Mode of action of glucocorticoid on the component change and DNA turnover of rat carrageenin granuloma

Variation of corticosteroid-induced inhibition of collagen synthesis at equivalent anti-inflammatory doses

At equivalent anti-inflammatory doses of corticosteroids, granuloma growth is not linearly related to the inhibition of granuloma collagen synthesis. However, the inhibition of granuloma collagen synthesis is linearly related to the inhibition of skin collagen synthesis. Therefore the decrease of collagen synthesis by corticosteroids is not related to anti-inflammatory activity but is related to the specific corticosteroid used.

Epidermal growth factor (EGF) prevents methylprednisolone-induced inhibition of wound healing

Subcutaneously implanted cylindrical hollow viscose cellulose sponges were used to study the effect of locally applied epidermal growth factor (EGF) on methylprednisolone-induced inhibition of granulation tissue formation in rats. In in vivo studies the sponges were treated immediately after implantation with a single injection of 2 mg (approximately 1.7 x 10(-3) M) of depot methylprednisolone or with its carrier solution only. Thereafter the implants were injected daily with 5 micrograms of EGF or with its carrier solution 0.1% albumin for 7 days. Methylprednisolone treatment decreased the accumulation of nucleic acids, collagen, and glycosaminoglycans in the developing granulation tissue. After daily injections of EGF the concentrations of these tissue components returned close to the control values. In cultures of rat granulation tissue fibroblasts, 10(-4) M and 10(-3)M methylprednisolone decreased collagen synthesis by 41 and 81% from the control level, respectively. In the presence of methylprednisolone EGF treatment could not increase collagen synthesis of fibroblasts. Methylprednisolone treatment resulted in a dose-dependent reduction in pro alpha 1(I) collagen mRNA levels, which was partially inhibited by low EGF concentrations (1 and 10 ng/ml). In the presence of methylprednisolone all concentrations of EGF increased fibronectin mRNA levels in a dose-dependent manner. It is concluded that EGF treatment can prevent the inhibitory effect of methylprednisolone on wound healing by stimulating fibroblast proliferation but does not stimulate collagen synthesis per cell.

Comparison between the effects of dexamethasone and indomethacin on bone wound healing

The area of wound holes made in the parietal bone of 4-week-old rats was measured at 1, 2 and 4 weeks after the operation using Alizarin red S staining without the use of histological sections. Dexamethasone and indomethacin were administered s.c. after the operation every day except Sunday. The inhibitory action of dexamethasone on bone wound healing was stronger than that of indomethacin, as was its inhibitory action on skin wound healing. Inhibition of the age-related decrease in radiolucency of femurs and some changes in serum calcium level were also observed by dexamethasone administration, but not by indomethacin. These results suggest that dexamethasone inhibits bone wound healing through its effects on calcium metabolism in addition to its general inhibitory action on wound healing which is shared with indomethacin. Dexamethasone also strongly inhibited the decrease in Alcian blue stainability which occurs with an increase in age, both in the normal portion and in the wound hole portion of the calvaria, whereas indomethacin showed a weak inhibitory effect only in the wound hole portion. This result suggests that one of the mechanisms by which dexamethasone inhibits bone wound healing may be based on the retardation of mineralization caused by the inhibition of removal of acid mucopolysaccharide.

Glucocorticoids: effects on prostaglandin release, cyclic AMP levels and glycosaminoglycan synthesis in fibroblast tissue cultures

Glucocorticoids (GCs) reduced cyclic AMP levels and inhibited glycosaminoglycan (GAG) synthesis in secondary embryonic mouse fibroblast cultures, when cells were incubated for short periods (30 min). The order of potency was dexamethasone greater than prednisolone greater than hydrocortisone. The effect was more marked, when cyclic AMP levels and GAG synthesis were increased by addition of PGE1. Glucocorticoids exerted no longer an inhibitory effect on cyclic AMP and GAG synthesis in cultures pretreated for 48 h with the steroids. Addition of PGE1 caused a stronger rise in cyclic AMP and GAG synthesis than in controls without GC-preincubation. This enhancement was even more pronounced, when PGE1 was added together with the GCs. The reversal of the inhibitory effect of the GCs into a potentiating effect following preincubation correlated to a reducation of endogenous PGE formation in the cultures. Short-term treatment with GCs did not reduce endogenous PGE levels, but prolonged incubation markedly decreased PGE levels. PGE formation recovered following addition of fresh medium after the 48 h incubation with the steroids, but the amount of PGE formed remained significantly lower than in untreated cultures. Non-glucocorticoid steroid hormones did not decrease PGE levels. The results indicate that the apparent loss of inhibitory activity of GCs on cyclic AMP and GAG synthesis observed after prolonged incubation may result from a reduction of endogenous PGE formation which renders the cells more sensitive to the stimulatory effect of exogenous PGE1.

Differences in the mode of exucative reaction between early phase and late phase of carrageenin-induced inflammation in rats

Differences in the mode of vascular permeability change induced by some stimulants such as chemical mediators between the early phase and the late phase of the carrageenin-induced granulomatous inflammation were investigated with the aid of 131I-human serum albumin as an indicator for the measurement of vascular permeability. In the early pregranulomatous phase of the inflammation, histamine injection into the inflammation locus markedly elevated local vascular permeability, while prostaglandins E1 and E2 showed no effect. On the other hand, in the late phase of the inflammation, where permanent granuloma tissue had been formed, prostaglandins E1 and E2 significantly enhanced the local vascular permeability, while histamine was inert.