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R T Weirich

Publications and source records attributed to R T Weirich.

4 recordsLinked to original sources
PubMed1987

An analysis of the interrelationship of nuclear and plasma triiodothyronine in the sea lamprey, lake trout, and rat: evolutionary considerations.

We have studied the interrelationship of plasma and hepatic nuclear T3 in two lower vertebrates, lake trout and sea lamprey. Specific nuclear T3-binding sites were observed in liver of both species. Binding affinities for T3 and several analogs in lamprey and trout were similar to those in rat liver. The findings of identical sedimentation coefficients, Stokes radii, and mol wt suggest a high degree of homology of the receptor molecule among these species. In lamprey ammocoete, both total (approximately 26 nM) and free (approximately 0.12 nM) T3 concentrations were 7- to 36-fold higher than in the trout or rat. The concentration of free T4 was 4 times greater than that in rat plasma despite somewhat lower total T4 levels. This resulted from a 6 times lesser binding of T4 by ammocoete plasma. Total and free T3 and T4 levels fell sharply during transformation to the adult form. In trout, a 27 times greater concentration of free T3 in hepatic nuclei than in cytosol, previously documented for rat liver, gave evidence of the early evolution of an active transport process between these compartments. Analysis of [125I]T3 interchange in trout indicated the existence of two kinetically distinct compartments within the liver, an outer compartment in rapid equilibrium with plasma, and a slowly equilibrating compartment decaying with a t1/2 of 3.7 h. T3 associated with the nuclear receptor appeared to be in equilibrium with the slower hepatic compartment. Despite the apparent resemblance of T3 receptors in these species to those in the rat, administration of T3 (200 micrograms/100 g BW for 4 days) to trout caused no increase in hepatic oxygen consumption or the activities of malic enzyme or alpha-glycerophosphate dehydrogenase. Further, such treatment produced no consistent changes in hepatic mRNA activity profiles analyzed by two-dimensional electrophoresis of in vitro translational products. As suggested by the high free T3 concentration in the larval lamprey ammocoete, T3 in early vertebrates may have a primarily developmental function, manifested over a restricted time frame.

Animals↗
PubMed1984

Nuclear receptors for L-triiodothyronine in quail liver.

Binding studies were conducted using in vitro-labeled quail liver nuclei to identify and characterize receptors for L-triiodothyronine (T3). Saturation binding experiments were analyzed by Scatchard analysis and indicated a single class of high-affinity, limited-capacity T3 binding sites. These receptors exhibited binding specificity as demonstrated by competition experiments between labeled T3 and unlabeled thyroid hormones or hormone analogs. Binding specificity was virtually identical in quail and rat liver nuclei. Thus, apparent differences between mammals and birds, in regard to the biological potency of T4 versus T3, are not apparent at the level of the nuclear T3 receptor.

Aging↗
PubMed1984

Responses to thyrotropin during development in Japanese quail.

Japanese quail, a species with a precocial pattern of development, were used as a model for studying the ontogeny of thyroid responses to TSH. Thiourea was administered to embryos early in incubation, and the effects were assessed by measuring thyroid 32P uptake, serum thyroid hormones, thyroid weights, and body weights. Thyroid stimulation after thiourea treatment indicated that maturation of thyroid-pituitary negative feedback occurs between days 9 and 10 of the 16.5-day incubation period. Since thyroid function continues to increase faster than thyroid size, hypothalamic or higher control of the pituitary appears to dominate over thyroid-pituitary feedback effects for the remainder of the embryonic period. TSH administration to embryos and chicks resulted in similar time-course and dose-response characteristics, as judged by the thyroid 32P uptake response. Single injections of TSH into 14-day-old embryos resulted in parallel increases in serum T3 and T4, with essentially no change in the T3 to T4 ratio. In contrast, the posthatching response of both 1-day-old chicks and adults to TSH involved significant increases in only T4 and resulted in decreased serum T3 to T4 ratios. Thus, there are developmental changes in the hormonal response to TSH. These results indicate that TSH effects on the embryonic thyroid cannot account for the increase in the T3 to T4 ratio during the perinatal hormone peak. Our data are consistent with the idea that T3 produced peripherally by monodeiodination of T4 accounts for the perinatal change in the thyroid hormone ratio.

Animals↗