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Biomedical subjects

G C Ness

Publications and source records attributed to G C Ness.

82 records · Page 5Linked to original sources
PubMed1973

Stimulation of hepatic beta-hydroxy-beta-methylglutaryl coenzyme A reductase activity in hypophysectomized rats by L-triiodothyronine.

Diurnally varying activity of hepatic beta-hydroxy-beta-methylglutaryl coenzyme A reductase (EC 1.1.1.34) was decreased to very low levels in hypophysectomized rats with no discernable diurnal rhythm retained. Administration of triiodothyronine (100 mug/100 g of body weight) produced a supranormal level of reductase activity, about 3-4 times the highest activity found in normal rats. Reductase activity began to rise about 30 hr after hormone administration, maintained a constant high level from 48 to 72 hr, and declined to the control level by 96 hr. The supranormal response was elicited equally well either during the day or at night. When normal animals received triiodothyronine, reductase activity was increased only to a level comparable to the highest level found in normal rats. Administration of hydrocortisone markedly inhibited the triiodothyronine-induced increase in reductase activity. This finding suggests that glucocorticoids might act to suppress and thus account for the smaller increase in reductase activity observed in normal rats given triiodothyronine. When actinomycin D was given before the triiodothyronine-induced rise in reductase activity, the increase was effectively blocked, indicating that the hormonal effect requires new RNA synthesis.

Alcohol Oxidoreductases↗
PubMed1973

Occurrence of the enzymes effecting the conversion of acetyl CoA to squalene in homogenates of hog aorta.

Homogenates and subcellular fractions of the intimamedia of hog aorta have been prepared and examined for the presence of the enzymes catalyzing the conversion of acetyl CoA to squalene. Enzyme activities effecting the conversion of acetyl CoA to 3-hydroxy-3-methylglutarate (HMG); HMG CoA to mevalonic acid; mevalonic acid to 5-phosphomevalonic acid, 5-pyrophosphomevalonic acid, and isopentenyl pyrophosphate; isopentenyl pyrophosphate to farnesyl pyrophosphate; and farnesyl pyrophosphate to squalene have been demonstrated in these homogenates. The overall conversion of mevalonate to squalene has also been demonstrated with recombined fractions of hog aorta homogenates. Data are also presented that suggest that phosphatases present in the crude homogenates act to cleave farnesyl pyrophosphate to farnesol, and phospho- and pyrophosphomevalonate to mevalonate.

Acetyl Coenzyme A↗
PubMedDate not supplied

Developmental expression of multiple forms of 3-hydroxy-3-methylglutaryl coenzyme A reductase mRNA in rat testes.

The developmental expression of 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase, the enzyme that catalyzes the rate-limiting reaction of mevalonate formation, was investigated in rat testes. Adult testes were found to contain three distinct forms of HMG-CoA reductase mRNA of 4.8, 4.2, and 4.0 kilobases (kb) in length. In testes from 26-day-old rats the 4.8-kb species was the major form present. By 40 days of age, large increases in the levels of the testes-specific 4.2- and 4.0-kb forms occurred, with a small decrease in the amount of the 4.8-kb form. The level of the 4.8-kb form appeared to be associated with the level of testicular HMG-CoA reductase activity.

Animals↗
PubMedDate not supplied

Pituitary regulation of the expression of the farnesyl pyrophosphate synthetase gene in the testes of the sexually maturing rat.

While investigating the coordinate regulation of 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase and farnesyl pyrophosphate synthetase, the authors observed that rat testes contained high levels of a farnesyl pyrophosphate synthetase mRNA that was larger than that found in most other tissues. This mRNA contains upstream AUG codons that may alter its rate of translation. The developmental and hormonal regulation of this testicular mRNA were investigated. Testicular levels of farnesyl pyrophosphate synthetase mRNA increased in rats between 30 and 40 days of age and remained elevated. Significant increases in serum testosterone concentrations and secondary sexual organ weights first occurred at 50 days of age. Hypophysectomy resulted in nearly undetectable levels of testicular farnesyl pyrophosphate synthetase mRNA. Treatment of hypophysectomized rats with gonadotropins increased the levels of this mRNA toward normal. These data indicate that an increase in farnesyl pyrophosphate synthetase mRNA takes place in testes just before the onset of puberty. This may be induced by the peripubertal rise in follicle-stimulating hormone.

Animals↗