Plasma catecholamines after thyrotropin-releasing hormone administration in hypothyroid patients before and during therapy

Standard hypothyroid treatment did not restore proper metabolic response to carbohydrate

PURPOSE

Hypothyroidism is associated with a lower metabolic rate, impaired glucose tolerance, and increased responsiveness of sympathetic nervous system to glucose ingestion. The Levothyroxine (LT4) monotherapy is the standard treatment for hypothyroidism; however to what extent this treatment restores the patients' metabolism has not been verified. The aim of this study was to test the hypothesis that standard LT4 therapy may not restore proper metabolic response to carbohydrate ingestion.

METHODS

Energy expenditure, glucose tolerance, and catecholamine response to glucose ingestion were compared in 18 subjects with pharmacologically compensated hypothyroidism (PCH) and controls, at baseline and during oral glucose tolerance test conditions.

RESULTS

Metabolic rate was significantly lower in PCH (P < 0.0001). Glucose tolerance was decreased in this group with no differences in insulin resistance indicators between both groups. Adrenergic activity (P < 0.05) as well as adrenergic reaction to glucose ingestion (P < 0.001) were stronger in PCH.

CONCLUSIONS

Standard treatment for hypothyroidism does not restore the normal metabolic reaction to carbohydrate which is observed in healthy people.

Impact of experimental hypothyroidism on monoamines level in discrete brain regions and other peripheral tissues of young and adult male rats

The levels of dopamine (DA), norepinephrine (NE) and serotonin (5-HT) in different brain regions as well as in blood plasma, cardiac muscle and adrenal gland of young and adult male albino rats were measured following experimentally induced hypothyroidism. Hypothyroidism induced by daily oral administration of propylthiouracil (PTU, 5mg/kg body wt) caused a significant reduction in DA levels in most of the tissues examined of both young and adult rats after 21 and 28 days, in NE levels after all the time intervals studied in young rats, and after 21 and 28 days in adult rats. 5-HT exhibited a significant reduction in the selected brain regions and blood plasma after 21 and 28 days and in cardiac muscle after all the time intervals in the two age groups of animals. It may be suggested that the changes in monoamine levels induced by hypothyroidism may be due to disturbance in the synthesis and release of these amines through the neurons impairment or may be due to an alteration pattern of their synthesizing and/or degradative enzymes.

Cortisol hypersecretion in unipolar major depression with melancholic and psychotic features: dopaminergic, noradrenergic and thyroid correlates

Evidence supports that hyperactivity of the hypothalamic-pituitary-adrenal axis has a pivotal role in the psychobiology of severe depression. The present study aimed at assessing hypothalamic-pituitary dopaminergic, noradrenergic, and thyroid activity in unipolar depressed patients with melancholic and psychotic features and with concomitant hypercortisolemia. Hormonal responses to dexamethasone, apomorphine (a dopamine receptor agonist), clonidine (an alpha 2-adrenoreceptor agonist) and 0800 and 2300 h protirelin (TRH) were measured in 18 drug-free inpatients with a DSM-IV diagnosis of severe major depressive disorder with melancholic and psychotic features showing cortisol nonsuppression following dexamethasone and 23 matched hospitalized healthy controls. Compared with controls, patients showed (1) lower adrenocorticotropin and cortisol response to apomorphine (p<0.015 and <0.004, respectively), (2) lower growth hormone response to clonidine (p=0.001), and (3) lower responses to TRH: 2300 h maximum increment in serum thyrotropin (TSH) level (p=0.006) and the difference between 2300 and 0800 h maximum increment in serum TSH values (p=0.0001). Our findings, in a subgroup of unipolar depressed inpatients with psychotic and melancholic features, are compatible with the hypothesis that chronic elevation of cortisol may lead to dopaminergic, noradrenergic and thyroid dysfunction.

Multihormonal responses to clonidine in patients with affective and psychotic symptoms

The neuroendocrine responses to the alpha(2)-adrenoreceptor agonist clonidine (CLO) (0.35 mg if body weight <65 kg or 0.375 mg if body weight> or =65 kg, PO) were studied in a large group of subjects: 134 drug-free inpatients--with either DSM-IV schizophrenia (SCZ, n=31), schizoaffective disorder (SAD, n=16), or major depressive episode (MDE, n=87) - and 22 hospitalized controls (HCs). Comparison with a previous placebo test performed in a subgroup of 92 subjects (46 MDEs, 20 SCZs, 8 SADs, and 18 HCs) showed that CLO induced a significant increase of growth hormone, prolactin (PRL) and thyrotropin (TSH) levels but no significant change in adrenocorticotropin and cortisol release. According to diagnostic categories, we found significantly lower GH stimulation in MDEs and in SADs compared to HCs or to SCZs. In addition, we found significantly lower CLO induced PRL and TSH stimulations in paranoid SCZ patients compared to controls and disorganized SCZ patients. Taken together, these results suggest a hyposensitivity of noradrenergic alpha(2)-receptors in patients with affective symptoms.

Increased cardiac sympathetic activity in patients with hypothyroidism as determined by iodine-123 metaiodobenzylguanidine scintigraphy

Clinical manifestations of hypothyroidism, such as bradycardia, suggest decreased sympathetic tone. However, previous studies in patients with hypothyroidism have suggested that increased plasma noradrenaline (NA) levels represent enhanced general sympathetic activity. As yet, cardiac sympathetic activity (CSA) in hypothyroidism has not been clarified. To evaluate CSA in patients with hypothyroidism, iodine-123 metaiodobenzylguanidine (MIBG) scintigraphy was performed in eight patients with hypothyroidism before therapy and in ten normal control patients. Planar images were obtained at 15 min and 4 h after injection of MIBG. The ratio of early myocardial uptake to the total injected dose (MU) and myocardial clearance of MIBG within 4 h p.i. (MC) were calculated. Plasma NA was also measured, and echocardiography was performed in all patients. Those patients with hypothyroidism in the euthyroid state after medical therapy were also evaluated in a similar manner. Left ventricular ejection fraction, measured by echocardiography, did not differ significantly between the groups. NA, MU and MC were significantly higher in patients with hypothyroidism than in controls, and all parameters were decreased after therapy. MC was well correlated with NA in hypothyroidism (r=0.86) before therapy. We conclude that CSA is increased in patients with hypothyroidism, in parallel with the enhanced general sympathetic activity.

Influence of the thyroid hormone status on tyrosine hydroxylase in central and peripheral catecholaminergic structures

We investigated the effect of hyper- and hypothyroidism on tyrosine hydroxylase protein concentration in the locus coeruleus (divided into anterior and posterior parts), the substantia nigra and the adrenals of adult rats. Rats were made hypothyroid with propylthiouracile (PTU, 0.02% in drinking water for 21 days) or hyperthyroid by thyroxine injection (100 or 250 micrograms/kg/day), for 3 or 17 days. PTU treatment resulted in statistically significant decrease of tyrosine hydroxylase in the anterior locus coeruleus (-13%) and the adrenals (-14%). After thyroxine treatment, in the anterior locus coeruleus, tyrosine hydroxylase was significantly higher (2 way ANOVA) after the 3 day treatment than after the 17 day treatment: tyrosine hydroxylase showed a trend to increase the 3 day treatment (+20% with the 250 micrograms/kg dose) and to decrease after the 17 day treatment (-15% with the 250 micrograms/kg dose). In the adrenals, tyrosine hydroxylase was increased by the 3 day treatment (+42% after the 250 micrograms/kg dose), but this increase was not observed after 17 days of treatment. Tyrosine hydroxylase was not altered in the posterior locus coeruleus and the substantia nigra, whatever the treatment. Together, our results support the hypothesis that in the anterior locus coeruleus and in the adrenals tyrosine hydroxylase level is positively modulated by thyroid hormones. After long-term treatment (17 days) this effect is not observed.