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Biomedical subjects

C H Hollenberg

Publications and source records attributed to C H Hollenberg.

50 records · Page 3Linked to original sources
PubMed1969

Regulation of DNA synthesis in fat cells and stromal elements from rat adipose tissue.

The incorporation of tritiated thymidine into the deoxyribonucleic acid (DNA) of adipose fat and stromal cells was followed under a variety of conditions. After in vitro incubation of adipose slices or up to 2 days after in vivo injection of the isotope, all DNA radioactivity was in the stromal cell fraction. From 2 to 15 days after thymidine injection total tissue DNA radioactivity was constant, while between 2 and 5 days after injection label in fat cell DNA increased markedly. Thus new labeled fat cells, initially collected in the stromal pool, required 2-5 days after completion of DNA synthesis to accumulate sufficient lipid to be harvested in the fat cell fraction. Fasting before thymidine injection practically abolished DNA synthesis in primordial fat cells and reduced less drastically formation of stromal elements. However fasting sufficient to deplete lipid stores by 50% neither destroyed mature fat cells nor impaired their capacity to reaccumulate fat with refeeding. Other studies evaluated the role of new fat cell formation in the process of lipid accretion accompanying refeeding. These experiments indicated that at least during the early phase of rapid weight gain, accumulation of fat was due to deposition of triglyceride in existing cells rather than to accelerated formation of new fat cells. Studies with hypophysectomized rats demonstrated that pituitary ablation variably affected stromal DNA synthesis and nearly abolished the formation and (or) maturation of primordial fat cells. In these animals growth hormone markedly enhanced thymidine incorporation into stromal DNA but had no effect on fat cell precursors. In intact animals the predominant effect of growth hormone was also on the stromal fraction, although an action of the hormone of lesser magnitude on fat cell precursors was also evident.

Acetone↗
PubMed1969

The mechanism of heparin stimulation of rat adipocyte lipoprotein lipase.

Free fat cells and stromal-vascular cells were prepared from rat adipose tissue by incubation with collagenase. NH(4)OH-NH(4)Cl extracts of acetone-ether powders prepared from fat cells contained lipoprotein lipase activity but extracts of stromal-vascular cells did not. Intact fat cells released lipoprotein lipase activity into incubation medium, but intact stromal-vascular cells did not. The lipoprotein lipase activity of the medium was increased when fat cells were incubated with heparin, and this was accompanied by a corresponding decrease in the activity of subsequently prepared fat cell extracts. Heparin did not release lipoprotein lipase activity from stromal-vascular cells. The lipoprotein lipase activity of NH(4)OH-NH(4)Cl extracts of fat cell acetone powders is increased by the presence of heparin during the assay. This increase is not due to preservation of enzyme activity, but to increased binding of lipoprotein lipase to chylomicrons. Protamine sulfate and sodium chloride have little effect on the binding of lipoprotein lipase to chylomicrons, but they inhibit enzyme activity after binding to substrate has occurred. These inhibitors do, however, inhibit the stimulatory effect of heparin on enzyme-substrate binding.

Adipose Tissue↗
PubMed1967

Distribution of radioactive glycerol and fatty acids among adipose tissue triglycerides after administration of glucose-U-14C.

Adipose lipid obtained from fed rats 15 or 60 min after injection of radioactive glucose was separated into 10 triglyceride classes of differing fatty acid compositions. The distribution among these classes of total and radioactive triglyceride-glycerol was determined and found to be the same. Thus newly synthesized adipose triglycerides resemble in kind and proportion the triglycerides which exist in the tissue. This finding is in accord with the concept that the structures of adipose triglycerides are stable over long periods and that the turnover rate of the several triglyceride species are similar. After administration of radioactive glucose, the specific activity of saturated fatty acids was higher in the more saturated triglyceride species. These data indicate that newly formed saturated acids do not mix completely with all adipose tissue fatty acids available for esterification. Fatty acids derived from plasma triglyceride influenced the composition of newly synthesized adipose tissue triglyceride and thus constitute an important source of adipose tissue lipid.

Adipose Tissue↗
PubMed1966

Polycystic ovaries associated with congenital adrenal hyperplasia.

Polycystic ovaries were found in a 16-year-old female with congenital absence of vagina, male-like external genitalia, and congenital adrenal hyperplasia. Masculinization was sufficiently severe to cause the patient to be reared as a male. Biochemical studies of ovarian tissue revealed hyperactivity and an imbalance of enzyme systems concerned with steroid-hormone biosynthesis, which led to production of large amounts of androgens. The pathway towards estrogens was preserved but less efficient than normal. Urinary steroid metabolites before and after hysterectomy and bilateral salpingo-oophorectomy revealed an absence of Porter-Silber chromogens and tetrahydrocortisone. Excretion of aldosterone was normal and that of corticosterone slightly higher than normal. The patterns of urinary 17-ketosteroids, pregnanediol, pregnanetriol and pregnanetriolone were similar to those commonly seen in congenital adrenal hyperplasia with steroid 21-hydroxylase deficiency. Urinary estrogens after panhysterectomy were low, being in the post-menopausal range. The pathogenesis of polycystic ovaries and their possible contribution to masculinization are discussed.

Adolescent↗
PubMedDate not supplied

Effects of aging on ribosomal protein L7 messenger RNA levels in cultured rat preadipocytes.

Ribosomal protein L7 mRNA is a cell cycle-independent message whose levels are lower in late passage "senescent" fibroblasts than early passage cultures. To determine whether decreases in L7 mRNA levels also occur during aging in tissues in vivo and whether reduced L7 mRNA is caused by terminal differentiation, we measured L7 and adipsin (a differentiation-dependent serine protease) mRNA levels in undifferentiated and differentiated preadipocytes and glyceraldehyde-3-phosphate dehydrogenase mRNA in differentiated preadipocytes cultured from perirenal fat depots of 3-, 17-, and 24-month-old male rats. L7 mRNA levels decreased with increasing age and were not affected by differentiation. In the same cultures, adipsin mRNA levels did not increase with age but did increase with differentiation, confirming that the preadipocytes exposed to enriched medium had, in fact, differentiated. Glyceraldehyde-3-phosphate dehydrogenase mRNA levels did not change with age indicating that the decrease in L7 mRNA was not a result of a general decrease in mRNA with age. These observations are consistent with the hypotheses that decreasing L7 mRNA levels are associated with aging and that late passage fibroblasts have features in common with senescence. The observations are not consistent with the hypothesis that senescent changes in cellular function are caused by terminal differentiation.

Adipocytes↗
PubMedDate not supplied

Ageing, differentiation, and gene expression in rat epididymal preadipocytes.

Ageing results in decreased replicative potential of preadipocytes, as well as reduced capacities for the lipid accumulation and increases in lipogenic enzyme activities during differentiation of preadipocytes into fat cells. To determine whether decreased differentiation is associated with decreased levels of mRNA for differentiation-dependent genes and whether early as well as late components of the differentiation programme are affected by ageing, we measured beta-actin, alpha-tubulin, lipoprotein lipase, and glycerol-3-phosphate dehydrogenase mRNA levels in undifferentiated and differentiated epididymal preadipocytes from 3-, 17-, and 24-month-old Fischer 344 rats. During ageing, diminished differentiation-related changes occurred in mRNAs affected early (actin, tubulin), midway through (lipoprotein lipase), and late (glycerol-3-phosphate dehydrogenase) in the preadipocyte differentiation process. Hence, early as well as late phases of the differentiation programme were affected by ageing. The effects involved changes in gene transcription or mRNA processing. Our results were not consistent with the hypothesis that age-related decreases in replication are caused by an increased tendency for cell differentiation.

Actins↗