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Plasma Thyroxine (plasma + thyroxine)
Selected AbstractsPlasma Thyroid Hormone Concentrations in Dogs Competing in a Long-Distance Sled Dog RaceJOURNAL OF VETERINARY INTERNAL MEDICINE, Issue 4 2003David L. Panciera Plasma thyroxine (T4), 3,5,3,-triiodothyronine (T3), total protein, and albumin concentrations were measured in 15 dogs both before and after completion, and in an additional 16 dogs before and 24 dogs after completion, of a long-distance sled dog race. The plasma T4 concentration (mean ± SD) decreased significantly from 18.2 ± 5.4 nmol/L before to 14.3 ± 3.5 nmol/L after the race in dogs evaluated at both times and decreased significantly from 21.8 ± 10.5 nmol/L before to 15.8 ± 4.9 nmol/L after the race in dogs sampled only before or only after the race. The mean plasma T3 concentrations in dogs measured twice decreased significantly from 1.20 ± 0.48 nmol/L before to 0.74 ± 0.42 nmol/L after the race, as well as in dogs measured either before (1.28 ± 0.36 nmol/L) or after (0.69 ± 0.28 nmol/L) the race, respectively. Plasma total protein and albumin concentrations decreased significantly after completion of the race. No significant change was noted in 4 control dogs that did not compete in the race and were tested during a similar time period. The plasma concentrations of T4 and T3 were lower than the normal reference range established for this laboratory in 23 and 39%, respectively, of Alaskan sled dogs tested before the race. Plasma thyroid hormone concentrations frequently are below normal in conditioned Alaskan sled dogs and are further reduced after prolonged submaximal exercise. [source] The effects of polychlorinated biphenyls (Aroclor 1242) on thyroxine, estradiol, molt, and plumage characteristics in the American kestrel (Falco sparverius)ENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 7 2002Michael J. Quinn Jr. Abstract The purpose of this experiment was to determine the effects of Aroclor 1242, a mixture of polychlorinated biphenyls (PCBs), on plumage characteristics and molt in the American kestrel, Falco sparverius. Several characteristics of plumage, including color and molt schedule, are modulated by hormonal signals and hence may be modified by endocrine-active contaminants. If so, the functions of plumage (e.g., communication for mating or territorial defense) may be compromised by exposure to such compounds. Captive American kestrels were fed Aroclor 1242 at 0, 6.0, and 60.0 ppm (n = 6 males and 6 females per treatment) mixed in their normal diet. Concentrations of plasma estradiol and thyroxine were measured weekly from the beginning of treatment. Measured plumage characteristics included width of the black subterminal band on the tail, color (a composite index of hue and saturation), reflectance from 230 to 800 nm, pattern of feather loss and regrowth on the tail and wing, and timing of onset and duration of molt. Aroclor 1242 depressed plasma thyroxine. Plasma estradiol levels remained low due to the phase of the breeding cycle. Treatments did not disrupt the measured plumage characteristics. This may be due to timing or dose of exposure or to genetic factors. [source] Thyroxine Modulates Corticotropin-Releasing Factor but not Arginine Vasopressin Gene Expression in the Hypothalamic Paraventricular Nucleus of the Developing RatJOURNAL OF NEUROENDOCRINOLOGY, Issue 8 2000N. Dakine Neonatal rats were daily injected with 100 ,g/kg T4 and killed at 4, 8 or 15 days. Circulating corticosterone and corticosteroid binding globulin concentrations increased in 8- and 15-day-old rats after T4 treatment. Plasma adrenocorticotropic hormone (ACTH) concentrations, pituitary ACTH content and pro-opiomelanocortin mRNA expression were unaffected in T4 -treated rats. T4 treatment induced an increase in corticotropin-releasing factor (CRF) mRNA expression in the whole population of CRF synthesizing cells of the paraventricular nucleus (PVN) that became significant at day 8 and disappeared at day 15. Double labelling in situ hybridization revealed that CRF gene expression in the CRF+/arginine vasopressin (AVP)+ subpopulation was increased at days 4 and 8 and decreased at day 15. CRF immunoreactivity in the zona externa of the median eminence increased with age but was not affected by the experimental hyperthyroidism. The degree of CRF and AVP colocalization, the concentration of AVP mRNA in the parvo and magnocellular cell bodies of the PVN and the density of immunoreactive AVP in the zona interna or zona externa of the median eminence did not change after T4 treatment. Our data demonstrate that experimental hyperthyroidism accelerates the maturation of hypothalamic CRF gene expression, including in particular in the CRF+/AVP+ subpopulation, during the stress hyporesponsive period. These observations suggest that the physiological peak of plasma thyroxine that occurs between days 8,12 may participate in the maturation of hypothalamic CRF cells. [source] Head circumference and linear growth during the first 3 years in treated congenital hypothyroidism in relation to aetiology and initial biochemical severityCLINICAL ENDOCRINOLOGY, Issue 1 2004Sze May Ng Summary aims, To determine the head circumference and linear growth in children with congenital hypothyroidism (CH) during the first 3 years of life in relation to the aetiology of CH and initial biochemical severity of thyroid function. methods, We examined the head circumference and linear growth of 125 patients with CH from diagnosis up to 3 years of age. All infants had radionuclide scans prior to treatment. Patients were categorized into athyreosis, ectopia and dyshormonogenesis. Occipito-frontal circumference (OFC) SD, length SD, initial plasma TSH, initial plasma thyroxine (T4) and age of suppression of plasma TSH were compared between the groups. Multiple linear regression analysis was used to determine factors affecting OFC SD at 3 years of age. results, There were 125 children in the study: athyreosis (n = 34), ectopia (n = 73) and dyshormonogenesis (n = 18). No difference was found in gestation, birth weight, age of starting L-T4 and initial dose of L-T4 in mcg/kg/day between groups. Confirmatory plasma total T4 at diagnosis was significantly lower for athyreosis when compared with ectopia and dyshormonogenesis. Median values for confirmatory TSH were significantly lower in dyshormonogenesis compared with the other two groups. At diagnosis, OFC were similar in all three groups. Children with athyreosis showed significantly larger OFCs compared with ectopia and dyshormonogenesis from 1 to 3 years. Length SD was within 1 SD of normal population standards at diagnosis and did not differ between the three groups throughout the 3 years. Spearman's correlation for OFC SD at 3 years of age showed a significant negative correlation with initial confirmatory plasma T4 (r = ,0·35, P = 0·01). Multivariate analysis for OFC SD at 3 years of age showed confirmatory T4 as the only independent risk factor. conclusion, Children with athyreosis showed significantly larger OFC from 1 to 3 years of age compared with ectopia and dyshormonogenesis, independent of linear growth. Our data shows that initial confirmatory T4 at diagnosis is an independent factor influencing head growth in the first 3 years of life. [source] | ||||||||||