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Biomedical subjects

L J Lyons

Publications and source records attributed to L J Lyons.

5 recordsLinked to original sources
PubMed1986

Avian hepatic T3 generation by 5'-monodeiodination: characterization of two enzymatic pathways and the effects of goitrogens.

The enzymatic nature of 5'-monodeiodination (5'-D) in avian liver homogenates was demonstrated by abolishment of activity by iopanoic acid (IOP). T3 production from T4 was dependent on enzyme and substrate concentrations, incubation time, incubation temperature, and pH. Two pathways of 5'-D activity were present in avian liver and exhibited characteristics similar to those described in mammalian tissues. Type II activity was identified as propylthiouracil (PTU)-insensitive activity. Type I (PTU-sensitive) was determined by difference between Total and Type II. Km values were 1.58 microM T4 for Total activity and 0.90 nM T4 for Type II, corresponding to the characteristics of the mammalian pathways. The effects of goitrogens on avian hepatic 5'-D were equivalent to those reported for the mammalian enzyme.

Animals↗
PubMed1984

Free thyroid hormones in altricial (ring doves) versus precocial (Japanese quail) development.

Ring doves (altricial development) and Japanese quail (precocial development) were used as models to compare differences in serum free hormone concentrations and the binding of thyroid hormones to serum protein fractions in adults, and the pattern of free thyroid hormones in the serum of altricial vs. precocial young. Total and free hormones were determined directly by RIA; free hormones also were determined by equilibrium dialysis. Binding protein fractions were identified by electrophoresis of serum preincubated with labelel hormones. Albumin bound the largest proportion of T4 in serum to both species; albumin also bound the largest proportion of T3 in doves, but globulin bound the largest proportion in quail. There were significant differences between species in the proportional binding of both thyroid hormones by different protein fractions at physiological pH. Electrophoretic separations at alkaline pH significantly altered hormone binding by different protein fractions from that at physiological pH. These data explain some conflicting results in the literature on thyroid hormone-binding proteins in different species. Free T4 and free T3 were below the sensitivity limits of the assays during the perinatal period in doves. After hatching, serum free T4 rose more rapidly than total T4. After day 12, hormone concentrations decreased, with a proportionately greater change in free T4 than in total T4. Serum free T3 concentrations were variable, but did not change significantly during development. These results demonstrate that the pattern of serum free thyroid hormones, like that of total hormones, is markedly different in altricial than in precocial development.

Animals↗