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Earlier experimental results show the role of altered pineal function in the development of the constant estrous-anovulatory (CEA) state induced by neonatal androgen sterilization (NA) or in the spontaneously developed anovulatory syndrome in the aging rat (AG-CEA state). Since norepinephrinergic (NE) innervation of pineal gland represents the main stimulus for melatonin secretion in mammals, in the present experimental series, the reactivity of pineal tissue to NE was investigated in in vitro perifusion system in rats suffering from NA-CEA or AG-CEA state, using the model of pineal body deprived from neural inputs. The data indicate that the 'melatonin deficiency' observed in the 2 types of anovulatory syndrome (NA-CEA and AG-CEA states) is due to disturbance of norepinephrinergic innervation of the pineal gland rather than to deficient secretory capacity of pineal tissue.

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Male Wistar Olac rats were kept in stainless steel cages at 24 +/- 1 °C. Three days before the experiment they were transferred into another room and kept 3 days at 30 °C. On the day of experiment, groups of 14-16 animals each were injected i.p. with 10 mg/kg morphine hydrochloride (MO), 1.5 mg pimozid (PI), 10 mg/kg cyproheptadine (CY) or with the combinations of MO+PI and MO+CY in the doses indicated above. Exactly after 30 min each animal was transferred to individual plexiglass cage and then a half of each group (consisting of 7-8 animals) was transferred to the cold room (4 °C), while the other half was kept at 30 °C. Precisely after 60 min the animals were quickly decapitated, the trunk blood was collected and thyrotropin (TSH) was estimated in serum using specific rat TSH radioimmunoassay kit supplied by National Pituitary Agency, Bethesda, Md. It was found that the level of TSH significantly decreased (P < 0.01) in PI injected group even at 30 °C as compared with all other groups. The same was found at 4 °C. In addition, at 4 °C the groups injected with CY, PI+MO and CY+MO showed the TSH level significantly decreased (P < 0.01) as compared with "cold control" and even with the group injected MO only. Since the animals injected with PI and CY irrespectively of MO were deeply sleeping and showed decreased body temperature and blood pressure, it was suggested that the effect of these and possibly some other drugs using for the study of the central regulation of cold stimulated TSH release may be at least partly, if not completely, unspecific.

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The effect of the removal of pineal gland, performed in adult age or during perinatal life, was investigated in the neonatal androgen sterility (NA-CEA) syndrome, in combination with drugs acting on serotonergic neurons. Perinatal pinealectomy (Px) was more potent in preventing the development of NA-CEA state than Px performed in the adult age. These data indicate that the masculinized hypothalamus becomes less sensitive to pineal influences during the lifespan. Effect of Px was potentiated by drugs increasing the central serotonergic tone. The results lead to the assumption that pineal hormones are influential on the maturation of serotonergic neurons, which might interfere with the sterilizing property of neonatal androgen treatment during the "critical" period of sexual differentiation.

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In the present experiments, extended studies were performed on long-term effect of perinatal neurotoxic damage of brain monoaminergic neurons exerted on Grown Hormone (GH) and on Thyrotrophic Hormone (TSH) secretion. Neurotoxins were applied for selective destruction of the different components of the monoaminergic neuron system. Deficient GH secretion and reduced TSH-mobilizing capacity were observed in consequence of perinatal injury of dopaminergic neurons, meanwhile in perinatal serotonergic lesion bearing rats, reduced GH secretion was associated with increased reactivity of the TSH-mobilizing mechanism. The results show that perinatal damage of monoaminergic neurons induce long-lasting alteration of the neural mechanisms regulating GH and TSH secretion.

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The aim of the present work was to study the basal secretion rate and the reactivity of the TSH-thyroid axis in adult rats neonatally exposed to drugs influencing monoaminergic and opioidergic neurons. The early postnatal administration of drugs antagonistic with the dopaminergic or serotoninergic neurons resulted in a persistent higher rate of basal secretion of TSH, while the administration of drugs synergistic with the monoaminergic neuron systems was weakly influential in this respect. The exposure to opioids in the perinatal period resulted in a permanent reduction of serum TSH levels which was even more pronounced when the exposure to morphine was advanced to the fetal period of life. These data raise the possibility that the permanent TSH depressing effect of perinatal administration of opioids is due to their effect exerted on the maturation of the monoaminergic neurons. From the other hand, our results lead to assume that there is a perinatal critical period in the maturation of monoaminergic neurons regulating TSH secretion in the adult age. In accordance with this assumption, the data obtained in rats bearing perinatal neurotoxic destruction of catecholaminergic neurons contribute to the concept that the disturbed maturation of monoaminergic neurons in the supposed critical period of development might lead to permanent deficiency also in the reactivity of the TSH-thyroid axis.

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The results of 11 experiments in a total of 571 rats (initial body weight of 150-250 g) are reported and some findings differing from those by others are discussed. It was repeatedly found that the animals after bilateral or even unilateral superior cervical sympathetic gangliectomy (GX) did not gain body weight during the first week after surgery. Though they started to grow later, for several weeks their body weight remained significantly less than that of sham operated controls (SH). Though such phenomenon has not yet been described, it may well explain the increase of thyroid weight (as expressed per body weight) after gangliectomy alone or combined with antithyroid drug treatment or hypophysectomy as described by others. It was suggested that such changes may depend on general metabolic changes resulting in a striking inhibition of body weight gain rather than on some specific effect of GX on the thyroid. This view was supported by evaluating the data on absolute and relative thyroid weight from 4 experiments in a total of 265 animals. The level of thyroxine (T4) and thyrotropic hormone (TSG) was repeatedly found to be significantly decreased after GX for until about 72 h and 24 h after surgery, respectively, which was in agreement with the data reported by others. However, the onset of such decrease was repeatedly found to appear at 6 or 8 h after surgery (in one experiment even at 3 h after surgery) which is also contrasting to the onset of T4 decrease at 14 h after surgery as found by others who suggested a correlation of such thyroid depression with a depletion of noradrenaline from the thyroid and may be even from median eminence. In these experiments, however, a decrease of T4 level was found several hours before the depletion of noradrenaline from the thyroid which appeared at 12 h after surgery and remained at similar level until 40 days, while no remarkable changes of that were found in SH animals (with the excretion of slight increase after 24 h). Between about 4 and 40 days after surgery no significant changes in T4 and TSH levels after GX were found as compared with SH animals is in agreement with others.4+n one experiment the increase of T4 at 2 h after TRH injection, resulting apparently from the effect of endogenous TSH, was significantly inhibited in GX animals at 8 days after surgery, while in other experiments (at 8 and 40 days after surgery) no difference in T4 level increase was found in GX animals as compared with SH ones. In general, it may be suggested that superior cervical sympathetic gangliectomy may result in some temporary and perhaps transient changes in pituitary-thyroid function in rats.

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Thyroxine level (T4) and total creatine kinase-activity (CK) were measured in serum samples from male Wistar-rats to investigate the relationships of serum titers after exposure to cold and thyroidectomy (TX). 72 hours exposure to cold (10 degrees C) produced a statistically significant elevation of T4 and a diminuation of CK-activity. In contrast to this protocol, TX (90 days after operations) reduced the T4 level and enhanced the CK-activity. These reactions were likewise statistically significant. The presented results are in agreement with the previous proposal which consists in inverse correlation between the T4 level and the CK-activity at hypo- and hyperthyroid states. Additionally it was shown that the highest activity of the serum CK appears in the first half of the light phase of the day under normal ambient temperature (24 degrees C) as well as under exposure to cold (10 degrees C).

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The effect superior cervical sympathetic ganglionectomy (Gx) exerted on the daily rhythm of serum testosterone levels was investigated in cold-exposed rats. Rhythmic changes in pineal and pituitary weights were also measured. 1. Exposure to cold (10 degrees C for 72 h) resulted in a significant decrease of serum testosterone level and in an increase of the pineal weight. 2. In neutral ambient temperature (24 degrees C) Gx, 30 d after operation, led to a moderate, statistically insignificant increase of serum testosterone levels and to decreased pineal weights (statistically significant). 3. The reactions provoked by cold exposure were counteracted by Gx. Testosterone levels, as well as the pineal weight, showed no remarkable change in the Gx, cold-exposed animals. 4. These results confirm our assumption that experimental manipulations of the pineal gland can provoke significant changes in the neuroendocrine system only under special loading circumstances, e.g., cold exposure. Sympathetic denervation of the pineal gland counteracts the cold-induced decrease of testosterone levels by counteracting the pineal antigonadotropic activity. 5. The empirical regression curves of the investigated parameters indicate that Gx or cold exposure provide a shift in the upper and lower limits of the daily rhythm. Partly inverted rhythms were also observed. 6. The presented results are discussed in relation to the parallel changes previously described in serum thyroxin, cholesterol, thyrotropin (TSH), and pituitary TSH levels. Thyroidal-gonadal interactions, as well as cold exposure as a stress-generating factor, have been considered in the possible explanation of the data herein reported.

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Serum thyroxin (T4), serum TSH, and pituitary TSH were measured by radioimmunoassay (RIA) and serum cholesterol by Liebermann-Burchard reaction in rats 4 times a day (light-dark cycle: 14 L: 10 D) after gangliectomy (bilateral extirpation of the Ganglia cervicalia superiora) at cold and normal temperature conditions. 80 male Wistar rats were divided into 4 groups: sham-operated group, 24 degrees C (297 K); sham-operated group, 10 degrees C (283 K); gangliectomy, 24 degrees C (297 K), and gangliectomy, 10 degrees C (283 K). We have sacrificed the rats 30 d after operations at the following day-times: middle light, middle darkness, 1 h after light "on" and 1 h after light "off" (they were exposed to cold 72 h before killing). It was found that gangliectomy significantly depressed blood level of thyroxin. On the other hand, it enhanced the serum cholesterol and TSH levels as well as the pituitary TSH content. Exposure to cold increased thyroxin, serum TSH and pituitary TSH. The cholesterol level, however, was significantly decreased. Gangliectomy causes a reduction of the cold-induced stimulation of thyroxin (significant), serum TSH, and pituitary TSH content (significant). The cholesterol (in relation to the cold-exposure alone) was significantly increased under these conditions. We have found similar results in another long-time experiment (90 d exposure) after gangliectomy as well as after pinealectomy. There also appears a lowered thyroxin and an increased cholesterol level (in dependency on the seasons). Gangliectomy induced a decrease of the pineal weight and a compensatory thyroid growth. Exposure to cold induced an increase of pituitary and pineal weights. Gangliectomy provokes a reduction of the cold-induced augmentation of the pineal weight. The results indicate that gangliectomy diminishes the total levels of circulating T4 in the presence of an intact pineal gland and reduces the cold-induced increase of T4 in long-time experiments (30 and 90 d post operationem). Both gangliectomy and cold condition led to an enhancement of serum TSH and pituitary TSH content. The exposure to cold was found to have a more severe influence. In the present study, we also have discussed the sympathetic denervation effect of the gangliectomy in relation to the thyroid and pineal gland. Due to certain contradictory data in the literature, we have also discussed the TRH-5-hydroxytryptamine (respectively melatonin) antagonism, though we were not able to determine whether peripheral and/or central mechanisms play the more important role in their regulation.

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Groups of male rats were inserted with polyethylene tubings into femoral artery and vein under pentobarbiturate anesthesia and small blood samples were frequently taken for the estimation of TSH and PRL under maintaining isovolemia. After a single injection of apomorphine (12 mg kg-1) or bromocryptine (20 mg kg-1) much more expressed effect of these drugs on a decrease of PRL level in plasma was found than that on a decrease of TSH level and similar observation was made with the use of continuous i.v. infusion of apomorphine (50 micrograms in 20 microliter per min for 180 min). Finally, under the above dose of infused apomorphine, the effect of TRH on the increase of TSH level was depressed at the 30th min as compared to that 0 and 120th min of infusion. In addition, at 120 min of infusion the effect of TRH was significantly higher than that at 0 min. These results suggest that the effect of apomorphine may take place at the pituitary level.

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Acute systemic administration of (D-Met2, pro5-NH2)-enkephalin (ENKamide), a very potent enkephalin analog, and of morphine not only diminished the basal levels of serum TSH under resting conditions, but also significantly reduced the enhanced serum TSH concentrations induced by goitrogen treatment or by bilateral thyroidectomy. Acute administration of opiates failed to inhibit the pituitary TSH response to exogenous TRH administration. The TSH release-inhibiting effect of ENKamide was reversed by pretreatment with the serotonin synthesis inhibitor, para-chlorophenylalanine (pCPA) or with the central serotonin receptor blocker, metergoline. These results furnish evidence in favour of the following concepts: (a) opioid compounds equally influence the tonic release of the TRH-TSH system under resting conditions, and also suppress the reactive changes of this circuit following specific loads, leading to an activation of this system; (b) opioids do not act directly at the pituitary level in inhibiting TSH secretion, but rather seem to suppress the release of TRH from the hypothalamus; (c) they may exert their inhibitory effect on the activity of the TRH-TSH-thyroid system by increasing the activity of the central nervous serotonergic system.

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The serotoninergic neuron system of the midbrain and hypothalamus was previously shown to inhibit the basal secretion of the TRH-TSH-thyroid axis. The aim of the present study was to investigate the influence of the serotoninergic system on the TSH response of the adenohypophysis to specific loads. Serum TSH levels were determined 7 days after thyroidectomy or the beginning of thiouracil administration. Animals were simultaneously treated either by intrahypothalamic implantation of serotonin-containing needles or by intraventricular or daily subcutaneous injections of the same drug. The thiouracil-induced goitre formation and increase in serum TSH concentration were significantly diminished by serotonin treatment. Similarly, the thyroidectomy-induced rapid rise in TSH blood level was also remarkably inhibited in the serotonin-treated animals. Serotonin was proved to influence rather TRH-output than pituitary TSH secretion, since exogenous TRH, injected to serotonin-pretreated animals had the same TSH-mobilizing potency as found in the not premedicated group. It is concluded that besides the inhibition of the basal secretion of the TRH-TSH-thyroid axis by serotonin, there is an integrative role of the serotoninergic system in the mediation of the reactivity of this circuit in reply to specific influences loading pituitary-thyroid function.

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1. Decrease of brain serotonin concentration, elicited by either parachlorophenylalanine treatment, surgical interruption of the ascending serotoninergic fibres, or by pinealectomy provokes an enhanced release both of TSH and LH. 2. Increased serotonin content of the brain, produced by intraventricular, intrahypothalamic or systemic administration of serotonin, results in a significant inhibition of the release of these two trophic hormones. 3. It is concluded that the serotoninergic neuron system of the brain stem represents an inhibitory mechanism in the neuroendocrine circuit regulating pituitary trophic hormone release.

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Thyroid function was investigated in adult male rats following the use experimental procedures which inhibit the activity of serotoninergic neuron system. Pharmacological blockade of the biosynthesis of sertonin by repeated administration of para-chlorophenylalanine (pCPA), or interruption (by Halász knife) of the serotoninergic pathways of the brain stem which terminate on hypothalamic nuclei equally resulted in an augmentation of the following parameters of hypothalamo-hypophysial-thyroid activity: T/S ratio, pituitary and blood TSH levels and blood thyroxine concentration as well as TRH content of the hypothalamus. The results suggest that the central nervous serotoninergic neuron system plays an inhibitory role in the regulation of TSH secretion, presumably acting upon the hypothalamus, thereby inhibiting hypothalamic TRH secretion.

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The fertility-inhibiting effects of long-term (8 weeks) consumption of maize infected with a fungus producing F2 toxin (zearalenone) was studied in adult male and female albino rats. The fertility rate was further decreased by 25-30% if the animals were kept on contaminated diet up to 14 weeks. The gonadal weight was decreased, follicular maturation and spermatogenesis were disturbed. The toxic diet consumed by mothers during pregnancy and lactation induced permanent changes in reproductive organs, disorders in vaginal cyclicity and disturbed fertility in the offspring. Neonatal administration of purified F2 toxin provoked similar changes. It is suggested that this fungal toxin may cause sterility syndrome in the offspring, similar to that produced by androgen or estrogen administration.

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Continuous light (CL) induces constant estrous anovulatory (CEA) syndrome and blockade of pineal gland activity. Chronic treatment with metatonin is able to overcome the anovulatory state in about 70% of CL-CEA rats, and the luteinizing effect of melatonin is significantly counteracted either by feeding the animals with a tryptophan-poor diet or by injecting methiothepin, a blocker of central serotoninergic receptors. It appears that melatonin elicits luteinization in CL-CEA rats through the brain serotoninergic system.

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