Low Serum T4 Levels Research Articles

Regression of a pituitary adenoma following levothyroxine therapy of primary hypothyroidism

Two patients are described who were suffering from primary hypothyroidism and who developed a pituitary microadenoma and macroadenoma with suprasellar extension, respectively, diagnosed by CT scan of the pituitary. Both patients originally presented with amenorrhea and galactorrhea. In addition to low serum T4 and T3 levels and an elevated TSH level, they also had hyperprolactinemia. The TRH test performed in one of the patients showed an exaggerated response of both TSH and PRL to TRH. Correction of hypothyroidism by prolonged (months) treatment with levothyroxine resulted in normalization of thyroid function tests as well as hyperprolactinemia and in regression of the pituitary tumor. It was concluded that primary hypothyroidism was the cause of the pituitary adenoma and the amenorrhea/galactorrhea syndrome. It is recommended that routine thyroid function tests be obtained for patients with hyperprolactinemia. Demonstrable primary hypothyroidism should be corrected for prolonged periods of time by levothyroxine therapy, and CT scanning of the pituitary should be repeated before any other treatment such as bromocriptine or surgery is attempted.

Serum triiodothyronine and other clinical and laboratory indices of alcoholic liver disease.

Admission serum triiodothyronine (T3) values in 124 patients hospitalized for alcoholic liver disease were correlated with clinical and laboratory indices of liver function and commonly used determinants of thyroid function. Patients with low admission serum T3 levels had significant alterations in serum albumin, bilirubin, prothrombin time, and alkaline phosphatase associated with clinical signs of portal hypertension and collateral circulation, with little difference in serum glutamic-oxaloacetic transaminase, serum gamma glutamyl transpeptidase, or serum ornithine carbamyl transferase. This group also had a significant decrease in free T3 index despite an increase in T3 uptake; the slight reduction in total thyroxine (T4) was associated with an increase in free T4 index and no change in serum thyrotropin (TSH). For patients with alcoholic liver disease, low admission serum T3 and free T3 index values when accompanied by normal serum T4, free T4 index, and TSH levels appear to be indicative of severe liver dysfunction and increased mortality risk.

Toxicity of Leucaena leucocephala. The effect of iodine and mineral supplements on penned steers fed a sole diet of Leucaena.

Steers fed a sole diet of Leucaena leucocephala cv. Peru (leucaena), rapidly developed a hypothyroid condition. Total serum thyroxine (T4) levels declined from c 120 n mol litre-1 to 13 n mol litre-1 within six weeks of full leucaena feeding. Associated with the hypothyroidism was a declined in feed intake, poor weight gain, hair loss, excessive salivation and the development of lesions on the oesophagus of some animals. Light steers (119 kg) were more severely affected than heavy steers (220 kg) and two light steers died. During the eight week period of full leucaena feeding animals gained only 0.18 kg head-1 day-1 compared with 0.73 kg head-1 day -1 for steers fed cowpea (Vigna sinensis) hay. Supplementation with minerals (Fe, Cu, Zn) significantly increased mean daily intake (85.4 v 68.9 g/kg0.75), daily liveweight gain, (334 v 14 g), and serum T3 resin uptake (42.5 v 39.6%); decreased hair loss and skin lesions but did not alleviate the low serum T4 levels. Iodine supplementation did not affect intake, bodyweight gain, serum T4 levels, serum T3 uptake or toxicity scores compared with unsupplemented leucaena fed steers. When the leucaena fed animals were subsequently fed cowpea hay, appetite improved and the serum T4 levels returned to normal within two weeks. For the heavy steers over this period, weight gain was similar to the controls; however, the light steers continued to gain poorly.

The effect of body temperature on thyroid hormone levels in patients with non-thyroidal illness.

During studies on the mechanism underlying the low serum T3 levels in euthyroid patients with various acute and chronic non-thyroidal illnesses, it became evident that body temperature may be one parameter associated with changes in serum T3 levels. Forty-nine hospitalized, euthyroid patients with hyperpyrexia caused by various non-thyroidal illnesses were studied. The levels of serum T3 were found to decrease gradually with increasing body temperature. T3 was already below the normal level +/- 2 S.D. at a body temperature of around 38 degrees C. Such low T3 levels as were seen at temperatures of above 40 degrees C are observed in thyroid patients only during severe hypothyroidism. The levels of T4 and TSH remained unchanged and within the normal range regardless of body temperature. The levels of reverse-T3 in the sera analyzed were found to be unchanged in some cases, while in others they paralleled body temperature. It is concluded that the body temperature must be taken into consideration when studying the serum levels of T3.

Propranolol in the treatment of thyrotoxicosis by subtotal thyroidectomy.

Subtotal thyroidectomy was performed in 40 patients with thyrotoxicosis in whom propranolol alone was used as preparation for surgery. Propranolol was given orally in a dose of 40 mg every 6 h for a mean preoperative period of 17 days (range 4-60 days) and continued for seven days after operation. The mean +/- SE blood loss at operation was only 160 +/- 20 ml. The period of follow-up was from three to nine months. Recurrent thyrotoxicosis has not occurred in any patient. Low levels of total serum triiodothyronine (T3) and total serum thyroxine (T4) were observed in the early postoperative weeks in some patients and were associated with symptoms of mild hypothyroidism, but by six months in the presence of a raised serum thyrotropin (TSH) the thyroid hormone levels returned to normal. Permanent hypothyroidism developed in only two patients. Despite normal or low total serum T3 and T4 levels, the TSH response to thyrotropin-releasing hormone (TRH) was absent in all patients one week after operation. At four weeks and at eight weeks, the response was absent or sub-normal in 70% and 20% of the patients respectively, indicating a delay in the recovery of the hypothalamo-pituitary axis previously exposed to high levels of T3 and T4. It is considered that subtotal thyroidectomy for thyrotoxicosis in patients prepared with propranolol is an acceptable procedure which has some advantages over the conventional preparation with carbimazole and potassium iodide, not the least of which are the potential reduction in preparation time, the more flexible timing of operation, and the reduced operative blood loss.

Thyroid hormone secretion rate in the lactating rat.

Summary. Thyroid secretion rate (TSR) was determined in lactating and non-lactating rats by the thyroxine substitution and `direct output' methods. In lactating rats, apparent TSR as determined by the substitution method was significantly greater than that of controls when dietary iodine was deficient. By the direct output method, TSR was significantly reduced even when dietary iodine was adequate. It is concluded that the substitution method measures the physiological demand for thyroid hormone, which is greater during lactation, but represents true TSR only if iodine supplies are adequate. Results obtained by the direct output method show the actual TSR to be significantly reduced both during lactation and when dietary iodine is limited. Mean thyroid acinar cell height significantly increased as thyroidal iodine was depleted. It is concluded that, during lactation, TSH was elevated but iodine was insufficient to support the demand for thyroid hormone. The low serum T4 level observed in lactating rats, as determined by a competitive binding method, supports these conclusions. Analysis of the methods of computation of TSR by direct output showed that (1) as thyroidal iodine supplies were depleted, thyroidal iodide accumulation became more efficient, (2) the iodine-deficient thyroid recycled a greater percentage of the available iodine, (3) thyroidal 131I uptake was reduced in lactating rats, (4) total thyroidal iodine was inversely correlated to its release rate (K4) from the thyroid, and (5) thyroidal iodine, and not K4, was the major factor influencing TSR under these experimental conditions.