Thyroid hormone regulation of beta-adrenergic receptors and catecholamine sensitive adenylate cyclase in foetal heart

A Longitudinal Study of Thyroid Markers Across Pregnancy and the Risk of Gestational Diabetes

CONTEXT

T3 is the biologically active thyroid hormone involved in glucose metabolism. The free T3 (fT3)/free T4 (fT4) ratio, a marker indicating conversion of fT4 to fT3, is also implicated in glucose homeostasis.

OBJECTIVE

To examine associations of fT3 and the fT3/fT4 ratio with gestational diabetes mellitus (GDM).

DESIGN

In a case-control study, thyroid markers (fT3, fT4, TSH) were measured and the fT3/fT4 ratio was derived across four visits in pregnancy, including first (gestational weeks 10 to 14) and second (weeks 15 to 26) trimester. Conditional logistic regression adjusting for thyroid autoimmunity status and major GDM risk factors estimated trimester-specific associations of thyroid markers with subsequent GDM risk.

SETTING

Twelve US clinical centers.

PARTICIPANTS

One hundred seven GDM cases and 214 non-GDM controls from a multiracial pregnancy cohort of 2802 women.

MAIN OUTCOME MEASURES

GDM diagnosis ascertained from medical records.

RESULTS

Both fT3 and the fT3/fT4 ratio were positively associated with GDM: adjusted OR (95% CI) comparing the highest vs lowest fT3 quartile was 4.25 (1.67, 10.80) at the first trimester and 3.89 (1.50, 10.10) at the second trimester. Similarly, the corresponding risk estimates for the fT3/fT4 ratio were 8.63 (2.87, 26.00) and 13.60 (3.97, 46.30) at the first and second trimester, respectively. Neither TSH nor fT4 was significantly associated with GDM.

CONCLUSIONS

Higher fT3 levels, potentially resulting from de novo synthesis or increased fT4 to fT3 conversion, may be an indicator of GDM risk starting early in pregnancy.

Ontogeny and effects of thyroid hormone on beta1-adrenergic receptor mRNA expression in ovine fetal kidney cortex

OBJECTIVE

Previous studies indicate that thyroidectomy (TX) decreases renin gene expression in ovine fetal renal cortex in late gestation. Fetal ovine renin-containing renocortical cells become increasingly responsive to beta-adrenergic stimulation as gestation proceeds. Increases in plasma thyroid hormone concentrations parallel this change, suggesting that there is a positive developmental relationship between the two. To examine this hypothesis, we determined the ontogeny of beta1-adrenergic receptor (beta1R) mRNA expression, and the effect of thyroid hormone on in vivo and in vitro expression in fetal sheep.

METHODS

Renocortical tissue was obtained from naive, TX, and sham-operated fetuses to determine beta1R mRNA levels. Renin-containing renocortical cells from TX or sham fetuses were treated with isoproterenol (Iso) or forskolin (FSK) for analysis of cellular cyclic adenosine monophosphate (cAMP) levels. Renocortical cells from naive fetuses were treated with triiodothyronine (T3) to assess cellular beta1R mRNA levels. Fetal plasma thyroxine (T4) level was determined.

RESULTS

Renocortical beta1R mRNA expression increased significantly between 100 and 140 days' gestational age (dGA), while TX attenuated this increase (P <.01). Renocortical cellular cAMP levels were higher in sham compared to TX fetuses following incubation with Iso or FSK (P <.05). Cells incubated with T3 exhibited significantly increased beta1R mRNA expression (P <.05).

CONCLUSION

The data suggest that thyroid hormone may be involved in modulating ovine fetal renocortical beta1R gene expression during development. We speculate that the increased beta1R mRNA expression in renal cortical cells as development progresses may mediate the increases in renin gene response to beta-adrenergic stimulation in late gestation.

Endocrine abnormalities in patients with central serous chorioretinopathy

PURPOSE

To investigate and to identify endocrine and metabolic abnormalities in patients with central serous chorioretinopathy (CSCR).

DESIGN

Observational case series.

PARTICIPANTS

Twenty-four patients with CSCR.

METHODS

Serum and urinary catecholamines, glucocorticoids, mineralocorticoids, serum testosterone, and thyroid-stimulating hormone (TSH) function were evaluated prospectively.

RESULTS

Fifty percent (12 of 24) of patients with active acute CSCR showed elevated 24-hour urine cortisol or tetrahydroaldosterone levels. Serum aldosterone levels were low in 7 of 24 (29.1%) patients. Single morning plasma catecholamine levels were elevated in 7 of 24 patients, although 24-hour urine metanephrines (catecholamine breakdown products) were normal. Serum testosterone and TSH levels were normal in nearly all (23 of 24) patients.

CONCLUSION

Many patients with acute CSCR have elevated 24-hour urine corticosteroids, which may contribute to the pathogenesis of the disorder. Endogenous mineralocorticoid dysfunction is a newly described feature of CSCR.

Effect of the Yang tonifying herbs on myocardial beta-adrenoceptors of hypothyroid rabbits

New Zealand White female rabbits were randomly divided into three groups, each contained six rabbits, i.e. thyroidectomized and untreated rabbits (group 1), thyroidectomized rabbits treated by the Yang tonifying herbs (group 2) and sham thyroidectomized rabbits as controls (group 3). The myocardial beta-adrenoceptor density (Bmax) and affinity (Kd) of each group of rabbits were determined by radioligand binding assay technique on the thirtieth postoperative day and the data were handled by using a computer program of the Woolf plot with weight regression. Moreover, the serum levels of thyroxine (T4) and triiodothyronine (T3) of each group of rabbits were measured by radioimmunoassay technique and their heart rates (HR) were also recorded on the preoperative and thirtieth postoperative day. The results showed that the Bmax, T4, T3 and HR in group 1 were lower significantly than that in group 3 (P < 0.01-0.001), but the change of Kd in group 1 was not significant; the deviation of the indices from the normal value in group 2 was less remarkably than in group 1 other than T4.

Beta-adrenoceptor-agonist and insulin actions on glucose metabolism in rat skeletal muscle in different thyroid states

1. The actions of the beta-adrenoceptor agonist isoprenaline on glucose and glycogen metabolism, in the presence of various concentrations of insulin, were investigated in isolated soleus muscle preparations taken from eu-, hyper- and hypothyroid rats. 2. Hyperthyroidism, induced by 3,3',5-tri-iodo-D-thyronine (T3) administration for 5 days, increased the rate of lactate formation and suppressed the rate of glycogen synthesis in soleus muscle in response to isoprenaline, even in the presence of physiological or supraphysiological insulin concentrations. 3. Hypothyroidism, induced by administration of 6-n-propyl-2-thiouracil for 4 weeks, decreased the rate of isoprenaline-stimulated lactate formation at all insulin concentrations, but significantly decreased the responsiveness of lactate formation only at low insulin concentrations. In the presence of 100 or 10,000 mu-units of insulin/ml, the ability of isoprenaline to suppress the rate of glycogen synthesis was markedly impaired (inhibition at 100 mu-units of insulin/ml and 1 micro-M-isoprenaline: eu- 72.6 +/- 2.9%; hypo-41.0 +/- 2.1%; P less than 0.001). 4. Hyperthyroidism had no effect on the number or affinity of beta-adrenoceptors, defined by 125I-pindolol binding, or beta-adrenoceptor- or forskolin-stimulated adenylate cyclase activity in membrane preparations of gastrocnemius muscle, whereas hypothyroidism increased the beta-adrenoceptor density and decreased the beta-adrenoceptor-stimulated adenylate cyclase activity, without affecting the receptor affinity or forskolin-stimulated adenylate cyclase activity. 5. It is concluded that there is a complex interplay between insulin, catecholamines and thyroid hormones to regulate skeletal-muscle glucose metabolism. The changes observed in muscles in hypothyroidism may be explained, at least in part, by changes in beta-adrenoceptor-G-protein-adenylate cyclase coupling affecting the generation of cyclic AMP and the regulation of some of the key enzymes of glycogen metabolism; in contrast, the changes observed in muscles in hyperthyroidism do not appear to result from alterations at the level of the receptor-mediated second-messenger generation.

The role of thyroid hormones in maturation of the adrenaline-sensitive lung liquid reabsorptive mechanism in fetal sheep

1. Following thyroidectomy at 106-118 days fetal sheep were infused continuously with triiodothyronine (T3) from 110, 118, 125 or 131 days (n = 12) or with thyroxine (T4) from 118 days (n = 4) until the fetuses were delivered. Lung liquid secretion or absorption rates, heart rate, blood pressure and arterial blood gases were measured before and during 45 min periods of fetal infusions of adrenaline (n = 60) at 3-8 day intervals. The effects of T3 or T4 replacement on the response to adrenaline were compared with data previously obtained in groups of euthyroid (control) and thyroidectomized (Tx) fetuses. 2. Fetuses infused with T4 (50 micrograms/day) following thyroidectomy had plasma T4 and T3 concentrations in the normal fetal range. Fetal plasma T3 levels in fetuses infused with T3 (60 micrograms/day) were at or above the high end of the normal range for full-term fetuses. Those receiving 120 micrograms of T3 per day had levels equivalent to those normally seen in the postnatal T3 surge. 3. Normal maturation in the lung of the reabsorptive response of fetal lung liquid to adrenaline was seen in the fetuses infused with T3 or T4 from 118 days. A marginal advance in maturation was seen in fetuses infused with T3 from 110 days and a delay in maturation in those infused with T3 from 125 and 131 days.