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We present empirical energy calculations on the binding of thyroxine analogs to the plasma protein prealbumin. The results of the calculations suggest a stronger binding affinity for the L isomer than the D, consistent with observed binding affinities. These calculations allow us to rationalize the significantly stronger binding of des-NH3+ than des-COO− analogs of the hormone to the protein.

Theoretical electronic structure calculations on the thyroid hormones and analogues, as well as model hormone--receptor interactions, have been carried out. These studies (a) support the concept that the 4'-OH group is a H-bond donor to the in vivo nuclear receptor and suggest that at the receptor this OH group is trans to the 3' (distal) substituent; (b) indicate that there is an important intramolecular interaction between 3' and 4' substituents, and those 3' substituents that most favor both 4' OH orientation trans to the 3' group and a more acidic OH group substantially increase binding and biological activity; and (c) support the concept that there is a direct correlation between the conformational free energy of the aromatic rings and biological activity.

The thyromimetic activity of 3,5-dimethyl-3'-isopropyl-L-thyronine (DIMIT), a nonhalogenated thyroid analog, was studied in adult men using suppression of TRH-induced TSH release to assess this activity. In nine men, aged 30-58 yr, the TSH increment after 500 microgram TRH iv was compared to the TSH response to TRH 24 h after oral administration of 1 mg DIMIT. Eight euthyroid subjects had normal baseline TSH levels of 1.5 +/- 0.2 (SE) microunit/ml that fell significantly to 0.7 +/- 0.2 microunit/ml 24 h after DIMIT (P less than 0.005). Their TSH increments after TRH fell from 15.3 +/- 2.8 to 6.7 +/- 1.6 microunit/ml 24 h after DIMIT (P less than 0.001). One subject with probable Hashimoto's thyroditis had an elevated TSH of 18 microunit/ml, with an exaggerated TSH response to TRH of 72 microunit/ml. His basal TSH fell to 7.6 and his TSH increment fell to 14.3 microunit/ml 24 h after DIMIT. The suppression of TSH was relatively prolonged. In four subjects, the TSH response to TRH was still blunted from 5-12 days after DIMIT. In one subject, the TSH increment returned to normal 15 days after DIMIT. DIMIT had no significant effect on PRL secretion. There was no evidence of toxicity in patients receiving DIMIT. DIMIT has effective thyromimetic activity in man, as shown by its significant and prolonged suppression of TSH secretion.

In order to determine the features of the phenolic ring in position 4 of [Asn1,Ile5]angiotensin II that contribute to pressor activity, analogues with selected aromatic substituents were synthesized by the solid-phase method. They showed pressor activities in the rat: [Asn1,Phe(4-NH2)4]AII, 24%; [Asn1,Phe(4-NO2)4AII, 0.1%; [Asn1,Tyr(3,5-Me2)4]AII, 2.2%; [Asn1,D-Tyr(3,5-Me2)4]AII, 1.4%. These results indicate that the activity contributed by the aromatic character of the phenyl ring in the side chain of position 4 is enhanced by a group in the para position that may function as a proton donor in hydrogen-bond formation. Bulky substituents ortho to this hydrogen-bonding group decrease activity by steric interference with hydrogen-bond formation. Bulky groups than cannot act as hydrogen donors in the para position of the aromatic ring drastically decrease the activating effect of the aromatic ring on pressor activity.

The present study was undertaken to study the binding of several thyroid hormones and structurally related compounds to human serum thyroxine-binding alpha-globulin (TBG). The source of TBG was normal human serum diluted 1:100 in 0.035 M barbital buffer, pH 7.4. In the binding assays, 125I-thyroxine, unlabeled thyroxine, and diluted serum were incubated for 20 h at 37 degrees in Plexiglas equilibrium dialysis units. Two orders of binding sites were discerned: a high affinity, low capacity binding site with an affinity constant of approximately 2.5 X 10(9) M-1, and a low affinity, very high capacity binding site with an affinity constant of less than 10(6) M-1. Studies with purified TBG, serum deficient in TBG, and purified human serum albumin indicated that the high affinity site represented binding to TBG and the low affinity site represented binging to albumin. The ability of several groups of thyroid hormone analogues to bind to TBG was then investigated. As a result of these studies, the following structural features of thyroid hormones were found to be important for optimal binding activity: (a) the L-alanine side chain conformation, (b) the presence of a 4'-hydroxyl group, (c) the presence of two substituents in the inner and outer rings (positions 3, 5, 3', and 5'), and (d) the presence of either bromines or iodines in the inner ring and iodines in the outer ring. Of lesser importance was the presence of an oxygen atom in the ether position.

The effects of an analog of thyroxine, 3,5-dimethyl-3'-isopropyl-L-thyronine (DIMIT), on fetal rat hepatocyte ultrastructure and microsomal function were investigated by using the techniques of quantitative electron microscopy and enzyme assays. Rats were injected with DIMIT (10 microgram/100 g BW) or vehicle daily from the 15th through the 19th day of pregnancy. Fetuses were sacrificed on the 20th day of gestation. In comparison with controls, DIMIT-treated livers 1) were devoid of glycogen; 2) contained smaller hepatocytes; 3) contained a greater number of hepatocytes; 4) had an increased volume density of mitochondria; and 5) had increased NADPH-cytochrome c reductase and glucose-6-phosphatase activities. Surface areas of rough and smooth surfaced endoplasmic reticulum were unaffected by the hormone analog, and cytochrome P-450 was not induced. All of the changes that were produced by DIMIT in the 20-day-old fetal rat, as well as smooth endoplasmic reticulum and cytochrome P-450 development, are observed in normal animals within the first 3 days after birth. The data suggest that thyroid hormone may be a physiological stimulus for certain aspects of early hepatic development, but that it acts in combination or in sequence with other factor(s) to produce the full complement of structural and functional changes that occur perinatally in the rat.

Quantitative structure-activity correlation studies of thyroid hormone analogues have been utilized to examine (1) in vivo rat antigoiter activities; (2) in vitro binding affinities to intact rat hepatic nuclei, solubilized rat hepatic nuclear protein receptors, and the plasma protein thyroxine binding globulin; and (3) correlations between in vivo antigoiter activities and in vitro binding to nuclear receptors. These studies provide a more precise elucidation of the relative importance of the physiochemical factors which influence thyromimetic activities. In particular, they (1) provide the first systematic QSAR examination of drug-receptor interactions and of the dependence of in vivo activity on such interactions; (2) demonstrate the importance of the interactive effects of the 3' and 5' substituents and of the 4'-OH with each other as well as with nuclear receptors in influencing binding affinity; (3) support the hypothesis that binding to nuclear receptors is the first step in initiating the events which lead to subsequent hormonal expression; (4) show that the free energy of binding to nuclear receptors can be factored into the contributing physicochemical properties of the substituents; and (5) suggest factors that need to be considered in designing new analogues.

Chronically catheterized maternal fetal monkey preparations were used to study pituitary suppression by thyroid hormones in the fetus. Baseline maternal T3, T4, and PRL were all significantly higher than fetal levels of these hormones. TRH was given iv (10 μg/kg) to the mother 3, 6, 12, 20, or 44 h after giving varying doses of T3 to the fetus. Amniotic fluid and fetal tracheal aspirate did not contain detectable TSH. Nonpregnant females and pregnant mothers showed complete suppression of the TSH response to TRH after receiving 20 μg T3 iv 24 h before TRH. Two micrograms of T3 iv to the fetus 3 h before TRH failed to suppress the TSH response (fetal δTSH, 26 μU/ml; δT4, 3.6 μg/dl). Six micrograms of T3 iv (three doses of 2 μg) to the fetus over 36 h achieved a basal T3 level of 2500 ng/dl and lowered fetal δTSH to 9.1 μU/ml. Six micrograms of T3 infused iv to the fetus over 24 h achieved fetal T3 blood levels of 5000 ng/dl, which suppressed δTSH to 2.7 μU/ml. 3,5,-Dimethyl-3'-isopropyl-L-thyronine (DIMIT;...

Relative anthocyanin and aurone concentrations have been measured spectrophotometrically in 25 of 27 possible color genotypes of the garden snapdragon, Antirrhinum majus . The results have allowed the following generalizations to be formulated for the case of gene-controlled pigmentation in A. majus . 1. 1. Increased numbers of recessive factors result in decreased anthocyanin production. 2. 2. Genotypes containing pelargonidin glycoside have a significantly lower concentration of anthocyanin than genotypes containing cyanidin glycoside. 3. 3. Highest concentration of aurone is associated with genotypes —yy. 4. 4. Increased numbers of dominant factors result in decreased aurone production. 5. 5. High anthocyanin concentration is related to low aurone concentration and, conversely, low anthocyanin concentration is related to high aurone concentration. 6. 6. The chemical consequence of heterozygosity is an alteration in the magnitude of the effect produced by the dominant alleles. A general pathway for the biosynthesis of the flavonoid pigments of A. majus has been proposed.

Zur weiteren Vorarbeit für die gaschromatographische Sequenzanalyse von Peptiden wurden Dipeptide untersucht, die trifunktionelle Aminosäuren enthalten. In Form der N-TFA-Dipeptid-dimethylester lassen sich α- und γ-Dipeptide der Glutaminsäure trennen. Bei tyrosin-haltigen Dipeptiden empfiehlt sich die O-Trimethylsilylierung der phenolischen Hydroxylgruppe oder deren Methylierung mit Diazomethan. Serin- oder threonin-haltige Dipeptide werden am besten vor der Gaschromatographie in die O-Trimethylsilyl-N-TFA-dipeptid-methylester mittels Hexamethyldisilazan verwandelt. Cystein- und cystin-haltige Verbindungen werden mit Raney - Nickel in Alanin-Verbindungen überführt. Hierbei gehen Methionin-Verbindungen in Derivate der α-Aminobuttersäure über. Zahlreiche Verbindungen der aufgeführten Gruppen wurden hergestellt, und ihre relativen Retentionswerte gegenüber Myristinsäure-methylester als Standard ermittelt.

On the basis of structural considerations and the activity of 2',6'-diiodothyronine (I), 4'-deoxy-4'-β-L-alanyl-3,5-diiodo-L-thyronine (VIIb) 1 and a mixture of related stereoisomers have been prepared and tested for activity as thyroxine antagonists in the rat antigoiter assay. The L,L-isomer (VIIb) proved moderately effective as an antagonist at a molar ratio to L-thyroxine of 100:1. The mixed DL,DL-isomers (VIIa) as well as the L,L-isomer (VIIb) were ineffective when tested at a molar ratio to L-thyroxine of 200:1.

The synthesis of, thyroxine analogs, 3,5-diiodo - 4 - (2′,3′ - dimethylphenoxy) - dl-phenylalanine and 3,5-diiodo-2′,3′-dimethyl-dl-thyronine is described. These compounds were prepared in order to study the effect on biological response of alkyl substituents in sterically oriented analogs of thyroxine. Both compounds displayed thyromimetic activity.

3′-Chloro-3,5-diiodo-L-thyronine was shown to be more active than 3′,5′- dichloro-3,5-diiodo-L-thyronine in the rat antigoiter assay. (Endocrinology 76: 312, 1965)

dl-3′-iodothyronine and dl-3′,5′-diiodothyronine were tested for their ability to inhibit the goiter-preventing effect of thyroxine in thiouracil-fed rats. They were shown to be without activity at a molar ratio of analog to l-thyroxine of 200 to 1.

Computer graphics modeling of the thyroxine-prealbumin complex provides a detailed picture of the interactions between thyroxine and prealbumin. A wide variety of thyroid hormone analogue-prealbumin complexes were modeled by calculating the molecular surfaces of the analogues and the prealbumin hormone-binding site. Analogues with high binding affinity were observed to fill more of the hormone-binding site than low-affinity analogues. These surface models described many aspects of the hormone-protein interaction which were not obvious using simple wire models and led us to develop a model which accounts for thyroid hormone-prealbumin structure-activity relationships and ultimately to predict and measure the relative binding affinities of four previously untested thyroid hormone analogues to prealbumin.

Theoretical electronic structure calculations on the thyroid hormones and analogues, as well as model hormone--receptor interactions, have been carried out. These studies (a) support the concept that the 4'-OH group is a H-bond donor to the in vivo nuclear receptor and suggest that at the receptor this OH group is trans to the 3' (distal) substituent; (b) indicate that there is an important intramolecular interaction between 3' and 4' substituents, and those 3' substituents that most favor both 4' OH orientation trans to the 3' group and a more acidic OH group substantially increase binding and biological activity; and (c) support the concept that there is a direct correlation between the conformational free energy of the aromatic rings and biological activity.

The effect of 3,5-dimethyl-3'-isopropyl-L-thyronine (DIMIT) a nonhalogenated thyroid hormone analog, on plasma and pituitary TSH levels was studied in euthyroid and 5-day-thyroidectomized (T-5d) rats. The minimal dose of DIMIT which suppressed basal plasma TSH for a 24-h period was 5.3 micrograms/100 g BW in the euthyroid rats and 5.2 micrograms/100 g BW in the T-5d group. The equipotent doses of T3 were 1.0 and 1.5 micrograms/100 g BW, respectively. Thus, the apparent DIMIT to T3 molar ratio ranged from 6.6 in the hypothyroid to 10 in the euthyroid group. The suppression of TRH-induced TSH release in the euthyroid rats required a high dose of DIMIT (9.2 micrograms/100 g BW), resulting in a DIMIT to T3 molar ratio of 17. Time-course studies comparing the effects of equipotent doses of DIMIT and T3 on TSH release rates in euthyroid and T-5d rats have shown a maximal suppression by 3--24 h after the administration of both T3 and DIMIT. However, the recovery from the effect was slower after T3. TSH synthesis in the T-5d group was similarly suppressed by DIMIT and T3. DIMIT has significant thyromimetic activity in euthyroid and hypothyroid rats, as evidenced by the suppresion of TSH synthesis and release.