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At least 181 records · Page 10Linked to original sources
PubMed1984

The effect of D- and L-thyroxine on sex hormone-binding globulin in rabbits.

Serum sex hormone-binding globulin (SHBG) concentration is increased in patients with thyrotoxicosis. SHBG is also present in rabbit serum, although it does not bind estradiol-17 beta (E2). Studies were carried out in female rabbits to determine the effects of thyroid hormone on SHBG. Serum concentrations of L-T4 cholesterol, E2, progesterone, free and total testosterone (T), and SHBG were measured in immature female rabbits (8-10 weeks of age). Rabbits were ovariectomized or subjected to sham surgery at puberty (age, 14-16 weeks) and restudied 6 weeks later. Values for serum T4, T, percent free T, free T, E2, progesterone and cholesterol were similar in ovariectomized and sham treated rabbits. Serum SHBG concentration progressively decreased in all rabbits from immaturity to age 20-22 weeks and values remained constant thereafter. Ovariectomy did not affect this age-related decrease in serum SHBG concentration. The 20- to 22-week-old ovariectomized and sham-operated rabbits were treated daily with either 30 micrograms/kg L-T4 or 150 micrograms/kg D-T4 for 2 weeks. This dose of L-T4 induced a 10-25% loss of BW, whereas D-T4 treatment did not, strongly suggesting that the L-T4 but not the D-T4-treated rabbits were hypermetabolic. D-T4 and L-T4 induced similar increases in serum SHBG (D-T4, delta 132 nM; L-T4, delta 146 nM). The increase in serum SHBG activity in response to D-T4 or L-T4 was reversible, since serum SHBG concentration returned to pretreatment values 5 weeks after thyroid hormone therapy was discontinued. The 27- to 29-week-old rabbits were then treated for 2 weeks with D-T4 (150 micrograms kg-1 day-1). Serum SHBG concentration significantly increased, and there were negative correlations between the thyroid hormone-induced increase in SHBG activity and both the percent free T and free T (P less than 0.01). D-T4 administration significantly lowered the serum cholesterol concentration without altering BW.

Animals↗
PubMed1982

Inhibition of insulin secretion by L-thyroxine and D-thyroxine treatment in rats under the influence of drugs affecting the adrenergic nervous system.

Both L-thyroxine and D-thyroxine induced an inhibition of glucose-induced insulin secretion with comparable time- and dose-dependent characteristics. L-thyroxine was ten times more potent than D-thyroxine. While L-thyroxine and a ten times higher dose of D-thyroxine had a similar potency in inducing hyperthermia and hypocholesterolaemia, hyperglycaemia in response to D-thyroxine was less pronounced than in response to L-thyroxine. This difference may be explained by a greater depletion of liver glycogen stores and consequently more limited capacity for provision of glucose for the circulation. The results support the view that the differences between L-thyroxine and D-thyroxine are quantitative. Adrenergic contribution to L-thyroxine- and D-thyroxine-induced inhibition of insulin secretion by rat pancreas is apparently of minor importance. Treatment of the rats with propranolol as well as with reserpine or 6-hydroxydopamine did not alleviate L-thyroxine- or D-thyroxine-induced inhibition of insulin secretion by rat pancreas.

Animals↗
PubMed1993

Large somatostatin-insensitive thyrotrophin-secreting pituitary tumour responsive to D-thyroxine and dopamine agonists.

A unique thyrotrophin (TSH)-secreting pituitary tumour is described in a patient with a history of recurrent thyrotoxicosis. Unlike other previously reported TSHomas, the tumour is insensitive to octreotide, a somatostatin analogue. It does not accumulate [111In]octreotide but expresses functional dopamine receptors and responds to the D-isomer of thyroxine, two characteristics beneficial in the management of the patient.

Bromocriptine↗
PubMed1998

D-thyroxine reduces lipoprotein(a) serum concentration in dialysis patients.

Uremia raises lipoprotein(a) (Lp(a)) serum concentration and the risk of arteriosclerosis in dialysis patients. The treatment of high Lp(a) levels is not satisfactory today. The decrease of Lp(a) in hypothyroid patients on L-T4 therapy raised the question of whether dextro-thyroxine (D-thyroxine) reduces not only serum cholesterol, but also Lp(a) serum concentration. In a single-blind placebo-controlled study, the influence of D-thyroxine therapy on Lp(a) serum concentration was evaluated in 30 hemodialysis patients with elevated Lp(a) serum levels. Lp(a) was quantified in parallel by two methods, i.e., rocket immunoelectrophoresis and nephelometry, and apo(a) isoforms were determined by a sensitive immunoblotting technique. Regardless of the apo(a) isoforms, 6 mg/d D-thyroxine reduced elevated Lp(a) levels significantly by 27 +/- 13% in 20 dialysis patients (P < 0.001) compared with 10 control subjects (-9.9 +/- 8.4%). In parallel, D-thyroxine therapy significantly lowered total cholesterol (P < 0.001), LDL cholesterol (P < 0.001), and LDL cholesterol/HDL cholesterol ratio (P < 0.01); raised T4 and T3 serum levels; and suppressed thyroid-stimulating hormone secretion without causing clinical symptoms of hyperthyroidism in any of the patients. D-Thyroxine reduces elevated serum Lp(a) concentration in dialysis patients. The effect in nondialysis patients can be expected but remains to be proven.

Aged↗