The syndrome of generalized resistance to thyroid hormone is characterized by elevated circulating levels of thyroid hormone in the presence of an overall eumetabolic state and failure to respond normally to triiodothyronine. We have evaluated a family with inherited generalized resistance to thyroid hormone for abnormalities in the thyroid hormone nuclear receptors. A single guanine -* cytosine replacement in the codon for amino acid 340 resulted in a glycine --arginine substitution in the hormone-binding domain of one of two alleles of the patient's thyroid hormone nuclear receptor 13 gene. In vitro translation products of this mutant human thyroid hormone nuclear receptor (3 gene did not bind triiodothyronine. Thus, generalized resistance to thyroid hormone can result from expression of an abnormal thyroid hormone nuclear receptor molecule.

The enzymatic action of highly purified chondroitin ABC lyase from Proteus vulguris is dependent on the size of the substrate, and the enzyme does not cleave tetrasaccharides, irrespective of their sulfation profiles [Sugahara, K., Shigeno, K., Masuda, M., Fujii, N., Kurosaka, A. & Takeda, K. (1994) Cuvbohydr: Res. 255, 145-1631. To characterize the enzyme action in more detail, we isolated nine sulfated hexasaccharides from commercial shark cartilage chondroitin sulfate D, after partial digestion with highly purified chondroitin ABC lyase, by means of gel chromatography and HPLC on an amine-bound silica column. Structural analysis by 500-MHz 'H-NMR spectroscopy, and enzymatic digestion in conjunction with HPLC, demonstrated that these hexasaccharides, with the common core saccharide structure d4HexA(rxl -3)GalNAc(~l-4)GlcA(j31-3)GalNAc(~1-4)GlcA(~1-3)GalNAc (where d4HexA and GlcA represent 4-deoxy-u-~-threa-hex-4-enepyranosyluronic acid and glucuronic acid, respectively) bear three or four sulfate groups in different combinations. In the hexasaccharides, the D disaccharide unit GlcA2-SO;@I -3)GalNAc6SO;, which is characteristic of chondroitin sulfate D, was arranged on the reducing side of the A disaccharide unit GlcA(~l-3)GalNAc4SO;, and thus formed an A-D tetrasaccharide sequence GIcA(j31-3)GalNAc4SO, @I -4)GlcA2SO;C(1'1-3)GalNAc6SO.;. Analysis of the degradation products of these hexasaccharides with highly purified chondroitin ABC lyase indicated that the enzyme preferentially acted on the unsaturated hexasaccharides in an exolytic fashion and removed an unsaturated disaccharide unit from the non-reducing termini, irrespective of the sulfation profiles of the hexasaccharides.

The stimulatory guanine nucleotide-binding protein (G s ) is required for hormone-stimulated cAMP generation. Gnas, the gene encoding the G s ␣-subunit, is imprinted, and targeted disruption of this gene in mice leads to distinct phenotypes in heterozygotes depending on whether the maternal (m؊/؉) or paternal (؉/p؊) allele is mutated. Notably, m؊/؉ mice become obese, whereas ؉/p؊ mice are thinner than normal. In this study we show that despite these opposite changes in energy metabolism, both m؊/؉ and ؉/p؊ mice have greater sensitivity to insulin, with low to normal fasting glucose levels, low fasting insulin levels, improved glucose tolerance, and exaggerated hypoglycemic response to administered insulin. The combination of increased insulin sensitivity with obesity in m؊/؉ mice is unusual, because obesity is typically associated with insulin resistance. In skeletal muscles isolated from both m؊/؉ and ؉/p؊ mice, the basal rate of 2-deoxyglucose uptake was normal, whereas the rate of 2-deoxyglucose uptake in response to maximal insulin stimulation was significantly increased. The similar changes in muscle sensitivity to insulin in m؊/؉ and ؉/p؊ mice may reflect the fact that muscle G s ␣ expression is reduced by ϳ50% in both groups of mice. GLUT4 expression is unaffected in muscles from ؉/p؊ mice. Increased responsiveness to insulin is therefore the result of altered insulin signaling and/or GLUT4 translocation. This is the first direct demonstration in a genetically altered in vivo model that G s -coupled pathways negatively regulate insulin signaling.Heterotrimeric guanine nucleotide-binding proteins (G proteins) 1 transduce signals from seven transmembrane receptors to intracellular effectors. Each G protein is composed of distinct ␣, ␤, and ␥ subunits (1). The ␣-subunit binds guanine nucleotide and interacts with specific effectors, such as adenylyl cyclase, phospholipase C, and ion channels. The ␣-subunit for G s (G s ␣) is ubiquitously expressed and transmits the stimulatory signal from hormone-bound receptors to adenylyl cyclase and is therefore required for hormone-stimulated cAMP generation. Both catecholamines (whose receptors activate G s ) and cAMP have been implicated as negative regulators of insulin signaling and insulin-stimulated glucose transport in various cell types, including adipocytes and muscle cells (2-6), although this has not been found universally (7-9). In one study administration of cholera toxin (which constitutively activates G s ␣) to rats led to decreased insulin sensitivity and glucose uptake in skeletal muscle (10).Heterozygous inactivating mutations of the gene encoding G s ␣ (GNAS1 at 20q13.2-13.3; Ref. 11) cause Albright hereditary osteodystrophy, an autosomal dominant disorder characterized by obesity, short stature, and skeletal defects (12). Paternal transmission of GNAS1 mutations produces offspring with Albright hereditary osteodystrophy alone (pseudopseudohypoparathyroidism), whereas maternal transmission produces offspring who also have multihormone resistance (ter...

We report a 48-year-old woman who developed hyperthyroidism following primary hypothyroidism. The serum T4 level was initially low and serum TSH level was high with clinical signs of hypothyroidism. The thyroid gland was not enlarged. Therapy with L-T4 was started. Three years later she developed hyperthyroidism; serum free T4 increased to 29.1 pmol/l after cessation of L-T4 therapy. The 123I thyroid uptake was increased with no suppression by exogenous T3. When she was hypothyroid, the activity of thyroid stimulating antibodies (TSAb) in serum measured by cyclic AMP production in cultured porcine thyroid cells were negative at 93.4% (normal less than 140%), while thyroid stimulation-blocking antibodies (TSBAb) determined by inhibition of TSH-induced cyclic AMP increase were positive at 96.1% (normal less than 40%). When hyperthyroidism subsequently occurred, TSBAb became negative (30.9%), while TSBAb became positive (163.3%). The findings indicate that hypothyroidism due to the potent TSBAb activity is not always persistent, but can be changed when various types of thyroid-relating antibodies change in the course of the disease.