Morphometry, topography and arterial supply of the thyroid gland in rhesus monkeys (Macaca mulatta Zimmermann, 1780)

The purpose of this research was to investigate the measures, topography, and vascularization of the thyroid gland in Macaca mulatta, a non-human primate. The study involved the dissection of ten male adult cadavers of Macaca mulatta. The length, width, and thickness of the right lobe of the thyroid were 2.552 ± 0.341, 1.019 ± 0.137, and 0.729 ± 0.137 cm. These measures in the left thyroid lobe were 2.406 ± 0.299, 1.013. ± 0.087, and 0.769 ± 0.083 cm. The study found no significant differences in the measures of the left and right lobes of the thyroid gland in rhesus monkeys. Regarding topography, the thyroid gland was located ventrolateral to the trachea, similar to its position in other mammal species. The cranial pole of the gland was closely related to the cricoid or thyroid cartilage, while the caudal pole showed variable positioning to the tracheal rings. The isthmus, a thin band of tissue connecting the lobes, was present in all specimens. The cranial thyroid artery was found to originate from the external carotid artery in most specimens. It supplied the thyroid gland and sent branches to muscles in the neck region. The caudal thyroid artery, originating from the common carotid artery, provides additional blood supply to the gland and sends a branch to the esophagus. This research contributes to knowledge about the thyroid gland in non-human primates, specifically Macaca mulatta. The findings provide critical information for comparative studies and understanding the thyroid gland's role in health and disease.

Simulations of radioiodine exposure and protective thyroid blocking in a new biokinetic model of the mother-fetus unit at different pregnancy ages

In the case of nuclear incidents, radioiodine may be released. After incorporation, it accumulates in the thyroid and enhances the risk of thyroidal dysfunctions and cancer occurrence by internal irradiation. Pregnant women and children are particularly vulnerable. Therefore, thyroidal protection by administering a large dose of stable (non-radioactive) iodine, blocking radioiodide uptake into the gland, is essential in these subpopulations. However, a quantitative estimation of the protection conferred to the maternal and fetal thyroids in the different stages of pregnancy is difficult. We departed from an established biokinetic model for radioiodine in pregnancy using first-order kinetics. As the uptake of iodide into the thyroid and several other tissues is mediated by a saturable active transport, we integrated an uptake mechanism described by a Michaelis–Menten kinetic. This permits simulating the competition between stable and radioactive iodide at the membrane carrier site, one of the protective mechanisms. The Wollf–Chaikoff effect, as the other protective mechanism, was simulated by adding a total net uptake block for iodide into the thyroid, becoming active when the gland is saturated with iodine. The model’s validity was confirmed by comparing predicted values with results from other models and sparse empirical data. According to our model, in the case of radioiodine exposure without thyroid blocking, the thyroid equivalent dose in the maternal gland increases about 45% within the first weeks of pregnancy to remain in the same range until term. Beginning in the 12th pregnancy week, the equivalent dose in the fetal thyroid disproportionately increases over time and amounts to three times the dose of the maternal gland at term. The maternal and fetal glands’ protection increases concomitantly with the amount of stable iodine administered to the mother simultaneously with acute radioiodine exposure. The dose–effect curves reflecting the combined thyroidal protection by the competition at the membrane carrier site and the Wolff–Chaikoff effect in the mother are characterized by a mean effective dose (ED₅₀) of roughly 1.5 mg all over pregnancy. In the case of the fetal thyroid, the mean effective doses for thyroid blocking, taking into account only the competition at the carrier site are numerically lower than in the mother. Taking into account additionally the Wolff–Chaikoff effect, the dose–effect curves for thyroidal protection in the fetus show a shift to the left over time, with a mean effective dose of 12.9 mg in the 12th week of pregnancy decreasing to 0.5 mg at term. In any case, according to our model, the usually recommended dose of 100 mg stable iodine given at the time of acute radioiodine exposure confers a very high level of thyroidal protection to the maternal and fetal glands over pregnancy. For ethical reasons, the possibilities of experimental studies on thyroid blocking in pregnant women are extremely limited. Furthermore, results from animal studies are associated with the uncertainties related to the translation of the data to humans. Thus model-based simulations may be a valuable tool for better insight into the efficacy of thyroidal protection and improve preparedness planning for uncommon nuclear or radiological emergencies.

CORRECTING EFFECT OF AQUEOUS EXTRACT FROM DUCKWEED LEMNA MINORFROND ON MORPHOLOGICAL STATE OF THYROID GLAND IN RATS WITH HYPOTHYROIDISM

The present work studied the effect of aqueous extract from duckweed Lemna minor frond on morphological state of the thyroid gland in the experimental hypothyroidism. Healthy albino rats weighing between 120 g and 150 g were used. The animalswere randomly allotted into four groups, each containing ten rats respectively. Three of the groups (II, III and IV) induced with hypothyroidism by 1 % solution of sodium perchlorate with drinking water for 20 days. Control (vehicle) rats were given normal saline. After 20 days hypothyroid groups (III and IV) of rats treated with aqueous extract from duckweed Lemna minor frond at a dose 0.5 ml/100 g of body weight and with Iodomarin 200 (reference drug) at a dose 12 µg/kg daily orally for 21 days. Results obtained from the study showed that the introduction of sodium perchlorate leads to morphological and functional changes in the structure of the thyroid gland in rats, accompanied by sings of hyperplastic tissue proliferation and corresponds with hypofunctional state. It was established that introduction of aqueous extract from duckweed Lemna minor frond has a positive effect on the restructuring of the thyroid gland in rats with hypothyroidism, increasing its functional activity. There is a decrease of proliferative processes by extrafolliсular epithelium and thyrocytes in the follicles. The outer diameter of follicles decreased by 7.65 % (P>0.05), the height and size of thyrocytes in the wall of the follicle were significantly decreased by 58.16 % and 18 41 %, respectively, compared to untreated hypothyroid group. The obtained results have practical significance for the development of drugs with thyroid-stimulating action for preventing or delaying the development of hypothyroidism and its complications.

Effect of soy isoflavones on thyroid hormones in intact and ovariectomized cynomolgus monkeys (Macaca fascicularis)

OBJECTIVE

Soy isoflavones are commonly used to alleviate menopause-related symptoms. Postmenopausal women are at increased risk for hypothyroidism, and there are concerns that isoflavones may be detrimental to thyroid health. The aim of this study was to examine the effects of soy protein and isoflavones on thyroid function and the relationship between thyroid function and ovarian function.

METHODS

Adult female cynomolgus monkeys (Macaca fascicularis) were randomized to consume two diets differing only in protein source: casein-lactalbumin (n = 44) or soy protein with isoflavones (n = 41). After 34 months, all animals were ovariectomized via laparotomy. Half of the monkeys from each diet treatment group continued to consume their preovariectomy treatment phase diet (either isolated soy protein [n = 19] or casein-lactalbumin [n = 21]) for an additional 34 months. The remaining animals did not continue their diets and thus were not considered further. Circulating progesterone, triiodothyronine, thyroxine, and thyroid-stimulating hormone were measured at baseline. Thyroid hormones were remeasured during each treatment phase.

RESULTS

Dietary soy increased triiodothyronine in preovariectomized monkeys and prevented a decline in thyroxine after surgical menopause (both P's < 0.05). Mean progesterone concentrations were positively correlated with triiodothyronine at baseline in preovariectomized monkeys (P < 0.01).

CONCLUSIONS

Progesterone levels and triiodothyronine are positively correlated in macaques. Dietary soy increases triiodothyronine in preovariectomized monkeys and prevents a decline in thyroxine after surgical menopause. The outcomes observed in this study suggest that soy protein and isoflavone consumption does not adversely affect-and may even preserve-thyroid function in postmenopausal women.

Paracrine interactions of thyroid hormones and thyroid stimulation hormone in the female reproductive tract have an impact on female fertility

Thyroid disease often causes menstrual disturbances and infertility problems. Thyroid hormone (TH) acts through its receptors, transcription factors present in most cell types in the body. Thyroid stimulating hormone (TSH) stimulates TH synthesis in the thyroid gland, but seems to have other functions as well in the female reproductive tract. The receptors of both TH and TSH increase in the receptive endometrium, suggesting that they are important for implantation, possible by influencing inflammatory mediators such as leukemia inhibitory factor. The roles of these receptors in the ovary need further studies. However, it is likely that the thyroid system is important for both follicular and embryo development. The association between thyroid disease and infertility indicate that TH and TSH affect the endometrium and ovary on the paracrine level.