Hypercholesterolemia impairs vascular remodelling after porcine coronary angioplasty

OBJECTIVE

To assess the effect of hypercholesterolemia on neointima formation and vascular remodelling after porcine coronary angioplasty.

METHODS

Left anterior descending coronary angioplasty was carried out in five control and 16 age-matched hypercholesterolemic miniature pigs. Vascular remodelling was measured by intravascular ultrasound. Neointima size and composition were assessed by quantitative image analysis. Coronary smooth muscle cells (SMC) from control and diet pigs were collected 1 h after angioplasty for in vitro study of the effect of hypercholesterolemic serum on SMC migration and of macrophage-induced matrix degradation on SMC adhesion.

RESULTS

Twenty-eight days after angioplasty, lumen increase was 0.08+/-1.7 mm(2) in diet and 2.7+/-2.7 mm(2) (P=0.016) in control pigs. Lumen increase correlated with vascular remodelling (IEL(post)/IEL(pre); R(2)=0.59; P<0.001) and with the circumferential gain relative to the neointima (R(2)=0.32; P<0.01) but not with neointimal area that was similar in control and diet pigs. Circumferential gain correlated with VSMC deposition at the site of the injury (R(2)=0.28; P<0.01) that correlated with organized collagen (R(2)=0.34; P<0.01). The VSMC and collagen content of neointima in diet pigs was lower whereas the macrophage content was higher. Hypercholesterolemic serum and oxidised LDL reduced migration of VSMC from diet pigs. Macrophage-induced degradation of VSMC extracellular matrix reduced VSMC adhesion (P=0.015).

CONCLUSION

Hypercholesterolemia impairs vascular remodelling of balloon-treated coronary arteries. It decreases VSMC and collagen accumulation at the site of injury. Our in vitro data suggest that this decrease can be due to macrophage-induced matrix degradation and reduced VSMC adhesion and to impaired VSMC migration. Oxidised LDL mimics the inhibitory effect of hypercholesterolemic serum.

[Intraoperative monitoring of intact parathyroid hormone during surgery for primary hyperparathyroidism]

The aim of the present study was to evaluate a new immunometric assay for intraoperative parathyroid hormone monitoring. The test was applied in 70 patients who underwent surgery for primary hyperthyroidism (pHPT) between 6/1999 and 6/2001. Among these patients, 61 showed a solitary adenoma, eight a hyperplasia and one a double adenoma. Intraoperative iPTH samples were taken at the beginning of the operation and 5, 10 and 15 min after removal of the parathyroid gland. Criterion for a successful operation were a decrease of iPTH levels of more than 50 % within 5 min and of more than 60 % within 15 min after parathyroidectomy. Following the removal of a solitary adenoma, iPTH levels decreased by 63 % (+/- 13 %) after 5 min and by 76 % (+/- 10 %) after 15 min respectively. In case of hyperplasia, a significant decrease of iPTH levels was not observed until a subtotal parathyroidectomy had been carried out. In the present study there were 2 false negative and one false positive results corresponding with a sensitivity of 97 % and a specificity of 89 % for prediction of a solitary adenoma. In our opinion, intraoperative iPTH monitoring using this new assay allows the safe distinction between adenoma and multiglandular disease. It represents a valuable adjunct to surgical skill as it permits minimally invasive operations for solitary adenomas, and in case of recurrent surgery helps to detect the region of interest by selective venous sampling for parathyroid hormone.

Minimally invasive parathyroidectomy using the 'focused' lateral approach. I. Results of the first 100 consecutive cases

BACKGROUND

A feasibility study of 'focused' minimally invasive parathyroidectomy (MIP) using a lateral approach was commenced in 1999. The aim of the present paper was to evaluate the effectiveness and safety of this procedure in the first 100 consecutive patients.

METHODS

This was a prospective, non-randomized case-control study. One hundred consecutive patients with primary hyperparathyroidism (mean age 63.1 years; 74 females, 26 males) who fulfilled the inclusion criteria underwent focused MIP between May 1999 and December 2000. The results for the first and last 50 consecutive patients were compared to see whether they were reflective of a learning curve. The role of intraoperative quick parathyroid hormone (QPTH) estimation was also evaluated.

RESULTS

Focused MIP was successfully completed in 93 of 100 patients, with seven conversions. Three (3.2%) of the 93 patients had persistent hyperparathyroidism. Quick PTH was measured in 81 patients and the results were true positive (for cure) in 72 patients, false negative in six patients, true negative in two patients and false positive in one patient. Transient recurrent laryngeal nerve paresis occurred in one patient. During the same time period, open parathyroidectomy was performed in 242 patients. The results were not different between the first and later 50 patients undergoing MIP, nor were the outcomes significantly different from patients undergoing open parathyroidectomy.

CONCLUSIONS

Focused MIP is a safe and effective operative approach for appropriately selected patients. Failed procedures were invariably related to shortcomings of the localization studies. Measurement of QPTH, although accurate, is unreliable in the presence of multigland disease.

Hypergastrinemia as a cause of chromogranin a increase in blood in patients suspected to have neuroendocrine tumor

BACKGROUND

Chromogranin A (CgA) is a sensitive marker for neuroendocrine neoplasia. Enterochromaffin-like cell hyperplasia secondary to hypergastrinemia also leads to CgA increase in blood. Treatment with inhibitors of acid secretion, atrophic gastritis and infection with Helicobacter pylori are prevalent conditions leading to hypergastrinemia. We therefore wanted to study whether concomitant determination of gastrin could increase the utility of CgA as a marker of neuroendocrine neoplasia.

METHODS

CgA and gastrin concentrations were determined by radioimmunoassay methods, while pepsinogen I (used to diagnose severe atrophic gastritis) was determined by a commercial immunoenzymatic assay.

RESULTS

Among 100 patients with elevated CgA, we found that 29% had hypergastrinemia. Vice versa, CgA was elevated in 23 out of 26 (88.5%) in a population of patients with hypergastrinemia. By determining pepsinogen I in blood in patients with hypergastrinemia, a proportion of them was diagnosed as having severe atrophic gastritis.

CONCLUSION

We conclude that determination of gastrin in blood in patients with CgA elevation will increase the utility of CgA in the diagnosis of neuroendocrine tumors.

Contribution of the microvessel network to the clonal and kinetic profiles of adrenal cortical proliferative lesions

Monoclonal adrenocortical lesions have been characterized by an inverse correlation between proliferation and apoptosis, and polyclonal lesions show a direct correlation. Their relationship with the vascular pattern remains unknown in adrenocortical nodular hyperplasias (ACNHs), adenomas (ACAs), and carcinomas (ACCs). We studied 20 ACNHs, 25 ACAs, and 10 ACCs (World Health Organization classification criteria) from 55 women. The analysis included X-chromosome inactivation assay (on microdissected samples), slide and flow cytometry, and in situ end labeling. Endothelial cells were stained with anti-CD31, and the blood vessel area and density were quantified by image analysis in the same areas. Appropriate tissue controls were run in every case. Regression analyses between kinetic and vascular features were performed in both polyclonal and monoclonal lesions. Polyclonal patterns were observed in 14 of 18 informative ACNHs and 3 of 22 informative ACAs, and monoclonal patterns were seen in 4 of 18 ACNHs, 19 of 22 ACAs, and 9 of 9 ACCs. A progressive increase in microvessel area was observed in the ACNH-ACA-ACC transition but was statistically significant between benign and malignant lesions only (191.36 +/- 168.32 v 958.07 +/- 1279.86 microm(2); P < .0001). In addition, case stratification by clonal pattern showed significant differences between polyclonal and monoclonal benign lesions; 6% of polyclonal and 57% of monoclonal lesions had microvessel area >186 microm(2) (P = .0000008). Monoclonal lesions showed parallel trends (but with opposite signs) for microvessel area and density in comparison with proliferation and apoptosis, whereas polyclonal lesions showed inverse trends. In conclusion, the kinetic advantage of monoclonal adrenal cortical lesions (increased proliferation, decreased apoptosis) is maintained by parallel increases in microvessel area and density.

[Evaluation of hemodynamic changes in inflammatory hyperplastic processes in the thyroid gland with the aid of ultrasound color mapping]

Ultrasound dopplerography techniques constitute an investigation of highly informative value, designed to study vascularization of pathological states of the thyroid gland. It permits the most effective and comprehensive evaluation of the organ circulation along the periphery of the capsule, in the parenchyma, in all pathological formations. This warrants the use of the method in diagnosing, in identification of the process dissemination beyond the organ into the surrounding tissues or regional lymph nodes. Colour Doppler-mapping of the thyroid gland is a highly sensitive method of investigation of neovascularization of the organ which comes to be changed in cancer depending on the stage of the process.

Changes in serum and hepatic cholesterol in lead-induced liver hyperplasia

Lead nitrate when injected intravenously as a single dose to male Wistar rats causes a strong hepatic proliferative response followed by reabsorption of excess tissue within 10-14 days. The rate of cell proliferation in this hyperplastic model was positively correlated with hepatic de novo synthesis of cholesterol, stimulation of the hexose monophosphate shunt pathway of glucose metabolism and with alterations in serum lipoproteins.

Relation of a common methylenetetrahydrofolate reductase mutation and plasma homocysteine with intimal hyperplasia after coronary stenting

BACKGROUND

Hyperhomocysteinemia has been identified as an independent risk factor for coronary artery disease. Recent studies have shown that a common mutation (nucleotide 677 C-->T) in the methylenetetrahydrofolate reductase (MTHFR) gene may contribute to mild hyperhomocysteinemia and, therefore, to the incidence of coronary artery disease. No information exists, however, regarding the association between the mutation of the MTHFR gene or plasma homocysteine levels and morphological analysis of coronary atherosclerosis using intravascular ultrasound.

METHODS AND RESULTS

To examine the potential influence of MTHFR genotype and homocysteine on coronaryarteries morphologically, we screened 62 patients with 65 lesions that were treated with 93 Palmaz-Schatz stents. The plasma homocysteine levels in the patients with the TT genotype were not significantly higher than those in the patients with non-TT (CC+CT) genotypes (13.1 +/- 5.5 versus 11.5 +/- 3.1 mmol/L, P=0.16). Angiographic analysis showed that the percent diameter stenosis in the patients with the TT genotype was significantly greater than that in those with non-TT genotypes (43.7 +/- 17.8% versus 29.0 +/- 22.0%, P=0.015). Intravascular ultrasound analysis showed that the TT genotype was significantly associated with greater intimal hyperplasia area (5.70 +/- 1.94 versus 3.72 +/- 1.38 mm2, P=0.001). In multiple stepwise regression analysis, the number of the T alleles was the only independent predictor of intimal hyperplasia after intervention (r2=0.21, P=0.004).

CONCLUSIONS

The homozygous mutant genotype of the MTHFR gene may increase the risk of in-stent restenosis more than does the normal homozygous or heterozygous genotype.

Adrenocorticotropin-independent unilateral adrenocortical hyperplasia with Cushing's syndrome: Immunohistochemical studies of steroidogenic enzymes, ultrastructural examination and a review of the literature

A 60-year-old woman presented with a history of palpitations, headaches and severe hypertension, which was resistant to hypotensive agents. She had a 2-year history of obesity and a moon face. Her plasma adrenocorticotropic hormone level was below the limits of detection and did not respond to corticotropin-releasing hormone. Urinary-free cortisol was elevated and the circadian rhythm of serum cortisol level had completely disappeared. Imaging analysis demonstrated a unilaterally functioning mass in the left adrenal gland. Serum cortisol level in the left adrenal vein was elevated. The resected adrenal mass measured 4 x 3.5 x 2.5 cm, and ranged from yellow to tan in color. The adrenal cortex adjacent to the nodule did not demonstrate cortical atrophy. The mass was well circumscribed but not encapsulated, and consisted of multiple cortical nodules. These nodules were composed predominantly of clear cortical cells, and partly of compact cortical cells. Immunoreactivity of steroidogenic enzymes including cholesterol side-chain-cleavage P450, 3beta-hydroxysteroid dehydrogenase, 21-hydroxylase cytochrome P450, 11beta-hydroxylase cytochrome P450 and 17alpha-hydroxylase cytochrome P450 was marked in cortical nodules, but minimal in non-nodular cortex. Ultrastructural examination of nodular cortical cells also demonstrated well-developed mitochondria and smooth endoplasmic reticulum, consistent with elevated steroidogenesis in these cells.

Hyperplasia and impaired involution in the mammary gland of transgenic mice expressing human FGF4

Fgf4, a member of the fibroblast growth factor family, is frequently amplified in a variety of human cancers, however, its expression in neoplastic tissues is rarely detectable. This makes uncertain its involvement in tumour aetiology, although several in-vitro studies link Fgf4 overexpression to malignant transformation and metastatization of culture cells. We generated a transgenic mouse model in which the whey acidic protein (WAP) promoter directs expression of human Fgf4 to mammary tissues during late pregnancy and throughout lactation, with the purpose of studying the involvement of this growth factor in mammary tumorigenesis. Expression of the transgene was specifically detected in lobular-alveolar cells of lactating mammary glands that, by histological analysis, displayed hyperplastic areas and a disorganized structure. This was accompanied by an increased number of red blood cells and expression, in alveolar epithelial cells, of the vascular endothelial growth factor, which is absent in wild type controls. The most striking effect caused by FGF4 overexpression was on the remodelling of mammary tissue at the end of lactation. Indeed, transgenic animals showed a delayed involution of the gland due to a dramatic reduction in the overall number of apoptotic cells, which are normally present in the organ after weaning. Nevertheless, none of the animals examined developed neoplastic lesions of the mammary gland even after several pregnancies and at old age. Our work represents the first in-vivo demonstration of the anti-apoptotic and angiogenic properties of FGF4.

The importance of erythroid expansion in determining the extent of apoptosis in erythroid precursors in patients with beta-thalassemia major

Beta-thalassemia major is characterized by ineffective erythropoiesis leading to severe anemia and extensive erythroid expansion. The ineffective erythropoiesis is in part due to accelerated apoptosis of the thalassemic erythroid precursors; however, the extent of apoptosis is surprisingly variable. To understand this variability as well as the fact that some patients undergoing allogeneic marrow transplantation are resistant to the myeloablative program, we attempted more quantitative analyses. Two groups of patients totaling 44 were studied, along with 25 healthy controls, and 7 patients with hemolysis and/or ineffective erythropoeisis. By 2 flow cytometric methods, thalassemic erythroid precursors underwent apoptosis at a rate that was 3 to 4 times normal. Because thalassemic marrow has between 5- to 6-fold more erythroid precursors than healthy marrow, this translated into an absolute increase in erythroid precursor apoptosis of about 15-fold above our healthy controls. In searching for the causes of the variability in thalassemic erythroid precursor apoptosis, we discovered tight direct correlations between the relative and absolute extent of apoptosis and the extent of erythroid expansion as measured either by the absolute number of marrow erythroid precursors or by serum soluble transferrin receptor levels. These results could mean that the most extreme rates of erythroid proliferation lend themselves to cellular errors that turn on apoptotic programs. Alternatively, extreme rates of erythroid hyperplasia and apoptosis might be characteristic of more severely affected patients. Lastly, extreme erythroid hyperplasia could generate such numbers of apoptotic erythroid precursors that marrow macrophages are overwhelmed, leaving more apoptotic cells in the sample.

Focal lobular spermatogenesis and pubertal acceleration associated with ipsilateral Leydig cell hyperplasia

Leydig cell tumors of the testis are the underlying cause in about 10% of the cases of precocious puberty in boys. Leydig cell hyperplasia is a less well-characterized cause, with an undocumented frequency. We describe a boy with precocious puberty associated with ipsilateral testicular enlargement and focal Leydig cell hyperplasia with spermatogenesis limited to the local adjacent testicular tissue.

Subclinical Cushing syndrome due to adrenocorticotropic hormone-independent macronodular adrenocortical hyperplasia: changes in plasma cortisol levels during long-term follow-up

A 63-year-old man with bilateral adrenal tumors was treated for hypertension and diabetes mellitus. Endocrinologic examination during follow-up revealed the production of cortisol to be independent of the regulation of the hypothalamo-pituitary-adrenal axis. Therefore, he was diagnosed as having subclinical Cushing syndrome, and these tumors were removed. Adrenocorticotropic hormone-independent macronodular adrenal hyperplasia (AIMAH) was endocrinologically and histopathologically diagnosed. This is the first report demonstrating that endocrinologic changes of AIMAH can be observed during long-term follow-up.

Histopathology and physiopathology of gastric mucous hyperplasia in rats heavily infected with Taenia taeniaeformis

Rats heavily infected with larval Taenia taeniaeformis show hyperplasia of the gastric mucosa accompanied by mucous cell proliferation, increase in the level of intragastric pH and hypergastrinemia. Sixty one rats were divided into 2 groups designed as infected (36 rats) and control (25 rats) group. These rats were examined with time course of the infection histopathologically and physiopathologically, during 14-112 days postinfection (DPI). In the infected rats, gastric mucosal hyperplasia began to be observed at 56 DPI, and the structural disturbance of zymogenic units in the corpus and mucous units in the antrum had increased with time. However, the degree of these changes in the antrum was weaker than those in the corpus. Alcianblue and/or PAS-positive cells increased in their numbers with time, and 4 types of cells other than typical surface mucous cell and mucous neck cell were observed by electron-microscopy. However, zymogenic and parietal cells decreased in their number after 56 DPI. Further, the infected rats showed changes in the serum concentration of alanine aminotransferase, aspartate aminotransferase, blood urea nitrogen, glucose and total protein. Some similarities with Menetrier's disease were discussed.

A case of Cushing's syndrome due to ACTH-independent bilateral macronodular hyperplasia associated with excessive secretion of mineralocorticoids

A 74-year-old man developed Cushing's syndrome and hypokalemia due to ACTH-independent bilateral macronodular adrenocortical hyperplasia (AIMAH) with excessive secretion of mineralocorticoid hormones. Plasma concentrations of weak mineralocorticoids were high. The increase in plasma cortisol did not have a diurnal rhythm, and was not suppressed by a high dose of dexamethasone. Plasma ACTH was undetectable, but plasma cortisol was increased by ACTH administration. The concentrations of mineralocorticoids, especially deoxycorticosterone and corticosterone were increased, and augmented the response to ACTH administration. Plasma renin activity and aldosterone concentrations were rather suppressed. Both adrenal glands, with a total weight of 110 g, were enlarged and contained several macronodules. These nodules were composed of hyperplasia of small cortical cells and usual clear cells. This is a rare case of ACTH-independent bilateral macronodular adrenocortical hyperplasia because there were excessive secretion of mineralocorticoid and hypokalemia.

C-cell hyperplasia and medullary thyroid carcinoma in patients routinely screened for serum calcitonin

Routine screening of calcitonin serum levels in patients with nodular thyroid disorders has led to an increased rate of total thyroidectomies. We investigated prevalence and interrelationship of C-cell hyperplasia (CCH) and medullary thyroid carcinoma (MTC) in patients with thyroid and parathyroid disorders that showed increased calcitonin serum levels detected by routine screening. Within two years, 30 (mean age, 60 +/- 14 years) of 667 patients had a pentagastrin-stimulated calcitonin level of more than 100 pg/mL. All 30 underwent total thyroidectomy and were tested for germ-line mutations of the ret protooncogene. Entire surgical specimens were blocked, and C-cell disorders were assessed using conventional histology and immunohistochemistry. C-cell hyperplasia was defined by the presence of more than 50 C cells/l low-power field in both lobes and was classified as focal, diffuse, nodular, or neoplastic. Nineteen patients (female/male = 14/5) had MTC, and 11 males but no females had CCH only. Six of 16 patients with sporadic MTC had concomitant CCH. Three patients were index cases of new MTC families. We conclude that MTC with concomitant CCH is an unreliable marker for hereditary MTC risk and that CCH has a preneoplastic potential in the absence of germ-line mutations. In this series, CCH alone was not found in females.

Adrenocorticotrophin-independent macronodular adrenal hyperplasia in a patient with lysine vasopressin responsiveness but insensitivity to gastric inhibitory polypeptide

The aetiology of ACTH-independent macronodular adrenal hyperplasia (AIMAH) is uncertain. We examined a 55 year old man with Cushing's syndrome due to AIMAH, whose cortisol levels increased after stimulation with lysine-8-vasopressin (LVP) in vitro as well as in vivo. Abdominal MRI revealed nodular enlargement of both adrenal glands. No adenoma was evident on pituitary MRI. 131I-adosterol scintigraphy exhibited marked uptake into both adrenal glands. Although baseline plasma cortisol levels were within normal limits, urinary free cortisol excretion was 3-fold higher than the upper limit of the normal range. Plasma ACTH levels were undetectable. Oral dexamethasone failed to suppress plasma cortisol levels irrespective of dose, and administration of corticotrophin releasing hormone failed to increase plasma ACTH and cortisol levels. LVP injection failed to increase plasma ACTH levels, but elicited an increase in plasma cortisol levels. The direct stimulatory effect of LVP on cortisol secretion was confirmed in vitro in cultured adrenocortical cells from macronodules obtained at surgery. Food intake, gastric inhibitory polypeptide (GIP), or octreotide administration, which were reported to regulate cortisol release in patients with AIMAH, failed to affect plasma cortisol levels. In conclusion, plasma cortisol responsiveness to LVP, GIP, and octreotide is heterogeneous in patients with AIMAH.

Preclinical Cushing's syndrome due to adrenocorticotropin-independent bilateral adrenocortical macronodular hyperplasia with concurrent excess of gluco- and mineralocorticoids

A 48-year-old with bilateral adrenal incidentalomas was studied. Although the serum cortisol level was normal, autonomous cortisol secretion was shown by the loss of diurnal rhythm, no suppressibility by dexamethasone, and complete suppression of plasma adrenocorticotropin levels. Imaging analyses revealed bilateral adrenal masses, showing isotope uptake. He was diagnosed as preclinical Cushing's syndrome due to adrenocorticotropin-independent bilateral adrenocortical macronodular hyperplasia, confirmed histologically. Despite the undetectable plasma adrenocorticotropin level and renin activity, serum mineralocorticoids levels were not suppressed, which were decreased after subtotal adrenalectomy. It was suggested that hyperplastic adrenal glands could produce both gluco- and mineralocorticoids concomitantly.

Autonomous nodular hyperplasia of the adrenal cortex: tertiary hypercortisolism?

Two cases of Cushing's syndrome are reported in which apparently autonomous adrenal adenomata were associated with the presence of pituitary tumours. In one case the patient was apparently cured by unilateral adrenalectomy, although she was noted to have radiological evidence of an intrasellar tumour; serum cortisol was not suppressed by dexamethasone and ACTH was undetectable. Serum ACTH in the second case was initially 31 ng/l but became undetectable during the course of investigation. Transsphenoidal removal of a corticotroph adenoma did not affect serum cortisol and she proceeded to unilateral adrenalectomy. The pathogenesis of autonomous macronodular hyperplasia is discussed, as well as the options for management.

[Somatostatin and growth hormone in post-colectomy intestinal hyperplasia in rats]

AIM

Somatostatin exerts significant effects on gastrointestinal function that may include mucosal growth regulation, probably through its action on growth hormone release. The aim of this work was to correlate somatostatin and growth hormone plasma levels and the hyperproliferative status of intestinal mucosa after colectomy.

EXPERIMENTAL DESIGN

Adult Wistar rats were divided into two groups: control sham operated (n = 8) and large bowel resection (n = 8). Seven days post-colectomy, the animals were killed. Ileal mucosal samples were assayed for proliferative status (morphometry, and proliferating cell nuclear antigen labeling) and blood samples for plasmatic somatostatin and growth hormone measurement.

RESULTS

A hyperproliferative status was observed with significant increases in villous length and crypt proliferating cell nuclear antigen labeling. Plasma somatostatin showed a 95% significant decrease while growth hormone levels increased significantly.

CONCLUSION

The intestinal adaptation seen after colectomy is associated with lower somatostatin and higher growth hormone plasma level, possibly by regulating the intestinal adaptative process.

Effect of thyroid stimulating hormone on the development and progression of rat thyroid follicular cell tumors

Time course changes in cell proliferative activity of thyroid focal hyperplastic and tumorous lesions as well as blood thyroid-related hormones in male F344 rats initiated with N-bis(2-hydroxypropyl)nitrosamine (DHPN: 2800 mg/kg body weight, single s.c. injection) were examined following chronic administration of 0.1% sulfadimethoxine (SM) in the drinking water for 1, 4, 8, 12 and 16 weeks and at the end of a subsequent 4-week recovery period. Serum thyroid stimulating hormone (TSH) levels increased rapidly from week 1 of SM treatment, reaching a peak at week 8, and then decreased gradually with prolongation of treatment period, although remaining significantly elevated as compared with the corresponding controls at all time points up to week 16. Follicular cell hyperplasias and adenomas of the thyroid occurred from week 4 and carcinomas from week 8. All of these lesions showed high cell proliferative activities corresponding to high serum TSH levels during the early stage, but the levels in hyperplasias and adenomas decreased rapidly with prolongation of SM treatment. After the recovery period, serum TSH levels had returned to below the normal range and cell proliferation in follicular hyperplasias and adenomas had stopped or was very low. Some carcinomas demonstrating invasive growth also showed remarkable decreases in the cell proliferative activity. The results of our study strongly suggest that a high serum TSH level plays an important role in the early stage of thyroid tumorigenesis and that some tumors exhibiting invasive growth are still dependent on TSH stimulation.