Mean Thyroxine Concentration Research Articles

Annual concentrations of thyroxin and progesterone in Karagouniko and Chios ewes

The circannual secretion of progesterone and thyroxin of two indigenous sheep breeds (Chios and Karagouniko, each n=10) with different reproductive pattern was investigated. Blood samples were collected weekly and the serum hormone's concentration was assayed by RIA. Between breeds, no difference was detected in the mean annual thyroxin concentration. Similarly, no differences were detected within breeds in the mean thyroxin concentrations for the periods of increasing and decreasing daylight. Clear thyroxin peaks were detected in both breeds a month or so prior to the transition to anestrus period; these peaks were higher in the Karagouniko breed. Breeding season duration was clearly shorter in Karagouniko in comparison with that of Chios; in the later breed many animals had substantially short anestrus. These results give strong indications that thyroid activity has a catalytic role in the regulation of the reproductive period in ewes.

Studies on the haematology and trace element status of adult Bactrian camels (Camelus bactrianus) in China.

Reference values were established for some haematological and serum biochemical constituents in Bactrian camels (Camelus bactrianus) in China. The contents of seven trace elements in the blood, hair, liver, kidney, heart, spleen, lung, cerebrum, cerebellum, rib, ovary, pancreas and gluteal muscle of Bactrian camels were also measured. Some of these values are reported for the first time for Bactrian camels in China. Most haematological and serum biochemical values were similar to those of cattle, yaks, sheep and dromedary camels, but the mean serum albumin concentration and the albumim/globulin ratio were significantly higher than those in other ruminants and the mean thyroxine concentration was half that in dromedary camels. The liver contained the highest concentrations of copper, zinc, manganese and iron, and the renal cortex contained the highest concentration of selenium. The concentrations of selenium, cobalt, zinc, manganese and molybdenum in the tissues were within the reference ranges for other ruminants, but the mean iron and copper concentrations in the liver were significantly higher than those in other ruminants.

Thyroxine concentrations are elevated in mares which continue to exhibit estrous cycles during the nonbreeding season

In two successive years, the pattern of secretion of thyroxine was compared in seasonally anestrous mares and a subpopulation of mares that exhibited estrous cycles during the nonbreeding season. Blood samples were collected two or three times per week between October and April from a total of 15 mares that exhibited estrous cycles during the nonbreeding season and 21 anestrous mares. Monthly mean concentrations of thyroxine during the period from October through April were greater (p<0.05) in cycling versus anestrous mares. However, it remains to be determined whether continuation of estrous cycles during the nonbreeding season and elevated concentrations of thyroxine are causally related.

Thyroid Function in Children with -Thalassemia Major in North Jordan

Basal thyroid function was assessed by serum thyroxine, tri-iodothyronine and thyroid-stimulating hormone levels in 90 patients 2-10 years old with beta-thalassaemia major. Based on measured serum ferritin levels, patients were classified into two groups: group (I) which included 63 patients with ferritin concentrations ranging from 300 to 7000 ng/ml (mild iron overload) and group (II) which included 27 patients with ferritin concentrations higher than 7000 ng/ml (severe iron overload). The results of thyroid function in both groups were compared with those of 50 control subjects. In group (I), the mean concentrations of all measured hormones were not significantly different from those of the controls. In group (II), the mean concentrations of thyroxine and tri-iodothyronine decreased by 29 and 35 per cent (P < 0.05), respectively, and the mean concentration of thyroid-stimulating hormone showed a 2.6-fold increase (P < 0.01) in comparison with those of the controls. The data clearly demonstrate the occurrence of impaired thyroid function and its possible association with iron overload in a considerable proportion of transfusion-dependent beta-thalassaemic patients.

Iodine Supplementation with Oral or Intramuscular Iodized Oil. A Two-Year Follow-up of a Comparative Trial

A controlled trial of iodine supplementation comparing oral with intramuscular iodized oil has been carried out in an iodine deficient area of Zaire. Two years after the administration of 2 ml of oral iodized oil to the population of four villages the overall goitre prevalence had fallen from 64 to 54%. In a further two villages given 2 ml of intramuscular oil the prevalence fell from 65 to 50%. The effectiveness of supplementation was also assessed by measuring changes in thyroid function in women of reproductive age. Among women in the villages given oral iodized oil, the geometric mean thyroxine concentration, measured in dried bloodspots, rose from 27.2 to 52.6 nmol/L at the two-year follow-up. This was similar to the response of the intramuscularly treated villages in which thyroxine levels rose from 32.1 to 65.4 nmol/L. There was no change in goitre prevalence or thyroid function in two control villages. Oral iodized oil is a cheaper and simpler alternative to the injected form providing effective iodine prophylaxis for up to two years after a single dose.

Decrease of free thyroxin in serum of lactating women.

We measured thyroid hormones and thyroxin-binding proteins in serum from 62 normal lactating and 52 nonlactating women at three months postpartum, and compared these values with those for 42 nonpregnant control women of similar age. Mean thyroxin concentrations in the lactating and nonlactating women were significantly (P less than 0.001) lower than that of the nonpregnant controls, but there was no significant difference (P greater than 0.2) in triiodothyronine concentration among these three groups. Free T4 concentration was significantly (P less than 0.01) lower in lactating women than in controls. The reverse-T3 concentrations in both lactating and nonlactating women were significantly (P less than 0.001) lower than in controls, and were significantly (P less than 0.001) lower in lactating than in nonlactating women. The concentration of thyroxin-binding globulin was significantly higher in lactating women than in controls, and the albumin concentration was significantly lower in women postpartum than in controls. Evidently, regulation of thyroid hormone in women postpartum, especially during lactation, differs from that in nonpregnant women.

Observations on serum thyroxine concentrations in lambs and ewes to assess iodine nutrition.

Thyroxine levels in serum of lambs and ewes were measured to determine their usefulness in assessing iodine nutrition of sheep. Lambs born on properties with no history of goitre had serum thyroxine concentrations more than twice that recorded in their mothers. These high values decreased to a level similar to that in the ewes after 8 weeks. In goitrous lambs younger than 2 weeks old, serum thyroxine concentrations were less than their ewe levels. Lambs born to ewes supplemented with iodine during pregnancy had higher thyroxine levels than lambs of control ewes. A survey of 80 flocks of ewes in Victoria showed that 40% had a low mean thyroxine concentration (less than 50 nmol/l), but only one of these properties had reported an outbreak of goitre. It is suggested that serum thyroxine levels in newborn lambs may provide a more sensitive indicator of hypothyroidism associated with iodine deficiency than ewe levels.

A rapid and precise sequential saturation radioimmunoassay for thyroxine.

A radioimmunoassay for the measurement of total thyroxine in unextracted serum or plasma is described. The assay is performed according to the sequential saturation principle in less than 4 h. The entire assay is carried out at room temperature. An antiserum of high affinity was used as binder, ammonium 8-anilino-1-naphthalene-sulphonate as displacing agent, and activated charcoal as adsorbent in the separation step. The standard curve was linear in the range 0-136 nmol/l serum. The precision in terms of SD was nearly the same through-out this range. Estimates of within-assay SD varied from 1.3 to 4.1 and between-assay SD from 0 to 3.3 nmol/l. The recovery of thyroxine added to normal plasma was 100% and the sensitivity was 6 nmol/l. Mean thyroxine concentration in plasma from young bulls was 92 nmol/l. The assay appears to be very well suited for experimental purposes when high precision is essential.

Thyroid hormones and thyrotropin in amniotic fluid.

Thyroid hormone and thyrotropin concentrations in amniotic fluid were studied by radioimmunoassays during pregnancy. The mean thyroxine concentration was 398 ng per 100 ml at 15 to 19 and 440 ng per 100 ml at 36 to 42 weeks. Although 3,3',5-tri-iodothyronine was undetectable (less than 25 ng per 100 ml), 3,3',5'-tri-iodothyronine levels were very high (range, 132 to 605 ng per 100 ml) at 15 to 30 weeks, but decreased substantially (range, 54 to 130 ng per 100 ml) thereafter. Thyrotropin was undetectable. The mean thyroxine and 3,3',5-tri-iodothyronine levels in amniotic fluid were much lower and the mean 3,3'5'-tri-iodothyronine much higher than the corresponding values in maternal serum at both 15 to 19 and 36 to 42 weeks of pregnancy. Measuring thyroid hormones in amniotic fluid, especially 3,3',5'-tri-iodothyronine, may aid in the diagnosis of fetal thyroid dysfunction and in identification of pregnancies of less than 30 weeks' gestation.

Thyroid Function in Relation to Dyslexia (Reading Failures)

Serum total thyroxine was measured in a group of 47 boys and 6 girls who suffered from functional dyslexia. Functional dyslexia is an actual reading level of, at least, 1½ years below mental expectancy. The thyroxine content of the serum of these children was markedly elevated compared to normal readers of similar age distribution (mean thyroxine concentration; dyslexic, 11.44 ug/dl; normal control = 7.69 ug/dl). These results indicate functional dyslexia is associated with systemic change in metabolism.

Serum thyrotropin and thyroxine concentrations in patients recieving lithium carbonate.

To determine the incidence of thyroid dysfunction in patients receiving therapy with lithium carbonate, serial determinations of serum thyrotropin (TSH) and thyroxine (T4) concentrations were made in 255 patients receiving lithium. The patients were followed for an average of 8 months and the longest period of lithium treatment was 65 months. The mean peak TSH level in the lithium treated patients was 3 times higher than in the control groups; elevated (>8 μU/ml) TSH levels occurred in 29.8% of the patients (76) at some time during treatment. At the time of final testing, 14.1% (36) of the patients had elevated serum TSH levels. The mean peak and final thyroxine concentrations in the lithium treated patients were only slightly lower than those in the control groups. In 15 patients whose final serum TSH levels were over 20 μU/ml, the mean thyroxine concentration was 2.9 μg/100 ml. A significantly higher incidence of positive anti-thyroglobulin antibody tests was found in these patients. Most were considered to have significant hypothyroidism and received thyroid treatment. In 27 patients pretreatment data were available. In these patients mean TSH levels significantly increased within the first 3 months of treatment and remained above pretreatment levels thereafter. Serum thyroxine levels did not change significantly. These results indicate that anti-thyroid effects of lithium, as manifested by elevated serum TSH levels, can be detected at some time in almost one-third of patients receiving it. With continued treatment, the anti-thyroid effect of lithium may either be lessened, with return of TSH levels to normal, or progress to the development of frank hypothyroidism.