Riboflavin metabolism in diabetes mellitus]

Riboflavin excretion with urine in children suffering from diabetes mellitus is found to be significantly higher in comparison with healthy adults, the riboflavin content in the serum being normal. The total riboflavin concentration in erythrocytes is substantially lower and administration of daily-required riboflavin doses does not increase this parameter. FAD-dependent glutathione reductase in erythrocyte hemolysates is approximately 1.5 times higher than that of healthy children and does not depend on the additional intake of polyvitamins. The seeming affinity of the enzyme with exogenous FAD in sick children is almost 40 times lower in comparison with this value in healthy children, that is why the FAD-effect value in diabetes mellitus children does not exceed 1.2. Peculiarities of the riboflavin metabolism at diabetes mellitus and possibility to use the investigated parameters as criteria of vitamin B2 supply are discussed.     

Glucose metabolism in insulin administered euthyroid, hypothyroid and hyperthyroid rats

Glucose metabolism was studied as evidenced by the sugar and pyruvic acid levels in blood and glycogen and pyruvic acid content of tissues in euthyroid, hypothyroid and hyperthyroid rats by giving insulin. Results show that in a normal thyroxine-excess insulin state, the rise in blood sugar was less, glycogenesis was much enhanced and glycolysis was reduced in comparison to these data in the euthyroid state. When tyroxine deficiency was associated with excess insulin, glycogenesis was enhanced further and an almost complete inhibition of glycolysis was observed. In excess thyroxine-excess insulin state glycogenesis was increased at the expense of glycolysis in comparison to the finding in the hyperthyroid state. Thus exogenous insulin in the euthyroid state altered the pattern of carbohydrate metabolism enhancing glycogenesis and inhibiting glycolysis. In a low thyroxine-excess insulin state, further enhancement of glycogenesis and inhibition of glycolysis were observed. But in an excess thyroxine-excess insulin state, the higher thyroxine activity was somewhat neutralized by higher insulin action allowing glycogenesis with glucose to proceed to some extent.     

Riboflavin analogs utilized for metabolism by a Lactobacillus casei mutant

Several new halogen-containing riboflavin analogs that are antagonists for the stock strain of Lactobacillus casei have been found to be utilized by a mutant strain of the microorganism for growth and acid production. Riboflavin analogs consisting of all combinations of a single aliphatic group (methyl or ethyl) and a single halogen group (chloro or bromo) in positions 7 and 8 of the isoalloxazine nucleus possess this property. The analog devoid of substituents in positions 7 and 8 and the analog possessing a methyl group in position 7 and a cysteinyl group in position 8, were inert for both strains of the microorganism.     

Maintenance of brain thyroid hormone level during peripheral hypothyroid condition in adult rat

Thyroid hormones are essential for normal functioning of adult mammalian brain. The present investigation deals with the understanding of the time course of thyroid hormone homeostasis in adult rat brain. Animals were rendered hypothyroid by PTU injections (2 mg/100 g bw) for 30 consecutive days. Serum and synaptosomal T3/T4 content, synaptosomal AChE and Na+-K+-ATPase activities were determined on alternate days. While serum T4 level initially increased on the second day compared to control, serum T3 declined in a triphasic pattern; the first phase lasting from the second day to the 6th day, the second phase ended on the 14th day and last phase continued till the 30th day. Cerebro-cortical synaptosomal T3 level increased on the 2nd day from the control, attained a peak on the 4th day, remained stable until the 18th day, and abruptly declined on the 20th day. Synaptosomal T4 content remained negligible or undetected throughout. Synaptosomal membrane Na+-K+-ATPase and AChE activity exhibited an inverse relationship during the experimental regime, being much more prominent on the 2nd, 18th and 20th day coinciding with the variations in brain T3 level. Thus, the study identifies the onset of central homeostasis between the first and second day, its continuation for about 16-18 days and its termination between the 18th and 20th day.     

Immunocytochemical location of thyrotropin-releasing hormone (TRH) in the B-cells of adult hypothyroid rat pancreas

Thyrotropin-releasing hormone (TRH) is present in small quantities in the rat adult pancreas. As hypothyroidism increases dramatically the pancreatic content of this peptide, this model was used to localize TRH in the gland by immunocytochemistry. Immunocytochemical staining of semithin (0.5–1.0 μm) and thin (golden) sections was performed as well as antibody and method controls to check the specificity of the immunoperoxidase staining. At the light microscope level, a very faint TRH-like immunoreactivity was apparent in the pancreas of normal untreated animals. In hypothyroid rats, a strong TRH immunostaining was observed in the central portion of the islets of Langerhans. On the contrary, in previously hypothyroid rats made euthyroid, no TRH-like immunoreactivity was found. Serial sections alternately labelled with TRH and insulin antisera revealed the simultaneous occurrence of both immunoreactivities. In addition, the TRH immunoreactive cells were distinct from glucagon- or somatostatin-containing cells. At the electron microscope level, immunoreactive TRH was found over the secretory granules of insulin-containing cells. Hypothyroid animals offer therefore a suitable model for the study of TRH in the pancreas.     

Brain metabolism in adult chronic hydrocephalus

Normal pressure hydrocephalus (NPH) is the most frequent form of chronic hydrocephalus in adults. NPH remains underdiagnosed although between 5% and 10% of all demented patients may suffer from this disorder. As dementia is an increasing demographic problem, treatable forms such as in NPH have become a central issue in neurology. Despite the traditional perception of hydrocephalus being a disorder of disturbed CSF dynamics, in NPH metabolic impairment seems at least as important. So far, the only valid animal model of NPH is chronic adult kaolin hydrocephalus. In this model, opening of alternative CSF outflow pathways leads to normal or near-normal intracranial pressure and CSF outflow resistance. Yet, various metabolic disturbances cause ongoing ventricular enlargement and characteristic symptoms including cognitive decline and gait ataxia. Delayed hippocampal neuronal death, accumulation of beta-amyloid and disturbed cholinergic neurotransmission may contribute to memory dysfunction. Compromised periventricular blood flow, decreased dopamine levels in the substantia nigra and damaged striatal GABAergic interneurons may reflect basal ganglia symptoms. At least in human hydrocephalus cerebrovascular co-morbidity of the white matter plays an important role as well. It seems that in hydrocephalus from a certain 'point of no return' metabolic impairment becomes decoupled from CSF dynamics and, at least partly, self-sustained. This is probably the reason why despite restored CSF circulation by shunting many patients with chronic hydrocephalus still suffer from severe neurological deficits. The present paper offers a comprehensive review of the experimental and clinical data suggesting metabolic disturbances in chronic hydrocephalus.     

Arachidonic acid metabolism by adult human osteoblast-like cells exhibits sexually dimorphic characteristics

The eicosanoids, including prostaglandin E₂ (PGE₂) and other bioactive arachidonic acid metabolites, are important local mediators of bone remodeling. Presumably, the limited or excessive synthesis of the eicosanoids could compromise bone homeostasis. We have noted that the stimulated release of arachidonic acid by adult male donor derived human osteoblast-like (hOB) cells exceeded the stimulated release measured for female-derived hOB cells by 1.5-fold. Assays of PGE₂ biosynthesis by cytokine-stimulated hOB cells also demonstrated a sex-linked difference, such that male hOB cell PGE₂ production exceeded female cell production by 1.6–2.2-fold. The calcium-dependent cytoplasmic phospholipase A₂ activity in subcellular fractions prepared from hOB cell homogenates was higher in both the cytosolic (1.6-fold) and particulate (1.5-fold) fractions from the male cells than in those prepared from female hOB cells, suggesting a molecular basis for the observed sexually dimorphic characteristics related to arachidonic acid metabolism by hOB cells. The relatively limited capacity of the female cells may limit needed intracellular and intercellular signaling during bone remodeling, thereby contributing to the development of bone pathology. J. Cell. Biochem. 71:74–81, 1998. © 1998 Wiley-Liss, Inc.     

Lipid and carbohydrate metabolism in euthyroid and hypothyroid chick embryo (Gallus domesticus).

1. The effect of propylthiouracil (PTU)-induced hypothyroidism on carbohydrate and lipid metabolism was studied in the chick embryo. 2. A single dose of PTU (250 micrograms/embryo) was administered on day 11 and embryos sacrificed on day 20 of incubation. 3. Thyroid glands were significantly enlarged (6 fold) by PTU administration. 4. Increased thyroid weight was associated with growth retardation and decreased plasma thyroxine levels. 5. Plasma glucose level was lower and phospholipids were significantly higher in the hypothyroid embryo. 6. Liver lipid concentrations in the control and hypothyroid embryos were not different but were significantly higher in both groups when compared to previously reported values in the young chick. 7. In contrast to PTU treatment after hatching, liver glycogen levels were not increased in the hypothyroid chick embryo. This was attributed to the high lipid nutrient condition of the chick embryo since a high lipid diet in the young chick decreased hepatic glycogen accumulation significantly.     

Characteristics of infertility and the improvement of fertility by thyroxine treatment in adult male hypothyroid rdw rats

We previously reported that rdw rats were infertile in both sexes. The present study was conducted to determine whether hypothyroidism in adult male rdw rats induced infertility by impairing sexual behavior or testicular function, whether the infertility could be reversed by thyroxine (T(4)) treatment, and whether the mutant could be produced by infertile rdw rats via in vitro fertilization. The sexual behavior was analyzed by pairing with normal female rats. The fertility of epididymal sperm was determined by in vitro fertilization. The results indicated that the infertility resulted from both defective sexual behavior and testicular function. No untreated rdw rats mated. The weights of epididymides were significantly low, whereas those of testes were not different from those of untreated normal rats. Epididymal sperm with cytoplasmic droplets were observed at a significantly high frequency. No fertilization was detected either in vivo or in vitro. Thyroxine treatment markedly increased serum T(4) levels and the weights of both epididymides and testes. Partial reversion of the impaired sexual behavior was observed, and the percentage of epididymal sperm with cytoplasmic droplets was markedly decreased after T(4) treatment. Fertility of epididymal sperm was completely reversed when determined both in vivo and in vitro, and homozygous embryos developed to term after transfer without loss of viability.     

Lysophosphatidylcholine uptake and metabolism in the adult rabbit lung

Tracer quantities of 3H-labeled lysoPC and 32P-labeled natural rabbit surfactant were given intratracheally via a bronchoscope and [14C]palmitate was given intravenously to 25 rabbits with labeled PC and lysoPC measured in the alveolar wash, lung homogenate, lamellar bodies and microsomes at five times from 10 min to 6 h after tracheal injection. Surprisingly, only 31% of the administered lysoPC remained in its original form in the total lungs (alveolar wash + lung homogenate) by 10 min, of which 77% was in the alveolar wash. Meanwhile, by 10 min an additional 37% was already converted to PC, of which more than 98% was in the lung homogenate. LysoPC continued to be rapidly and efficiently converted to PC, with 62% conversion measured at 3 h. The converted lysoPC initially appeared with high specific activity in microsomes, then in lamellar bodies, and finally in the alveolar wash. The intravascular palmitate labeled lung PC had similar specific activity-time profiles in the subcellular fractions, while intratracheally administered natural rabbit surfactant had a constantly low specific activity in microsomes and much higher specific activities in lamellar bodies and alveolar wash. Another 25 rabbits received intratracheal lysoPC labeled in both the choline and palmitate moieties and then were studied from 1 to 24 h after tracheal injection. The ratio of the palmitate to choline labels indicated uptake and conversion to PC primarily by direct acylation rather than transacylation and by intact reuptake and conversion rather than breakdown and resynthesis. LysoPC is an attractive 'metabolic probe' of surfactant metabolism which undergoes very rapid and efficient intracellular conversion to PC via a subcellular pathway that parallels the remodeling and de novo synthetic pathways.     

Thyroid hormone induces sprouting angiogenesis in adult heart of hypothyroid mice through the PDGF‐Akt pathway

Study of physiological angiogenesis and associated signalling mechanisms in adult heart has been limited by the lack of a robust animal model. We investigated thyroid hormone‐induced sprouting angiogenesis and the underlying mechanism. Hypothyroidism was induced in C57BL/6J mice by feeding with propylthiouracil (PTU). One year of PTU treatment induced heart failure. Both 12 weeks‐ (young) and 1 year‐PTU (middle age) treatment caused a remarkable capillary rarefaction observed in capillary density. Three‐day Triiodothyronine (T3) treatment significantly induced cardiac capillary growth in hypothyroid mice. In cultured left ventricle (LV) tissues from PTU‐treated mice, T3 also induced robust sprouting angiogenesis where pericyte‐wrapped endothelial cells formed tubes. The in vitro T3 angiogenic response was similar in mice pre‐treated with PTU for periods ranging from 1.5 to 12 months. Besides bFGF and VEGF₁₆₄, PDGF‐BB was the most robust angiogenic growth factor, which stimulated notable sprouting angiogenesis in cultured hypothyroid LV tissues with increasing potency, but had little effect on tissues from euthyroid mice. T3 treatment significantly increased PDGF receptor beta (PDGFR‐β) protein levels in hypothyroid heart. PDGFR inhibitors blocked the action of T3 both on sprouting angiogenesis in cultured LV tissue and on capillary growth in vivo. In addition, activation of Akt signalling mediated in T3‐induced angiogenesis was blocked by PDGFR inhibitor and neutralizing antibody. Our results suggest that hypothyroidism leads to cardiac microvascular impairment and rarefaction with increased sensitivity to angiogenic growth factors. T3‐induced cardiac sprouting angiogenesis in adult hypothyroid mice was associated with PDGF‐BB, PDGFR‐β and downstream activation of Akt.