Communication: angle-resolved thermal dissociative sticking of CH4 on Pt(111): further indication that rotation is a spectator to the gas-surface reaction dynamics.

Effusive molecular beam measurements of angle-resolved thermal dissociative sticking coefficients for CH(4) impinging on a Pt(111) surface, at a temperature of 700 K, are reported and compared to theoretical predictions. The reactivity falls off steeply as the molecular angle of incidence increases away from the surface normal. Successful modeling of the thermal dissociative sticking behavior, consistent with existent CH(4) supersonic molecular beam experiments involving rotationally cold molecules, required that rotation be treated as a spectator degree of freedom.

An effusive molecular beam technique for studies of polyatomic gas-surface reactivity and energy transfer.

An effusive molecular beam technique is described to measure alkane dissociative sticking coefficients, S(T(g), T(s); ϑ), on metal surfaces for which the impinging gas temperature, T(g), and surface temperature, T(s), can be independently varied, along with the angle of incidence, ϑ, of the impinging gas. Effusive beam experiments with T(g) = T(s) = T allow for determination of angle-resolved dissociative sticking coefficients, S(T; ϑ), which when averaged over the cos (ϑ)/π angular distribution appropriate to the impinging flux from a thermal ambient gas yield the thermal dissociative sticking coefficient, S(T). Nonequilibrium S(T(g), T(s); ϑ) measurements for which T(g) ≠ T(s) provide additional opportunities to characterize the transition state and gas-surface energy transfer at reactive energies. A resistively heated effusive molecular beam doser controls the T(g) of the impinging gas striking the surface. The flux of molecules striking the surface from the effusive beam is determined from knowledge of the dosing geometry, chamber pressure, and pumping speed. Separate experiments with a calibrated leak serve to fix the chamber pumping speed. Postdosing Auger electron spectroscopy is used to measure the carbon of the alkyl radical reaction product that is deposited on the surface as a result of alkane dissociative sticking. As implemented in a typical ultrahigh vacuum chamber for surface analysis, the technique has provided access to a dynamic range of roughly 6 orders of magnitude in the initial dissociative sticking coefficient for small alkanes on Pt(111).

Clinical features and prognostic factors associated with adrenocortical carcinoma: Lahey Clinic Medical Center experience.

Adrenocortical carcinoma is a rare tumor associated with a commonly poor prognosis. However, data on the natural history and response to therapy of patients with this malignancy have often been conflicting. Our objective of this retrospective study was to evaluate the clinical course and survival of patients with adrenocortical carcinoma and to identify relevant prognostic factors. Between 1966 and 1996, 31 patients with histologically documented adrenocortical carcinoma were observed at the Lahey Clinic Medical Center. Patient information was obtained from chart review. At the time of diagnosis, 48 per cent of patients had endocrine symptoms with compatible hormonal studies, 19 per cent had involvement of the inferior vena cava by tumor thrombus, and 32 per cent had metastatic disease. The median survival time was 17 months (range, 1-205 months) for the entire group, and the 5-year survival rate was 26 per cent. Age <54 years, absence of metastatic disease at the time of diagnosis, and completeness of surgical resection were associated with better prognosis. Evaluation of survival with the Cox proportional hazards model suggested that age <54 years, absence of metastatic disease, and nonfunctioning tumor status were independently associated with improved survival. The prognosis of patients with adrenocortical carcinoma is poor but appears more favorable in patients <54 years, with localized disease, or nonfunctioning tumor status. Complete tumor resection may be associated with improved survival.

An association between acromegaly and thyroid carcinoma.

Acromegaly has been associated with goiter as well as with benign and malignant tumors. Three cases of thyroid carcinoma in patients with acromegaly had been reported in the literature. We previously reported two additional cases of thyroid carcinoma and now present a third from 100 patients with acromegaly, exceeding the expected prevalence. All three thyroid carcinomas were multifocal, suggesting a generalized promotion toward malignancy. These patients had elevated levels of growth hormone and somatomedin-C [insulin-like growth factor (IGF-1)] at the time of thyroid carcinoma diagnosis. We discuss the role of IGF-1 in both benign and malignant thyroid growth, including the presence of IGF-1 receptors on thyroid cells, stimulation of thyroid cell replication by IGF-1, and paracrine secretion of IGF-1 and its binding proteins by thyroid cells. We propose possible mechanisms for the development of thyroid carcinoma in patients with acromegaly and discuss implications for the physician treating patients with acromegaly.

Subclinical hypothyroidism. Understanding is the key to decision making.

Subclinical hypothyroidism is defined by elevated concentrations of thyrotropin (TSH) and normal levels of serum thyroxine in the absence of overt symptoms. Autoimmune thyroid disease is the most frequent cause. Prevalence is between 2.5% and 10%, depending on the patient population. The disorder may not be as asymptomatic as previously thought; mild but consistent hypothyroid symptoms may exist in 25% to 50% of patients. Subtle cardiac defects may be present and are probably most clinically relevant in patients with existing heart disease. Mild disturbances in cholesterol metabolism are a more common finding. Treatment of subclinical hypothyroidism must be individualized. The lowest dose of levothyroxine sodium (Levothroid, Levoxine, Synthroid) required to normalize TSH levels and improve symptoms yet avoid unnecessary side effects should be used.

MRI appearances of an ectopic pituitary adenoma: case report and review of the literature.

MR images of an ectopic pituitary adenoma have been published in only a single case, a suprasellar mass. We present a patient with Cushing's disease in whom MRI revealed a pituitary adenoma within the sphenoid sinus. Radiologic characteristics of ectopic pituitary adenomas are reviewed, with emphasis on MRI, which demonstrates a soft tissue mass, isointense with gray matter on T1-weighted images, which enhances in a heterogeneous manner.

Benign and malignant tumors in patients with acromegaly.

Growth hormone and its principal mediator insulinlike growth factor I are known promoters of normal growth. To determine whether excessive secretion of growth hormone is associated with an increased occurrence of benign and of malignant tumors, we studied records of 87 patients with acromegaly seen in the Lahey Clinic Medical Center (Burlington, Mass) from 1957 to 1988 and compared the rate of tumor occurrence with a control group of patients with pituitary tumors (198) and with findings from a cancer registry. Patients with acromegaly had a 2.45-fold increased rate of malignant tumors (95% confidence interval, 0.98 to 5.04) compared with findings from the tumor registry. Female patients had a higher rate than male patients. The rate of carcinoma of the thyroid was excessive and previously underscribed, but the rate of carcinoma of the colon was not increased as reported by others. Among benign lesions, goiters, predominantly nodular, were seen in 25% of patients in addition to a large number of mesenchymal lesions.

Insulin-like growth factor-I stimulates the growth of rat thyroid cells in culture and synergizes the stimulation of DNA synthesis induced by TSH and Graves'-IgG.

The present studies were undertaken to examine the factors that influence the growth of cells of endocrine gland origin, particularly the possible interactions between "nonspecific" growth factors and the trophic hormone for a target endocrine cell. As a model system, we explored the individual and conjoint effects of insulin-like growth factor-I (IGF-I) and TSH on the growth of FRTL5 cells, a nontransformed line of cloned rat thyroid follicular epithelium. In these cells, IGF-I and TSH each produced a dose-dependent enhancement of DNA synthesis and cell proliferation. When added together, IGF-I and TSH were markedly synergistic in stimulating DNA synthesis, producing increases in 3H-thymidine incorporation that were far greater than the sum of the effects of each alone. A similar effect of IGF-I was evident in the case of the stimulation of DNA synthesis produced by immunoglobulin G (IgG) preparations from the blood of patients with Graves' disease. Such IgG bind to the TSH receptor and mimic the actions of TSH therein. It is suggested, therefore, that there exist in the FRTL5 cell line at least two mechanisms for the regulation of growth, one activated at the level of the IGF-I receptor and the other at the level of the TSH receptor. When the two pathways are activated concurrently, a synergistic enhancement of DNA synthesis takes place. The findings indicate that the FRTL5 cell line is an excellent model in which to study these complex interactions and that IGF-I may be a determinant of thyroid cell growth, both normally and in certain thyroid diseases.