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Biomedical subjects

S W Spaulding

Publications and source records attributed to S W Spaulding.

At least 19 recordsLinked to original sources
PubMed1992

Studies on the biological activity of triiodothyronine sulfate.

Hepatic microsomes and isolated hepatocytes in short term culture desulfate T3 sulfate (T3SO4). We, therefore, wished to determine whether T3SO4 could mimic the action of thyroid hormone in vitro. T3SO4 had no thyromimetic effect on the activity of Ca(2+)-ATPase in human erythrocyte membranes at doses up to 10,000 times the maximally effective dose of T3 (10(-10) mol/L). In GH4C1 pituitary cells, T3SO4 failed to displace [125I]T3 from nuclear receptors in intact cells or soluble preparations. Thus, T3SO4 was not directly thyromimetic in either an isolated human membrane system or a pituitary cell system in which nuclear receptor occupancy correlates with GH synthesis. Thyroid hormones inhibit [3H]glycosaminoglycan synthesis by cultured human dermal fibroblasts, and T3SO4 displayed about 0.5% the activity of T3 at 72 h. Human fibroblasts contained roughly the same level of microsomal p-nitrophenyl sulfatase activity as that previously observed in hepatic microsomes. Propylthiouracil (50 mumol/L) did not affect the action of T3SO4, suggesting that deiodination was not important for this activity of T3SO4. Thus, it appears T3SO4 has no intrinsic biological activity, but, under certain circumstances, may be reactivated by desulfation.

Calcium-Transporting ATPases↗
PubMed1991

HMG 14 and protamine enhance ligation of linear DNA to form linear multimers: phosphorylation of HMG 14 at Ser 20 specifically inhibits intermolecular DNA ligation.

HMG 14 and protamine can be used to enhance intermolecular ligation of low concentrations of linear DNA. Adding HMG 14 (50 moles per mole DNA) caused 50% of blunt-ended DNA to form predominantly dimers, and all cohesive-ended DNA to form multimers (greater than 6-mer) in response to T4 ligase. Protamine was maximally effective at 40:1, producing mostly dimers and trimers. Adding higher concentrations of HMG 14 did not affect the ligation pattern of cohesive-ended DNA, while higher concentrations of protamine inhibit the formation of multimers. Phosphorylation of HMG 14 at Ser 20 by Ca(++)-phospholipid dependent protein kinase abolished the ability of HMG 14 to stimulate intermolecular ligation, but did not substantially interfere with intramolecular ligation, or the binding of HMG 14 to linear or circular DNA as assessed by gel mobility. Thus Ser 20, which is located in the amino terminal DNA-binding domain of HMG 14, appears to modulate DNA-DNA interactions.

Animals↗
PubMed1991

Thyroxine increases epidermal growth factor levels in the mouse thyroid in vivo.

Immunoreactive epidermal growth factor (EGF) has been detected in the thyroid, which raises questions concerning the source of thyroidal EGF and what affects its levels. We therefore have examined the effects of manipulating thyroid function on the immunoreactive EGF levels in plasma, thyroid, submaxillary gland (SMG), and kidney of adult male BALB/c mice, and we also analyzed the prepro-EGF messenger RNA in these tissues. Groups of six mice received daily injection of T4 (1 microgram, 5 micrograms, or 25 micrograms) or bovine TSH (1 mU) for up to 14 days. The plasma EGF concentration was 0.31 +/- 0.01 ng/ml in control animals, and T4 (5 micrograms) decreased the plasma levels by about one-half within 1 week. The thyroidal EGF was 0.50 +/- 0.14 ng/mg protein in control animals, and T4 (5 micrograms) increased the thyroidal EGF 8-fold within 1 week. There was a negative correlation between plasma and thyroidal EGF concentration (r = -0.93, P less than 0.01). Increasing doses of T4 also increased the SMG EGF content, while plasma levels fell (r = -0.88, P less than 0.01). The TSH treatment did not significantly alter the plasma or tissue EGF levels. Studies on mRNA prepared from these three tissues, using the reverse transcription and the polymerase chain reaction, indicated that the prepro-EGF mRNA was present in thyroid, SMG, and kidney. In conclusion, it appears that at least some thyroidal EGF is synthesized in the thyroid. Our observations that T4 increases the level of intrathyroidal EGF in a dose- and time-dependent fashion, while plasma levels fall, suggest the possibility that intrathyroidal EGF represents a shortloop feedback for the autocrine and/or paracrine regulation of thyroid function.

Animals↗
PubMed1991

Cyclic adenosine 3',5'-monophosphate-dependent phosphorylation of HMG 14 inhibits its interactions with nucleosomes.

The high mobility group protein HMG 14, which is preferentially associated with nucleosomes containing active gene sequences, is phosphorylated on different sites according to the tissue and stimulus being studied. In the thyroid, HMG 14 displays TSH-dependent phosphorylation that is mediated by cAMP-dependent protein kinase (A-kinase). We have, therefore, studied how phosphorylation of HMG 14 on its major and minor A-kinase sites (Ser-6 and -24) affects its interactions with nucleosomes and various forms of DNA, since this could reflect a means of regulating its function of binding to active chromatin. Approximately twice as much Ser-6 phospho- and 4 times as much Ser-6,24 diphospho-HMG 14 were required to produce the same degree of nucleosome band displacement as that caused by native unphosphorylated HMG 14. Phosphorylation also reduced the ability of HMG 14 to protect the ends of nucleosomal DNA from thermal denaturation. When the electrophoretic mobility of naked DNA was examined, the Ser-6 phospho-HMG 14 was about half as effective as native HMG 14 in retarding the various forms of double stranded DNA, and Ser-6,24 diphospho-HMG 14 was even less effective. Our data demonstrate that electrostatic interactions between DNA and basic amino acids in two highly conserved regions (residues 1-5 and 16-27) can be modulated by phosphorylation at Ser-6 and Ser-24. The ability of mammalian HMG 14, but not HMG 17, to display hormone-dependent phosphorylation may indicate a route for differentially modulating their binding to transcriptionally active chromatin.

Animals↗
PubMed1990

Epidermal growth factor inhibits radioiodine uptake but stimulates deoxyribonucleic acid synthesis in newborn rat thyroids grown in nude mice.

We have studied the effect of altering the level of circulating epidermal growth factor (EGF) on the function and growth of newborn rat thyroids transplanted into nude mice. Preliminary studies confirmed that sialoadenectomy reduced circulating EGF levels in nude mice (from 0.17 +/- 0.02 to 0.09 +/- 0.02 ng/ml), and that ip injection of 5 micrograms EGF raised EGF levels (the peak level of 91.7 +/- 3.3 ng/ml was achieved at 30 min, with a subsequent half-life of about 1 h). The radioiodine uptake by newborn rat thyroid transplants in the sialoadenectomized and sham-operated animals correlated inversely with the circulating EGF levels determined when the mice were killed (r = -0.99). Low-dose TSH treatment (0.1 microU/day) generally stimulated the radioiodine uptake, but high-dose TSH groups (100 microU/day) were not significantly different from the control group. The 5-day nuclear [3H]thymidine labeling index was 6.8 +/- 0.5% IN newborn rat thyroid transplants grown in sialoadenectomized animals, 13.1 +/- 0.3% in sham-operated animals, and 16.8 +/- 0.5% in nude mice receiving 5 micrograms EGF ip daily. In general, both low-dose and high-dose TSH promoted DNA synthesis under low EGF conditions but were ineffective in the presence of higher levels of EGF. Adult rat thyroid transplants showed no significant responses. Although sialoadenectomy may alter other factors besides EGF, it appears that changes in the levels of circulating EGF within the physiological range affect the function and growth of newborn rat thyroid transplants. Circulating EGF may play a role in thyroid maturation and may also be involved in the regulation of thyroid function throughout life.

Animals↗
PubMed1979

Early effects of thyrotropin on ribonucleic acid transcription in the thyroid.

Previous studies on the effects of TSH on the incorporation of labeled precursors into RNA have demonstrated an increase in the percentage of label in the phosphorylated nucleotide precursors of RNA. To avoid this nonspecific effect of TSH, we chose to measure RNA transcription in a system which uses exogenous phosphorylated precursors. Isolated nuclei were prepared from the thyroids of dogs which had been injected 90 min earlier with TSH. TSH caused a mean increase of 168% above control in total transcriptional activity, 193% in polymerase II-mediated (alpha-amanitin-sensitive) activity, and 155% in RNA polymerase I- and III-mediated (alpha-amanitin-resistant) activity. To determine whether part of this early effect of TSH was due to increased activity of RNA polymerase, incubations were also carried out in the presence of actinomycin D, which blocks transcription of endogenous template but does not inhibit transcription of added synthetic template poly deoxyadenylic-deoxythymidylic acid (dA.dT). Under these conditions, about half of the TSH-induced increase in the transcription of endogenous template could still be detected. Thus part of the early effects of TSH on RNA synthesis appears to be mediated through increased polymerase activity as well as enhanced template activity.

Amanitins↗
PubMed1979

Nitrogenous compounds reversibly inhibit the adenosine 3',5'-monophosphate response to thyrotropin: this effect is dissociated from altered guanine 3',5'-monophosphate levels.

Nitrogenous compounds were studied for their effect on cGMP levels in the thyroid. Several agents, including sodium nitrite and hydroxylamine, could generate a rise of over 100-fold in cGMP. At a concentration of 20 mM, HN2OH and NaNO2 significantly reduced cAMP levels previously generated by 0.5 mU/ml TSH. If the slices were rinsed and placed in new buffer without the latter nitrogenous compound, the cAMP response to TSH was restored even though intracellular cGMP levels remained elevated. Thus, the counterregulatory effect of these agents on cAMP levels is not correlated with the presence of high levels of cGMP per se. Both the rise in cGMP and the fall in cAMP could still be detected when Ca++ was deleted from the incubation medium, in contrast to other reported stimuli that elevate cGMP levels in the thyroid.

Animals↗
PubMed1978

Time course of thyrotropin-dependent protein phosphorylation in thyroid slices.

The time course of TSH-dependent protein phosphorylation was studied in calf thyroid slices labeled in vitro with 32Pi. Several of the proteins identified by two-dimensional electrophoresis displayed striking increases in 32P labeling in the presence of TSH. Phosphorylation of histones H3 and H1 (two subgroups) was enhanced about 3.7-and 10-fold, respectively, after incubation with TSH (15 mu/ml) for 70 min. Histone phosphorylation showed a lag after exposure to TSH; a major increase occurred only after 30-min incubation but then increased progressively up to 2 h. The lag in histone phosphorylation was also observed with slices prelabeled with 32P before the addition of TSH. In contrast, phosphorylation of a minor basic protein, A5 was also increased by 15 mU/ml TSH but displayed different kinetics, increasing substantially at 10 min. This time course correlates well with the rise in intracellular cAMP levels and protein kinase activity in thyroid slices after TSH.

Animals↗
PubMed1977

Effect of increased iodide intake on thyroid function in subjects on chronic lithium therapy.

Thyroid function tests were obtained in 10 patients on chronic lithium therapy before and after the administration of potassium iodide 250 mg q.i.d. Mean serum TSH rose by 8.9 muU/ml and mean serum T3 rose from 70 to 101 ng/dl. Two patients became hypothyroid; a third showed a rise in TSH without any change in T3 or T4. A fourth patient developed hyperthyroidism probably secondary to the Jod-Basedow phenomenon. Pharmacologic doses of iodine should be administered with caution to patients on chronic lithium therapy.

Adult↗
PubMed1976

Effect of caloric restriction and dietary composition of serum T3 and reverse T3 in man.

To evaluate the effect of caloric restriction and dietary composition on circulating T3 and rT3 obese subjects were studied after 7-18 days of total fasting and while on randomized hypocaloric diets (800 kcal) in which carbohydrate content was varied to provide from 0 to 100% calories. As anticipated, total fasting resulted in a 53% reduction in serum T3 in association with reciprocal 58% increase in rT3. Subjects receiving the no-carbohydrate hypocaloric diets for two weeks demonstrated a similar 47% decline in serum T3 but there was no significant change in rT3 with time. In contrast, the same subjects receiving isocaloric diets containing at least 50 g of carbohydrate showed no significant changes in either T3 or rT3 concentration. The decline in serum T3 during the no-carbohydrate diet correlated significantly with blood glucose and ketones but there was no correlation with insulin or glucagon. We conclude that dietary carbohydrate is an important regulatory factor in T3 production in man. In contrast, rT3 concentration is not significantly affected by changes in dietary carbohydrate. Our data suggest that the rise in serum rT3 during starvation may be related to more severe caloric restriction than that caused by the 800 kcal diet.

Adult↗
PubMed1976

The effect of aspirin and indomethacin on the TRH response in man.

A double-blind study of the effect of two inhibitors of prostaglandin synthesis on the TRH stimulation of serum TSH and prolactin was carried out in 35 normal males. The subjects were evaluated before and after the administration of indomethacin or aspirin for one week. Both indomethacin and aspirin lowered plasma prostaglandin E and F levels significantly. Indomethacin treatment had no effect on the serum TSH or prolactin response to 100 mug TRH or the serum T3 and T4 levels. In contrast, aspirin treatment significantly decreased the serum TSH response to TRH and significantly lowered mean total serum T3 (RIA) and T4 (D). There was no effect on the prolactin response to TRH. These findings suggest that aspirin blocks TRH responsiveness by a mechanism other than the inhibition of prostaglandin synthesis, probably by its previously demonstrated effect on increasing the fraction of unbound thyroid hormone.

Adolescent↗
PubMed1975

Effect of PGE1 and TSH on cAMP-dependent protein kinase activity in the thyroid.

PGE1, like TSH, can increase cAMP-dependent protein kinase activity in calf thyroid slices. The intracellular levels of cAMP produced by either of these agents alone appeared to correlate well with the degree of kinase activation. PG synthesis did not appear to be necessary for TSH action in this system, since indomethacin, and inhibitor of prostaglandin synthesis, did not alter either cAMP levels or kinase activity in slices incubated with TSH. Both the cAMP level and kinase activity rose when a submaximally effective dose of TSH was added to a maximal dose of PGE1. However, neither the cAMP levels nor the kinase activity produced by a maximal dose of TSH was affected by the addition of PGE1.

Animals↗
PubMed1975

Dopamine infusion acutely inhibits the TSH and prolactin response to TRH.

Ten normal males were given 100 mug TRH, and blood samples obtained for serum TSH and serum prolactin. After a period of at least one week, the TRH test was repeated while the patients were receiving a dopamine infusion. Both the TSH and prolactin response to TRH were inhibited by dopamine. Dopaminergic neurons may act through the pituitary-portal system to play a role in the regulation of TSH and prolactin secretion.

Adult↗