Imaging considerations for in vivo 13C metabolic mapping using hyperpolarized 13C-pyruvate.

One of the challenges of optimizing signal-to-noise ratio (SNR) and image quality in (13)C metabolic imaging using hyperpolarized (13)C-pyruvate is associated with the different MR signal time-courses for pyruvate and its metabolic products, lactate and alanine. The impact of the acquisition time window, variation of flip angles, and order of phase encoding on SNR and image quality were evaluated in mathematical simulations and rat experiments, based on multishot fast chemical shift imaging (CSI) and three-dimensional echo-planar spectroscopic imaging (3DEPSI) sequences. The image timing was set to coincide with the peak production of lactate. The strategy of combining variable flip angles and centric phase encoding (cPE) improved image quality while retaining good SNR. In addition, two aspects of EPSI sampling strategies were explored: waveform design (flyback vs. symmetric EPSI) and spectral bandwidth (BW = 500 Hz vs. 267 Hz). Both symmetric EPSI and reduced BW trended toward increased SNR. The imaging strategies reported here can serve as guidance to other multishot spectroscopic imaging protocols for (13)C metabolic imaging applications.

Two mouse retinal degenerations caused by missense mutations in the beta-subunit of rod cGMP phosphodiesterase gene.

We report the chromosomal localization, mutant gene identification, ophthalmic appearance, histology, and functional analysis of two new hereditary mouse models of retinal degeneration not having the Pde6brd1("r", "rd", or "rodless") mutation. One strain harbors an autosomal recessive mutation that maps to mouse chromosome 5. Sequence analysis showed that the retinal degeneration is caused by a missense point mutation in exon 13 of the beta-subunit of the rod cGMP phosphodiesterase (beta-PDE) gene (Pde6b). The gene symbol for this strain was set as Pde6brd10, abbreviated rd10 hereafter. Mice homozygous for the rd10 mutation showed histological changes at postnatal day 16 (P16) of age and sclerotic retinal vessels at four weeks of age, consistent with retinal degeneration. Retinal sections were highly positive for TUNEL and activated caspase-3 immunoreactivity, specifically in the outer nuclear layer (ONL). ERGs were never normal, but rod and cone ERG a- and b-waves were easily measured at P18 and steadily declined over 90% by two months of age. Protein extracts from rd10 retinas were positive for beta-PDE immunoreactivity starting at about the same time as wild-type (P10), though signal averaged less than 40% of wild-type. Interestingly, rearing rd10 mice in total darkness delayed degeneration for at least a week, after which morphological and functional loss progressed irregularly. With the second strain, a complementation test with rd1 mice revealed that the retinal degeneration phenotype observed represents a possible new allele of Pde6b. Sequencing demonstrated a missense point mutation in exon 16 of the beta-subunit of rod phosphodiesterase gene, different from the point mutations in rd1 and rd10. The gene symbol for this strain was set as Pde6bnmf137, abbreviated nmf137 hereafter. Mice homozygous for this mutation showed retinal degeneration with a mottled retina and white retinal vessels at three weeks of age. The exon 13 missense mutation (rd10) is the first known occurrence of a second mutant allele spontaneously arising in the Pde6b gene in mice and may provide a model for studying the pathogenesis of autosomal recessive retinitis pigmentosa (arRP) in humans. It may also provide a better model for experimental pharmaceutical-based therapy for RP because of its later onset and milder retinal degeneration than rd1 and nmf137.

A study of metabolism of deaminated and sulfoconjugated iodothyronines by rat placental iodothyronine 5-monodeiodinase.

The interaction of the rat placental type III iodothyronine 5-monodeiodinase (5-MD) with acetic acid (AA), propionic acid (PA), and sulfoconjugate (SA) derivatives of thyroid hormones has been investigated in comparison with hepatic iodothyronine type I MD. PA and AA derivatives of both T3 and T4 were potent inhibitors of 5-monodeiodination of [125I]T3 by rat placental microsomes. 3,5,3'-Triiodothyroacetic acid (T3AA) and 3,5,3'-triiodothyropropionic acid (T3PA) were comparable to T3 in their ability to inhibit 5-monodeiodination of [125I]T3, whereas T4AA and T4PA were more potent than T4. 3,5,3'-triiodothyrosulfonic acid (T3SA), T4SA, and rT3SA caused little or no inhibition of placental 5-MD activity. Among various analogs of T3 or T4, the order of relative potency of inhibition of hepatic 5'-MD was PA > AA > SA > parent iodothyronine. The metabolism of T3 and its derivatives by rat placental microsomes was studied by determining the rates of disappearance of the various substrates and the production of the metabolites generated by inner ring monodeiodination of the substrate. T3AA and T3PA were metabolized at a rate comparable to that of T3. Under the same conditions, essentially 100% of T3SA remained intact. Kinetic studies of placental inner ring monodeiodination of T3, T3AA, and T3PA demonstrated comparable values for Km (1.3, 1.8, and 2.3 nM, respectively) and maximum velocity (44, 57, and 74 fmol/micrograms.h, respectively). All derivatives of T3 studied were deiodinated by hepatic type I MD more avidly than the parent iodothyronine. Our data suggest that 1) deamination does not appreciably influence, while sulfoconjugation markedly inhibits type III 5-monodeiodination of T3; and 2) deamination may be even more conducive to degradation of thyroid hormone than sulfoconjugation.

Thyromimetic effects of 3,5,3'-triiodothyronine sulfate in hypothyroid rats.

Several parameters of the effects of thyroid hormone were examined in hypothyroid thyroidectomized (Tx) rats treated with T3 sulfate (T3S) or T3 [0.46 (low dose) or 2.3 (high dose) nmol/day for 10 days, ip]. Tx rats showed a marked degree of growth retardation, which improved significantly after treatment with both doses of T3S and T3. The mean serum GH level was markedly reduced in Tx rats, and it improved significantly to similar levels after treatment with the high dose of T3S and the low dose of T3. Type I monodeiodinase (MD) activity was markedly reduced in liver and kidney tissues of Tx rats. It increased significantly in Tx rats treated with the high dose of T3S; the latter values were similar to those observed in Tx rats treated with the low dose of T3. Hepatic and renal type I MD activities increased to supranormal levels in Tx rats treated with the high dose of T3. Cardiac outer ring (5') monodeiodination of 3',5'-diiodothyronine to 3'-monoiodothyronine was also significantly reduced in Tx rats, but it improved significantly only after treatment with the high dose of T3. Type III 5-MD activity was significantly reduced in the cerebral cortex of Tx rats. It was restored to normal in Tx rats treated with the high dose of T3S and both doses of T3. Serum TSH, markedly elevated in Tx rats, was appreciably reduced only in rats treated with the high dose of T3. In another study, significant suppression of serum TSH was observed when Tx rats were treated with T3S (11.5 nmol/day) or T3 (2.3 nmol/day) for 3 days. We conclude that administration of T3S to hypothyroid rats produces thyromimetic effects, with a potency approximately one fifth that of T3.

A study of the characteristics of hepatic iodothyronine 5'-monodeiodinase in various vertebrate species.

Rat type I iodothyronine 5'-monodeiodinase (5'-MD) has recently been shown to be a selenium-containing enzyme. In the present study we compared the characteristics of the 5'-MD from liver microsomes of rat, mouse, guinea pig, man, beef, pig, sheep, and chicken. Aurothioglucose (ATG), a known potent inhibitor of selenium-containing enzymes, was a consistent, very potent inhibitor of 5'-MD activity in all species studied, with a 50% inhibitory dose in the narrow range of 5.8-12 nM. ATG was also a potent and selective inhibitor of [125I]bromoacetyl T3 affinity labeling of 5'-MD. Thus, in the species studied, only one affinity-labeled band, which was selectively displaced by gold, was identified. The mol wt of the affinity-labeled proteins in various liver microsomal preparations ranged between 28-36 kilodaltons (kDa), and the ATG concentrations necessary for the inhibition of affinity labeling of microsomes with [125I]bromoacetyl T3 were comparable to those required for inhibition of the enzyme activity in all species except the pig. The pig liver microsomes demonstrated a dominant affinity-labeled 36-kDa band, but much higher ATG concentrations (micromolar) were required for inhibition of affinity labeling. In view of the potent inhibition of pig liver 5'-MD activity by ATG, it appears unlikely that this band in the pig corresponds only to the substrate-binding site of 5'-MD, but this issue requires further study. A synthetic peptide of 16 amino acids corresponding to the carboxy-terminal portion of rat 5'-MD was synthesized, and rabbits were immunized with the peptide-BSA conjugate. Western blot studies using the rabbit antiserum showed one specific 29-kDa band in rat liver and kidney microsomes and thyroid homogenate. No specific bands were observed in other adult rat tissues studied or in fetal rat liver. No specific bands were observed when Western blot studies with antibody against the carboxy-terminal portion of rat 5'-MD were performed in liver microsomes from species other than the rat. In conclusion, our studies indicate that selenium is a likely component of type I 5'-MD in all species studied. However, substantial structural differences exist between the rat type I 5'-MD and that in various other species.

A study of the 3,5,3'-triiodothyronine sulfation activity in the adult and the fetal rat.

We have employed a new in vitro assay for study of the T3 sulfation activity in rat tissues. The assay measures by RIA the generation of T3 sulfate (T3S) during incubation of T3 with cytosol of rat tissues as the source of phenol sulfotransferase(s) and 3-phosphoadenosine-5'-phosphosulfate as the sulfate donor. The conversion of T3 to T3S proceeded rapidly for 30 min at 37 C, and the optimal pH of the reaction was 8.0. Heating the cytosol at 44 C for 15 min decreased T3S production to 63% of its value at 37 C. T3 sulfation activity was plentiful in rat liver, brain, and kidney, but little activity was demonstrable in other tissues. The Km and maximum velocity of the hepatic conversion of T3 to T3S were 114 microM and 159 pmol/mg protein.h, respectively. There was a marked inhibition of the conversion of T3 to T3S with salicylamide, 3'-monoiodothyronine, thyronine, and rT3; the IC50 of these inhibitors approximated 15, less than 0.1, 9.5, and 43 microM, respectively. On day 17 of gestation, the T3 to T3S conversion activity was more abundant in fetal skin than in other fetal tissues. However, the activity decreased in fetal skin while it increased in fetal liver, kidney, and brain nearer to term on day 20. Placenta demonstrated lower T3 to T3S conversion activity than several fetal or maternal tissues. There was no effect of hypothyroidism or hyperthyroidism on T3 sulfation activity. We conclude that T3 sulfation activity in the rat is 1) most abundant in liver, kidney, and brain tissues of the adult; 2) inhibited more avidly by 3'-monoiodothyronine than other thyronines; 3) very abundant in fetal skin early in gestation; and 4) little affected by the thyroidal status of the animal.

A study of the characteristics of the rat placental iodothyronine 5-monodeiodinase: evidence that it is distinct from the rat hepatic iodothyronine 5'-monodeiodinase.

Recent studies have demonstrated that rat liver type I iodothyronine 5'-monodeiodinase (5'-MD) characteristically contains selenocysteine. The present study was undertaken to characterize rat placental type III iodothyronine 5-MD and to compare it with 5'-MD. Solubilized rat placental microsomes were delipidated by carboxymethyl cellulose-Sephadex chromatography. Phospholipids and proteins were recovered in two distinct peaks, which did not show 5-MD activity. 5-MD activity was recovered fully, however, by combining the two components (phospholipids and protein) and partially after the addition of exogenous phospholipids to protein. Tissue selenoproteins were labeled by injection of radioactive selenium (75Se; 50 microCi, iv; on days 5, 10, and 15 of gestation) to pregnant rats. Subcellular fractions of maternal and fetal tissues were resolved by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, followed by autoradiography. No specific seleno-labeled proteins were evident in the microsomes of placenta or maternal or fetal brain. A 27- to 29-kilodalton (kDa) band previously suggested to be 5'-MD was observed, however, in maternal liver and kidney microsomes. Aurothioglucose inhibited rat placental 5-MD, but the dose required for 50% inhibition was over 50-fold greater than that for Se-containing hepatic 5'-MD (430 vs. 8 nM). The mechanism of the inhibition was noncompetitive for 5-MD, whereas it was competitive for 5'-MD. A synthetic peptide of 16 amino acids corresponding to the carboxy-terminal portion of 5'-MD was synthesized, and rabbits were immunized with the peptide-BSA conjugate. Western blots studies using the rabbit antiserum showed one specific 29-kDa band in rat liver microsomes. However, no specific bands were observed in 5-MD-rich placental or fetal brain microsomes. Bromoacetyl T3 (BrAcT3) was a potent inhibitor of rat placental 5-MD. Affinity labeling of solubilized rat placental microsomes with [125I]BrAcT3 showed a predominant band of 31 kDa, distinct from the 27- to 29-kDa band found in liver and kidney. The labeling of the 31-kDa band was enhanced by 10 mM dithiothreitol, inhibited 60% by 150 microM T3, and prevented by 40 microM aurothioglucose. A dominant affinity-labeled 31-kDa band was also observed in fetal brain microsomes. Some tissues without 5-MD activity (testes and spleen) also showed weak binding.(ABSTRACT TRUNCATED AT 250 WORDS)

A radioimmunoassay of 3,5-dimethyl-3'-isopropyl-L-thyronine.

A simple, sensitive, and specific RIA has been developed to measure 3,5-dimethyl-3'-isopropyl-L-thyronine (DIMIT) in unextracted serum. The RIA employs a DIMIT-binding antibody obtained from a rabbit immunized with DIMIT-human serum albumin conjugate and [125I]T3 as the radioligand. 8-Anilino-1-naphthalene sulfonic acid and barbital buffer (0.075 M; pH 8.6) were used to minimize serum binding of DIMIT and [125I]T3. The detection threshold of the RIA was 0.03 microgram/dl. Recovery of nonradioactive DIMIT added to serum averaged 104%. 3,5,3'-Triiodothyroacetic acid cross-reacted maximally (78%) in the RIA, followed by T3 (56%), 3,5-diethyl-3'-isopropyl thyronine (43%), 3,3'-diiodothyronine (T2; 12%), tetraiodothyroacetic acid (6.7%), 3'-monoiodothyronine (T1; 0.54%), 3.5-T2 (0.34%), 3-T1 (0.26%), and T4 (0.25%); rT3, 3',5'-T2, thyronine, iodotyrosines, and KI cross-reacted 0.1% or less. The coefficient of variation averaged 7.4% within an assay and 9.0% between assays. After ip administration of DIMIT to the rat, the mean serum DIMIT concentration rose in a dose-related fashion from less than 0.12 microgram/dl in the controls to 44 micrograms/dl in those receiving 200 micrograms/100 g BW daily for 3 days; serum T4 and TSH levels declined significantly in animals receiving 3.2 micrograms DIMIT/(100 g BW X day) or more. After a single ip injection of DIMIT to the rat, serum DIMIT levels increased from a control value of 0.04 to 9.8 micrograms/dl at 2 h and then decreased progressively, with a half-life approximating 7.2 h. Serum TSH was suppressed for up to 24 h, while serum T4 and T3 were suppressed for up to 48 h after the injection. Concentrations of DIMIT 15 h after a dose of 10 micrograms, ip, to approximately 150-g rats were (nanograms per g; mean +/- SE) 19 +/- 2.3 in serum, 30 +/- 3.5 in liver, 23 +/- 2.4 in kidney, 19 +/- 4.7 in heart, 16 +/- 3.4 in skeletal muscle, and 20 +/- 3.0 in brain. DIMIT administration to pregnant rats [3 micrograms/(100 g BW X day) for 3 days, im] resulted in mean +/- SE DIMIT concentrations (micrograms per dl) of 0.51 +/- 0.14 in maternal serum, 0.57 +/- 0.04 in fetal serum, and 0.46 +/- 0.07 in amniotic fluid. A DIMIT dose of 10 micrograms/(100 g BW X day) for 3 days in maternal rats resulted in mean DIMIT concentrations (micrograms per dl) of 1.8 +/- 0.06 in maternal serum, 1.4 +/- 0.10 in fetal serum, and 1.3 +/- 0.17 in amniotic fluid.(ABSTRACT TRUNCATED AT 400 WORDS)

Effect of 3,5,3'-triiodothyronine-induced hyperthyroidism on iodothyronine metabolism in the rat: evidence for tissue differences in metabolic responses.

We studied the effect of T3-induced hyperthyroidism on the outer ring (5' or 3') monodeiodination of T4 (to T3) and 3',5'-diiodothyronine [3',5'-T2; to 3'-monoiodothyronine (3'-T1)] and on the inner ring (3 or 5) monodeiodination of 3,5-T2 (to 3-T1) by various rat tissues. Weight-matched pairs of male Sprague-Dawley rats were given either saline or T3 (20 micrograms/100 g BW daily) ip for 3 days. The metabolism of the iodothyronines was studied on day 4 in homogenates of the tissues in the presence of 25 mM dithiothreitol. Hyperthyroidism was associated with a significant (P less than 0.05) increase in T4 to T3 monodeiodinating activity in the liver (mean, 95%), kidney (mean, 60%), and heart (mean, 153%), but not in skeletal muscle, small intestine, spleen, testis, cerebral cortex, or cerebellum. The monodeiodinating activity converting 3',5'-T2 to 3'-T1 was greatly increased (P less than 0.05) in the heart (mean, 750%), spleen (mean, 462%), and skeletal muscle (mean, 167%), but not in liver, kidney, small intestine, testis, cerebral cortex, or cerebellum. In the case of liver and kidney, however, there was evidence of an activation of 3',5'-T2 monodeiodinating activity, as suggested by a significant increase in the activity in the absence of added dithiothreitol. The monodeiodination of 3,5-T2 to 3-T1 increased significantly only in the cerebral cortex (mean, 525%) and liver (mean, 69%) and not in any other tissue. The time course of the above-mentioned changes in iodothyronine metabolism was studied in groups of rats (five per group) given T3 (20 micrograms 100 g BW-1 day-1) 6-72 h before death. Significant increases in 3',5'-T2 (to 3'-T1) monodeiodination in the heart and 3,5-T2 (to 3-T1) monodeiodination in the cerebral cortex were evident within 6 h of T3 administration. Changes in T4 to T3 monodeiodinating activity in the kidney and liver, however, did not become statistically significant until 24 and 72 h, respectively. The various effects of T3 on the tissues became maximal between 48 and 72 h after the initiation of T3 treatment. Our data suggest that most tissues, including some that have been considered unresponsive to thyroid hormones, e.g. brain and spleen, demonstrate substantial metabolic changes after T3 administration. The tissue responses are variable in degree; in some instances, they are specific for the substrate and type of tissue.(ABSTRACT TRUNCATED AT 400 WORDS)

A study of cardiac effects of thyroid hormones: evidence for amelioration of the effects of thyroxine by sodium ipodate.

We studied the effects of daily ip administration of T4 (200 micrograms/100 g BW) or T3 (50 micrograms/100 g) to the rat (six per group) for 3 days with or without sodium ipodate (6 mg/100 g), propylthiouracil (PTU; 2 mg/100 g), propranolol (0.5 mg/100 g), or amiodarone (2.5 mg/100 g) on cardiac weight, 3',5'-diiodothyronine (3',5'-T2) to 3'-monoiodothyronine monodeiodinating activity (MA), mitochondrial alpha-glycerophosphate dehydrogenase (alpha GPD), and/or cytosolic ornithine decarboxylase (ODC). T4 treatment caused a 28% increase in cardiac weight, about an 11-fold increase in 3',5'-T2 MA, about a 27% increase in alpha GPD activity, and about a 129% increase in ODC activity. Administration of ipodate with T4 abolished all effects of T4 on the heart. PTU abolished the effect of T4 on alpha GPD and markedly reduced its effect on 3',5'-T2 MA and ODC activity; it had little effect on cardiac hypertrophy caused by T4 treatment. Propranolol reduced the increase in cardiac weight following T4 administration from 28% to 11%, but had a modest or no effect on T4-induced changes in other metabolic variables studied. Amiodarone also reduced the effect of T4 on heart weight, but had little or no influence on 3',5'-T2 MA, the only metabolic variable studied. T3 treatment of the rat caused a 35% increase in heart weight, about a 15-fold increase in 3',5'-T2 MA, about a 35% increase in alpha GPD, and about a 100% increase in ODC activity. Ipodate and PTU reduced the increase in 3',5'-T2 MA following T3 administration, but had no appreciable influence on heart weight, alpha GPD, and/or ODC activity. Propranolol and amiodarone had no significant effect on any of the changes studied after T3 administration. It was concluded that: 1) ipodate markedly lessens or abolishes the effects of T4 on the heart; 2) propranolol and amiodarone decrease cardiac hypertrophy in response to T4 administration, but have little or no effect on metabolic changes due to T4; 3) PTU curtails the metabolic effects of T4 on the heart but has little effect on cardiac hypertrophy; 4) none of the drugs studied affects cardiac changes occurring after T3 administration. The changes observed in 3',5'-T2 MA after ipodate and PTU treatment may have been a result of direct interaction of the drugs with the deiodinase.

A radioimmunoassay for measurement of thyroxine sulfate.

A highly sensitive, specific, and reproducible RIA has been developed to measure T4 sulfate (T4S) in ethanol extracts of serum. rT3 sulfate (rT3S) cross-reacted 7.1%, and T3S cross-reacted 0.59% in the RIA; T4, T3, rT3, and 3,3'-diiodothyronine cross-reacted 0.004% or less. The recovery of nonradioactive T4S added to serum averaged 95%. The detection threshold of the RIA was 18 pmol/L. The coefficient of variation averaged 6.9% within an assay and 12% between assays. T4S was bound by T4-binding globulin and albumin in serum. The free fraction of T4S in four normal sera averaged 0.06% compared to a value of 0.03% for T4 (P < 0.001). The serum concentration of T4S was (mean +/- SE) 19 +/- 1.2 pmol/L in normal subjects, 33 +/- 10 in hyperthyroid patients with Graves' disease, 42 +/- 15 in hypothyroid patients, 34 +/- 6.9 in patients with systemic nonthyroidal illnesses, 21 +/- 4.3 in pregnant women at 15-40 weeks gestation, and 245 +/- 26 in cord blood sera of newborns; the value in the newborn was significantly different from normal (P < 0.001). The mean concentration of T4S in amniotic fluid samples at 15-38 weeks gestation was 106 +/- 22 pmol/L (cf. normal adults; P < 0.001). Administration of sodium ipodate (Oragrafin; 3 g, orally) to hyperthyroid patients was associated with a transient increase in serum T4S. The T4S content of the thyroid gland was less than 1/4000th that of T4. We conclude that 1) T4S is a normal component of human serum, and its levels are markedly increased in newborn serum and amniotic fluid; and 2) the sulfation pathway plays an important role in the metabolism of T4 in man.

A competitive ligand binding assay for measurement of thyroid hormone-binding inhibitor in serum and tissues.

A competitive ligand-binding assay (CLBA) is described for measurement of an inhibitor(s) of serum binding of T4 in ether extracts of serum and in homogenates and extracts of tissues. The CLBA is based on the effect of thyroid hormone binding inhibitor (THBI) on partition of a constant amount of radiolabeled ligand [(125I]T4) between fixed amounts of serum and an anti-T4 antibody. The method is convenient, rapid, sensitive, and reproducible. The coefficient of variation averaged 8.9% within an assay and 12.8% between assays. Several fatty acids, e.g. arachidonic acid, lauric acid, linolenic acid, and linoleic acid, had potent THBI activity in the CLBA; arachidonic acid was more potent than the other fatty acids. Since oleic acid cross-reacted substantially with T4-binding sites on anti-T4, its THBI activity was examined by an equilibrium dialysis method; it was about 77% as potent as arachidonic acid. Arachidic, myristic, palmitic, and stearic acids, choleserol, various phospholipids and triglycerides (triolein and tripalmitin) had little or no THBI activity in the CLBA. THBI activity was detected in the sera of 50% (60% when serum T4 was low and 42% when it was normal) of 34 patients with nonthyroid illnesses (NTI) when studied by CLBA and in 59% (67% when serum T4 was low and 53% when it was normal) of patients when determined by the inhibitory ratio (normalized dialysis ratio/normalized binding ratio). THBI values obtained by the CLBA correlated significantly (r = 0.58; P less than 0.001) with those obtained by the inhibitory ratio method. The dose-response curve of an ether extract of pooled sera of hospitalized patients was parallel to that of arachidonic acid in the CLBA. Among various rat tissues, the small intestine had the most THBI activity in both homogenates and ether extracts of homogenates. Ether (2 vol) extracted about 63% of the THBI activity in small intestine homogenate at pH 5.2. THBI activity was demonstrable in all particulate fractions (especially mitochondria and endoplasmic reticulum) of small intestine homogenate; cytosol contained little or no THBI activity. THBI activity changed little after treatment of small intestine homogenate with trypsin or protease inhibitors.(ABSTRACT TRUNCATED AT 400 WORDS)

Detection of tumors with 19F magnetic resonance imaging.

Previous 19F magnetic resonance imaging studies showed that the reticuloendothelial system can be imaged with an emulsion of perfluorooctyl bromide (PFOB). Similar techniques can be used to detect previously implanted RIF-1 tumors in mice after intravenous PFOB administration. Accumulation of PFOB within these neoplasms is due to egress of the emulsion through tumor capillary fenestrations. This is the first report in which 19F MRI and PFOB are used to detect tumors. This technique may allow clinical detection of cancer with 19F MRI.

Sex-related differences in iodothyronine metabolism in the rat: evidence for differential regulation among various tissues.

Various aspects of thyroid hormone metabolism were examined in vitro in age-matched (experiment I) and weight-matched (experiment II) male and female Sprague-Dawley rats; unless specified otherwise, results were similar in both experiments. The activity and content of iodothyronine 5'-monodeiodinase (type I-MD) in the liver of the female rat were markedly reduced, but there was no sex-related difference in these parameters in the kidney. The activity of the brain type III-MD was also not significantly influenced by the sex of the rat. Hepatic triiodothyronine (T3) sulfation activity in the females was only about 20% of that of the males. However, kidney and brain did not show this decrease in T3 sulfation. Similarly, hepatic T3 sulfate (T3S) desulfation activity was significantly reduced in the liver of the female rat (P < .001), whereas the activity in the kidney was either similar to (experiment I) or higher than (experiment II) that in the male, and the activity in the brain was similar in the two sexes. The mean serum T3S concentration in the female rat was no greater than 25% of the corresponding value measured in the male rat. The mean serum thyroxine (T4) concentration in female rats was similar to that in age-matched males (experiment I), whereas it was somewhat lower than that in weight-matched males (P < .05, experiment II). No significant difference in the mean serum T3 concentration was observed in rats of female and male sex. However, the mean serum thyrotropin (TSH) concentration in the female rat was significantly lower than that in the male.(ABSTRACT TRUNCATED AT 250 WORDS)

Thyromimetic effects of 3,5-dimethyl,3'-isopropyl thyronine (DIMIT) and 3,5-diethyl,3'-isopropyl thyronine (DIET) in various tissues of the rat.

We have examined the effects of treatment of the rat with 3,5-dimethyl-3'-isopropyl thyronine (DIMIT) and 3,5-diethyl-3'-isopropyl thyronine (DIET) on serum thyrotropin (TSH) concentration, heart weight, hepatic outer ring (5'-) monodeiodination of T4 to T3, cardiac outer ring monodeiodination of 3'-5'-diiodothyronine (3',5'-T2) to 3'-monoiodothyronine (3'-T1), and cerebral cortical monodeiodination of 3,5-T2 in the inner ring to 3-T1. Groups of four to seven rats were injected intraperitoneally either once a day or at eight-hour intervals for three days with saline or thyronines. Serum TSH was measured by radioimmunoassay. The various monodeiodinations were studied in homogenates of the tissues at optimal pH (7.35 for outer ring monodeiodinations and 8.0 for inner ring monodeiodination) and temperature (37 degrees C) in the presence of an excess of dithiothreitol. DIMIT was clearly active in all thyromimetic effects studied. It was about 10% as active as T4 in suppression of TSH. It stimulated hepatic monodeiodination of T4 to T3 in a similar manner to T4. DIMIT was also more comparable to T4 than to T3 in effect on heart weight and cardiac metabolism of 3',5'-T2 to 3'-T1. It was highly active, apparently more so than either T4 or T3, in cerebral cortical stimulation of metabolism of 3,5-T2 to 3-T1. In distinction to DIMIT, DIET had very little thyromimetic activity.(ABSTRACT TRUNCATED AT 250 WORDS)

A procedure for using proton magnetic resonance imaging to determine stereotaxic coordinates of the monkey's brain.

Because of great inter-individual variability in the sizes and configurations of monkey brains, consistent intracerebral stereotaxic placements are not possible when a general brain atlas is relied upon to derive placement coordinates. We describe a procedure that allows the determination of brain atlases for individual monkeys using proton magnetic resonance imaging and the translation of image coordinates to stereotaxic coordinates. The latter is accomplished by chronically implanting glass beads filled with copper sulfate into the skull to establish a plane horizontal to the stereotaxic plane and to provide reference points for zeroing stereotaxic carriers during intracerebral implants. The efficacy of this procedure was confirmed experimentally.

Retinal degeneration mutants in the mouse.

The Jackson Laboratory, having the world's largest collection of mouse mutant stocks and genetically diverse inbred strains, is an ideal place to look for genetically determined eye variations and disorders. Through ophthalmoscopy, electroretinography and histology, we have discovered disorders affecting all aspects of the eye including the lid, cornea, iris, lens and retina, resulting in corneal disorders, cataracts, glaucoma and retinal degenerations. Mouse models of retinal degeneration have been investigated for many years in the hope of understanding the causes of photoreceptor cell death. Sixteen naturally occurring mouse mutants that manifest degeneration of photoreceptors in the retina with preservation of all other retinal cell types have been found: retinal degeneration (formerly rd, identical with rodless retina, r, now Pde6b(rd1)); Purkinje cell degeneration (pcd); nervous (nr); retinal degeneration slow (rds, now Prph(Rd2)); retinal degeneration 3 (rd3); motor neuron degeneration (mnd); retinal degeneration 4 (Rd4); retinal degeneration 5 (rd5, now tub); vitiligo (vit, now Mitf(mi-vit)); retinal degeneration 6 (rd6); retinal degeneration 7 (rd7, now Nr2e3(rd7)); neuronal ceroid lipofuscinosis (nclf); retinal degeneration 8 (rd8); retinal degeneration 9 (Rd9); retinal degeneration 10 (rd10, now Pde6b(rd10)); and cone photoreceptor function loss (cpfl1). In this report, we first review the genotypes and phenotypes of these mutants and second, list the mouse strains that carry each mutation. We will also provide detailed information about the cpfl1 mutation. The phenotypic characteristics of cpfl1 mice are similar to those observed in patients with complete achromatopsia (ACHM2, OMIM 216900) and the cpfl1 mutation is the first naturally-arising mutation in mice to cause cone-specific photoreceptor function loss. cpfl1 mice may provide a model for congenital achromatopsia in humans.