Factors modulating the secretion of thyrotropin and other hormones of the thyroid axis

Pulmonary arterial hypertension and thyroid disease

Recent studies have suggested an association between pulmonary arterial hypertension (PAH) and thyroid diseases (hypothyroidism and hyperthyroidism). This combination has a good prognosis, because the increase in the pulmonary artery pressure is usually slight and reverses after the treatment of the thyroid disease. Although the exact mechanism involved in the pathogenesis of this combination has not yet been established, it has been hypothesized that thyroid hormones and autoimmunity have a direct influence. Due to the high prevalence of thyroid disease in patients with PAH, thyroid function tests should be considered in the investigation of every patient with PAH. In this review, we describe the prevalence of PAH in patients with thyroid diseases and the prevalence of thyroid disease in patients with PAH, as well as addressing the principal effects that thyroid diseases have on the respiratory system. In addition, we report the treatment effects in patients with these diseases.

[Thyroid dysfunction in patients with pulmonary arterial hypertension. A cohort study of 58 patients]

BACKGROUND AND OBJECTIVE

Thyroid disease (TD) is more prevalent in patients with pulmonary arterial hypertension (PAH) than in the general population. The frequency and the cause of this association are not well established. We aimed to quantify and analyze the incidence and characteristics of TD in a cohort of PAH patients (idiopathic or preferentially associated with systemic diseases) and review the literature.

PATIENTS AND METHOD

Fifty eight PAH patients were prospectively studied, according to a previously established protocol (that included right heart catheterization); TSH, T(4), and antithyroglobulin and antiperoxidase antibodies were determined. TD was defined as an abnormal TSH level and/or elevated antithyroid antibodies (TAbs). Clinical, biological and hemodynamic variables were compared between patients with and without TD.

RESULTS

TD was detected in 30 patients (51%): high TSH levels were observed in 21 (36,21%); hyperthyroidism in 2 (3,45%); and TAbs in 16 of 54 (27,59%), 7 of whom were euthyroid. In the TD group, PAH evolution time was longer (4,62 vs 2,61 years; P=.005, CI 95%, 0,63-3,38), more patients were in functional class IV (13;43,3% vs 5;15,8%, P=.046, CI 95% ,0,05-11,75), cardiac output was lower (P=.032, CI 95%, 3,16-4,89) and epoprostenol treatment was more frequently used (14;46,6% vs 4;14,3%, P=.008, CI 95%, 1,46-18,85; OR=5,25).

CONCLUSIONS

The frequency of TD detected in this PAH cohort reaches 51% and it was associated with a longer evolution time of PAH and worse hemodynamic situation. Although epoprostenol was used more frequently in TD patients, a causal relationship with TD could not be established.

[Effect of iodine, copper and zinc supplements to rations with a high quota of rapeseed extract meal on the growth and thyroid function of fattening swine. 3. The effect on weight and the histomorphometric findings in the thyroid and on the serum T3 and T4 concentrations]

Studies were made with a total of 272 fattening pigs. Iodine deficiency both in rations of soya bean meal and rape seed meal increased the weight of the thyroid gland and the height of the epithelium cells and significantly reduced the T4 and T3 level in the serum. Iodine supplements to the rape seed meal rations distinctly diminished the goitrogenic effect, did not, however, cancel it out. Stage of goiter and depression of consumption were--different shown by the T3 and T4 level in the serum. Highly significant relations were calculated between live weight gain, weight and the height of the epithelium cells on the one hand and the T4 level in the serum on the other. Iodine supplementations of rations without thyrostatic components should amount to greater than or equal to 0.1 mg/kg. Iodine supplementations of 0.5 mg/kg feed are at present recommended to rations with rape seed meal quotas of less than 8%.

Thyroid function tests in thyroid and nonthyroid disease

Modern day evaluation of thyroid disorders requires a combination of accurate clinical judgement and reliable, sensitive, and specific thyroid functions tests. Principle among the latter are thyroxine (T4) 3, 5, 3'-triiodothyronine (T3), and thyroid-stimulating hormone (TSH). Also playing an important role in special situations are free thyroxine, an assessment of bound and unbound thyroid-binding globulin, TRH stimulation, long-acting thyroid stimulator (LATS), antibodies to thyroid hormone and to thyroid receptors. Basic to interpretation of these tests in the clinical setting is a comprehension of the relationship of the hypothalamus, the pituitary, and the thyroid gland as well as a knowledge of the peripheral metabolism of thyroxine and triiodothyronine. The role of each of these laboratory tests in the evaluation of hyper- and hypometabolic states, their alteration in nonthyroid and other endocrine disorders, and the effects of environmental and physiological factors on these tests are reviewed.

The effects of prostacyclin (PGI2) on prolactin secretion in vitro

Continuously superfused rat anterior pituitary cells were used to study the effects of exogenous prostaglandins (PGs) and thromboxanes (TXs) on the secretion of prolactin (PRL). No change in hormone release was observed upon superfusion with TXB2 (10(-5)M) or the TX synthesis inhibitor, imidazole (1.5 mM). PGs A2, B2, D2, E1, E2, F1 alpha, F2 alpha, and endoperoxide analogs, U-44069 and U-46619, also had no effect on PRL secretion (all at 10(-5)M). In contrast 10(-5)M PGI2 was repeatedly found to stimulate PRL release to a level at least 125% above control, while producing no apparent change in the amount of hormone secreted in response to TRH. Somatostatin (SRIF), at a dose of 10(-6)M, maximally inhibited TRH-induced PRL output, but failed to alter the PRL response to PGI2. These studies indicate that PGI2 may have a direct effect on the anterior pituitary to modify PRL secretion.