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R J Boado

Publications and source records attributed to R J Boado.

At least 73 records · Page 4Linked to original sources
PubMed1988

Thyroid autoregulation. Inhibition of goiter growth and of cyclic AMP formation in rat thyroid by iodinated derivatives of arachidonic acid.

Thyroid autoregulation has been related to intraglandular content of an unknown putative iodocompund. Data from different laboratories have shown that the thyroid is capable of producing different iodolipids, including iodinated derivatives of arachidonic acid; such as 5-hydroxy-6-iodo-8, 11, 14-eicosatrienoic-delta-lactone (IL-delta). Previous results from our laboratory showed that a semi-purified preparation of iodinated arachidonic acid exerts an inhibitory action in vitro on calf thyroid. In the present studies three purified iodinated derivatives of arachidonic acid were synthesized: IL-delta; 14-iodo-15-hydroxy-5, 8, 11-eicosatrienoic acid (I-OH-A) and its corresponding omega-lactone (IL-omega). Their action on MMI-induced goiter was studied in rats. Administration of MMI to rats during 10 days increased thyroid weight by 124%. This effect was significantly inhibited by the simultaneous injection of 5 micrograms/day of I-OH-A (57% inhibition of MMI action), IL-W (39%), IL-delta (33%) and T3 (95%), while arachidonic acid was without action. No inhibition was found with 1.25 micrograms/day Kl, a dose equivalent to that which could be originated from total dehalogenation of the iodocompounds. These results support the idea that these iodocompounds have an intrinsic biologic activity and that there is a correlation between action and chemical structure. Serum TSH was increased around 15-20 fold after MMI administration. Chronic or acute injection of I-OH-A failed to alter TSH levels, indicating that this iodocompound exerts its action directly on the gland, without altering TSH concentration.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1988

Enzyme binding-inhibiting assay for iodothyronine 5'-monodeiodinase (5'-MD) and its application to isolation of complementary deoxyribonucleic acid clones for the 5'-MD in rat liver.

To identify and/or quantify type I T4 5'-monodeiodinase (5'-MD) immunologically, polyclonal antibodies were produced by immunization of rabbits with solubilized microsomal proteins (SMP) from rat liver. Pilot studies showed that the antibody binds to, but does not neutralize, rat liver enzyme. We have employed the polyclonal antibody to develop a 5'-MD enzyme binding-inhibiting assay (MBIA). For this purpose, active, inactive, or synthetic 5'-MD was preincubated with rabbit antibody and removed by Staphylococcus aureus protein-A (Staph-A). The 5'-MD-binding sites that were left on the Staph-A-bound rabbit antibody were assayed by adding active 5'-MD in fresh liver SMP. After centrifugation of Staph-A, the unbound 5'-MD enzyme activity was measured in the supernatant using [125I]rT3 in the presence of dithiothreitol. Incubation with 3.2 +/- 0.9 micrograms (mean +/- SEM; n = 4) rat liver SMP inhibited the binding of active 5'-MD to protein-A-bound antibody by 50%. Based on doses with similar 50% binding inhibitory activity, liver SMP were 2.3 times more potent than liver microsomes and 19 times more potent than liver homogenate; liver nuclei and mitochondria showed little or no inhibition of the binding of 5'-MD to antibody. The relative 5'-MD content of liver, kidney, pituitary, placenta, and cerebral cortex based on relative potency in the MBIA approximated 100:25:8:3:3. The threshold of the MBIA approximated 0.9 micrograms liver SMP/tube. The coefficient of variation approximated 2% within an assay and 6% between assays. To obtain a cDNA clone for 5'-MD we used the SMP antibody to screen a rat liver lambda gt11 cDNA expression library. Of 16 positive (antibody-reactive) clones that were isolated, the fusion proteins from only 2 (no. 23 and 54) inhibited the binding of 5'-MD in rat liver SMP to protein-A-bound rabbit antibody in a dose-dependent manner. Western blot analysis showed that the molecular size of liver protein encoded by clones 23 and 54 approximates 31K. Sequence analysis showed that clone 23 insert is 804 basepairs long, contains a single long open-reading frame, and is identical to clone 54. Southern blot analysis showed that clones 23 and 54 did not cross-hybridize DNA from other SMP antibody-positive clones. Northern blot analysis using clone 23 insert cDNA as the probe showed a hybridization band corresponding to a mRNA approximating 2.8 kilobases.(ABSTRACT TRUNCATED AT 400 WORDS)

Amino Acid Sequence↗
PubMed1988

A radioimmunoassay for measurement of thyronine and its acetic acid analog in urine.

A sensitive and specific RIA has been developed to measure thyronine (To) in urine. The RIA used an anti-To antibody obtained from a rabbit immunized with a L-To-human serum albumin conjugate and [3H]To as the radioligand. The acetic acid analog of To (ToAc), that is the diphenyl structure with an acetic acid side-chain, cross-reacted strongly with the antibody. Relative to To, it cross-reacted 160% in phosphate-buffered saline, pH 7.4, and 100% in 0.075 mol/L barbital buffer, pH 8.6, containing sodium salicylate (final concentration, 8 mg/mL). The latter conditions were employed for the RIA, and the results reported thus reflect the presence of To and/or ToAc. 3-Monoiodothyronine, 3'-monoiodothyronine, 3',5'-diiodothyronine, and 3,5-diiodothyronine cross-reacted with the anti-To antibody 1.9%, 1.7%, 0.3%, and 0.2%, respectively; the cross-reactivity of other To derivatives and tyrosine and its derivatives was less than 0.05%. Urinary To and/or ToAc excretion in 12 normal subjects averaged 16 +/- 2 (+/- SE) micrograms/day (59 +/- 9 nmol/day) or 14 +/- 2 micrograms/g creatinine (5.9 +/- 0.6 nmol/mmol creatinine). Treatment of urine from normal subjects with beta-glucuronidase or sulfatase did not significantly alter the To content. Column and thin layer chromatographic studies revealed that 83% and 61%, respectively (range, 37-100%), of urinary To immunoreactivity was attributable to ToAc. The mean daily excretion of To in 20 patients with nonthyroidal illness [NTI; 22 +/- 4 micrograms/day (82 +/- 17 nmol/day)] was similar to that in normal subjects, but was elevated when expressed as nanomoles per mmol creatinine (20 +/- 2; P less than 0.001), because creatinine excretion was reduced in the NTI patients. The mean daily urinary To excretion in 13 patients with hyperthyroidism due to Graves' disease was slightly elevated [29 +/- 6 micrograms/day (108 +/- 21 nmol/day); P less than 0.1], but was clearly elevated when expressed as nanomoles per mmol creatinine (37 +/- 8; P less than 0.001), again because creatinine excretion was reduced in these patients. The mean urinary To excretion was subnormal in 13 patients with hypothyroidism and was significantly (P less than 0.005) less than that in the NTI patients regardless of the manner in which the results were expressed. Analysis of pronase hydrolysates of thyroid glands obtained at autopsy from euthyroid patients suggested that the To content of the thyroid approximates only 1.2% that of T4, supporting the thesis that prior iodination of tyrosine is critical for the coupling process in the thyroid.(ABSTRACT TRUNCATED AT 400 WORDS)

Acetates↗
PubMed1987

The effect of free radicals on hepatic 5'-monodeiodination of thyroxine and 3,3',5'-triiodothyronine.

Free radicals have been implicated in many pathological processes, including ischemia, inflammation, and malignancy. Since a reduction in extrathyroidal outer ring monodeiodination of T4 and rT3 occurs in virtually all systemic illnesses, we have studied the effect of free radicals on iodothyronine (T4 and rT3) 5'-monodeiodinating activity (MA) of liver tissue in vitro. Rat liver microsomes or homogenate were preincubated in Tris buffer for 30 min with a free radical-generating system (FRGS) and then incubated with T4 (2.5 microM) or [125I]rT3 (0.4 nM) and dithiothreitol (DTT; 5-20 mM with T4 and 20-150 mM with [125I]rT3) in the same buffer for 10 or 30 min. T3 generated during incubation was quantified by RIA of ethanol extracts of the incubation mixture. 125I generated from [125I]rT3 was quantified after precipitation of the incubation mixture with trichloroacetic acid or by paper chromatography. Free radicals caused 55% or more reduction in hepatic T4 MA and 44% or more reduction in rT3 MA in various experiments. The inhibition of hepatic rT3 MA after incubation with FRGS persisted despite removal of FRGS and washing of microsomes preincubated with FRGS before studying the MA. However, inclusion of DTT (1-60 mM) during preincubation of tissue with FRGS prevented the FRGS-induced inhibition of rT3 MA. Depletion of the iodothyronine substrate did not occur when FRGS inhibited T4 and rT3 5'-monodeiodination. Free radical scavengers, i.e. superoxide dismutase (600 IU/ml), catalase (300 U/ml), tocopherol (10 mg/ml), thiourea (0.15 M), and tert-butanol (0.15 M), all significantly reduced the inhibition of hepatic rT3 MA caused by FRGS. The FRGS-induced inhibition of hepatic T4 MA was reduced by the same doses of tocopherol, thiourea, and tert-butanol, but not by superoxide dismutase or catalase. Since free radicals may effect tissue damage by lipid peroxidation and since the latter results in generation of malondialdehyde (MDA) as a by-product of the reaction, we studied MDA by its reaction with 2-thiobarbituric acid. Incubation with FRGS caused an approximately 100-fold increase in MDA formation in liver microsomes. Serum MDA was significantly higher in 16 NTI patients than in 8 normal subjects and also higher in turpentine oil-injected rats [an experimental model of nonthyroidal illness (NTI)] than in saline-injected control rats. The data suggest that generation of free radicals may contribute to the reduced extrathyroidal 5'-monodeiodination of T4 and rT3 in NTI.(ABSTRACT TRUNCATED AT 400 WORDS)

Adult↗
PubMed1987

Inhibition of the response of thyrotrophin to thyrotrophin-releasing hormone by thyroxine in hypothyroid rats treated with iopanoic acid: evidence suggesting an intrinsic biological activity of thyroxine without prior conversion to 3,5,3'-tri-iodothyronine.

The effects of a physiological replacement dose of thyroxine (T4) on the response of plasma TSH to TRH in hypothyroid rats were studied. Animals were treated with iopanoic acid (IOP; 5 mg/100 g body weight) or vehicle 24, 12 and 1.5 h before the experiment. Thereafter, 800 ng T4/100 g body weight were administered i.v. and 20 min later 1 microgram TRH/100 g body weight was injected i.v. In control rats the basal concentration of TSH was 1450 +/- 300 (S.E.M.) mu./1. The plasma concentration of TSH 10 min after injection of TRH increased to 167 +/- 14% of the mean basal value (P less than 0.001). The injection of T4 significantly (P less than 0.005) reduced the TSH response to TRH in both IOP-treated (118 +/- 15%) and vehicle-treated (108 +/- 15%) rats compared with untreated controls. Tri-iodothyronine (T3) was undetectable in the plasma of all rats, whereas the plasma concentration of T4 was 121 +/- 19 nmol/l in IOP-treated and 139 +/- 23 nmol/l in vehicle-treated rats 30 min after injection of 800 ng T4/100 g body weight. In pituitary cells of control rats, cytoplasmic radioactivity 30 min after injection of [125I]T4 was 1.28 +/- 0.13 X 10(-2)% (76 +/- 6% T4 and 17 +/- 3% T3), whereas that in nuclei reached 0.42 +/- 0.36 X 10(-2)% (51 +/- 4% T4 and 28 +/- 3% T3) of the injected dose.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1986

Changes in growth hormone and prolactin release after superior cervical ganglionectomy of rats.

Superior cervical ganglionectomy (SCG X) decreased significantly serum growth hormone (GH) levels in rats 14-96 h after surgery, during and immediately after anterograde degeneration of regional sympathetic terminals. At later times (up to 28 days after SCG X) an increase in serum GH was observed. SCG X augments prolactin (PRL) release, but only at the earliest time examined (14 h after surgery). Injection of the alpha-adrenoceptor blocker, phenoxybenzamine, but not of the beta-blocker, propranolol, negated the depression in serum GH found in SCG X rats 14 h after surgery, without affecting PRL release.

Animals↗
PubMed1986

Early inhibition and changes in diurnal rhythmicity of the pituitary-thyroid axis after superior cervical ganglionectomy of rats.

The effect of superior cervical ganglionectomy (SCGx) on the pituitary-thyroid axis was examined in rats. SCGx decreased serum thyrotropin (TSH) and thyroxine (T4) levels for up to 4 days after surgery, during and immediately after completion of anterograde degeneration of regional sympathetic terminals. At later times TSH levels in control and SCGx rats did not differ, but a significant increase of serum T4 was found two weeks after SCGx. A diurnal rhythm in serum TSH and T4 levels with maxima at 11.00 h (TSH) and at 14.00 and 22.00 h (T4) was found in sham-operated rats 3 days after surgery. At this time SCGx evoked a general depression of TSH levels as well as a shift of 3 h in their maximum. A similar shift of the afternoon peak and abolition of the nocturnal peak in serum T4 were detectable in SCGx rats. In SCGx animals examined during anterograde nerve degeneration, i.e. 14 h after surgery, injection of the alpha 1-adrenoceptor blocker phenoxybenzamine negated denervation-induced changes of TSH and counteracted partially T4 effects. The beta-adrenergic blocker propranolol did not modify serum TSH levels in SCGx rats but further decreased serum T4 concentration. Treatment with both drugs simultaneously did no affect TSH release compared to SCGx, phenoxybenzamine-treated rats but effectively decreased serum T4. These results further support the involvement of superior cervical ganglion neurons in the control of thyroid function.

Animals↗
PubMed1985

Role of the sympathetic nervous system in the control of thyroid compensatory growth of normal and hypophysectomized rats.

Compensatory thyroid growth in rats subjected to unilateral thyroidectomy (Tx) and superior cervical ganglionectomy (SCGx) performed ipsilaterally to the remaining lobe was about 2-fold that of rats subjected hemiTx alone, when assessed 7-15 days after surgery. HemiTx depressed serum T4 levels by 33% and increased serum TSH by 80% in control rats. Unilateral SCGx, which did not affect circulating T4 or TSH by itself, prevented hemiTx-induced changes of hormone levels. After hypophysectomy (Hpx) thyroid involution ensued. The subsequent hemiTx of Hpx rats did not affect Hpx-induced thyroid regression 7 days later, but abolished it 15 days later. At this time a factorial analysis of variance revealed lack of significant interaction between Hpx and hemiTx thus suggesting that a similar thyroid growth ensues after hemiTx regardless of pituitary intactness. However, both serum T4 and TSH levels were very low in Hpx rats regardless of whether one or two thyroid lobes were present indicating that thyroid growth in the absence of pituitary was not accompanied by increased secretory activity. SCGx performed ipsilaterally to the remaining lobe blunted the growth of the lobe in Hpx hemiTx rats. Moreover, the denervated thyroid lobe regressed in Hpx rats to values significantly lower than those of Hpx rats having intact sympathetic nerves both in the presence or in the absence of a contralateral thyroid lobe. SCGx did not modify the very low serum TSH and T4 levels of Hpx rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1984

Studies on the regulation of RNA labeling and on the biochemical constituents of normal and abnormal human thyroid.

The present studies were performed in order to analyze the incorporation of 3H-uridine into RNA and its hormonal regulation as well as the content of total iodine, T3, T4, RNA, DNA and protein in normal and abnormal human thyroid obtained at surgery. The content of protein, RNA and DNA is not significantly changed in follicular adenoma and in adenomatous goiter, RNA labeling from 3H-uridine showed similar values in slices from normal and abnormal glands. TSH and cyclic AMP increased the labeling of RNA in normal tissue but had no effect in the follicular adenoma and adenomatous goiter. A significant decrease in total iodine, T3 and T4 concentration was found in the pathological samples when compared to normals. The present results would suggest that in these patients the biochemical abnormalities lie at a step distal to the TSH receptor and the adenylate cyclase.

Adenoma↗
PubMed1983

The sympathetic superior cervical ganglia as "little neuroendocrine brains".

The superior cervical ganglia (SCG) provide sympathetic innervation to the pineal gland, cephalic blood vessels, the choroid plexus, the eye, carotid body and the salivary and thyroid glands. Removal of the ganglia brings about several neuroendocrine changes in mammals, including the disruption of water balance in pituitary stalk-sectioned rats and the alteration of normal photoperiodic control of reproduction and thyroid function in hamsters, ferrets, voles, rams and goats. These effects are commonly attributed to pineal denervation. However, pinealectomy does not always mimic ganglionectomy in its neuroendocrine sequelae. This paper discusses several examples illustrating the differences in ganglia and pineal removal, including the acute and chronic effects of ganglionectomy on the control of thyroid response to TSH in rats. A functionally relevant link between SCG and the hypothalamus occurs in rats, inasmuch as ganglionectomy depresses norepinephrine uptake and increases the number and responses of alpha-adrenoceptors in medial basal hypothalamus. Lastly the SCG are active points of concurrency for hormone signals, as revealed by the metabolic changes induced by steroid and anterior pituitary hormones in these structures, even in the absence of intact preganglionic connections, as well as by the existence of putative receptors for some of the hormones, namely estradiol, testosterone and corticosteroids. The SCG appear to constitute a peripheral neuroendocrine center.

Adrenal Cortex Hormones↗
PubMed1983

Ipsilateral thyroid growth and depressed thyroid hormone synthesis and content after unilateral superior cervical ganglionectomy in rats.

The role of the sympathetic nervous system in the control of the goitrogenic response was examined in adult male rats subjected to unilateral superior cervical ganglionectomy 12-30 days earlier. A spontaneous goiter as well as an increased thyroid growth after the administration of the goitrogenic agents methylmercaptoimidazole and thyrotropic stimulating hormone (TSH) were found in the ipsilateral lobe. Norepinephrine and epinephrine content decreased significantly by 80 and 31%, and thyroxine (T4) and triiodothyronine (T3) content by 24 and 15%, in the ipsilateral lobe. After the injection of a tracer dose of 125I, percent radioactivity incorporation to diiodotyrosine (DIT) was higher, and that to monoiodotyrosine (MIT) lower, in the ipsilateral lobe; additionally a lower ratio "labeled T3 + T4/labeled DIT" was found in the denervated thyroid lobe. These results suggest that the sympathetic nerve terminals in the thyroid gland modulate the organ's response to circulating TSH.

Animals↗