Real‐time curing characteristics of experimental resin composites containing amorphous calcium phosphate

The real‐time polymerization of light‐curable experimental resin composites filled with amorphous calcium phosphate (ACP) was monitored. Experimental composites were based on a 2,2‐bis[4‐(2‐ethoxy‐3‐methacryloyloxy propoxy)phenyl]propane (Bis‐EMA)/triethyleneglycol dimethacrylate (TEGDMA)/2‐hydroxyethyl methacrylate (HEMA) resin photoactivated by a camphorquinone/tertiary amine system. Four ACP composites were prepared, containing 40 wt% ACP and 0/10 wt% reinforcing fillers (barium glass and silica). Additionally, two control composites were prepared which contained only reinforcing fillers (40–50 wt%). The degree of conversion (DC) was monitored in real time using a Fourier‐transform infrared (FTIR) spectrometer with an attenuated total reflectance accessory. During the light curing (1,219 mW cm^?2) for either 20 or 40 s, infrared spectra were collected from the bottom of 2‐mm‐thick composite specimens at the rate of two spectra per second over 5 min. When cured for 40 s, the ACP composites attained a high DC (89.1%–92.4%), while the DC of control composites was significantly lower (53.5%–68.4%). All materials showed a lower DC for the shorter curing time (20 s) and various extents of 5‐min postcure polymerization: 12.9%–21.5% for the ACP composites and 2.7%–5.2% for the control composites. The control composites reached the maximum reaction rate much earlier (4.1–4.3 s) and at lower DC (9.9%–10.4%) than did the ACP composites (17.4–22.0 s and 43.5%–49.3%, respectively).     

Gemcitabine does not prevent acute rejection of the transplanted liver in rats

Abstract Our study was designed to determine effect of gemcitabine on acute rejection of liver in rats. Liver transplantation was performed in rats of the Dark Agouti (DA) and Lewis (LEW) strains. Recipients were divided into three groups: A, DA-to-LEW without immunosuppression; B, DA-to-LEW, treated with cyclosporine A; C, DA-to-LEW, treated with gemcitabine. Immunosuppressants were subcutaneously injected for seven consecutive days after transplantation. On day 7, blood samples and liver graft tissue specimens were harvested. Group A showed severe rejection changes (RAI 8/9); in group B no rejection changes were present (RAI 0/9), and in group C moderate rejection changes were observed (RAI 6/9). Differences were significant between B vs C and A vs C groups; P >0.05. Serum creatinine and urea levels in the gemcitabine group were significantly lower than those in the cyclosporine A group. We did not confirm gemcitabine ability to prevent liver allograft rejection.     

Interaction of organophosphorus compounds with carboxylesterases in the rat

 Carboxylesterases (CarbE) are involved in detoxication of organophosphorus compounds (OPC) through two mechanisms: hydrolysis of ester bonds in OPC which contain them and binding of OPC at the active site of CarbE which reduces the amount of OPC available for acetylcholinesterase inhibition. This study of the interaction of rat plasma and liver CarbE with dichlorvos, soman and sarin in vitro and in vivo was undertaken in order to contribute to better understanding of the role of CarbE in detoxication of OPC. The results obtained have shown that inhibitory potency (I₅₀) of dichlorvos, sarin and soman towards rat liver CarbE was 0.2 μM, 0.5 μM and 4.5 μM, respectively, for 20-min incubation at 25°C. Second-order rate constants (k_a) for liver CarbE inhibition were 2.3×10⁵ M^-1 min^-1, 6.9×10⁴ M^-1 min^-1 and 1.1× 10⁴ M^-1 min^-1 for dichlorvos, sarin and soman, respectively. The corresponding values for plasma CarbE could not be calculated because of dominant spontaneous reactivation of inhibited CarbE. CarbE inhibited with these OPC in vitro spontaneously reactivate with half-times of 18, 143 and 497 min for sarin, dichlorvos and soman in plasma and 111, 163 and 297 min for sarin, soman and dichlorvos in liver, respectively. These results were also confirmed in experiments in vivo in which rats were subcutaneously treated with 0.5 LD₅₀ of these agents. The half-times of spontaneous reactivation of rat plasma CarbE in vivo were 1.2, 2.0 and 2.7 h for dichlorvos, sarin and soman, respectively. These findings have changed current understanding of the mechanism of interaction of CarbE with OPC and involvement of the enzymes in detoxication of OPC, suggesting an active and important role of the enzymes in metabolic conversions of OPC to their less toxic metabolites. Received: 4 July 1995/Accepted: 26 September 1995     

Regulation of sex hormone-binding globulin production by growth factors

Sex hormone-binding globulin (SHBG) is a glycoprotein whose production has been demonstrated to be regulated by both sex steroids, as well as by thyroid hormone and peptide hormones such as insulin. However, none of these regulatory factors would explain the marked decrease in serum SHBG seen throughout the prepubertal and pubertal time period in both boys and girls. Furthermore, current in vitro data show that both androgens and estrogens can stimulate SHBG production by the human hepatoblastoma cell line Hep G2; yet, in vivo androgens appear to suppress SHBG levels, while estrogens are associated with elevated levels. This study was undertaken to determine possible mechanisms to explain this phenomenon. Hep G2 cell cultures were incubated with insulin-like growth factor I (IGF-I), epidermal growth factor (EGF), transforming growth factor alpha (TGF-alpha), or dehydroepiandrosterone (DHEA). Significant decreases in the level of SHBG in the culture medium relative to control cultures occurred for each of the growth factors (P less than .01), whereas an increase in SHBG levels was observed in the medium of DHEA-treated cells. When cells were coincubated with IGF-I and thyroxine (T4), which alone stimulates SHBG production both in vivo and in vitro, the SHBG response to T4 was blunted. These results suggest that growth factors, as well as insulin, may be important determinants in SHBG production.     

Cortical potentials after electrical intraneural stimulation of the optic nerve during orbital enucleation

Background

The aim of this study was to present cortical potentials after electrical intraneural stimulation of the optic nerve during orbital enucleation due to malignant melanoma of the choroid or the ciliary body. These cortical potentials were related to cortical potentials after electrical epidural stimulation of the optic nerve, recorded during non-manipulative phases of neurosurgery for central skull base tumors.

Methods

Cortical potentials were recorded with surface occipital electrode (Oz) in six patients undergoing orbital enucleation under total intravenous anesthesia. Two thin needle stimulating electrodes were inserted inside the intraorbital part of the optic nerve. The electrical stimulus consisted of a rectangular current pulse of varying intensity (0.2?C10.0?mA) and duration (0.1?C0.3?ms); the stimulation rate was 2?Hz; the bandpass filter was 1?C1,000?Hz; the analysis time was 50?C300?ms.

Results

Cortical potentials could not be obtained or were inconsistently elicitable in three patients with longstanding history (>3?months) of severe visual deterioration, while they consisted of several positive and negative deflections in a patient with a short history of mild visual impairment. In two other patients, cortical potentials consisted of N20, P30 and N40 waves.

Discussion

Cortical potentials after electrical intraneural stimulation of the optic nerve could be recorded in patients with a short history of visual deterioration and without optic nerve atrophy and appear more heterogeneous than cortical potentials after electrical epidural stimulation of the optic nerve, recorded during non-manipulative phases of neurosurgery for central skull base tumors.