Effect of gonadotropin (FSH-LH) and thyrotropin (TSH) treatment in adolescence on TSH-sensitivity in adult rats

Hormonal imprinting is characteristic of the neonatal age, in which the receptor of the target cell matures, i.e. acquires its adult binding capacity, and cellular response becomes established in presence of the adequate hormone. The normal course of imprinting may be altered by certain molecules (related hormones, hormone analogons) which are able to bind to the receptor of the adequate hormone. The chemically related gonadotropic and thyrotropic hormones may overlap on each other's receptors not only in the perinatal age, but also in the early adulthood, and this overlap of the binding may give rise to an imprinting-like effect. An example of this phenomenon was observed in the present study, in which rats of seven weeks of age treated with gonadotropin showed a significant decrease in thyroidic response to TSH, and exposure to TSH failed to increase their basic thyroxine concentration to the normal (control) level. This depressive effect of gonadotropin was slightly reduced in the presence of LPS (endotoxin), causing membrane perturbation, while pretreatment with LPS and TSH accounted for an increased sensitivity to TSH in later phases of the rat's life. These experimental observations support the possibility of a special form of imprinting in adolescence.     

Effect of gonadotropin (FSH + LH) and thyrotropin (TSH) administered with or without endotoxin at the age of three weeks on the response capacity of the thyroid gland in adult rats

At the age of three weeks the experimental animals received either thyrotropin (TSH), or gonadotropin (FSH + LH), or endotoxin (LPS) alone or in combination. The effectivity of the treatments was evaluated at the age of two months (with or without further hormone treatment). Contrastingly to neonatal TSH treatment, TSH treatment at the age of three weeks did not give rise to imprinting. In female animals, however, TSH treatment increased the sensitivity to the related gonadotropin hormone. At the age of three weeks gonadotropin treatment--on its own--did not cause damages to the TSH receptors of the thyroid gland. While in previous experiments neonatal endotoxin treatment damaged considerably the thyroxin production of the adult thyroid gland, after treatments at the age of three weeks no similar effect could be observed. The treatment, however, decreased the sensitivity of the receptors to TSH. In female animals simultaneous administration of endotoxin and TSH led, even without further hormone treatment, to constant increase in T4 level (the increase could also be detected in the adult animal). Imprinting, however, did not develop. In male animals simultaneous administration of endotoxin and gonadotroph hormone decreased considerably the T4 baseline level, and further TSH or gonadotropin treatment was unable to enhance T4 production.     

Long lasting amplification and deformation of thyroid receptors after thyrotropin (TSH) and gonadotropin (GTH) treatment of chickens in the foetal period

Gonadotropin or TSH treatment of the chick embryo influences the T4 production of the one-month-old animal if TSH is given on a second occasion. Hormone treatment on the 8th day of life was ineffective, while previous treatment of the 12-day-old embryo resulted in a significantly more pronounced elevation of serum T4 level compared to the control when provoked by TSH in the one-month-old animal and a significant reduction in the animals subjected to gonadotropin pretreatment.     

Dose dependence of the thyrotropin (TSH) receptor damaging effect of gonadotropin in the newborn rats

A single gonadotropin treatment of newborn rats influenced the thyrotropin (TSH) provoked thyroxine (T4) production of 2 months old animals. On pretreatment with 10, 20, 50, 100 and 200 I.U. of gonadotropin, the T4 blood level of animals given 10 and 200 I.U. differed scarcely from the controls treated only by TSH, while intermediary doses had a damaging effect as the T4 values were well below the control values measured in animals treated by TSH in adulthood.     

Postnatal development of TRH and TSH rhythms in the rat

We previously observed that under a 12-hour light/12-hour dark schedule (lights off at 19.00 h), adult male Sprague-Dawley rats showed a circadian rhythm for serum thyroid-stimulating hormone (TSH) with a zenith near midday. In the present work, the ontogenesis of serum TSH rhythm was determined as well as pituitary TSH variations. In addition, hypothalamic and blood TRH were measured in these rats aged 15, 25, 40 and 70 days when sacrificed. As from the first age studied (15 days), a hypothalamic thyrotropin-releasing hormone (TRH) circadian rhythm was present. The mesor and the amplitude of this hypothalamic TRH rhythm increased while the rats were growing up, in contrast with the decrease observed for these parameters as far as blood TRH circadian rhythm is concerned. The time of the acrophase moved from 17.32 h in the 15-day-old rats to 13.57 h in the 70-day-old rats, being constantly in phase opposition with the blood TRH acrophase. The low amplitude pituitary TSH circadian rhythm detected in the young rat disappeared in the adult while, in contrast, the serum TSH rhythm became consistent to reach the well-characterized circadian midday peak in the 70-day-old rats.     

Influence of pituitary hormones (hCG, TSH, Pr, GH) on testosterone level and on the functional activity of the Leydig cell in rat fetuses

One day after the cessation of treatment the Leydig cells of the fetuses of pregnant rats, treated between the 11th and 15th or the 16th and 20th days of gestation, reacted to pituitary hormones. This finding indicates that both the receptors and the postreceptor mechanisms were in operative state. The effect of the thyrotropic hormone (TSH) overlaps the effect of related gonadotropic hormone (hCG), although this effect becomes smaller from the 21st day. The parameters investigated - the spectrocyto-fluorimetrically measured RNA-DNA ratio and the plasma testosterone level - ran generally in parallel. Similarly to the above-mentioned hormones, prolactin also increased the testosterone level (though to lesser degree than hCG and TSH did), however, while it increased the RNA level but at the age of 16 days, it decreased it the age of 21 days. Somatotropin (GH) also increased somewhat the testosterone level; however, the effects of the two related hormones (Pr and GH) fell far beyond the effect of either TSH or hCG.     

Influence of hormonal imprinting on hormone level. Permanent receptor damaging effect of pituitary hormones administered to newly-hatched cockerels

The overlapping effect of TSH and FSH on the gonad and on the thyroid gland can be demonstrated in cockerels even at the age of five weeks. These hormones influence the secretion of testosterone in a similar way and to a similar extent, while on the thyroxine level the influence of the specific hormone is more pronounced. Neonatal FSH and TSH treatment considerably decreased the basal testosterone level measured at the age of five weeks. Neonatal FSH treatment increased the basal T4 level while TSH treatment decreased it. The effect of TSH treatment administered at the age of five weeks in increasing the testosterone level was weakened after neonatal pretreatment with any iodine hormone. The effect of TSH treatment could only be inhibited by neonatal FSH pretreatment. Neonatal pretreatment with any of the trophormones caused a diminution of the T4 level augmenting of FSH and TSH administered at the age of five weeks.     

Effects of intraventricular injection of gastrin on release of LH,prolactin, TSH and GH in conscious ovariectomized rats

Conscious ovariectomized (OVX) rats bearing a cannula implanted in the 3rd ventricle were injected with 2 μl of 0.9% NaCl containing varying doses of synthetic gastrin and plasma gonadotropin, GH and TSH levels were measured by RIA in jugular blood samples drawn through an indwelling silastic catheter. Control injections of saline iv or into the 3rd ventricle did not modify plasma hormone levels. Intraventricular injection of 1 or 5 μg gastrin produced significant suppression of plasma LH and prolactin (Prl) levels within 5 min of injection. Injection of 1 μg gastrin had no effect on plasma GH, but increasing the dose to 5 μg induced a progressive elevation, which reached peak levels at 60 min. By contrast, TSH levels were lowered by both doses of gastrin within 5 min of injection and the lowering persisted for 60 min. Intravenous injection of gastrin had no effect on plasma gonadotropin, GH and TSH, but induced an elevation in Prl levels. $\text{In}$$\text{vitro}$ incubation of hemipituitaries with gastrin failed to modify gonadotropin, GH or Prl but slightly inhibited TSH release at the highest dose of 5 μg gastrin. The results indicate that synthetic gastrin can alter pituitary hormone release in unrestrained OVX rats and implicate a hypothalamic site of action for the peptide to alter release of a gonadotropin, Prl and GH. Its effect on TSH release may be mediated both via hypothalamic neurons and by a direct action on pituitary thyrotrophs.     

Abnormalities of the thyroid hormone negative feedback regulation of TSH secretion in spontaneously hypertensive rats.

Spontaneously hypertensive rats (SHR) are characterized by several neuroendocrine abnormalities including a chronic hypersecretion of thyrotropin (TSH) of unknown etiology. We hypothesized that the inappropriately high TSH secretion in SHR may be the result of an impaired thyroid hormone negative feedback regulation of hypothalamic thyrotropin-releasing hormone (TRH) and/or pituitary TSH production. To test this hypothesis, SHR or their normotensive Wistar-Kyoto (WKY) controls were treated with either methimazole (0.02% in drinking water) to induce hypothyroidism or administered L-thyroxine (T4) at a dose of 0.8 or 2.0 micrograms/100 g body weight/day to induce hyperthyroidism. All treatments were continued for 14 days after which animals were killed under low stress conditions. TSH concentrations in plasma and anterior pituitary tissue were 2-fold higher (P less than 0.01) in euthyroid SHR compared to WKY control rats while thyroid hormone (T3 and T4) levels were in the normal range. Hypothyroidism induced by either methimazole or thyroidectomy caused a significant (P less than 0.01) rise of plasma TSH levels in both WKY and SHR rats. However, relative to the TSH concentrations in control animals, the increase of plasma TSH in SHR was significantly blunted (P less than 0.01) in comparison to the WKY group. Hypothyroidism caused a significant depletion of TRH in stalk-median eminence (SME) tissue in both groups of rats. However, no differences between SHR and WKY rats were observed. The administration of thyroid hormone caused a dose dependent suppression of plasma TSH levels in both strains of rats. However, at both doses tested plasma TSH concentrations in SHR rats were significantly less suppressed (P less than 0.05) than those in WKY animals. Under in vitro conditions basal and potassium induced TRH release from SMEs derived from SHR was significantly (P less than 0.05) higher than that from WKY rats, whether expressed in absolute terms or as percent of content. These findings suggest that the thyroid hormone negative feedback regulation of TSH secretion may be impaired in SHR rats. Our data do not allow conclusions as to whether defects in the regulation of TSH production are located exclusively at the hypothalamic level. Since the overproduction of hypothalamic TRH and hypophysial TSH should lead to an increased thyroid hormone biosynthesis other defects in the hypothalamus-pituitary-thyroid-axis may contribute to the abnormal regulation of TSH secretion in SHR rats.     

Effects of thyroidectomy, propylthiouracil, and thyroxine on pituitary content and immunocytochemical staining of thyrotropin (TSH) and thyrotropin releasing hormone (TRH)

Previous studies have demonstrated immunocytochemical staining for beta chains of thyroid stimulating hormone (TSH-beta) in rough endoplasmic reticulum of pituitary cells hypertrophied after thyroidectomy ("thyroidectomy cells") (Moriarty CG(1976): J Histochem Cytochem (24:846; Moriarty GC, Tobin RB (1976): J Histochem Cytochem 24:1140). Here we report the localization of thyrotropin releasing hormone (TRH) in serial sections of the same pituitaries to determine if it could be found at similar sites. No staining for TRH was found in hypertrophied TSH cells formed 42 days after the surgery, or after 14, 34, and 70 days of propylthiouracil (PTU) treatment. The loss in immunostaining in the PTU-treated rats was correlated with radioimmunoassay (RIA) measurements that showed a 65% reduction in anterior pituitary TRH content after 34, 70, and 98 days of PTU treatment (from 22.9--7.8 pg/mg wet wt) and a 50% reduction in TSH content after 34 days of treatment. When thyroxine was administered to hypothyroid rats for 3 days before death, our previous studies had demonstrated intense staining for TSH in granules inside the rough endoplasmic reticulum. In this study, the radioimmunoassay showed that TSH content rose dramatically in the hypothyroid animals treated with PTU for 77 days and thyroxine for 2 days before death (from 8.5--64.1 mU/mg wet wt); however, the rise in TRH content was minimal (5.8--9.8 pg/mg wet wt). The immunocytochemical stain for TRH correlated well with the RIA showing a weak reaction mainly on small granules in the cytoplasm. No reaction for TRH was found in rough endoplasmic reticulum. These results suggest that TRH and TSH storage sites are dissimilar in the hypothyroid rat. The presence of stain for TRH in granules in the cytoplasm suggests that it might play a role in the storage or packaging of TSH. Its absence in profiles of rough endoplasmic reticulum staining intensely for TSH suggests that it is not synthesized at this site. No definite conclusions about its origin can be drawn at this time.     

Alteration of stimulated TSH and prolactin response in children treated with growth hormone.

The plasma TSH and prolactin responses to thyrotropin releasing hormone (TRH) were measured in 5 children with isolated growth hormone deficiency prior to, during and after the administration of human growth hormone (hGH). TSH and prolactin secretory patterns were not uniformly concordant. TSH responses to TRH infusion were suppressed in 4 subjects after 5 days or 1 month of hGH administration despite normal serum thyroxin concentrations. Prolactin responses were suppressed in all 5 subjects after 5 days of hGH administration. After 8 months of hGH therapy both TSH and prolactin responses returned toward pre-hGH values. Our finding that suppression of the TRH-induced TSH and prolactin secretory responses are reversible during hGH administration supports the concept of altered neuroregulation in this form of hypothalamic disorder.     

Exaggerated TSH responses to TRH in patients with goiter and 'normal' basal TSH levels

BACKGROUND/AIM: The availability of sensitive thyrotropin (TSH) assays decreased the diagnostic value of thyrotropin-releasing hormone stimulation tests (TRH-ST) in subclinical hypothyroidism. In this study we aimed to evaluate the relation between basal and stimulated serum TSH levels on TRH-ST and to determine the prevalence of patients with normal basal serum TSH and exaggerated TSH responses. METHODS: 179 patients (117 girls, 123 pubertal) with a median age of 12 (2.7-21.4) years who presented with goiter were enrolled and evaluated for their pubertal stage, height, thyroid autoimmunity, ultrasonography, thyroid function, and TRH-ST. Serum TSH concentrations were determined by sensitive assays. At TRH-ST, a peak serum TSH level >25 mIU/l was considered as an exaggerated response. RESULTS: 30 (17%) patients had an exaggerated TSH response. In patients with serum TSH levels between 2 and 4.68 mIU/l (upper half the normal range), an exaggerated TSH response was observed in 19.5%. A positive correlation between basal and TRH-stimulated TSH levels was determined (r = 0.536, p < 0.01). In patients with an exaggerated TSH response, 23 had normal (discordant) and 7 had high basal TSH levels (concordant). The mean basal serum TSH level was lower in the discordant group compared to the concordant group (p < 0.01). CONCLUSION: Basal serum TSH levels might not be sufficient for diagnosing subclinical hypothyroidism. Stimulated TSH levels on TRH-ST are valuable, especially when serum TSH concentrations are in the upper half of the normal range.     

Impact of a single neonatal gonadotropin (FSH + LH) or thyrotropin (TSH) treatment on the sexual behaviour of the adult male rat

A single gonadotropin (FSH + LH) treatment of neonatal male rats resulted in depression of sexual activity in adulthood. It appears that not only steroids, but also gonadotropins may alter adult sexual behaviour by a single neonatal exposure. The chemically related hormone thyrotropin (TSH) had a similar, but much less pronounced, effect on adult sexual activity.     

Age-dependent effect of Freund's adjuvant on 24-hour rhythms in plasma prolactin, growth hormone, thyrotropin, insulin, follicle-stimulating hormone, luteinizing hormone and testosterone in rats

The effect of Freund's adjuvant administration on 24-hour changes of plasma prolactin, growth hormone (GH), thyrotropin (TSH), insulin, follicle-stimulating hormone (FSH), luteinizing hormone (LH) and testosterone were studied in young (2 months) and aged (18 months) male Wistar rats. Rats were injected s.c. with Freund's adjuvant or adjuvant's vehicle and, 18 days later, they were killed at 6 different time intervals throughout a 24-hour cycle to measure circulating hormone levels by specific RIAs. Young rats receiving adjuvant's vehicle exhibited significant time-of-day-dependent variations in plasma TSH, LH and testosterone, with maximal levels at 1300 h, 0100 h and 1700 h, respectively. Prolactin and insulin levels, analyzed globally in a factorial ANOVA, showed significant time-of-day changes with maximal levels at 1300 - 1700 h and 2100 h, respectively. The daily rhythms in plasma LH and testosterone found in young rats were not longer observed in Freund's adjuvant-injected rats, while as far as TSH, a second peak was observed at 0100 h after Freund's adjuvant administration. Twenty-four hour rhythms in circulating TSH, LH and testosterone were blunted in old rats receiving either Freund's adjuvant or its vehicle. Aged rats exhibited significantly higher circulating levels of prolactin, and lower levels of GH, TSH, FSH and testosterone. The results indicate that secretion of prolactin, GH, TSH, FSH and testosterone are age-dependent, as are the responses of TSH, LH and testosterone to Freund's adjuvant administration.     

Age and thyroid hormone as factors in the responses of BHE rats to starvation-refeeding

The interacting effects of thyroid hormone, age, and duration of starvation on the enzyme and liver lipid responses of BHE rats to starvation-refeeding were studied. Rats were starved for 2, 4, or 7 days and refed a 65% glucose diet for 2 days. The rats were either 150 or 420 days of age and injected daily with either saline or 10 micrograms thyroxine/100 g body weight. Neither age nor duration of starvation affected the glucose-6-phosphate dehydrogenase or malic enzyme activity or liver lipid response to starvation-refeeding. However, thyroxine treatment potentiated the response to starvation-refeeding in the 420-day-old rats when the duration of starvation increased from 2 to 7 days.     

Potentiation by indomethacin of TRH-induced TSH secretion in the rat.

We have studied the effect of two inhibitors of prostaglandin synthesis on the basal and TRH-stimulated plasma TSH levels in the rat. Animals were injected sc daily with indomethacin 3 mg/0.5 ml) or aspirin (16--30 mg/0.5 ml) for 3 days. The plasma T4 and T3 were consistently lower in the indomethacin or aspirin groups than in the controls, while the basal TSH levels did not change. Indomethacin treatment significantly potentiated the TSH response to synthetic TRH (20 ng. iv) in intact and thyroidectomized rats. The pituitary TSH content was markedly increased by indomethacin, while hypothalamic TRH content did not change. In contrast, aspirin inhibited the TSH response to TRH in intact rats, when pituitary TSH content decreased significantly. No potentiation by aspirin of TRH-stimulated TSH response in the thyroidectomized rats was observed. The increased sensitivity of plasma TSH response to exogenous TRH in the indomethacin group is presumably due to higher pituitary TSH content than in the controls. The action of indomethacin appears to be mediated, at least in part, at the pituitary level. In addition, there is a dissociation between the action of indomethacin and the action of aspirin in the TSH response to TRH.     

Diagnostic value of thyrotrophin releasing hormone tests in elderly patients with atrial fibrillation.

A prospective study was carried out to compare clinical and biochemical thyroid states with responses of thyroid stimulating hormone (TSH) to thyrotrophin releasing hormone (TRH) in elderly patients with either atrial fibrillation (n = 75; mean age (SD) 79.3 (6.0) years) or sinus rhythm (n = 73; mean age 78.4 (5.6) years) admitted consecutively to the department of geriatric medicine. No patient in either group had symptoms or signs of hyperthyroidism. Overall, the TSH responses to TRH did not differ significantly between the two groups. Ten (13%) of the patients with atrial fibrillation (of whom four had raised thyroid hormone concentrations) and five (7%) of the patients with sinus rhythm showed no TSH response to TRH while 26% of each group (20 and 19 patients, respectively) showed a much reduced response. Only one of 13 patients with apparently isolated atrial fibrillation showed no TSH response to TRH, and none of these 13 patients was hyperthyroid. In particular, three patients (two with atrial fibrillation and one with sinus rhythm) who showed no TSH response to TRH at presentation exhibited a return of TSH response to TRH at follow up six weeks later. In conclusion, reduced or absent TSH responses to TRH are common in sick elderly patients whether they have atrial fibrillation or sinus rhythm and whether they are euthyroid or hyperthyroid biochemically. An absence of response is therefore an uncertain marker of hyperthyroidism in these groups of patients, and diagnosis and ablative treatment should be based at least on the presence of raised circulating free triiodothyronine or free thyroxine concentrations, or both.     

Seminiferous tubule fluid and interstitial fluid production. I. Effects of age and hormonal regulation in immature rats

Efferent duct ligation was used to assess seminiferous tubule fluid (TF) production and studies of the kinetics of TF production following this procedure were performed on 25-day-old rats. The rate of TF production was linear for 48 h, thereafter reached a plateau until 72 h and began decreasing at 96 h post-ligation. Using a 16-h ligation period, the onset of TF production was investigated in groups of immature rats from 15 days of age. TF secretion was not detected prior to 15 days but rose rapidly after Day 20 coincident with the prepubertal rise in serum FSH. The acute effect of hormone on TF production following unilateral efferent duct ligation (EDL) was evaluated in 25-day-old rats in which interstitial fluid production (IF) was also assessed in the unligated testis by the method of Sharpe (1977). Single subcutaneous injections of the following hormones were given to groups of rats at the time of EDL: a) NIH follicle-stimulating hormone (FSH) S13 (20 micrograms/rat); b) NIH luteinizing hormone (LH) S22 (200 micrograms/rat); c) testosterone propionate (2 mg/rat); d) human chorionic gonadotropin (hCG) (10 IU/rat); or e) NIH prolactin (Prl) 14 (200 micrograms/rat). A significant rise in TF production occurred following FSH treatment but no effect was noted in any of the other groups. In contrast, a marked stimulation of IF production occurred in rats treated with LH or hCG.     

Effects of age and luteinizing hormone antiserum on human chorionic gonadotropin-stimulated testosterone secretion in young male rats

The steroidogenic capacity of young male rats of different ages was studied. Two days prior to sacrifice at 5, 10, 15, 20, 25 and 30 days of age, the rats in treatment groups were given intramuscularly either human chorionic gonadotropin (HCG) at 20 I.U. twice daily/rat or luteinizing hormone (LH) antiserum (AS) at 0.25 ml twice daily/rat. Either saline or normal sheep serum (NSS) was given to control rats. The serum and testicular testosterone concentrations in the control rats averaged 0.85 +/- 0.03 ng/ml and 1.35 +/- 0.06 ng/mg testicular protein, respectively. At day-15 the serum and testicular testosterone concentrations in the HCG-treated rats had significantly increased to 9.30 +/- 0.85 ng/ml and 11.92 ng/mg of testicular protein, respectively. At the same age, the HCG-induced higher levels of serum and testicular testosterone concentrations were significantly reduced to 2.80 +/- 0.70 ng/ml and 6.02 +/- 1.00 ng/mg protein by concomitant administration of LH/AS and HCG. Our results suggest that the testosterone production in response to HCG stimulation is age-related. It was also determined that neutralization of circulating gonadotropin in LH/AS-treated rats decreased the sensitivity of Leydig cells to gonadotropin stimulation. This in vivo model should provide an excellent opportunity for the investigation of the testicular function in developing young males.     

Investigation of gonadotropin-thyrotropin overlapping and hormonal imprinting in the rat testis

In the neonatal period both gonadotropin and thyrotropin increase the weight of the testis, influence considerably the diameter of the contorted tubules increase the occurrence of Sertoli cells and decrease the number of spermatogonia. These phenomena can still be observed at the age of seven days but they disappear by the age of six weeks; at that time the hormones decrease the weight of the testis. One single TSH treatment administered in the neonatal period considerably increased the weight of the testis and the diameter of the channels when investigated at the age of six weeks. Gonadotropin had none of these effects. The phenomenon of imprinting could be proved as in the animals pretreated with TSH, gonadotropin given at the age of six weeks decreased the weight of the testis and both hormones decreased the diameter of the seminiferous cords.