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Biomedical subjects

C A Conover

Publications and source records attributed to C A Conover.

98 records · Page 6Linked to original sources
PubMed1985

Somatomedin C-binding and action in fibroblasts from aged and progeric subjects.

Aging is associated with diminished cell growth, which has been ascribed in part to decreased cellular responsiveness to serum mitogens. To investigate whether there is an age-related loss of responsiveness to somatomedin-C (SM-C), we studied SM-C binding and action in early passage fibroblasts from normal donors, aged 7-96 yr, and one progeric subject. SM-C stimulated [3H]thymidine incorporation 4- to 16-fold in young cells, 4- to 17-fold in aged cells, and 4- to 11-fold in progeric cells. SM-C was synergistic with 0.25% human hypopituitary serum in stimulating [3H]thymidine incorporation in all cell lines. Dose-response curves for SM-C stimulation of thymidine incorporation were not significantly altered in aged or progeric cells. Half-maximal responses occurred at 5-15 ng/ml SM-C for all cell lines. [3H]Thymidine incorporation results were supported by cell replication studies. In addition, binding of [125I] SM-C was virtually identical in all cell lines, with 50% displacement at 2-5 ng/ml SM-C. Thus, in vivo aging does not appear to be associated with either an alteration in SM-C receptors or a diminished cellular responsiveness to SM-C's mitogenic effects.

Adolescent↗
PubMed1985

Aging alters somatomedin-C-dexamethasone synergism in the stimulation of deoxyribonucleic acid synthesis and replication of cultured human fibroblasts.

The effects of dexamethasone on somatomedin-C (SM-C) stimulation of [3H]thymidine incorporation and cell replication were studied in early passage fibroblasts from normal donors, aged 7-24 yr (young) and 85-96 yr (old), and one patient with progeria. Preincubation of cells from young donors with dexamethasone dramatically enhanced SM-C stimulation of [3H]thymidine incorporation [e.g. 19- vs. 3-fold in serum-free medium; 66- vs. 14-fold in 0.25% human hypopituitary serum (HHS)], with no alteration in the timing of peak thymidine incorporation. In contrast, preincubation of cells from old and progeric donors with dexamethasone resulted in a 6- to 12-hr lengthening of the prereplicative period and, generally, little or no synergism with SM-C. Cells from old and progeric donors had a normal replicative response to SM-C with or without 0.25% HHS. In cells from young donors, dexamethasone enhanced the SM-C-stimulated increase in cell number 32-49% in serum-free medium and 70-189% in 0.25% HHS. In comparison, dexamethasone had no potentiating effect on SM-C stimulation of multiplication of cells from old and progeric donors. These data indicate that dexamethasone and SM-C are synergistic in stimulating DNA synthesis and replication of fibroblasts from young donors, but that this synergism is impaired in cells from aged and progeric donors.

Adolescent↗
PubMed1984

Density-associated loss of functional receptors for somatomedin-C/insulinlike growth factor I (SM-C/IGF-I) on cultured human fibroblast monolayers.

The mitogenic activity of somatomedin-C/insulinlike growth factor-I (SM-C/IGF-I) appears to be greatly influenced by cell culture conditions, especially the presence of other growth factors and nutrients in the culture medium. To investigate the effect of cell density on SM-C/IGF-I activity, we have evaluated SM-C/IGF-I binding and stimulation of DNA synthesis and cell replication as a function of cell density in cultured human fibroblast monolayers. At fibroblast concentrations of 2.7 X 10(5) and 1.48 X 10(6) cells per 60-mm dish, specific binding of [125I]SM-C/IGF-I per 10(6) cells was 170% higher in sparse than dense monolayers (9.3% vs. 3.4%). Increased binding in sparse monolayers was attributable to approximately twice as many receptors in sparse as in dense cells (31,000 vs. 16,000 sites per cell), as well as to a modest increase in the affinity constant. Similarly, half-maximal stimulation of [methyl-3H]thymidine incorporation was achieved at SM-C/IGF-I concentrations of 2.5 ng/ml in sparse cells but required 20 ng/ml in dense cells. Although this required only 45% occupancy of membrane receptors on sparse cells, and almost 80% occupancy on dense cells, the total number of occupied receptors was similar in both sparse and dense cells (approximately 13,000 receptors/cell for half-maximal stimulation). The presence of increased numbers of "functional receptors" on sparse fibroblasts thus results in enhanced sensitivity to SM-C/IFG-I stimulation of DNA synthesis and cell replication. Progressive decreases in the number of functional receptors, secondary to cell crowding, may contribute to density-dependent inhibition of fibroblast growth.

Adult↗
PubMed1983

Insulin-like growth factor I/somatomedin-C (IGF-I/SM-C) and glucocorticoids synergistically regulate mitosis in competent human fibroblasts.

In serum-free medium, insulin-like growth factor-I/somatomedin-C (IGF-I/SM-C) was weakly mitogenic for adult human fibroblasts in culture. However, in the presence of 0.5% human hypopituitary serum (HHS), which by itself had little effect, there was a marked dose-dependent response to IGF-I/SM-C with a 10- to 20-fold increase in [3H]thymidine incorporation at 25 ng/ml IFG-I/SM-C. With the further addition of dexamethasone or hydrocortisone to the combination of IGF-I/SM-C + 0.5% HHS, there was a dramatic synergistic effect resulting in a 60- to 70-fold increase in [3H]thymidine incorporation. This stimulation was two times greater than that seen with 20% FCS. In contrast, glucocorticoids had no effect in serum-free medium or with HHS alone. These [3H]thymidine incorporation results were clearly supported by cell replication studies. Dose-response curves for 125I IGF-I/SM-C binding and IGF-I/SM-C stimulation of [3H]thymidine incorporation were similar with 1/2 maximal effects for both at 5 ng/ml. However, the striking synergism seen with glucocorticoids occurred in the absence of any glucocorticoid-induced change in IGF-I/SM-C binding, indicating that the interaction of IGF-I/SM-C and glucocorticoids occurs at a postreceptor level. These data demonstrate that in the presence of a low concentration of HHS, IGF-I/SM-C and glucocorticoids stimulate complete cell cycle traverse and replication of human fibroblasts.

Adult↗
PubMed1981

Regulation of ornithine decarboxylase in skeletal muscle: evidence for the involvement of an insulin-dependent serum factor.

Previous studies in vivo have shown that the activity of ornithine decarboxylase (ODC), the rate-controlling enzyme in polyamine biosynthesis, is markedly decreased in muscle of diabetic rats and is restored to normal by insulin therapy. Also, muscle ODC is diminished by starvation and increased by refeeding. To investigate the basis for these findings, the regulation of ODC was studied in vitro using rat soleus and extensor digitorum longus muscles. Incubation of muscles from fed rats in Krebs-Henseleit solution resulted in a 75% decrease in ODC activity within 1 h. Addition of insulin and amino acids had no effect; however, 50% rat serum increased ODC activity four- to seven-fold after the initial decrease. Rat serum also increased ODC in muscles from starved rats. The effect of serum was blocked by both cycloheximide and antinomycin D. Serum from diabetic rats was only 50% as effective as serum from normal rats in increasing ODC activity. Addition of physiologic levels of insulin to diabetic serum had no effect; however, treatment of diabetic rats with insulin in vivo restored serum activity to normal. These findings suggest that insulin modulates the synthesis of ODC via production of a second circulating factor, the activity of which is diminished in serum of diabetic rats. They also suggest that the stimulation of polyamine biosynthesis by this factor may be an integral component of the growth-promoting effect of insulin on muscle in vivo.

Animals↗
PubMed1980

Ornithine decarboxylase activity in insulin-deficient states.

The activity of ornithine decarboxylase, the rate-controlling enzyme in polyamine biosynthesis, was determined in tissues of normal control rats and rats made diabetic with streptozotocin. In untreated diabetic rats fed ad libitum, ornithine decarboxylase activity was markedly diminished in liver, skeletal muscle, heart and thymus. Ornithine decarboxylase was not diminished in a comparable group of diabetic rats maintained on insulin. Starvation for 48h decreased ornithine decarboxylase activity to very low values in tissues of both normal and diabetic rats. In the normal group, refeeding caused a biphasic increase in liver ornithine decarboxylase; there was a 20-fold increase in activity at 3h followed by a decrease in activity, and a second peak between 9 and 24h. Increases in ornithine decarboxylase in skeletal muscle, heart and thymus were not evident until after 24-48h of refeeding, and only a single increase occurred. The increase in liver ornithine decarboxylase in diabetic rats was greater than in normal rats after 3h of refeeding, but there was no second peak. In peripheral tissues, the increase in ornithine decarboxylase with refeeding was diminished. Skeletal-muscle ornithine decarboxylase is induced more rapidly when meal-fed rats are refed after a period without food. Refeeding these rats after a 48h period without food caused a 5-fold increase in ornithine decarboxylase in skeletal muscle at 3h in control rats but failed to increase activity in diabetic rats. When insulin was administered alone or together with food to the diabetic rats, muscle ornithine decarboxylase increased to activities even higher than in the refed controls. In conclusion, these findings indicate that the regulation of ornithine decarboxylase in many tissues is grossly impaired in diabetes and starvation. They also suggest that polyamine formation in vivo is an integral component of the growth-promoting effect of insulin or some factor dependent on insulin.

Animals↗