Coincidence of counter-antigonadal and counter-antithyroid action of melatonin administration via the drinking water in male golden hamsters

The morphological and functional characteristics of the pineal gland

Introduction

The pineal gland is a photo-neuro-endocrine organ situated inside the brain, that secretes serotonin, melatonin and N,N-dymethyltriptamine. This narrative review will address the latest information gathered on this function of the gland as well as the unknown roles it may have. The different histological and pathological findings of the pineal gland have demonstrated a role in clinical manifestations of numerous endocrine, neurological and psychiatric pathologies.

Materials

For this narrative review we used the NCBI website database PubMed. The search terms were “Pineal Gland” AND/OR “histology, melatonin, DMT, pathology”. Total number of articles included were 86.

Results

We have reviewed physiological information of melatonin and DMT, anatomical, histological and histopathological information on the pineal gland and its role in endocrine, neurological and psychiatric pathology.

Conclusion

The role of melatonin in immunity and its potential therapeutic effects show promising potential for further research. DMT seems to have a role in psychiatric pathology and potential therapeutic effects. Proper tumoral screening and diagnostic protocol are required.

Effect of methimazole-induced hypothyroidism on adrenal and gonadal functions in male Japanese quail (Coturnix japonica)

To investigate the effect of hypothyroidism on gonadal and adrenal functions in male Japanese quail (Coturnix japonica), hypothyroidism was induced in male adult Japanese quail by daily administration of 2-Mercapto-1-methylimidazole (methimazole) in their drinking water. Four weeks after methimazole treatment, the Japanese quail were sacrificed, and the plasma concentrations of free triiodothyronine (FT3), free thyroxine (FT4), total T3 (TT3), total T4 (TT4), corticosterone, testosterone, LH and immunoreactive (ir) inhibins were measured by radioimmunoassay, the testes and adrenal glands were removed and weighed and the thyroid glands and testes were fixed in 4% paraformaldehyde for histological observation. The results showed that the hypothyroidism induced by methimazole caused a significant decrease in body and testes weight; the plasma levels of FT3, FT4 and TT4 significantly decreased, and the hypothyroid quail possessed a greater number of small follicles and more follicular epithelial cells in the thyroid gland. In addition, hypothyroidism resulted in a significant decrease in the plasma concentrations of corticosterone, LH, testosterone and ir-inhibin. Furthermore, no spermatogenesis was found in the seminiferous tubules of the methimazole treatment groups. These results clearly demonstrate that hypothyroidism caused both gonadal and adrenal disturbances in the adult male Japanese quail.

Daily timed melatonin feedings mimic effects of short days on testis regression and cortisol in circulation in Siberian hamsters

This study tested the efficacy of timed oral administration of melatonin as an alternative both to invasive methods (daily injections, timed infusions) and to untimed oral administration in Siberian hamsters (Phodopus sungorus), an important model for the study of photoperiodism. Hamsters readily consumed a small piece of melatonin-treated apple immediately when presented and circulating melatonin was rapidly elevated with a half-life of approximately 3.5 h. Melatonin-treated apple was fed to hamsters for 3 weeks at 2 h before lights off to extend the duration of the nighttime rise in endogenous melatonin. Melatonin treatment induced testicular regression and elevated serum cortisol, effects comparable to those in hamsters exposed to short days. These findings support the hypothesis that timed oral administration of melatonin can mimic the effects of short days and provide a method by which melatonin can be delivered without the potentially confounding effects of handling and injection stress.

Effects of Hypothyroidism on Gonadal Function after Transition of Short Day Photoperiod in Male Golden Hamsters (Mesocricetus auratus)

Thyroid hormones permit the annual reproductive transition of seasonal breeders. Although, precise function of thyroid hormones in seasonal breeding is not well understood. In the present study, we examined effects of hypothyroidism on the hypothalamus-pituitary-gonadal axis in adult male golden hamsters after transition of the short-day photoperiod (SD; 8 h light: 16 h dark) condition. We confirmed that hypothyroid, which had been induced by administration of thiouracil in drinking water for 4 weeks, did not have direct effects on testes in male hamsters under the long-day photoperiod. Plasma concentrations of free T3 and T4 decreased 15 weeks after transition of SD condition. Plasma concentrations of testosterone in the hypothyroid group decreased earlier than in the control group after the transition from LD to SD. In animals treated with testosterone after castration, plasma concentrations of LH in the hypothyroid group decreased earlier than in the control group after the transition of SD. On the other hand, pituitary response to GnRH for LH release did not change in castrated hamsters as a result of hypothyroidism. These results suggest that thyroid hormones act the hypothalamus and might be required to maintain GnRH secretion in male golden hamsters.

Inhibitory influence of late afternoon melatonin injections and the counter-inhibitory action of melatonin-containing pellets on thyroid growth process in male Wistar rats: comparison with effects of other indole substances

Previous studies performed in our laboratory indicated that melatonin, when administered in late afternoon (1600-1800) as s.c. injections for 10 days, exerted an inhibitory effect on thyroid growth in mice and Sprague-Dawley rats. The goal of the present study was to examine the effects of melatonin and other indole substances (5-methoxytryptophol, N-acetylserotonin, 6-methoxytryptamine), administered for 10 days, for either 4, 8, or 10 weeks, on thyroid growth processes in adult male Wistar rats. We have also compared the action of melatonin administered in late afternoon as s.c. injections with effects of the melatonin-released chronically from s.c. implanted beeswax pellets containing 1 mg of the hormone. Additionally, the effects of melatonin injections in animals with the pineal gland removed and in thyroid stimulating hormone (TSH)-injected rats have been studied. We examined the mean mitotic activity rates (MMARs) of thyroid follicular cells (TFC) and the wet thyroid weights. We concluded that melatonin, of the examined substances, is the most potent inhibitor of thyroid growth; the hormone reduced the MMAR of TFC and the thyroid weight at all time-points. 5-Methoxytryptophol, like melatonin, exerted the inhibitory influence on the mitotic activity; however, it did not affect thyroid weight. The influence of other indole substances was much less pronounced. It was shown that melatonin-pellets prevented the inhibitory effect of late afternoon melatonin injections on thyroid growth processes. This observation is consistent with results of other authors concerning the counter-antithyroid effect of melatonin on thyroid hormone secretion. Pinealectomy revealed the stimulatory effect on thyroid growth processes, while melatonin treatment reversed the effect of the surgery.(ABSTRACT TRUNCATED AT 250 WORDS)

Circannual oscillations of thyroxine and cholesterol levels after pinealectomy and ganglionectomy related to the weight changes of the pineal, pituitary, and thyroid glands

Circannual rhythms of thyroxine (T4) and cholesterol blood levels, as well as of pineal, pituitary and thyroid weights were compared in intact, pinealectomized (Px), and ganglionectomized (Gx) rats. Special emphasis was put on the similarities and differences between the effect of Px and of Gx exerted on the neuroendocrine regulation of thyroid function. Animals were kept under changing lighting schedules simulating the natural seasonal conditions (December, L:D 8:16; June, L:D 16:8; March and September, L:D 12:12). Animals were killed 90 d after surgical interventions in the above-mentioned 4 months. In each season, animals were killed at four time points of the daily rhythm, and the means of the four data of a single day were used for further analysis evaluating circannual changes. All the investigated five parameters showed a monophasic circannual rhythm. The lowest T4 blood level was measured in summer; in contrast, cholesterol level and organ weights had a maximum in the same season of the year. The annual mean value of T4 level was diminished, while cholesterol level and pituitary and thyroid weights were increased in Px and Gx animals. Pineal weight showed a decrease in the Gx animals. Both Px and Gx failed to influence the circannual rhythms of the measured parameters. However, a significant T4-decreasing effect of Px and Gx was observed in the second half of the year, whereas a cholesterol-level-increasing effect, as well as thyroid hypertrophy, was registered in the first half of the year. These results suggest a prothyroid function of the pineal gland.

Changes in the daily rhythm of serum testosterone levels following superior cervical sympathetic ganglionectomy in the cold-exposed rat: the role of the pineal

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.

The pineal gland: anatomy, physiology, and clinical significance

Since the discovery of melatonin approximately 25 years ago, there has been intense study regarding the details of the structure and function of the pineal gland. This work is reviewed, with particular emphasis on those aspects of importance to human physiology and disease.

Effects of pinealectomy and melatonin administration on thyroid follicles of blind Syrian hamsters

Since previous studies have shown that an active pineal gland exerts an inhibitory effect on circulating levels of thyroxin in the Syrian hamster, a study was conducted to determine whether the histology and ultrastructure of the thyroid gland supported the conclusions drawn from the hormone data. The ultrastructure of thyroid glands of blinded male Syrian hamsters was compared to that of intact controls kept under a 14L/10D photoperiod, to that of blinded hamsters also pinealectomized, and to that of blinded hamsters receiving 80 micrograms/ml of melatonin in the drinking water. Serum thyroxin (T4) and serum thyrotropin (TSH) concentrations were determined by radioimmunoassay. After 10 weeks serum thyroxin concentrations were less than 50% of controls and concentrations were significantly reduced. EM examination revealed that blinded hamsters had an increased number of follicular cells with flattened epithelium and nondilated endoplasmic reticulum compared to intact controls. In blinded hamsters that were pinealectomized or treated with melatonin in the drinking water, the ultrastructure of the thyroid was not different from controls and serum thyroxin concentrations were restored to near normal. These ultrastructural data support the conclusion that the pineal gland is required to obtain inhibition of the pituitary-thyroid axis in blinded hamsters and that melatonin has a counter-inhibitory effect when administered via the drinking water.