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The detergent-soluble extract of rat ovary plasma membranes contained a Gs protein of about 100 kDa as shown by its elution behavior on a Bio Gel A-1.5m column. However, the cell membranes exposed to hCG (37° C, 15 min) contained in addition a higher molecular weight Gs protein complex of 300 kDa comprised of human chorionic gonadotropin (hCG) receptor (hCGR) and Gs. The complex bound with an affinity column of GTP-Sepharose and could be released with Gpp(NH)p and GTP inhibited this binding. The presence of the hCGR in the complex was shown by its binding to 125I-hCG. Furthermore, GTP inhibited the binding of hCG to the complex. These results indicate the presence of hCGR and Gs protein complex in the hCG-treated membranes. hCGR and Gs protein were individually purified and reconstituted into phospholipid vesicles. The protein-phospholipid vesicles showed saturation kinetics of binding of 125I-hCG and 3H-Gpp(NH)p. Incubation of phospholipid vesicles with hCG resulted in a 2–3-fold increase in the binding of 3H-Gpp(NH)p and GTPase activity. Activation of Gs protein was dependent on the length of incubation and the hormone concentration. Deglycosylated hCG was about 10 times less potent than hCG suggesting a role of carbohydrates of hCG in inducing hCG-Gs protein interactions. The data with the in vitro reconstitution system rule out the involvement of a carbohydrate-binding lectin in the function of the hormone. 相似文献
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Prakash N. Rao PhDa f Xin Cai MDa f Raman Venkataramanan PhDb Jeffrey L. Platt MDd Anthony Demetris MDa c Allen Thunberg MDe Connie Faltynek PhDe Thomas Starzl MD PhDa Prem Kumar MDf 《The Journal of allergy and clinical immunology》1995,95(6)
Reperfusion after ischemia results in endothelial cell injury and Kupffer cell activation. Inflammatory cytokines thus released can induce major histocompatibility complex antigens and increase the immunogenecity of the graft. An orthotopic rat liver allotransplant model was used to test the hypothesis that prevention of reperfusion injury by infusion of polyethylene glycol superoxide dismutase (PEG-SOD) would result in long-term allograft survival in the presence of subthreshold immunosuppressive dosages. ACI rats were used as donors, and Lewis strain rats as recipients. Orthotopic liver transplantation was initially performed to identify a subthreshold dose of the immunosuppressant FK-506, which would be unable to extend survival longer than control untreated rats with this strain combination. After testing three intramuscular FK-506 doses of 0.04, 0.08, and 0.16 mg/kg, it was observed that an FK-506 dose of 0.04 mg/kg/day for 14 days was unable to extend survival longer than in untreated recipients. This dose of FK-506 was used in combination with PEG-SOD at doses of 1000, 3000, 10,000, or 30,000 units. Recipient animals were treated intravenously with PEG-SOD as a loading dose to facilitate tissue penetration on day 1, and beginning on the day of transplantation, every 2 days for the duration of the study. Results of histologic studies and mean survival time were compared in untreated recipients and in rats treated with PEG-SOD plus 0.04 mg/kg/day FK-506. Mean survival time was increased significantly in these animals (p < 0.007) to 40.6 ± 25.6 days as compared with either untreated rats (10.0 ± 2.7 days) or rats treated with 0.04 mg/kg FK-506 alone (13.7 ± 4.2 days). Histologic examination demonstrated a significant reduction in the cellular infiltrate in rats treated with PEG-SOD plus FK-506, as compared with recipients treated with either agent alone or left untreated. Our results therefore suggest a potential approach to reducing immunosuppression in transplantation. (J ALLERGY CLIN IMMUNOL 1995;95:1276-81.) 相似文献
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Carcinoma of the cervix is typically treated with a combination of intracavitary brachytherapy and external beam radiation. The external beam dose is delivered with whole pelvis fields followed by split fields that protect midline organs at risk (bladder and rectum) while treating the parametria. Three approaches have been developed to shield midline structures: a simple rectangular block, a block customized to a single brachytherapy isodose line, and a step wedge filter constructed to conform to multiple brachytherapy isodose lines. A customized step wedge filter has the potential to produce a more homogeneous dose distribution but has not achieved widespread use due to labor intensive construction. We have developed a simple, novel method to produce a custom midline step wedge using dynamic multileaf collimation (dMLC). A comparison of film measurements in a phantom with the dose calculated by a commercial treatment planning system demonstrated agreement within 3% or 3 mm. The technique requires delivery times comparable to conventional techniques. 相似文献
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Shen S Duan J Fiveash JB Brezovich IA Plant BA Spencer SA Popple RA Pareek PN Bonner JA 《Medical physics》2003,30(12):3196-3205
The capability of a commercial respiratory gating system based on video tracking of reflective markers to reduce motion-induced CT planning and treatment errors was evaluated. Spherical plastic shells (2.8-82 cm3), simulating the gross target volume (GTV), were placed in a water-filled body phantom that was moved sinusoidally along the longitudinal axis of the CT scanner and the accelerator for +/- 1 cm at 15-30 cycle/min. During gated CT imaging, the x-ray exposure was initiated by the gating system shortly before the end of expiration (so that the imaging time would be centered at the end of expiration); it was terminated by the scanner after completion of each slice. In nongated CT images, the target appeared distorted and often broken up. GTVs volume errors ranged 16%-110% in axial scans, and 7%-36% in spiral scans. In gated CT images, the spheres appeared 3 and 5 mm longer than their actual diameters (volume errors 2%-16%), at the respective respiration rates of 15 and 20 cycles/min. At 30 cycles/min the target appeared 1 cm longer, and volume error ranged 25%-53%. During treatment, gating kept the beam on for a duration equal to the CT acquisition time of 1 s/slice. The difference in positional errors between gated CT and portal films was 1 mm, regardless the size of residual motion errors. Because of the potential of suboptimal placement of the gating window between CT imaging and treatment, an extra 1.5-2.5 mm safety margin can be added regardless of the size of residual motion error. For respiratory rates > or = 30 cycles/min, the effectiveness of gating is limited by large residual motion in the 1 s CT acquisition time. 相似文献
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Dosimetric effect of respiration-gated beam on IMRT delivery 总被引:3,自引:0,他引:3
Intensity modulated radiation therapy (IMRT) with a dynamic multileaf collimator (DMLC) requires synchronization of DMLC leaf motion with dose delivery. A delay in DMLC communication is known to cause leaf lag and lead to dosimetric errors. The errors may be exacerbated by gated operation. The purpose of this study was to investigate the effect of leaf lag on the accuracy of doses delivered in gated IMRT. We first determined the effective leaf delay time by measuring the dose in a stationary phantom delivered by wedge-shaped fields. The wedge fields were generated by a DMLC at various dose rates. The so determined delay varied from 88.3 to 90.5 ms. The dosimetric effect of this delay on gated IMRT was studied by delivering wedge-shaped and clinical IMRT fields to moving and stationary phantoms at dose rates ranging from 100 to 600 MU/min, with and without gating. Respiratory motion was simulated by a linear sinusoidal motion of the phantom. An ionization chamber and films were employed for absolute dose and 2-D dose distribution measurements. Discrepancies between gated and nongated delivery to the stationary phantom were observed in both absolute dose and 2-D dose distribution measurements. These discrepancies increased monotonically with dose rate and frequency of beam interruptions, and could reach 3.7% of the total dose delivered to a 0.6 cm3 ion chamber. Isodose lines could be shifted by as much as 3 mm. The results are consistent with the explanation that beam hold-offs in gated delivery allowed the lagging leaves to catch up with the delivered monitor units each time that the beam was interrupted. Low dose rates, slow leaf speeds and low frequencies of beam interruptions reduce the effect of this delay-and-catch-up cycle. For gated IMRT it is therefore important to find a good balance between the conflicting requirements of rapid dose delivery and delivery accuracy. 相似文献