To determine whether the relative decline in cardiac myosin isoenzyme V1 with maturation continues progressively into senescence and whether thyroxine could reverse age-associated changes in the myosin isoenzyme profile and contraction, rats 2, 8, and 24 months old were treated with thyroxine, 6.4 mg/kg, for 7 days. Myosin isoenzymes, Ca2+-myosin ATPase activities, and isometric contractile fun...

Subcutaneous administration of L-thyroxine (75 pg/lOO g of body weight per day) to rats for 10 to 14 days caused a decrease in the activity of kynurenine 3-hydroxylase to about 50% of the control value. Enzymic properties of kynurenine 3-hydroxylase of mitochondrial outer membrane preparations isolated from normal and L-thyroxine-treated rats were almost identical, suggesting that L-thyroxine a...

Thyroxine and triiodothyronine are transported in the blood as noncovalent complexes with certain serum proteins. This has been shown by many investigators and was the subject of an extensive recent review by Robbins and Rall (1). The binding proteins are an a-globulin (called thyroxine-binding globulin), a prealbumin, and serum albumin. The first appears to be the most significant binder of th...

Thyroxine and triiodothyronine are transported in the blood as noncovalent complexes with certain serum proteins. This has been shown by many investigators and was the subject of an extensive recent review by Robbins and Rall (1). The binding proteins are an a-globulin (called thyroxine-binding globulin), a prealbumin, and serum albumin. The first appears to be the most significant binder of th...

BACKGROUND Guinea pigs (Cavia porcellus) are often presented as patients in veterinary practice. Nevertheless, only limited information is available about endocrine diseases or thyroxine reference values for the species. OBJECTIVE The aim of this study was to determine serum thyroxine concentrations in a well-defined population of clinically healthy pet guinea pigs. METHODS Between October ...

Resting O2 consumption rate (BMR) or minimal O2 consumption rate (MOC) declines with age. Data are presented that suggest that a newly described function of the pituitary may be responsible for a considerable part of the total 75% decline in the MOC with age. The new function appears to decrease the responsiveness of peripheral tissues to thyroid hormones. Response curves to injected thyroxine ...

We have developed a highly sensitive radioimmunoassay of thyroxine and thyrotropin for mass screening for neonatal hypothyroidism. This assay involves a single disc (3 mm diameter) of dried blood on filter paper. The minimum detectable concentrations are 15 pg/tube (10 microgram/L) for thyroxine and 15 nano-int. units/tube (10 milli-int. units/L) for thyrotropin; intra- and interassay CV's are ...