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PubMed1986

Thyroidectomy of SHR: effects on ventricular relaxation and on SR calcium uptake activity.

Ventricular hypertrophy and hypothyroidism are each characterized by impaired cardiac muscle relaxation and sarcoplasmic reticulum (SR) calcium uptake activity. A previous report also showed that hypothyroidism does not reverse ventricular hypertrophy (left-to-right ventricular weight ratios) of spontaneously hypertensive rats (SHR). We characterized the effects of thyroidectomy of 8 wk duration on relaxation of ejecting hearts and on SR calcium uptake activity from SHR and nonhypertrophic Wistar-Kyoto rat (WKY) controls. Relaxation was quantified by plotting maximum left ventricular pulse pressure (Pmax) vs. the area under the falling phase of the left ventricular pressure wave at three different pressure loads. Ventricles of euthyroid SHR were characterized by impaired relaxation and depressed SR calcium uptake activity compared with those of euthyroid WKY, confirming earlier studies. Thyroidectomy reduced ventricular relaxation and SR calcium uptake activities to about the same extent in SHR and WKY strains so that these measurements were most depressed in the SHR hypothyroid group. When all groups were considered, the extent of mechanical relaxation ex vivo and the rate of SR calcium uptake in vitro were well correlated.

Animals↗
PubMed1992

Response of hypothalamic peptide mRNAs to thyroidectomy.

Using in situ hybridization histochemistry, we have investigated the effect of thyroid hormone on the expression of several peptide mRNAs in the hypothalamic paraventricular nucleus (PVN) of adult male rats. Hypothyroidism was induced by surgical ablation of the thyroid gland. The animals (control sham-operated, thyroidectomized, thyroidectomized+T4 replaced rats) were studied 28 and 50 days after surgery. Sections of the PVN were hybridized using synthetic oligonucleotide probes complementary to mRNA for thyrotropin-releasing hormone (TRH), corticotropin-releasing hormone (CRH), galanin (GAL), enkephalin (ENK), neurotensin (NT), vasoactive intestinal polypeptide (VIP) and vasopressin (VP). GAL mRNA was also analyzed in the anterior paraventricular, arcuate, and dorsomedial nuclei of the hypothalamus. At the PVN level, a feedback effect of thyroid hormone on TRH synthesis was demonstrated by the TRH mRNA increase in hypothyroidism and by its decrease in hyperthyroidism. Hypothyroidism caused a dramatic decrease in GAL mRNA in parvo- and magnocellular PVN neurons both 28 and 50 days after thyroid ablation, whereas no effect was seen in VP mRNA, the main peptide hormone coexisting with GAL. The T4 replacement prevented the GAL mRNA impairment. Hypothyroidism did not influence GAL mRNA in the anterior PVN, perifornical area or in the arcuate nucleus, whereas a decrease in GAL mRNA was observed in the dorsomedial nucleus. VIP mRNA, which is undetectable in the PVN of normal animals, was present in several PVN neurons after thyroidectomy. CRH mRNA was decreased after thyroidectomy, whereas the T4 restitution caused an upregulation. The levels of ENK or NT mRNA were not significantly affected by the thyroid status. The present results show that, in addition to TRH mRNA, other hypothalamic peptide mRNAs are affected by thyroid hormone levels.

Animals↗
PubMed1987

Beneficial effect of thyroidectomy in canine hemorrhagic shock.

To further evaluate the relationship between plasma thyroid hormone concentrations and mortality in shock, 10 thyroidectomized and 9 normal dogs were bled rapidly to a mean arterial pressure of 40 mm Hg. After 60 min of hypotension, the reservoir line was clamped for 30 min. The shed blood was then reinfused. Thyroidectomy produced a hypodynamic, hypometabolic state. During shock, these animals exhibited fewer major hemodynamic derangements than the control group. Only one thyroidectomized dog died, whereas 5 of 9 control animals died (p less than 0.05). Thus, circulating thyroid hormones are not determinants of survival in canine hemorrhagic shock. We hypothesize that thyroidectomy, perhaps by modulating catecholamine metabolism or stimulating liberation of thyrotropin releasing hormone, promotes salutary hemodynamic-metabolic effects during circulatory collapse and enhances survival.

Animals↗
PubMed1987

Effects of thyroidectomy and thyroxine replacement on the release of luteinizing hormone and gonadotropin-releasing hormone in vitro.

The effects of thyroidectomy and thyroxine (T4) replacement on the release of luteinizing hormone (LH) and gonadotropin-releasing hormone (GnRH) in ovariectomized (Ovx) rats were studied. Immediately after ovariectomy, rats were thyroidectomized (Tx) or sham-Tx. The Ovx-Tx rats were injected subcutaneously with either saline or T4 (2 micrograms/100 g body weight) daily for 30 days before sacrifice. Sham-Tx rats were treated with saline only. Twenty hours after the last injection, the blood sample was obtained by decapitation. The excised anterior pituitary gland (AP) was bisected and incubated in vitro with or without 0.1, 0.5, 2.5, and 50 ng GnRH at 37 degrees C for 4 h. The mediobasal hypothalamus (MBH) was bisected and incubated with or without the AP of Ovx donor rat in vitro. Concentrations of LH and GnRH in the medium and that of LH in the serum were measured by radioimmunoassay. LH in the serum of Tx rats was higher than that in the serum of sham-Tx and Tx-T4 rats. Thyroidectomy resulted in an increase of LH release by Ovx rat AP, stimulated with or without 0.1 and 50 ng GnRH, as well as in an increase of immunoreactive GnRH release from MBH of Ovx rats in vitro. After a 4-hour incubation with donor APs, the LH in the medium containing MBH obtained from Tx rats was significantly higher than that obtained from sham-Tx and Tx-T4 rats. LH concentrations, in both sera and media, as well as GnRH concentration in the media of euthyroid and T4-replaced Tx groups were nonsignificantly different. These results suggest that T4 is inhibitory to the basal and GnRH-stimulated LH release as well as to the release of GnRH in the absence of ovarian hormones.

Animals↗
PubMed1982

Development of bile acid biogenesis in the rat: effect of neonatal thyroidectomy, adrenalectomy, and streptozotocin-induced diabetes.

Effect of neonatal thyroidectomy, adrenalectomy and streptozotocin-induced diabetes in rats on the bile acid pool size and composition at weaning was examined. Adrenalectomy caused a significant (p less than 0.05) decrease in the total bile acid pool with significant reductions (p less than 0.05) in both cholic and chenodeoxycholic acids. Thyroidectomy on the other hand caused a specific decrease (p less than 0.05) in chenodeoxycholic acid pool. Streptozotocin-induced diabetes caused (a) a decrease (p less than 0.05) in total bile acid pool with a significant (p less than 0.05) reduction in chenodeoxycholic acid, and (b) an increase in plasma cholesterol levels.

Adrenalectomy↗
PubMed1994

Parathyroid autotransplantation in patients undergoing a total thyroidectomy: a review of 261 patients.

Parathyroid autotransplantation was first described in 1907 by Halsted. However, this simple and effective method of preserving parathyroid function has been used with increasing frequency only during the past 25 years. Beginning in the late 1960s, our group has transplanted normal parathyroid tissue into the ipsilateral sternocleidomastoid muscle whenever these glands could not be preserved in situ with adequate blood supply. In addition, if the blood supply of all four parathyroid glands appeared compromised, cryopreservation of parathyroid tissue was performed in case the autotransplanted tissue did not function after surgery. Since 1970, 393 patients underwent a total thyroidectomy. Parathyroid glands that could not be saved in situ were biopsied to confirm their identity by frozen section and then autotransplanted. Of the 393 patients who underwent a total thyroidectomy, 261 patients required transplantation of one or more glands. Among those 261 patients who underwent selective parathyroid autotransplantation, 33 (13%) required temporary calcium and vitamin D supplementation. Of these 33 patients, 2 (less than 1%) had permanent hypoparathyroidism and are receiving long-term vitamin D therapy.

Adolescent↗
PubMedDate not supplied

Frequency of thyroid carcinoma in a recent series of 539 consecutive thyroidectomies for multinodular goiter.

AIMS AND BACKGROUND: The aim of the study was to analyze the frequency of thyroid carcinoma in a consecutive series of 539 thyroidectomies for multinodular goiter (MNG) and to assess the influence of sex and age as cancer risk factors. METHODS: In a 2-year period, 539 patients underwent subtotal or total thyroidectomy for MNG at the institute of General Surgery, University of Padova, Padova, Italy: 455 were females and 84 males (F/M = 5.5/1); mean age was 46 years (min. 17, max 78). Only 17 patients (3.1%) (16 females and 1 male) were aged 21 years or less. RESULTS: A malignancy was found in 41 patients: 38 females and 3 males; 39 older and 2 younger than 21 years. The frequency of cancer in MNG was 7.6%: 8.3% in females and 3.6% in males; 7.5% in patients older than 21 and 11.7% under 21 years. CONCLUSIONS: The combination of MNG and carcinoma should always be carefully considered but not overemphasized, and the policy of surgically treating all patients with MNG is not justified. Sex and age cannot be considered as factors of a higher risk of cancer.

Adult↗
PubMed1994

Thyroidectomy does not affect the daily or free-running rhythms of plasma melatonin in European starlings.

Thyroidectomy results in the suppression of reproductive photoperiodic responses in starlings. Could this be a consequence of an effect on perception of daylength or on circadian pacemakers? Daily changes in plasma melatonin concentrations were monitored in intact and thyroidectomized starlings held in long days (LD 16:8) and short days (LD 8:16), and in intact and thyroidectomized starlings allowed to free-run in constant darkness from long days or short days. In long days and short days, melatonin was low during the light period and high during darkness. There was no difference between intact and thyroidectomized birds. In free-running birds, the melatonin profile of the preceding long day or short day was retained during the first day of constant darkness, with peak levels occurring at the same time they did during the light-dark cycles. Again there was no difference between intact and thyroidectomized birds. These data demonstrate that either the photoreceptive and circadian mechanisms driving melatonin secretion are independent of those concerned with reproductive photoperiodic responses, or that thyroidectomy affects reproduction "downstream" from the photoreceptive-circadian apparatus.

Animals↗
PubMedDate not supplied

Thyroid cancer: extent of thyroidectomy.

BACKGROUND: Surgical resection is the key to management of thyroid cancer, but determining the optimal surgical procedure for individual cases has been controversial. METHODS: The author reviews several large data bases that allow examination of prognostic criteria for long-term outcomes. RESULTS: Patients can be classified into good- or poor-risk groups that assist defining the optimal surgical procedure. Routine use of total thyroidectomy in all patients with thyroid cancer is best avoided; however, patients with medullary cancer generally need total thyroidectomy. CONCLUSIONS: The definition of risk groups has clarified the options regarding choice of primary surgical therapy for differentiated thyroid cancer.

Humans↗
PubMed1976

An immunocytochemical study of TSH beta storage in rat thyroidectomy cells with and without D or L thyroxine treatment.

Binding sites to the beta chain of thyroid stimulating hormone (TSH) were localized in pituitaries of thyroidectomized rats. Immunocytochemical staining was observed in hypertrophied TSH cells ("thyroidectomy cells") and primarily located in dilated rough endoplasmic reticulum. Staining was also found on the few secretory granules and on some of the intracisternal granules. Some of the thyroidectomy cells stained intensely, while others exhibited very little staining. When thyroidectomized rats were treated with thyroxine 4 days before death, the TSH cells contained more secretory granules, and the intracisternal granules were larger and more numerous. L-thyroxine was 10 times as potent as D-thyroxine in promoting the build-up of granules. Both types of granules stained intensely.

Animals↗
PubMed1981

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.

Animals↗
PubMed1987

Thyroidectomy significantly alters carbonic anhydrase III concentration and fiber distribution in rat muscle.

Thyroidectomy has a dramatic effect on rat muscle, greatly increasing the number of Type I fibers and the concentrations of carbonic anhydrase III (CAIII) in the muscle. Carbonic anhydrase III is not confined to the Type I fibers, as was previously believed, but also occurs in fibers that exhibit a level of ATPase staining less than that of 2A fibers but greater than 2B. These fibers are rare in normal muscle but become numerous after thyroidectomy, when they stain heavily for CAIII.

Adenosine Triphosphatases↗
PubMed1984

Thyroid lysosomal enzyme activity and ultrastructure after subtotal thyroidectomy.

Subtotal thyroidectomies were performed in rats to increase the level of endogenous TSH, creating a condition of chronic TSH stimulation. The activities of various classes of lysosomal enzymes (cathepsin D, beta-glucuronidase, and aryl sulfatase A) were studied in thyroid tissue remaining in situ at various time intervals after subtotal thyroidectomy (sub-tx). These alterations were correlated with morphometric and ultrastructural changes in tissue lysosomes and with serum T4 and TSH. Specific activities of all three lysosomal enzymes were elevated in the residual tissue as compared with those in control tissue during 7 weeks after sub-tx in the first experiment. In the second experiment, the activities of all three enzymes were elevated both 3 and 6 weeks after sub-tx, and the activities of cathepsin D and aryl sulfatase A in the postnuclear homogenate (S2) were significantly elevated. Plasma TSH was elevated and T4 was decreased both 3 and 6 weeks after sub-tx. The results of the third experiment determined that there were significant alterations in nuclear cytoplasmic ratios as well as in the number, area, and volume density of lysosomes in both groups compared with respective control values. In addition, both lysosomal area and volume density in animals 6 weeks after sub-tx were significantly larger than those in animals 3 weeks after sub-tx. We conclude that chronic stimulation of residual thyroid tissue 6 weeks after sub-tx causes alterations in lysosomal ultrastructure as well as in lysosomal enzyme activity.

Animals↗
PubMed1988

Effect of thyroid hormone on the protein inhibitors for Ca2+-dependent proteinase in brain: evidence for the induction by thyroidectomy of irreversible changes in immature rats.

The effects of thyroid hormone on the levels of protein inhibitors for Ca2+-dependent proteinase were studied in rat brain. Four different inhibitory proteins (I, II, III, and IV) were isolated from immature (7-day-old) rat brain. The molecular weights of these inhibitory proteins, which were estimated by gel-exclusion chromatography on Sephacryl S-200 column, were approximately 280,000 (I), 70,000 (II), 50,000 (III), and 35,000 (IV). All of these inhibitory proteins were decreased by thyroidectomy. Four-day T4 administration (100 micrograms/kg daily) to thyroidectomized-immature animals restored proteins I, II, and IV. However, protein III was not recovered with the same treatment of the rats. In mature rats (40-day-old), four different inhibitory proteins were identified in the brain. The molecular weights were identical to those obtained in immature rat brain. As observed in immature rats, all of these inhibitory proteins were decreased by thyroidectomy. In contrast to the results obtained in immature animals, however, inhibitory protein III, as well as I, II, and IV, was restored by T4 administration (100 micrograms/kg daily) to thyroidectomized mature rats. The results suggested that thyroid hormone increases protein inhibitors for Ca2+-dependent proteinase in brain, and that irreversible decrease in one of the inhibitors is induced by thyroid hormone deficiency in immature animals. The phenomenon may be related to the neonatal hypothyroidism-induced irreversible damage to the central nervous system in patients with cretinism.

Aging↗
PubMed1991

Role of the thyroid gland in seasonal reproduction: thyroidectomy blocks seasonal suppression of reproductive neuroendocrine activity in ewes.

Seasonal reproductive transitions in ewes are generated endogenously and are synchronized by annual changes in photoperiod. Previous evidence indicates that thyroidectomy prevents the transition to anestrus in ewes maintained in a fixed day length, suggesting that the thyroid is needed for endogenously generated reproductive arrest. Here we tested the hypothesis that the thyroid is required for endogenous seasonal suppression of the neuroendocrine mechanism that regulates pulsatile LH secretion. Ewes were thyroidectomized (n = 6) in summer, 6 weeks before the onset of the breeding season, or they remained thyroid intact (n = 6). They were housed in a simulated natural photoperiod until the winter solstice; thereafter, they remained on that photoperiod (10 h of light, 14 h of darkness). To monitor pulsatile LH secretion, the ewes were ovariectomized and implanted with estradiol, and LH was measured in both frequent (every 6 min for 4 h) and infrequent (twice weekly) blood samples. In this model, high LH indicates low response to estradiol negative feedback and reproductive induction; low LH signifies high response to estradiol negative feedback and reproductive arrest. LH levels (samples twice weekly) rose some 50-fold in both groups concurrently at the start of the breeding season in September. Frequent sampling in midbreeding season (autumn) revealed that both thyroidectomized and thyroid-intact ewes exhibited frequent LH pulses, with no group difference, in either the presence or absence of the estradiol implant. A marked group difference, however, emerged at the end of the breeding season. LH fell to basal values in thyroid-intact ewes (onset of low values Feb 3 +/- 8 days), whereas levels remained elevated in thyroidectomized ewes through the end of the study (April 26). At this time, thyroidectomized ewes had more frequent LH pulses than thyroid-intact ewes both in the presence and absence of estradiol. The circadian pattern of melatonin secretion and the seasonal change in PRL were found to be unaffected by thyroidectomy. These observations support the hypothesis that the thyroid is necessary for endogenous suppression of neuroendocrine mechanisms that generate LH pulses, a suppression crucial for the transition to anestrus.

Animals↗
PubMed1991

Triiodothyronine-receptor complex in rat brain: effects of thyroidectomy, fasting, food restriction, and diabetes.

In vitro saturation analysis combined with quantification of T3, by an isotopic equilibrium technique or RIA, were used to examine the effects of thyroidectomy, fasting, diabetes, and food restriction on T3 concentration and specific binding in cerebral cortex and cerebellum. Fasting and food restriction did not affect the T3 binding parameters in the brain areas studied. Both thyroidectomy and diabetes were accompanied by a reduction in T3 content in nuclei from both cerebral cortex and cerebellum, but a decrease in T3 binding sites was only observed in both brain areas of diabetic animals. No significant differences in the binding affinity values among the experimental groups were seen. The diabetes-induced decrease in T3 content and receptor number were completely reversed by insulin treatment. Studies with fractionated nuclei from cerebral cortex and cerebellum showed that diabetes resulted in a reduction in T3 content and the number of receptors in glial nuclei from both brain areas. Although T3 content was also decreased in neuronal nuclei, the receptor concentration in these nuclear preparations did not change in concentration or affinity under the same conditions. These observations indicate that glial cells, not only have T3-binding characteristics similar to those of neuronal cells, but the T3 receptor number is decreased in the diabetes state.

Animals↗
PubMed1993

Measurement of the secretion of a small peptide at the single cell level by the cell immunoblot assay: thyroidectomy increases the number of substance P-secreting anterior pituitary cells.

The present study developed a technique for quantification of a small peptide secreted by single endocrine cells and investigated the cellular basis for the effects of endocrine environments on their secretion by using this technique. To quantify substance P (SP) secreted by monodispersed rat anterior pituitary cells and to estimate the relative abundance of SP-secreting cells, the cell immunoblot assay was improved by several modifications, including the use of incubation chambers and addition of immunostaining procedures of fixation by paraformaldehyde and elimination of nonspecifically stained blots. Single pituitary cells formed SP-specific blots on protein-blotting transfer membranes that constituted a floor portion of the incubation chamber. A combination of microscopic image analysis and SP standard curve made it possible to quantify the amount of SP stained as blots. SP secretion from single pituitary cells showed a large variation ranging from 0.14-144 fg/cell.h. The mean SP secretion and the number of SP-secreting cells were increased in an incubation time-dependent manner, with plateau levels of 20.3 fg/cell and 30.2 in a chamber area of 8 x 8 mm, respectively, at 3 h. Thyroidectomy significantly increased the number of SP-secreting cells and the total amount of SP secretion but decreased the mean SP secretion from single pituitary cells. This decrease in the mean SP secretion in the thyroidectomized rats was found to be due to a relative abundance of cells that secrete small amounts of SP. The present study demonstrates that the cell immunoblot assay is useful for quantifying peptide secretion at the single cell level and suggests that thyroidectomy-induced increase in SP secretion from anterior pituitary cells is not due to an increase in SP secretion per cell but due to an increase in the number of SP-secreting cells.

Animals↗
PubMed1976

Propranolol in the treatment of thyrotoxicosis by subtotal thyroidectomy.

Subtotal thyroidectomy was performed in 40 patients with thyrotoxicosis in whom propranolol alone was used as preparation for surgery. Propranolol was given orally in a dose of 40 mg every 6 h for a mean preoperative period of 17 days (range 4-60 days) and continued for seven days after operation. The mean +/- SE blood loss at operation was only 160 +/- 20 ml. The period of follow-up was from three to nine months. Recurrent thyrotoxicosis has not occurred in any patient. Low levels of total serum triiodothyronine (T3) and total serum thyroxine (T4) were observed in the early postoperative weeks in some patients and were associated with symptoms of mild hypothyroidism, but by six months in the presence of a raised serum thyrotropin (TSH) the thyroid hormone levels returned to normal. Permanent hypothyroidism developed in only two patients. Despite normal or low total serum T3 and T4 levels, the TSH response to thyrotropin-releasing hormone (TRH) was absent in all patients one week after operation. At four weeks and at eight weeks, the response was absent or sub-normal in 70% and 20% of the patients respectively, indicating a delay in the recovery of the hypothalamo-pituitary axis previously exposed to high levels of T3 and T4. It is considered that subtotal thyroidectomy for thyrotoxicosis in patients prepared with propranolol is an acceptable procedure which has some advantages over the conventional preparation with carbimazole and potassium iodide, not the least of which are the potential reduction in preparation time, the more flexible timing of operation, and the reduced operative blood loss.

Female↗