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 130,125 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Circulating levels of T3 and T4, as well as T3 and T4 content of the thyroid glands were measured by radioimmunoassay in the neotenic and metamorphosed axolotl Ambystoma mexicanum. In the two experiments which were performed plasma T4 concentrations were more elevated in metamorphosed axolotls, especially in the first experiment (2.12 +/- 0.40 ng/ml vs. 369 +/- 30 pg/ml). T3 plasma values which were only estimated in the second experiment were about five times higher in metamorphosed animals (63.2 +/- 7.4 pg/ml vs. 12.5 +/- 0.8 pg/ml). Also the thyroid hormone content of the glands was higher after metamorphosis. Nevertheless the neotenic gland still contained considerable amounts of T3 (14.7 +/- 1.8 ng and 48.3 +/- 4.8 ng/thyroid, respectively, in the first and second experiment) and T4 (530 +/- 61 ng; 2173 +/- 291 ng/thyroid). Because of the higher T3/T4 ratio found in the plasma compared to the thyroid gland, it was suggested that circulating T3 may be derived partly from peripheral T4 conversion, mainly after metamorphosis. An intravenous injection of 10 micrograms synthetic TRH was able to induce a very significant increase of the plasma T4 concentration (which was maintained during 24 hr) in the metamorphosed axolotls of the first experiment, however, not in those of the second experiment nor in the neotenic animals. Following an injection of 10 mU bovine TSH (first experiment) circulating levels of T4 were raised in both groups. The opposing TRH results could be related with the different control levels of T4 in the two experiments. However, the results indicate that TRH is capable of functioning as a possible thyrotropin-releasing factor in the metamorphosed axolotl.
Gen Comp Endocrinol 1988 Apr
PMID:Thyroxine and triiodothyronine in plasma and thyroids of the neotenic and metamorphosed axolotl Ambystoma mexicanum: influence of TRH injections. 313 Nov 85

The tissue concentration of thyroxine (T4) in larval flounder (Paralichthys olivaceus) was studied at various stages of their metamorphosis using a specific radioimmunoassay developed for samples obtained by quantitative extraction of the hormone from fish eggs and larvae. T4 concentrations were below the limit of detection in extracts of fertilized eggs and larvae until the end of prometamorphosis. Several dorsal fin rays continued growing from premetamorphosis until the end of prometamorphosis. The hormone became detectable at the onset of metamorphic climax when the elongated dorsal fin rays stopped growing. A sharp increase in tissue T4 concentration was observed in midclimax of metamorphosis, and the high level of T4 (11-13 ng/g body weight) was maintained until the end of the climax. The period of elevated T4 levels coincided with resorption of the elongated dorsal fin rays. The right eye completed translocation from the right to the left side of the body during metamorphic climax. The tissue T4 level declined to about a half of the peak value during postclimax, and then increased moderately in later adult-type juveniles. The results of an additional experiment, in which fertilized eggs and newly hatched larvae were treated with T4 and/or thiourea, suggested the presence of negative feedback regulation of pituitary-thyroid axis, implying an involvement of thyroid hormones even in early premetamorphic larvae. These results suggest that metamorphic climax is induced by a surge of thyroid hormone, and that thyroid hormone may also regulate development before and after the metamorphosis.
Gen Comp Endocrinol 1988 Apr
PMID:Thyroxine surge in metamorphosing flounder larvae. 313 Nov 86

We studied 13 untreated Graves' disease subjects in a clinical research unit using endocrine, psychiatric, and neuropsychological assessments. We used SADS interviews, RDC, standardized symptom rating scales, and motor activity monitoring to update earlier studies and quantified psychiatric symptoms to elucidate any correlations between endocrine and psychiatric status. Nine of 13 subjects had major depression, 8/13 had generalized anxiety disorder, and 3/13 were hypomanic. Anxiety levels were much higher than in other hospitalized medical patients. Using a broad battery of neuropsychological testing, we found mild deficits in attention, memory, and complex problem solving that were consistent with previous studies of hyperthyroid patients. The severity of psychiatric symptoms could easily result in an inappropriate referral to a psychiatrist prior to the diagnosis of hyperthyroidism. The relationship between psychiatric symptoms and possible CNS effects of excess levels of thyroid hormone is discussed.
Gen Hosp Psychiatry 1988 Jan
PMID:A psychiatric and neuropsychological study of patients with untreated Graves' disease. 334 7

Thyroid function was examined during the annual cycle of Richardson's ground squirrel, Spermophilus richardsoni. A number of facets were measured to facilitate comparison of thyroid function in active, dormant, and aroused animals. This report discusses changes in the serum thyroid hormone and binding as assessed by radioimmunoassay, equilibrium dialysis, and competitive binding assays. During the hibernation phase (both dormant and aroused), total serum T3 (trioodo-L-thyronine) and T4 (L-thyroxine) are elevated over active levels, two- to fivefold and four- to sixfold, respectively. However, in dormant squirrels, both free T3 and free T4 are reduced compared with both active and aroused phases of the annual cycle, while in aroused squirrels there is an increase in free T3 but no change in free T4 compared with active squirrels. The difference between changes in total and free thyroid hormone levels in the three groups is due to changes in serum binding of thyroid hormone. There is a more than twofold increase in the capacity of a saturable T3-binding site in serum of both dormant and aroused squirrels, and there is an increase in serum binding affinity at the low core temperature of dormant squirrels (6 degrees). Therefore, even though serum total T3 and T4 are elevated during dormancy, free T3 and T4 levels are reduced to half of the levels in active squirrels as a consequence of increased serum binding capacity and affinity. In aroused animals, however, increased serum binding capacity only partially buffers the increase in total T3 and T4, so that free thyroid hormone levels exceed those of active squirrels.
Gen Comp Endocrinol 1988 Mar
PMID:Thyroid hormone resistance in hibernating ground squirrels, Spermophilus richardsoni. I. Increased binding of triiodo-L-thyronine and L-thyroxine by serum proteins. 336 Feb 93

Hepatic nuclear triiodo-L-thyronine (T3) receptors were studied to investigate the mechanism of thyroid hormone resistance in Richardson's ground squirrels, Spermophilus richardsoni, during the hibernation phase of the annual cycle. The cycle is divided into an active phase and a hibernation phase, the latter composed of alternating dormancy and arousal bouts. In addition to animals in these three states, a group of cold-exposed animals was also examined (those animals held at 6 degrees which showed no indications of entering hibernation). Binding of T3, to squirrel hepatic nuclei from all groups, was characterized as high affinity, Kd ranging from 111 to 267 pM, and low capacity, 50 to 314 fmol T3/mg DNA. Based on these data, other criteria examined, and models established in the literature for other species, this binding site has been tentatively identified as a T3 receptor. Receptor concentrations in nuclei from dormant and aroused squirrels were only 15-20% of the concentration in active animals. There were no differences in the affinity of the T3 receptor over the annual cycle estimated by the in vitro assay at 24-26 degrees. The reduction in nuclear T3 receptors, together with the previously reported increase in serum binding of thyroid hormone, provides an explanation for thyroid hormone resistance during the hibernation phase in S. richardsoni.
Gen Comp Endocrinol 1988 Mar
PMID:Thyroid hormone resistance in hibernating ground squirrels, Spermophilus richardsoni. II. Reduction of hepatic nuclear receptors. 336 Feb 94

Plasma prolactin (PRL) concentration increases markedly at late metamorphic climax (stage XXIV of Taylor and Kollros (1946)) in Rana catesbeiana. Two series of experiments were performed in order to elucidate the mechanisms involved in this phenomenon. First, thyroidectomized tadpoles (stages XVI-XVIII) were kept in tap water with or without thyroxine (T4). Tadpoles in tap water did not develop beyond stage XX and showed no sign of hypersecretion of PRL by the time T4-treated tadpoles reached stage XXIV. In thyroidectomized tadpoles treated with T4, plasma PRL levels showed a conspicuous rise at stage XXIV. Second, the pituitary stalk was transected, or the adenohypophysis was ectopically autografted at early climax (stage XXII). These tadpoles metamorphosed as intact controls did, but their plasma PRL levels remained low. Treatment of operated tadpoles with T4 failed to elevate plasma PRL levels. It is concluded that hypothalamic stimulation is necessary for the elevation of plasma PRL levels at the late climax stage and that the stimulatory system develops in the hypothalamus under the influence of thyroid hormone.
Gen Comp Endocrinol 1986 Oct
PMID:Effects of thyroid hormone, stalk section, and transplantation of the pituitary gland on plasma prolactin levels at metamorphic climax in Rana catesbeiana. 349 49

Indirect immunofluorescent staining was used to detect and localize thyroxine (T4) in blood smears from different species of adult amphibians, namely, Rana pipiens, Rana catesbeiana, Bufo marinus, Xenopus laevis, and Notopthalmus viridescens. Fluorescence, indicative of T4, was observed in both plasma and erythrocytes (RBC) from all individuals of the five species studied. It was weak and diffuse in the plasma and in the cytoplasm of the RBC but was intense in the nuclei (especially the nuclear perimeter) of these cells. The finding of intracellular T4 suggests that thyroid hormone may be of some physiological importance in adult amphibians.
Gen Comp Endocrinol 1986 Dec
PMID:Immunofluorescent detection and localization of thyroxine in blood of adult amphibians. 354 99

Although viral infection has been suspected as the cause of some thyroid disorders, there has been limited data to support this contention seriously. Now we report the first evidence that lymphocytic choriomeningitis virus can persist in the thyroid gland, particularly thyroid epithelial cells in which thyroglobulin (Tg) the precursor of thyroid hormone, is synthesized. Concomitant with the infection of these cells is a significant reduction in Tg mRNA and in the level of circulating thyroid hormones. Another virus (lactate dehydrogenase virus) that causes persistent infection but does not replicate in the thyroid gland failed to alter levels of circulating thyroid hormones. These observations in an experimental model support the hypothesis that viruses may account for some thyroid disorders in man.
J Gen Virol 1987 Jul
PMID:Lymphocytic choriomeningitis virus can persistently infect thyroid epithelial cells and perturb thyroid hormone production. 359 62

Two experiments were carried out to clarify the effects of thyroxine (T4) and triiodothyronine (T3) on flounder metamorphosis. In the first experiment, three doses of T4 were administered to premetamorphic flounder larvae together with thiourea (TU). Thiourea treatment (30 ppm in ambient seawater) alone caused metamorphic stasis in the fish, although the beginning of the right eye migration was not completely inhibited. T4 at 100 and 10 ppb in ambient seawater induced metamorphosis in the thiourea-treated larvae. The fish of these groups completed translocation of the right eye to the left side and resorption of elongated dorsal fin rays. However, 1 ppb T4 failed to induce metamorphic climax. The elongated dorsal fin rays continued to grow until the end of the experiment in the group treated with TU alone and in combination with 1 ppb T4. In the second experiment, premetamorphic flounder larvae were treated with two doses of T4 and three doses of T3. The T3 treatment was several times more potent than T4 treatment in the induction of metamorphosis. The results of the present study suggest that the metamorphic events of flounder larvae are dependent on the thyroid hormone concentration, and the relative biological potency of T4 and T3 on flounder metamorphosis is similar to that observed in mammals and amphibia.
Gen Comp Endocrinol 1987 Sep
PMID:Effects of various doses of thyroxine and triiodothyronine on the metamorphosis of flounder (Paralichthys olivaceus). 366 11

Response surface models were developed by multiple regression techniques to describe daily rhythms of plasma thyroid hormones in young chickens during acclimation to a wide range of ambient temperatures (Ta). Seventy-two Leghorn cockerels were raised in six environmental chambers under a 12L:12D light/dark cycle. Beginning at 21 days of age, two replicate chambers provided Ta treatments of 10, 24, or 38 degrees. During Day 6 of acclimation, blood samples were obtained at 0800, 1200, 1600, 2000, 2400, and 0400 hr for thyroid hormone analyses. Plasma triiodothyronine (T3) levels showed a convex response to the experimental region (10 to 38 degrees, and 0800 to 0400 hr under a 12L:12D light/dark cycle), whereas the plasma thyroxine (T4) response surface was concave. In particular, heat exposure (38 degrees) depressed (P less than .01) plasma T3 levels (2.8 ng/ml) below those of birds held at 24 degrees (4.5 ng/ml), whereas elevated (p less than 0.05) T3 concentrations were found in the 10 degrees treatment (5.0 ng/ml). Plasma T3 levels rose gradually during photophase and slowly declined during scotophase. Plasma T4 concentrations followed an opposite pattern with the daily zenith in scotophase and the nadir during photophase. Plasma T4 levels were sharply elevated in birds maintained at 38 degrees, particularly during scotophase. Although Ta did not change the daily amplitude or circadian frequency of the plasma T3 rhythm, an increased frequency or ultradian rhythm of plasma T4 was observed in cold-acclimated birds. The counter-responses of T3 and T4 to heat exposure and phase of the light/dark cycle were best seen in the molar ratio of plasma T3/T4 levels. The average daily T3/T4 molar ratio for heat-exposed birds was 0.16 while the average T3/T4 ratio was higher (P less than 0.01) for the 10 degrees (0.46) and 24 degrees (0.41) treatments. The opposing responses of plasma T3 and T4 levels to a wide range of Ta and phase of the light/dark cycle support a major role for circulating T3 in metabolic adjustments that chickens make to changes in the photothermal environment.
Gen Comp Endocrinol 1987 Oct
PMID:Response surface of daily thyroid hormone rhythms in young chickens exposed to constant ambient temperature. 366 17


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