Considerable evidence suggests that the concentration of free thyroxine, circulating unbound to serum proteins, is more closely relattd to a subject's thyroidal status than is the concentration of total thyroxine (1). Because of the intense binding of thyroxine by the serum proteins, the concentration of free thyroxine is very small and not measurable by conventional chemical methods. Robbins a...

Thyrotoxicosis is a condition of excess circulating thyroid hormones. Maternal thyrotoxicosis has been related to the development craniosynostosis (CS) in approximately 3% births. CS occurs when cranial sutures skull fuse prematurely. However, mechanism for hormone-induced those cases unclear. Currently, we are establishing an avian model thyroxine-induced study these mechanisms. Two groups fer...

Craniosynostosis (CS) is the premature fusion of cranial sutures during embryonic development, and this results in intracranial pressure skull deformities. Thyrotoxicosis, specifically maternal hyperthyroidism, has been linked to development CS. Our lab currently validating an avian model thyroxine-induced CS study mechanism involved thyroxine-enhanced ossification. We hypothesized that thyroxi...

The effects of thyroid hormone analogues on modulation of angiogenesis have been studied in the chick chorioallantoic membrane model. Generation of new blood vessels from existing vessels was increased 3-fold by either l-thyroxine (T4; 10(-7) mol/L) or 3,5,3'-triiodo-l-thyronine (10(-9) mol/L). T4-agarose reproduced the effects of T4, and tetraiodothyroacetic acid (tetrac) inhibited the effects...

We have studied whether, or not, tissue-specific regulatory mechanisms provide normal 3,5,3'-triiodothyronine (T3) concentrations simultaneously in all tissues of a hypothyroid animal receiving thyroxine (T4), an assumption implicit in the replacement therapy of hypothyroid patients with T4 alone. Thyroidectomized rats were infused with placebo or 1 of 10 T4 doses (0.2-8.0 micrograms per 100 gr...

The effects of propranolol (DL-propranolol) and D-propranolol on thyroid hormone metabolism were studied in six euthyroid volunteers receiving L-thyroxine (T4) and six hypothyroid patients receiving T4 replacement. D-propranolol as well as propranolol decreased L-triiodothyronine (T3) concentrations and the ratio of T3 to T4 in the euthyroid subjects, and D-propranolol decreased these variables...

The thyroid gland is an endocrine organ that secretes the hormones triiodothyronine (T3) and thyroxine (T4), which are, in turn, under the influence of the TSH and the TRH. Though hyperand hypothyroidism remain the common clinically manifesting condition of the thyroid, in some cases, the patient remains symptomless with either excess or decrease in thyroxine levels, along with normal TSH level...

A 75-year-old man was admitted to our hospital with syncope. Electrocardiogram showed complete atrioventricular block and bradycardia with the minimum heart rate of 22 beats/ min. There was a possible indication for temporary cardiac pacemaker implantation. Laboratory data on admission revealed high TSH level with low free T4 level. To rule out functional atrioventricular block, we treated seve...

The aim of this study was to evaluate total iodine, triiodothyronine (T3) and thyroxine (T4) status in the blood serum of Holstein cows on six farms in central Iran. Total iodine, T3 and T4 concentrations were measured in 90 blood serum samples (15 per farm). Mean concentrations of total iodine (38.80 ± 1.52 µg/l) and T3 (1.57 ± 0.10 nmol/l) were lower but the mean concentration of T4 (45.60 ± ...

Introduction: Neuropeptide Y (NPY) is the most abundant peptide present in mammals' brains. The majority of NPY-producing neurons is in arcuate and paraventricular nuclei of hypothalamus which affect hypophysiotrapic factors secretion. In this study we investigated the effect of intravenous injections of various doses of NPY on thyroxine (T4) and triiodothyronine (T3) serum concentrations. ...