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C N Mariash

Publications and source records attributed to C N Mariash.

At least 73 records · Page 4Linked to original sources
PubMed1984

Hepatic messenger ribonucleic acid activity profiles in experimental azotemia in the rat. Relationship to food intake and thyroid function.

We have studied the hepatic messenger RNA (mRNA) activity profile in chronically azotemic rats and sought to determine whether the observed changes could be mediated either by reduced food intake or diminished thyroid function at the tissue level. mRNA activity profiles were produced by two-dimensional gel electrophoretic separation of radioactively labeled products of an in vitro reticulocyte lysate system which had been programmed by hepatic RNA. Of the approximately 240 translational products identified in this system, seven sequences were consistently altered in azotemia. In pair-fed animals six of these also decreased, but the alterations in three were depressed to a significantly lesser extent in the pair-fed group. Moreover, analysis of covariance suggested that food intake could account for the differences in only one sequence. The possibility that the mRNA activity profile in azotemia could represent the effects of diminished thyroid function was minimized by the finding that the reductions in plasma thyroxine (T4) and triiodothyronine (T3) levels observed were due largely to reduced plasma protein binding, with maintenance of the mean free T4 and free T3 concentrations within the normal range. The changes in only one mRNA sequence could be related to free T3 levels alone. Our findings, therefore, indicate that although diminished food intake and reduced thyroid function may contribute to some of the observed changes in the mRNA activity profiles, the bulk of alterations in azotemia appear to be mediated by other mechanisms. The striking overlap between the sequences affected by azotemia and pair-feeding raises the speculation that altered gene expression in azotemia may reflect an impaired hepatic response at the pretranslational level to metabolic signals associated with food intake.

Animals↗
PubMed1983

Growth hormone acts at a pretranslational level in hepatocyte cultures.

We have examined the effects of ovine growth hormone and recombinant DNA synthesized human growth hormone on hepatocytes maintained in serum free cultures. Both growth hormone preparations augmented or attenuated 3 specific mRNA sequences as revealed by two-dimensional gel electrophoresis of [35S] methionine labeled products synthesized in vitro in an mRNA dependent rabbit reticulocyte lysate system. The results clearly indicate that growth hormone, free of potential pituitary contaminants, acts directly on hepatocytes at a pretranslational level.

Animals↗
PubMed1983

Starvation and hypothyroidism exert an overlapping influence on rat hepatic messenger RNA activity profiles.

To assess the effect of starvation and to explore the potential interrelationship of starvation and thyroid status at the pretranslational level, we have analyzed by two-dimensional gel electrophoresis, the hepatic translational products of starved and fed euthyroid and hypothyroid rats. 5 d of starvation resulted in a statistically significant change in 27 of 240 products visualized, whereas hypothyroidism caused a change in 20, both in comparison with the fed euthyroid state. Of considerable interest was that 68% of all changing messenger (m)RNA sequences were common to the hypothyroid and starved groups and showed the same directional shift. Further, both starvation and hypothyroidism yielded comparable decreases in total hepatic cytoplasmic RNA content. Although it has been well established that the level of circulating triiodothyronine (T3) and the level of hepatic nuclear receptors fall in starvation, this reduction cannot account for the observed decrease of total hepatic RNA nor for all of the alterations in the concentrations of specific mRNA sequences. Thus, administration of T3 to starved animals in a dose designed to occupy all nuclear T3 receptors fails to prevent the fall in total RNA and the majority of starvation-induced changes in the level of mRNA sequences. Moreover, starvation of athyreotic animals results in a further decrease in total RNA and in a further change in the level of individual mRNA species. We conclude, therefore, that although the reduced levels of circulating T3 and the nuclear T3 receptors can contribute to the observed results of starvation, the starvation-induced changes are not exclusively mediated by this factor. The striking overlap in the genomic response between hypothyroid and starved animals raises the possibility that those biochemical mechanisms regulated at a pretranslational level by T3 are either not helpful or injurious to the starving animal. The reduction in circulating T3 and nuclear receptor sites together with T3-independent mechanisms initiated in the starved animal may constitute redundant processes designed to conserve energy and substrate in the nutritionally deprived organism.

Animals↗
PubMed1983

Effects of triiodothyronine and glucose on cultured rat hepatocyte gene expression.

Both thyroid hormone and carbohydrate feeding are known to influence hepatic gene expression in vivo. In order to determine whether these compounds act directly on the liver, we have utilized an isolated adult rat hepatocyte culture to examine the in vitro influence of either T3 or glucose on a wide range of mRNA activities. RNA was extracted from hepatocyte cultures, translated in the rabbit reticulocyte system, and the translated products separated by two-dimensional gel electrophoresis. We have found a strong similarity between the hepatic mRNA response to T3 administered either to the animal or added to the culture medium and between the response to high carbohydrate feeding and an increase in the medium glucose concentration. Our studies suggest that the isolated hepatocyte culture is a useful model for the study of the influence of hormones and metabolites on the expression of specific mRNA's.

Animals↗
PubMed1982

Paradoxical effects of cycloheximide on the ultra-rapid induction of two hepatic mRNA sequences by triiodothyronine (T3).

Triiodothyronine (T3) rapidly induces the accumulation of two hepatic mRNA sequences (spot 14 and spot CyT) in thyroidectomized rats as revealed by two-dimensional gel electrophoresis of in vitro translated products of isolated poly(A) containing RNA. T3 acting alone induced a 29-fold increase of spot 14 within 4 h, an increase which was completely inhibited by the concomitant administration of cycloheximide. On the other hand, CyT could be detected only after the administration of cycloheximide, and the combined action of cycloheximide and T3 resulted in a 4-fold increase in CyT 4 h after administration of both agents. These observations suggested that the early cellular action of T3 is contingent on the participation of rapidly turning over protein and mRNA.

Animals↗
PubMed1982

Thyroid hormone-carbohydrate interaction at the hepatic nuclear level.

We have studied the interaction between triiodothyronine (T3) and carbohydrate (CHO) in the induction of hepatic lipogenic enzymes under both in vivo and in vitro conditions. Our studies demonstrate a synergistic relationship between T3 administration and CHO feeding in the induction of these enzymes. Likewise, in states characterized by CHO deprivation such as starvation and diabetes, the response to T3 is also inhibited. Studies in the aging animal have documented a diminished response both to CHO and to T3. Our studies suggest that T3 multiplies a primary CHO-generated signal by a constant factor, and that this signal declines with age. Additional studies with primary hepatocyte cultures provide evidence that glucose is the main factor responsible for the induction of hepatic malate dehydrogenase: decarboxylating (EC 1.1.1.40) (ME). Glucose induces ME in the absence of changes in extrahepatic hormones or metabolites and in the complete absence of T3. In the cultured hepatocyte system, T3 also acts as a constant multiplier of the primary glucose-derived signal. Our results provide further support for the thesis that the primary action of T3 at the molecular level is a multiplication of other nuclear signals. The complexity of response pattern to both T3 and CHO administration, however, is illustrated by recent studies in which we have analyzed the translated products of total poly(A+) RNA extracted from livers of rats subjected to various physiological stimuli.

Aging↗
PubMed1982

Resistance to thyroid hormones. A disorder frequently confused with Graves' disease.

Five patients from two unrelated families were found to have goiter and elevated serum concentrations of thyroxine (T4) and triiodothyronine (T3) without symptoms or signs of hyperthyroidism. All had measurable concentrations of thyroid stimulating hormone (TSH), and in four who were tested, there was an increase in TSH concentration following thyrotropin releasing hormone (TRH) administration. We believe these five patients have general resistance to the effects of thyroid hormones and need elevated concentrations of T4 and T3 to maintain a eumetabolic state. Study of nuclear T3 receptors from cultured fibroblasts of one patient disclosed a normal equilibrium association constant and a maximal binding capacity that was greater than normal control values. These findings suggest that thyroid hormone resistance in this patient is not due to a decrease in either the affinity or the number of specific nuclear T3 receptors. This disorder can easily be confused with Graves' disease and result in inappropriate treatment for hyperthyroidism, as was the case in three of our patients.

Adult↗
PubMed1981

Thyroid hormone-carbohydrate interaction in the rat: correlation between age-related reductions in the inducibility of hepatic malic enzyme by triiodo-L-thyronine and a high carbohydrate, fat-free diet.

Previous studies from this laboratory have demonstrated an age-related decrease in hepatic malic enzyme (ME) levels and in the response of ME to triiodo-l-thyronine (T(3)). Moreover, we have recently shown a synergistic interaction of T(3) and a high carbohydrate diet in the induction of this enzyme. Studies were therefore undertaken to assess the response of aging rats to a high carbohydrate diet and to test the effect of such dietary manipulations on the responsiveness of ME to T(3). For this purpose, a new radio-immunoassay for ME was developed that, because of a 10-fold higher sensitivity, was particularly suited to the measurement of the low concentrations of hepatic enzyme in older animals. The level of ME per milligram of DNA fell approximately 70% between 1 and 6 mo with only minor further changes demonstrated between 6 and 18 mo. In contrast, the level of ME per milligram DNA in brain was slightly increased in the older animals. Although the absolute increment of hepatic ME resulting from seven daily injections of T(3) (15 mug/100 g body wt) fell with age, the ratio of the ME content per milligram DNA to that observed in control animals maintained on a regular chow diet remained relatively constant with an average value of 11.1. The responsivity of hepatic ME to a high carbohydrate, fat-free diet also decreased with age and could not be attributed exclusively to a reduction in food consumption. The age-related reduction in ME responsivity to dietary stimuli appeared to be due to a reduction in the formation of the specific messenger, (m)RNA for ME as determined in an in vitro translational assay. Our data are consistent with the following hypothesis. There is an age-related decreased hepatic responsivity to a high carbohydrate dietary stimulus. Thyroid hormone administration, as previously postulated by us, interacts with a product or an intermediate of carbohydrate metabolism in a multiplicative fashion. As a consequence, the absolute increment of ME induced by T(3) administration also declines with age.

Aging↗