of their adherence to the uterus. The inhibition by antiestrogens of decidual induction could not be explained on the basis of the current understanding of mechanisms of estrogen action. The discrepancies were that no latent period between the time of antiestrogen administration and decidual induction was observed and no difference was observed in the inhibitory activities of the isomers of clomiphene.     

Inhibition of Calotropis procera latex-induced inflammatory hyperalgesia by oxytocin and melatonin

The latex of the wild growing plant Calotropis procera produces inflammation of the skin and mucous membranes upon accidental exposure. On local administration it elicits an intense inflammatory response due to the release of histamine and prostaglandins that is associated with hyperalgesia. In the present study we have evaluated the anti-inflammatory and antinociceptive activity of oxytocin and melatonin against rat paw edema induced by dried latex (DL) of C procera and compared it with that against carrageenan-induced paw edema. Aqueous extract of DL of C procera or carrageenan (1%) was injected into the subplantar surface of the rat paw and the paw volume was measured at 0, 1, 2, 3, 4, 6, 10, and 24 hours. The associated hyperalgesic response and functional impairment were also evaluated concomitantly by dorsal flexion pain test, motility test, and stair climbing ability test. The inhibitory effect of oxytocin and melatonin on edema formation and hyperalgesic response was compared with dexamethasone. DL-induced edema formation was maximum at 2 hours and was associated with decreased pain threshold and functional impairment. Treatment with melatonin significantly attenuated the edematous response while both oxytocin and melatonin increased the pain threshold and improved functional parameters. Both oxytocin and melatonin significantly inhibited the hyperalgesia associated with DL-induced paw edema. Oxytocin was found to be as effective as melatonin in ameliorating the hyperalgesic response. However, it was found to be less effective than melatonin in attenuating edema formation.     

Thorium induced testicular changes in rats.

Daily intraperitoneal administration of thorium nitrate produced progressive morphological and biochemical alterations with the increase in thorium concentration in rat testis. The degenerative changes in the seminiferous tubules increased with the duration of treatment and after 90 days calcification occurred in about 25% of the tubules and in the connective tissue of the tunica albuginea. The activity of adenosine triphosphatase and alkaline phosphatase increased markedly as a result of thorium administration. An attempt has been made to interrelate histopathological and enzymatic changes and the metal concentration in the testicular tissue.     

Disturbance of plasma melatonin profile by high dose melatonin administration inhibits testicular maturation of precocious male masu salmon

We have previously shown that the testicular development of underyearling male masu salmon Oncorhynchus masou reared under a long photoperiod was accelerated by oral melatonin treatment (0.5 mg melatonin/kg body weight/day), suggesting that melatonin mediates photoperiodic signaling. In this study, we further examined the effects of a disturbance in the plasma melatonin profile on gonadal development in underyearling male masu salmon by administering a higher dose of melatonin. Fish randomly selected in June were divided into two groups. They were reared under a light:dark (LD) cycle of 16:8 (lights on 04:00-20:00 hr) and fed with pellets sprayed with melatonin or vehicle twice a day at 08:30 and at 15:30 hr (7.5 mg melatonin/kg body weight/day) until October. Fish were sampled on Day 0, 25, 60, 90 and 120. The plasma melatonin levels were high in the dark phase and low in the light phase in the control group, while they were constantly high with no significant change in the melatonin-treated group. Melatonin treatment had inhibitory effects on the gonadosomatic index and plasma testosterone levels. Pituitary salmon gonadotropin-releasing hormone content and luteinizing hormone content were significantly lower in the melatonin-treated group on Day 60 and 90, respectively. These results indicate that the plasma melatonin profile is important for mediating photoperiodic signals that regulate brain-pituitary-gonadal axis in underyearling precocious male masu salmon.     

Vasoprotection by melatonin and quercetin in rats treated with cisplatin

Cisplatin-based chemotherapy has a variety of vascular side effects. The aim of the present study was to evaluate the beneficial effect of melatonin and cisplatin on the alterations in vascular reactivity and structure of cisplatin-treated rats. Phenylephrine (PHE) and KCl-caused concentration-dependent contractions of rat aorta. Pretreatment with cisplatin increased the sensitivity but not the max response to PHE and KCl. In rats treated with melatonin or quercetin before cisplatin, the EC50 values, but not the maximal response to both agents were significantly higher than cisplatin-treated group. Compared to the control group, cisplatin-treatment significantly reduced the luminal area of the aorta. In melatonin and quercetin-treated aortas the luminal area values were significantly higher than cisplatin-treated group. The results demonstrate for the first time that melatonin and quercetin treatment may protect the aorta in cisplatin-based chemotherapy.     

Inhibition of metaphit-induced audiogenic seizures by APV in rats.

The influence of APV ((+/-)-2-amino-5-phosphonovaleric acid) on EEG activity and behavior was studied on a model of epilepsy induced by intraperitoneal administration of metaphit (1-(1-(3-isothiocyanatophenyl)-cyclohexyl)-piperidine). Male Wistar rats received an injection of metaphit (10 mg/kg) and were subjected to intense audio stimulation (100+/-3 dB, 60 s) at hourly intervals during the experiment. The seizures were classified according to a four point scale ranging from 0 (no seizure) to 3 (tonic convulsions). In our report we studied the time course which revealed the maximum incidence and severity of seizures 7-12 h after the injection (10 out of 12 rats, with severity of 2.25+/-0.32). APV (0.05, 0.1, 0.2 and 0.3 micromol) was injected intracerebroventricularly at the time of fully developed convulsions. APV inhibited seizures in a dose-dependent manner. The minimum dose, which completely blocked seizures in all animals, was 0.3 micromol, while ED50 were 0.11, 0.10 and 0.07 micromol against running, clonus and tonus, respectively. In contrast to behavioral inhibition of convulsions, metaphit-provoked epileptiform activity was not abolished by APV, and represented a prerequisite for the reappearance of behavioral seizures. It is suggested that APV is rather an anticonvulsant than an antiepileptic agent in this model of epilepsy.     

Gonadotropin binding and testicular function in old rats.

Serum testosterone levels, testicular LH binding and the spermatogenic cycle were analyzed in rats 4 and 22 mo of age. With age, serum testosterone levels decreased from 3.2 to 0.63 ng/ml serum. There was no age related decline in testicular LH binding or changes in the spermatogenic cycle.