Thyrotropin-releasing hormone increases plasma atrial natriuretic peptide levels in human

Fluoride Exposure Induces Inhibition of Sodium-and Potassium-Activated Adenosine Triphosphatase (Na+, K+-ATPase) Enzyme Activity: Molecular Mechanisms and Implications for Public Health

In this study, several lines of evidence are provided to show that Na + , K + -ATPase activity exerts vital roles in normal brain development and function and that loss of enzyme activity is implicated in neurodevelopmental, neuropsychiatric and neurodegenerative disorders, as well as increased risk of cancer, metabolic, pulmonary and cardiovascular disease. Evidence is presented to show that fluoride (F) inhibits Na + , K + -ATPase activity by altering biological pathways through modifying the expression of genes and the activity of glycolytic enzymes, metalloenzymes, hormones, proteins, neuropeptides and cytokines, as well as biological interface interactions that rely on the bioavailability of chemical elements magnesium and manganese to modulate ATP and Na + , K + -ATPase enzyme activity. Taken together, the findings of this study provide unprecedented insights into the molecular mechanisms and biological pathways by which F inhibits Na + , K + -ATPase activity and contributes to the etiology and pathophysiology of diseases associated with impairment of this essential enzyme. Moreover, the findings of this study further suggest that there are windows of susceptibility over the life course where chronic F exposure in pregnancy and early infancy may impair Na + , K + -ATPase activity with both short- and long-term implications for disease and inequalities in health. These findings would warrant considerable attention and potential intervention, not to mention additional research on the potential effects of F intake in contributing to chronic disease.

Clinical Use of Laboratory Tests for the Identification of Secondary Forms of Arterial Hypertension

The prevalence of secondary hypertension can be underestimated if appropriate tests are not performed. The importance of selecting patients with a high pre-test probability of secondary forms of hypertension is first discussed. The laboratory tests currently used for seeking a cause of hypertension are critically reviewed, with emphasis on their operative features and limitations. Strategies to identify primary aldosteronism, the most frequent form of secondary hypertension, and to determine its unilateral or bilateral causes are described. Treatment entails adrenalectomy in unilateral forms, and mineralocorticoid receptor blockade in bilateral forms. Renovascular hypertension is also a common, curable form of hypertension, that should be identified as early as possible to avoid the onset of cardiovascular target organ damage. The tests for its confirmation or exclusion are discussed. The various tests available for the diagnosis of pheochromocytoma, which is much rarer than the above but extremely important to identify, are also described, with emphasis on recent developments in genetic testing. Finally, the tests for diagnosing some rarer monogenic forms and other renal and endocrine causes of arterial hypertension are explored.

The role of thyroid hormone in blood pressure homeostasis: evidence from short-term hypothyroidism in humans

Arterial hypertension is known to be frequently associated with thyroid dysfunction, with a particularly high prevalence in chronic hypothyroidism. However, to our knowledge no comprehensive study addressed causal mechanisms possibly involved in this association. We here report the physiological relationships between blood pressure and neuro-humoral modifications induced by acute hypothyroidism in normotensive subjects. Twelve normotensive patients with previous total thyroidectomy were studied. Ambulatory 24-h blood pressure monitoring was performed, and free T(3), free T(4), TSH, PRA, aldosterone, cortisol, adrenaline, and noradrenaline were assayed 6 wk after oral L-T(4) withdrawal (phase 1) and 2 months after resumption of treatment (phase 2). During the hypothyroid state (TSH, 68.1 +/- 27.7 microIU/ml; mean +/- SD), daytime arterial systolic levels slightly, but significantly, increased (125.5 +/- 9.7 vs. 120.4 +/- 10.8 mm Hg; P < 0.05), and daytime diastolic levels (84.6 +/- 7.9 vs. 76.4 +/- 6.8 mm Hg; P < 0.001), noradrenaline (2954 +/- 1578 vs. 1574 +/- 962 pmol/liter; P < 0.001), and adrenaline (228.4 +/- 160 vs. 111.3 +/- 46.1 pmol/liter; P < 0.05) also increased. PRA remained unchanged (0.49 +/- 0.37 vs. 0.35 +/- 0.21 ng/ml.h; P = NS), whereas both aldosterone (310.3 +/- 151 vs. 156.9 +/- 67.5 pmol/liter; P < 0.005) and cortisol (409.2 +/- 239 vs. 250.9 +/- 113 pmol/liter; P < 0.02) significantly increased. By using univariate logistic regression daytime arterial diastolic values, noradrenaline and aldosterone were found to be significantly related to the hypothyroid state (P < 0.02, P < 0.036, and P < 0.024, respectively). In conclusion, our data show that thyroid hormones participate in the control of systemic arterial blood pressure homeostasis in normotensive subjects. The observed sympathetic and adrenal activation in hypothyroidism, which is reversible with thyroid hormone treatment, may also contribute to the development of arterial hypertension in human hypothyroidism.

Neuroendocrine evidence for an association between hypothyroidism, reduced central 5-HT activity and depression

OBJECTIVE

The incidence of depression in those with hypothyroidism is increased compared to healthy populations, though the mechanism for this is unclear. We tested the hypothesis that central 5-HT activity is reduced in hypothyroidism, and that this subsequently lowers the threshold for developing depression.

PATIENTS

Twenty subjects entered the study: 10 drug free hypothyroid patients and 10 age, sex, weight and menstrual cycle matched controls.

MEASUREMENTS

Patients were diagnosed as being depressed using DSM-IIIR criteria and rated using the Hamilton Rating Scale for Depression (HAM-D) and Beck Depression Inventory (BDI). Cortisol and prolactin responses to dexfenfluramine, a centrally acting 5-HT releasing agent, were used as an index of central 5-HT responsivity.

RESULTS

Both cortisol and PRL responses were reduced in the hypothyroid group relative to the controls. Peak cortisol responses were inversely correlated to TSH levels. Four of the 10 patients were clinically depressed. Depressed patients had higher TSH levels than their non-depressed counterparts, and TSH levels were positively correlated with HAM-D and BDI scores.

CONCLUSIONS

These findings support animal work suggesting that hypothyroidism reduces central 5-HT activity. They also suggest a threshold effect in that higher TSH levels predicted both lower 5-HT mediated endocrine responses and the presence of clinical depression.