Serum modulation of insulin action: effects on rat gingival fibroblast metabolism.

Serum is reported to reduce the sensitivity of cells in culture to insulin. The effect of serum concentration in the growth medium on the responsiveness of control (C) and streptozotocin diabetic (D) rat gingival fibroblasts to insulin was measured by monitoring cellular DNA, RNA, total protein and medium hydroxyproline (collagen) levels, as well as the cellular uptake of C14-alpha-NH2-isobutyrate (alpha-AIB) and H3-2-deoxyglucose (2DG). The cells were grown in alpha-MEM at 5, 10, 15 or 20% FCS with 0, 10(-12), 10(-10), 10(-8) and 10(-6) M insulin used at each serum level. Insulin effects in the absence of serum were not assessed. For both the C and D rat cells, the DNA increased proportionately with increasing serum and insulin levels. In contrast, RNA and total cell protein increased with increase in insulin and decrease in serum, the magnitude of the effect being greater in C than in D cells. The insulin stimulation of both 2DG and alpha-AIB uptake and of collagen secretion varied inversely with serum concentrations. The magnitude of the insulin-serum interaction on metabolite uptake was greater for the D rat cells. These data indicate that serum significantly reduced the cell response to insulin stimulated metabolite uptake and collagen secretion, but was without apparent effect on the intracellular insulin responsive parameters. They suggest that serum factor(s) interfere with the availability of insulin to the cell and that the D rat cells are most affected.

Comparative effects of local anesthetic preparations on gingival fibroblasts of the rat.

Cultures of rat gingival fibroblasts were exposed to various dilutions of lidocaine hydrochloride (Xylocaine), mepivacaine hydrochloride (Carbocaine), and prilocaine hydrochloride (Citanest). All three anesthetics produced cell-rounding and detachment from the substrate, which varied depending on the anesthetic, its concentration in the medium, and the duration of exposure (p less than 0.001). Effects were not pH-dependent in the range of 7.0-7.4 and were not modified by epinephrine in the concentration normally present in commercially prepared anesthetic solutions. Prilocaine produced morphological changes at a greater rate and at a lower concentration than did lidocaine or mepivacaine (p less than 0.001). The effects elicited by prilocaine were irreversible, since prolonged exposures to it resulted in various toxic effects: (1) detachment of the cells from the substrate, and (2) development of pyknotic nuclei and circumferential halos in cells that remained attached. The study strongly suggested that prilocaine has the potential to be more toxic to fibroblasts than either mepivacaine or lidocaine, a situation of potential clinical importance.