This study was to evaluate the effect of androgen deficiency on thyroid immunoreactive C-cells and bone structure and function in a male orchidectomized middle-aged rat model. Fifteen-month-old male Wistar rats were divided into orchidectomized (Orx) and the sham-operated control (Sham) group. In the Orx group significant decreases (P < 0.05) were found in the volume of C cells (by 14%), their relative volume density (by 13%) and serum calcitonin concentration (by 54%) compared to the controls. Analyses of trabecular microarchitecture of the proximal tibia metaphysis showed that Orx induced marked decreases of cancellous bone area, trabecular thickness and trabecular number (by 52, 20 and 19% respectively; P < 0.05), whereas trabecular separation was increased by 27% (P < 0.05). In Orx rats, serum osteocalcin concentration was increased by 119% (P < 0.05), while serum calcium and phosphorus were 6 and 14% (P < 0.05) lower, respectively, compared to the levels in the Sham. In addition, urine calcium content was considerably higher (by 129%; P < 0.05) in Orx animals. These findings indicate that the androgen deficiency caused by Orx in middle-aged rats modulated the structure of C cells and diminished secretion of calcitonin. Histomorphometrical and biochemical analyses demonstrated a decrease of cancellous bone mass and increased bone turnover.

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Androgen deficiency is one of the major factors leading to the development of osteoporosis in men. Since calcitonin (CT) is a potent antiresorptive agent, in the present study we investigated the effects of androgen deficiency and subsequent testosterone and estradiol treatment on CT-producing thyroid C cells, skeletal and hormonal changes in middle-aged orchidectomized (Orx) rats. Fifteen-month-old male Wistar rats were either Orx or sham-operated (SO). One group of Orx rats received 5 mg kg À1 b.w. testosterone propionate (TP) subcutaneously, while another group was injected with 0.06 mg kg À1 b.w. estradiol dipropionate (EDP) once a day for 3 weeks. A peroxidase-antiperoxidase method was applied for localization of CT in the C cells. The studies included ultrastructural microscopic observation of these cells. The metaphyseal region of the proximal tibia was measured histomorphometrically using an IMAGEJ public domain image processing program. TP or EDP treatment significantly increased C cell volume (Vc), volume densities (Vv) and serum CT concentration compared with the Orx animals. Administration of both TP and EDP significantly enhanced cancellous bone area (B.Ar), trabecular thickness (Tb.Th) and trabecular number (Tb.N) and reduced trabecular separation (Tb.Sp). Serum osteocalcin (OC) and urinary Ca concentrations were significantly lower after these treatments in comparison with Orx rats. These data suggest that testosterone and estradiol treatment in Orx middle-aged rats affect calcitonin-producing thyroid C cells, which may contribute to the bone protective effects of sex hormones in the rat model of male osteoporosis.

These findings indicate that daidzein treatment stimulates thyroid C cells, increase trabecular bone mass, and decrease bone turnover in Orx middle-aged rats, which is the model of male osteoporosis.

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Body weight depends on the balance between energy intake and consumption. An interaction between ghrelin and thyroid function has been reported only in pathophysiological states. We examined whether intracerebroventricular (ICV) administration of ghrelin affects the structure and function of the pituitary-thyroid axis in young adult male rats. Ghrelin (0.3 nmol/5 μl PBS) or an equal volume of PBS were injected every 24 h into the lateral cerebral ventricle for 5 days. Two hours after the last treatment the animals were killed, their pituitaries and thyroids excised and prepared for further histological, immunohistochemical and morphometric investigation. Serum TSH levels were measured by RIA, while the total T₄ and T₃ levels were examined by ECLIA. Ghrelin treatment increased pituitary weight (p < 0.05) when compared to the controls, with no effect on the thyroid weight. Smaller, degranulated TSH-immunopositive cells were noticed within the pituitaries of ghrelin-treated animals; their cellular and nuclear volume as well as the relative volume density of thyrotrophs decreased (p < 0.05) in comparison to the control values. The level of serum TSH was reduced (p < 0.05). In the thyroid parenchyma of ghrelin-treated rats, an increased number of hypofunctioning follicles was noticed, characterized by flattened, weakly Tg-immunoreactive epithelium and colloid distension. The relative volume densities of the follicles and colloid increased (p < 0.05), while the thyroid index of activation rate and the serum level of total T₄ decreased (p < 0.05). In conclusion, centrally applied ghrelin modulated the immunohistomorphometric features of pituitary TSH cells and decreased the level of serum TSH, consequently changing thyroid morphology and function, by reducing the T₄ hormone level in the serum.

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