Increased insulin action in cultured hepatocytes from rats with diabetes induced by neonatal streptozotocin

Pharmacological investigation on the wound healing effects of Radix Rehmanniae in an animal model of diabetic foot ulcer

ETHNOPHARMACOLOGICAL RELEVANCE

Radix Rehmanniae (RR) has a very long history of usage in traditional Chinese medicine and is usually one of the principal herb found in many herbal formulae used in diabetic foot ulcer.

AIM OF THE STUDY

RR aqueous extract was investigated for its wound healing effects in a diabetic foot ulcer rat model and its detailed mechanism of actions.

MATERIALS AND METHODS

A previously established diabetic foot ulcer rat model was used to assess the effect of RR extract on wound area reduction, tissue regeneration and angiogenesis. Carrageenan-induced inflammation rat model was used for inflammation study; and diabetic control was evaluated using a neonatal streptozotocin-induced diabetic rat model.

RESULTS

In the RR treated group, a trend of reduction of the wound area was observed from days 8 to 18 and a significant difference (as compared with control group) was found on day 8. The ulcer healing effect of RR extract was further supported by better developed scars and epithelialization as well as good formation of capillaries with enhanced VEGF expression. Carrageenan-induced inflammation was also significantly alleviated with RR extract.

CONCLUSIONS

Our results demonstrated for the first time that Radix Rehmanniae was effective in promoting diabetic foot ulcer healing in rats through the processes of tissue regeneration, angiogenesis and inflammation control, but not glycemia control. The present study provided scientific basis to support the traditional use of Radix Rehmanniae in diabetic foot ulcer.

Eicosanoid production by placental and amnion tissues from control and non-insulin-dependent diabetic rats. Influence of oxytocin in the incubating medium

Eicosanoid production by intrauterine tissues from control and neonatal-streptozotocin induced diabetic rats during late pregnancy was evaluated. In diabetic placenta the release of 6-keto-PGF1alpha was found diminished when compared to controls. In addition, LTB4 generation was increased in diabetic placenta. No alterations in the production of TXA2, PGE2, PGE1 and PGF2alpha was found when diabetic and control placenta were compared. In amnion tissue a decreased generation of 6-keto-PGF1alpha was observed in the diabetic group, but no alteration in any other eicosanoid evaluated was found. Oxytocin (5 mU/ml, in vitro), which increases prostaglandin synthesis in rabbit and human amnion tissues, did not modify eicosanoid generation in control rat amnion. In contrast, in diabetic amnion the presence of oxytocin further decreased the release of 6-keto-PGF1alpha and diminished PGE1 generation. The present results suggest that this mildly diabetic state induces alterations in eicosanoid production in intrauterine tissues, abnormalities probably enhanced during parturition, when endogenous concentrations of oxytocin are elevated.

Altered prostanoid production by cumulus-oocyte complexes in a rat model of non-insulin-dependent diabetes mellitus

Ovulation, oocyte maturation and PGE and PGF2 alpha production by oocyte-cumulus complexes were evaluated in rats with non-insulin-dependent diabetes induced by neonatal streptozotocin. Diabetic rats had normal estrous cycles, but ovulated a lower number of oocytes at estrus. When oocytes from control and diabetic rats obtained at proestrus were matured "in vitro" during 1, 2 or 4 hours (hr) of culture, differences were not found in the percent of germinal vesicle breakdown between both experimental groups. PGE and PGF2 alpha accumulation was higher in ovulated oocyte-cumulus complexes when compared to immature or "in vitro"-matured oocyte-cumulus complexes in both normal and diabetic rats. When control and diabetic rats are compared, more PGE and PGF2 alpha accumulation was observed in immature, "in vitro"-matured and in ovulated oocyte-cumulus complexes. A lower number of oocytes ovulated and increased oocyte-cumulus complexes prostaglandin production has been observed in this mildly diabetic experimental model. These abnormalities are similar to those previously found when 10 day embryos were evaluated in non-insulin-dependent diabetic rats.

Eicosanoid production, metabolism and contractile activity in the isolated uterus from non-insulin-dependent diabetic rats during late pregnancy

Eicosanoid production, glucose (Glu), glycogen (Gly) and triglyceride (TG) metabolism, spontaneous contractile activity, PGF2 alpha and oxytocin-induced contractions have been studied in uterine tissue obtained from control (C) and non-insulin-dependent diabetic (D) rats prior to parturition. Parturition occurs on day 22 of gestation in control animals, whereas a 24 hr delay was observed in diabetic rats. Production of PGE2, PGE1, 6-keto-PGF1 alpha, PGF2 alpha, TXB2 and LTB4 was similar in uterine tissue obtained from control and diabetic rats on day 21 of pregnancy. Uterine metabolism, on day 21 of pregnancy, based on the production of 14CO2 from U14C-glucose was lower in tissues obtained from diabetic rats than in controls. Levels of TG were similar at 0 hr and after 60 min incubation in Glu or Glu-free medium in both experimental groups. Initially Gly levels in diabetic and control uteri were similar. After 60 minutes of incubation, levels of Gly in control tissue decreased only in the absence of Glu in the incubation medium. In contrast, in diabetic uterine strips, levels of Gly decreased after 60 minutes of incubation either in Glu or Glu-free medium. "In vitro" isometric-developed tension (IDT) evaluated on day 21 (C and D) and 22 (D) of pregnancy was similar at 0 hr in control and diabetic uterine preparations, but IDT in both diabetic groups was decreased after a 40 minute incubation when compared to controls. Alterations in PGF2 alpha-induced uterine responses were not seen in 21 or 22 days pregnant diabetic uterine tissue when compared to controls. In contrast, impaired oxytocin responses were observed in diabetic uteri on day 21 of gestation, but they were similar to control responses of uterine tissue from day 22 diabetic rats. We conclude that in the non-insulin-dependent late pregnant rat, there are no alterations in uterine tissue eicosanoid production, but metabolic and contractile abnormalities are present. Involvement of these alterations in the delayed initiation of parturition is discussed.

Eicosanoid production and phospholipase A2 activity in uterine tissue from castrated rats with non-insulin dependent diabetes mellitus

In uterine tissue obtained from castrated control and non-insulin dependent diabetic (NIDDM) rats, eicosanoid production and its regulation by glucose levels and by the activity of phospholipase A2 (PLA2) was assessed. Basal outputs of prostaglandins (PGs) PGE2, PGE1, PGF2 alpha, 6-keto-PGF1 alpha (indicating the production of prostacyclin), thromboxane B2 (TXB2) (indicating the generation of TXA2) and leukotriene B4 (LTB4) were similar in control and NIDDM uterine preparations as assessed by RIA. When uterine conversion of labelled arachidonate into different prostanoids was evaluated, generation of 6-keto-PGF1 alpha, PGE2 and PGF2 alpha was similar in control and NIDDM uterine tissue, while TXB2 production was higher in the diabetic group. Moreover, when control tissue was incubated in the presence of elevated concentrations of glucose (22 mM) and compared to control tissue incubated in concentrations of glucose 11 mM, similar generation of 6-keto-PGF1 alpha, PGE2 and PGF2 alpha was observed, and higher concentrations of TXB2 were found, similar to those observed in diabetic uterine tissue. When NIDDM uterine tissue was incubated in the presence of glucose 22 mM, no difference in any prostanoid evaluated was observed when compared to values obtained in the presence of glucose 11 mM. In this work we have observed in NIDDM uterine tissue a normal TXA2 production when evaluated by RIA from endogenous arachidonic acid (AA) and a higher TXA2 generation from exogenous labelled AA. In addition PLA2 activity was found diminished in the NIDDM uteri in comparison to control uteri. A role of the diminished PLA2 as a protective mechanism that avoids TXA2 overproduction in uterine tissue from NIDDM rats is discussed.

Glucose metabolism, triglyceride and glycogen levels, as well as eicosanoid production in isolated uterine strips and in embryos in a rat model of non-insulin-dependent diabetes mellitus during pregnancy

Spontaneous contractile activity, glucose (Glu), glycogen (GLY), triglyceride (TG) metabolism and eicosanoid production, was evaluated in isolated uterine strips from control and non-insulin-dependent diabetic rats on day 10 of pregnancy. Metabolism of Glu, levels of GLY and TG and eicosanoid production were also studied in day 10 embryos obtained from both experimental groups. "In vitro" isometric developed tension (IDT), was similar at 0 hr in control and diabetic uterine preparations, but IDT was decreased after a 60 min incubation in the diabetic group. The frequency of contractions (FC) was similar at 0 hr and after 60 min incubation in both experimental groups. On the other hand, the production of 14CO2 from U14C-glucose was lower in isolated uteri and embryos obtained from diabetic rats than in controls. Initial TG levels were similar in uteri isolated from control and diabetic rats, and higher in embryos obtained from diabetic mothers than in controls. Levels of TG in uterine strips suspended in Glu or Glu-free medium did not differ at 0 hr or at 60 min either in controls or in diabetic rats. On the contrary GLY levels in uterine strips from diabetic animals were higher than in controls, whereas in embryos from diabetic mothers GLY levels were similar to controls. Levels of GLY in uterine strips from controls and diabetic animals decreased after 60 min incubation only in the absence of Glu in the incubation medium. Production of PGE2, PGE1, 6-keto-PGF1 alpha, PGF2 alpha, TXB2 and LTB4 was studied in uterine strips and embryos obtained from control and diabetic rats. No differences were found between control and diabetic uterine prostanoid production, but lower production of LTB4 was observed in diabetic uteri. However production of PGE2 and PGF2 alpha was greater in embryos obtained from diabetic mothers than in controls. In this study, we observed lower uterine metabolic alterations than in the pancreatectomized diabetic rat model studied previously, but important anomalies in the embryos obtained from non-insulin-dependent diabetic mother were found.

Insulin resistance and mechanical dysfunction in hearts of Wistar rats with streptozotocin-induced non-insulin-dependent diabetes mellitus

The present study correlates the insulin resistance seen in the myocardium of rats with streptozotocin-induced non-insulin-dependent diabetes mellitus with insulin secretory defects, hyperglycaemia and disease duration. Two-day-old male Wistar rats were given a bolus injection of streptozotocin (0.09 mg/g body weight) which caused glucose intolerance when these animals reached adulthood. Although these rats developed a progressive resistance to the actions of insulin in the heart this did not correlate with the development of glucose intolerance. However, a correlation was seen with a shift in insulin secretory response from hyper- to hypo-secretion which developed between 6 and 14 months of age. Moreover, this shift in secretory pattern can be associated with the onset of a cardiac mechanical malfunction.