Beef Carcass Size and Aging Time Effects on Yield and Color Characteristics of Top Round Steaks

Variation in cut size and weight of fabricated subprimals is a challenge of increased beef carcass weights. Subsequently, variation in carcass size has resulted in consistency challenges during retail display. The objective of this study was to assess three aging periods of commercially available top rounds from varying carcass weights as it relates to yield and color characteristics. In the current study, 21 industry average weight (AW; 340 to 409 kg; no industry discount) beef carcasses and 21 oversized (OS; exceeding 454 kg; receive a discount) beef carcasses were evaluated. Carcasses were selected at a commercial beef packing plant, where the left and right (paired) top round subprimals of each carcass were procured. Paired top rounds were assigned to a short (8 d), average (23 d), or extended (42 d) postmortem aging period. After wet-aging, subprimals were fabricated into steaks for additional analysis. Steaks were evaluated as whole top round steaks or further fabricated into “ superficial ” and “ deep ” portions at 5.08 cm from the superficial edge of the Semimembranosus and the Adductor muscle. Top rounds and steaks from OS carcasses were larger (P < 0.01) than those from AW carcasses. Quantitative color of the anatomically deep locations of the OS steaks had the greatest mean L* (lightness; P < 0.01), a* (redness; P < 0.01) and b* (yellowness; P < 0.01) values. Extending the aging timeline increased L* (lightness; P < 0.01), decreased a* (redness; P < 0.01), and decreased b* (yellowness; P < 0.01). Alternative top round steak fabrication that separates the deep and superficial anatomical locations could be an effective means of providing more uniform steaks.

Extending the Shelf Life of Beef Steaks Using Acerola Cherry Powder and Rosemary Extract

Improvements in retail shelf life of exported beef will help with merchandising and increase competitiveness in the worldwide market for United States beef products. The objective of this study was to determine the effect of topically applying acerola cherry powder or rosemary extract from various suppliers on beef bone-in short rib steak and chuck roll steak shelf life. USDA Choice beef bone-in short ribs (IMPS 123A) and chuck rolls (IMPS 116A) were aged (0°C) for 28 d postfabrication. Following aging, 1.02-cm-thick steaks were cut (N = 126) and systematically assigned to a treatment based on steak location within the subprimal. Treatments included untreated control (C), topically sprayed (2 mL) with an acerola cherry powder solution (0.05%) from 1 of 3 suppliers (C1, C2, C3), or topically sprayed (2 mL) with a rosemary extract solution (0.10%) from 1 of 3 suppliers (R1, R2, R3). Half of the steaks were assigned to day 0 lipid oxidation, metmyoglobin-reducing activity (MRA), and oxygen consumption; the remaining steaks were assigned to color evaluation over 4 d of retail display followed by day 4 lipid oxidation and MRA. Short rib steaks treated with antioxidants had a brighter oxygenated lean color than control steaks (P < 0.001). There was an interaction (P = 0.028) between time of retail display and MRA. Short rib steaks treated with C3 and R2 did not change in MRA between day 0 and 4 (P = 0.620, P = 0.428, respectively). Chuck roll steaks treated with C1, C2, C3, R2, and R3 all had a higher, or more desirable, MRA than the control steaks on day 0 (P < 0.001). Applying topical antioxidants improves the shelf-life stability of steaks from beef bone-in short ribs and chuck rolls aged for an extended period.

Impact of beef carcass size on chilling rate, pH decline, display color, and tenderness of top round subprimals

Beef carcass weights in the United States have continued to increase over the past 30 yr. As reported by the United States Department of Agriculture, grid-based carcass weight discounts begin when carcasses exceed 408 kg. Despite weight discounts, beef carcass weights continue to increase. At the same time, an increased prevalence of discoloration and color variability in top round subprimals has been observed throughout the industry which may be influenced by the increases in carcass weights. The objectives of this study were to assess the effects of beef carcass size and its relationship to chill time, color, pH, and tenderness of the beef top round. In the current study, eight industry average weight beef carcasses (AW, 341–397 kg) and eight oversized beef carcasses (OW, exceeding 432 kg) were evaluated. Temperatures and pH measurements were observed on both sides of all carcasses for the initial 48 h postharvest at a consistent superficial and deep anatomical location of the respective top rounds. Carcasses were fabricated into subprimals at 48 h and top rounds were aged at 2 °C for an additional 12 d. The superficial location of both AW and OW carcasses cooled at a faster rate (P < 0.01) than the deep locations. The deep location of OW carcasses had a lower pH and a more rapid (P < 0.01) initial pH decline. Quantitative color of steaks from OW carcasses had greater mean L* (lightness; P = 0.01) and initial b* (yellowness; P < 0.01) values. The delayed temperature decline and the accelerated pH decline of the deep location of the top round of OW carcasses occur at different rates than AW carcasses. Delayed rate of cooling leads to irreversible impacts on steak appearance of top round steaks fabricated from OW beef carcasses when compared with AW carcasses.

Using Genetic Panels to Predict Tenderness in Beef Cattle

Genetic panel use as a selection tool has grown in popularity in the beef industry. The objective of the study was to determine whether beef cattle genetically selected for tenderness generated a tender product. Igenity® (IT) panel results were provided by a cattle producer for 52 steers, which were harvested at a commercial harvest facility. Boneless strip loins (Institutional Meat Purchase Specifications #180; United States Department of Agriculture [USDA] Choice, n = 32; USDA Prime n = 20) were collected from the left side of each carcass and transported to the University of Idaho Meat Science Laboratory. Four steaks were cut from each subprimal and assigned to aging periods of 7, 14, and 21 d for Warner-Bratzler Shear Force (WBSF) analysis or 21 d for consumer sensory analysis. Carcasses were assigned to tenderness groups based on their IT tenderness indexes (Low IT, 3 – 6, n = 30; High IT, 7 – 10, n = 22). Data were analyzed using the mixed model procedure of SAS version 9.4 (SAS Institute Inc., Cary, NC). An interaction was observed between tenderness group and USDA quality grade (P = 0.015) when analyzing WBSF. All of the cattle had less than 4.14 kg of WBSF; however, USDA Prime steers that were in the High IT tenderness group produced more tender steaks than High IT USDA Choice, Low IT USDA Prime, and Low IT USDA Choice steers. Consumers were not able to detect tenderness differences between IT tenderness groups (P = 0.11) or USDA quality grades (P = 0.11), but they found USDA Prime steaks to be more acceptable (P = 0.01), juicier (P = 0.01), and more flavorful (P = 0.02) than USDA Choice steaks. In conclusion, regardless of tenderness group, USDA Prime steaks were preferred by consumers over USDA Choice steaks in terms of flavor, juiciness, and acceptability.

Assessing outcomes of genetic selection panels to predict marbling in crossbred beef cattle

The objective of this study was to evaluate the effectiveness of genetic panel marbling indexes [Igenity (IT) and PredicGEN (PG)] to predict marbling and tenderness of crossbred cattle. Steers (n = 23) were harvested at the University of Idaho Meat Science Laboratory, and blood samples were submitted to Neogen and Zoetis for genetic panel analysis. Forty-eight hours postharvest, one boneless strip loin was collected from each carcass, and six 2.54-cm thick steaks were cut from each strip loin. Steaks were aged for 14 and 21 d and assigned to consumer sensory evaluation or Warner–Bratzler Shear Force (WBSF) analysis. Results were analyzed using the Mixed Model procedure of the Statistical Analysis System (SAS Institute, Inc., Cary, NC). Carcasses were grouped by marbling index score into Low IT (IT indexes 3–6; n = 16; marbling score (MS) = 410), High IT (IT indexes 7–10; n = 7; MS = 496), Low PG (PG index <50; n = 9; MS = 398), or High PG (PG index ≥50; n = 14; MS = 458). Mean MS was observed to be greater in High IT steaks than Low IT (P < 0.01) and greater in High PG steaks than Low PG (P = 0.01). There was a trend observed in WBSF between IT marbling groups (P = 0.06); however, no difference in WBSF was observed between PG marbling groups (P = 0.83). Consumers did not report differences between IT marbling groups in terms of acceptability (P = 0.99) or tenderness (P = 0.24). Additionally, consumers could not detect differences between PG marbling groups in terms of acceptability (P = 0.75) or tenderness (P = 0.40). Consumers consistently preferred Choice steaks over Select steaks in terms of acceptability (P = 0.02) and tenderness (P = 0.02). In conclusion, though consumers were not able to tell the difference between steaks from each of the genetic panels, using genetic panels to predict marbling, in conjunction with proper nutrition and handling practices, could be a beneficial tool to producers making decisions about retaining ownership at the feedlot.

Skin compatibility and efficacy of a cosmetic skin care regimen with licochalcone A and 4-t-butylcyclohexanol in patients with rosacea subtype I

BACKGROUND

Patients with rosacea often show facial sensitivity to cosmetics or skin care products that can influence the severity of symptoms and exacerbate erythema and inflammation. Nevertheless, special skin care is necessary to address cosmetic concerns and reduce the potential side-effects of topical or oral treatment of the disease. Appropriate skin care should comprise gentle cleansing, effective moisturization, soothing actives, UV protection and concealing pigments to help neutralize the appearance of redness.

OBJECTIVE

To determine the compatibility and efficacy of a skin care regimen (consisting of a cleanser, a day care with SPF25 and a night care) containing licochalcone A (Lic A), an anti-irritant from the licorice plant Glycyrrhiza inflata, and 4-t-butylcyclohexanol (SymSitive(®) ), a substance which acts as a sensitivity regulator, in female subjects with clinically determined subtype I rosacea.

METHODS

Thirty-two test subjects with mild to moderate rosacea used the skin care regimen daily for 8 weeks. Clinical assessment of erythema, subjective irritation and clinical photography were performed at baseline and after 4 and 8 weeks. Additionally, a quality-of-life questionnaire was filled out by the test subjects at baseline and week 8. The subjects completed a self-assessment questionnaire on product properties after 4 and 8 weeks of product use.

RESULTS

Clinical assessments and subject response confirmed very good tolerability of the regimen, a statistically significant improvement in clinical grading for erythema and tactile roughness at weeks 4 and 8 and on telangiectasia at week 8 when compared to baseline scores. A statistically significant improvement in facial redness (a*) values, based on the L*a*b* colorimetric system, was determined at week 4 and 8 in comparison to baseline. No difference in corneometric measurement was detected at week 4 and 8 compared to baseline.

CONCLUSION

The skin care regimen was found to be highly compatible with the sensitive facial skin of patients with rosacea subtype I and effective in improving signs of rosacea. Therefore, the daily use of skin care products containing LicA and SymSitive(®) in patients with rosacea improves the overall skin appearance and the quality of life of these patients.

Skin tolerance, efficacy, and quality of life of patients with red facial skin using a skin care regimen containing Licochalcone A

BACKGROUND

Patients with rosacea and red facial skin often show sensitivity to skin care products which can exacerbate inflammation and subjective irritation. Besides pharmacologic management, special skin care is prudent to avoid cosmetically induced irritation and address cosmetic concerns. Appropriate skin care should provide gentle cleansing, UVA/UVB protection, effective moisturization, and concealing pigments to neutralize the appearance of redness.

AIMS

To evaluate skin compatibility and efficacy of a skin care regimen containing licochalcone A (Lic A), an anti-irritant from the licorice plant Glycyrrhiza inflata, for subjects with mild to moderate facial redness.

PATIENTS/METHODS

Sixty-two patients with mild to moderate red facial skin used a four-product skin care regimen for 8 weeks. Clinical assessments of erythema and subjective irritation, cross-polarized photography, and self-assessment questionnaires were completed at baseline, and after 4 and 8 weeks of use. A quality of life questionnaire was given at baseline and week 8.

RESULTS

Clinical evaluations, subject response, and photography confirmed very good tolerability of the regimen and effective neutralization of redness by the pigmented products. Significant improvements in average erythema scores were observed at 4 and 8 weeks (P < 0.05), and an improvement in quality of life was confirmed by the patient questionnaires.

DISCUSSION

The skin care regimen containing Lic A was found to be compatible with the sensitive facial skin of patients with rosacea and improved the appearance of persistent facial redness. The products were also observed to be compatible with daily metronidazole treatment.

US vascular mapping before hemodialysis access placement

PURPOSE

To prospectively assess the effect of preoperative ultrasonographic (US) mapping on surgical selection, placement of arteriovenous fistulas (AVFs) and grafts, and negative surgical exploration rates.

MATERIALS AND METHODS

US assessment of the upper extremity arterial and venous anatomy was performed in 70 patients with chronic renal failure before surgical evaluation. The surgeon documented the planned access procedure, which was based on physical examination results, and then reviewed the US preoperative mapping report. The surgical procedure and outcome were recorded.

RESULTS

Fifty-two of the 70 patients who underwent mapping had vascular access placement. Preoperative US mapping resulted in a change in the planned surgical procedure in 16 (31%) of the 52 patients. An AVF rather than the planned graft was placed in eight (15%) patients. The AVF placement rate increased from 32% (126 of 395 patients) to 58% (30 of 52 patients). Unsuccessful surgical explorations decreased from 11% (28 of 256) to 0%.

CONCLUSION

Preoperative US mapping before hemodialysis access placement can result in a change in surgical management, with an increased number of AVFs placed and an improved likelihood of selecting the most functional vessels preoperatively. Further study is needed to determine longer term outcomes.

Doppler sonographic enhancement of hepatic hemangiomas and hepatocellular carcinomas after perflenapent emulsion: preliminary study

Ultrasonographic microbubble contrast agents improve Doppler signals by increasing blood backscatter. We retrospectively reviewed our experience with perflenapent (EchoGen), an emulsion of liquid dodecafluoropentane, in the evaluation of 13 patients with focal hepatic lesions (10 hemangiomas and six hepatocellular carcinomas). Perflenapent improved the detection of color Doppler flow signals within the lesions. The hemangiomas showed peripheral nonpulsatile signals and the hepatocellular carcinomas showed more diffuse enhancement with both arterial and venous type signals. This preliminary study suggests that perflenapent administration may aid in the sonographic differentiation of these focal lesions.

Hemodialysis access graft stenosis: US detection

PURPOSE

To prospectively evaluate the sensitivity of ultrasonography (US) in diagnosing stenosis of hemodialysis access grafts and their drainage veins in patients clinically suspected of having graft dysfunction.

MATERIALS AND METHODS

Thirty-eight patients in whom dysfunction of their hemodialysis access grafts was suspected underwent both Doppler US and angiography. Gray-scale and color US were combined with spectral analysis of the graft, anastomoses, and venous outflow. Flow velocity at anastomoses and suspected stenotic areas was measured. The volume of flow in the graft was also measured. The prospective US criterion for diagnosis of stenosis was a focal twofold or higher elevation of peak systolic velocity (PSV) compared with the PSV immediately upstream. A blinded angiographic evaluation of the graft and drainage veins followed US. Angiographic diagnosis of stenosis required at least 50% narrowing in luminal diameter. US and angiographic results were then compared.

RESULTS

Angiography allowed diagnosis of 43 stenoses in 34 patients. US depicted 92% (37 of 40) of these stenoses, with a 94% positive predictive value for any individual patient. Focal 2- to 2.9-times PSV elevation was associated with 75% or greater stenosis. Graft flow volume and resistive index change did not correlate with stenosis.

CONCLUSION

US reliably depicts stenoses of hemodialysis access grafts and drainage veins in a clinically selected population when PSV criteria are used.

Carotid artery stents: early and intermediate follow-up with Doppler US

PURPOSE

To determine whether ultrasound (US) is a sensitive follow-up method after placement of a carotid artery stent for the detection of significant stenosis, occlusion, and other complications at early and intermediate follow-up.

MATERIALS AND METHODS

Doppler US examinations were performed after stent placement in 170 carotid arteries in 119 patients with angiographic correlation. Prospective diagnostic US criteria for stenosis were peak-systolic velocity greater than 1.25 m/sec, internal carotid artery (ICA) to common carotid artery (CCA) peak-systolic velocity ratio of greater than or equal to 3:1, and intrastent doubling of peak-systolic velocity. Retrospective criteria for stenosis were also applied: peak-systolic velocity greater than 1.7 m/sec, ICA end-diastolic velocity greater than 0.4 m/sec, ICA/CCA peak-systolic velocity ratio greater than 2.0, and ICA/CCA end-diastolic velocity ratio greater than 2.4.

RESULTS

Eighty-seven immediate and 83 intermediate (average, 7.3 months) follow-up US examinations were performed. Two stent occlusions were detected. One or more prospective US criteria were abnormal in 26 arteries with a stent. One or more retrospective criteria were positive in 47 arteries. Angiography showed corresponding findings, with only one significant stenosis (63%) in the ICA stents. Moderate collapse of a CCA stent was depicted at US.

CONCLUSION

Only one significant recurrent stenosis was detected, and no significant stenoses were missed at US. US successfully depicted carotid artery stent occlusion and a moderate stent collapse. Sensitivity in the detection of intrastent stenosis is promising. Further study to refine US criteria in a study with longer term follow-up is needed owing to the lack of significant recurrent stenosis in the intermediate follow-up group.

Cervical carcinoma: determination of recurrent tumor extent versus radiation changes with MR imaging

PURPOSE

To evaluate the effectiveness of magnetic resonance (MR) imaging for assessment of the present and extent of tumor recurrence as determined with pathologic and surgical findings.

MATERIALS AND METHODS

MR findings were retrospectively examined in 37 patients with a history of cervical carcinoma. Inter- and intraobserver variability was analyzed. Surgical or pathologic results were acquired in 34 of these patients; the remaining three patients were clinically followed up for at least 4 years.

RESULTS

MR imaging allowed correct detection of recurrent tumor in 18 of 21 patients who had histologically documented recurrence. It helped correctly exclude recurrent disease in 15 of 16 patients. Sensitivity and specificity for detection of recurrence was 86% and 94%, respectively. Good intra- and interobserver agreement was demonstrated.

CONCLUSION

MR imaging is a useful modality for differentiation of recurrent cervical carcinoma from radiation changes. Determination of the extent of recurrence with MR imaging may offer clinical assistance in the selection of optimal therapy.

Doppler US assessment of maternal kidneys: analysis of intrarenal resistivity indexes in normal pregnancy and physiologic pelvicaliectasis

Duplex ultrasound was performed in both kidneys of 156 normotensive pregnant women without suspected renal disease and 25 nonpregnant women of childbearing age to determine if resistivity indexes are different between pregnant and nonpregnant women and to assess whether the "physiologic" pelvicaliectasis of pregnancy causes elevated resistivity indexes. The mean intrarenal resistivity index for pregnant patients was 61.1, and that for nonpregnant women was 61.0. There were no statistically significant differences between the resistivity indexes of pregnant and nonpregnant women, regardless of whether the pregnant patients were considered as a composite group or subdivided by trimester. Twenty-nine right kidneys and four left kidneys in pregnant patients had moderate dilation of the collecting system attributed to physiologic pelvicaliectasis of pregnancy. No statistically significant differences were detected between the resistivity indexes of kidneys with and without pelvicaliectasis. Normal, uncomplicated pregnancy has no significant effect on resistivity indexes obtained in maternal kidneys. Physiologic pelvicaliectasis of pregnancy is likely to be partially a result of obstruction; this too, however, is not reflected by changes in resistivity indexes. An elevated resistivity index during pregnancy should not be attributed to the normal physiologic changes of pregnancy.

Diagnosis of placenta previa during the third trimester: role of transperineal sonography

Placenta previa can be difficult to diagnose with transabdominal sonography during the third trimester of pregnancy, because of difficulties in imaging the cervix late in pregnancy. Although transperineal sonography offers an additional view of the cervix, its value in the diagnosis of placenta previa has not been studied. Accordingly, we performed transperineal sonography on 164 patients who had had transabdominal scans that had shown placenta previa or had been inconclusive during the third trimester of pregnancy. Transabdominal sonograms had been inconclusive for placenta previa in 157 of these patients because the cervix was not visualized. The remaining seven patients had transabdominal scans that showed placenta previa. Transperineal sonography successfully visualized the internal surface of the cervix in all 164 patients, allowing determination of the presence or absence of placenta previa in all cases. Transperineal sonograms showed absence of placenta previa in 154 patients. At delivery, none of these patients had evidence of placenta previa. Transperineal sonography showed placenta previa in 10 patients. In nine of these patients, placenta previa was confirmed at delivery. The 10th patient did not have clinically significant placenta previa at delivery. Our study shows that transperineal sonography is a valuable technique to complement transabdominal sonography for detection of placenta previa during the third trimester of pregnancy. Use of transperineal sonography should be strongly considered when a definitive diagnosis regarding placenta previa is not possible by transabdominal sonography because the cervix is not visualized. In such cases, transperineal sonography will usually show the internal surface of the cervix without overlying placental tissue, allowing confident exclusion of placenta previa. Occasionally, however, transperineal sonography will show a placenta previa that was not seen with transabdominal sonography.

Sonography of the cervix during the third trimester of pregnancy: value of the transperineal approach

Transabdominal sonography reliably depicts the cervix during the first and second trimesters of pregnancy, but cervical visualization becomes increasingly difficult as the third trimester progresses. To evaluate the possibility of using a perineal approach to bypass the fetus and image the cervix during the third trimester, we used transperineal sonography to image the cervix of 158 third-trimester patients in whom transabdominal visualization was inadequate. The internal os and upper cervix were successfully visualized on transperineal sonograms in all 158 patients, but the region of the external os was obscured by rectal gas in 22 (14%) cases. In some patients in whom the external portion of the cervix was obscured by bowel gas, the problem could be overcome by scanning with the patient in the lateral decubitus position or by rotating the patient. Transperineal sonography is an effective technique for imaging the cervix during the third trimester of pregnancy, allowing cervical visualization in most patients in whom transabdominal sonography of this area is unsuccessful.

Transperineal US: alternative technique to improve visualization of the presenting fetal part

Transperineal ultrasound (TPU) was used as an alternative imaging technique to evaluate the anatomy of the presenting part in 27 second- and third-trimester fetuses when transabdominal ultrasound (US) images were suboptimal. Use of TPU improved visualization of the distal fetal spine in 20 of 21 breech cases, providing sufficient information regarding bone anatomy to rule out splaying of the posterior elements. In addition, the intact skin surface overlying the distal spine, not seen at transabdominal US, was well demonstrated at TPU in 18 of these fetuses. TPU was used to improve assessment of intracranial anatomy in six cases with a cephalic presentation in which the fetal head was located low in the maternal pelvis and could not be adequately visualized with the transabdominal technique. In one of these cases, TPU offered improved visualization of anencephaly. Use of TPU should be considered to optimize visualization of the presenting fetal part when results at transabdominal US are suboptimal and the poorly seen part overlies the maternal cervix.

Therapy of serious skin and soft tissue infections with ofloxacin administered by intravenous and oral route

We evaluated the safety and efficacy of ofloxacin administered both by the intravenous route and orally in 26 men with serious skin and soft tissue infection. Twenty-one patients completed antimicrobial therapy and were fully evaluable. Of these, 18 were judged to be cured, while 3 failed therapy either during or within 2 weeks after completion of therapy. Overall, Staphylococcus aureus was the most commonly isolated pathogen and was found to be susceptible to ofloxacin in 12 of 14 patients. Two patients, 1 with a tolerant isolate of S. aureus, the other patient with a resistant isolate of S. aureus, responded clinically to ofloxacin therapy; a third patient with an initially ofloxacin-sensitive isolate failed therapy, and on subsequent culture an ofloxacin-resistant S. aureus was isolated. Ofloxacin was well tolerated and efficacious in the treatment of skin and soft tissue infections including those caused by staphylococci and streptococci.

Subcellular distribution and phosphorylation state of insulin receptors from insulin- and isoproterenol-treated rat adipose cells

Rat adipose cells treated with insulin followed by isoproterenol exhibit a change in glucose transporter intrinsic activity (lowered maximal activity) and a decrease in insulin sensitivity (rightward shift of the concentration-response curve) when assayed for 3-O-methylglucose transport. To investigate the latter phenomenon, the distribution and phosphorylation state of insulin receptors was examined. Isoproterenol augmented the effect of insulin to reduce cell surface receptors by 20-30%. These receptors were recovered in microsomal fractions. Isoproterenol also markedly reduced insulin-stimulated [32P]phosphate incorporation into the plasma membrane receptor beta-subunit. These effects may account for the effect of isoproterenol to decrease the sensitivity of the glucose transport response to insulin.

Qualitative and quantitative comparison of glucose transport activity and glucose transporter concentration in plasma membranes from basal and insulin-stimulated rat adipose cells

Conditions are described which allow the isolation of rat adipose-cell plasma membranes retaining a large part of the stimulatory effect of insulin in intact cells. In these membranes, the magnitude of glucose-transport stimulation in response to insulin was compared with the concentration of transporters as measured with the cytochalasin-B-binding assay or by immunoblotting with an antiserum against the human erythrocyte glucose transporter. Further, the substrate- and temperature-dependencies of the basal and insulin-stimulated states were compared. Under carefully controlled homogenization conditions, insulin-treated adipose cells yielded plasma membranes with a glucose transport activity 10-15-fold higher than that in membranes from basal cells. Insulin increased the transport Vmax. (from 1,400 +/- 300 to 15,300 +/- 3,400 pmol/s per mg of protein; means +/- S.E.M.; assayed at 22 degrees C) without any significant change in Km (from 17.8 +/- 4.4 to 18.9 +/- 1.4 nM). Arrhenius plots of plasma-membrane transport exhibited a break at 21 degrees C, with a higher activation energy over the lower temperature range. The activation energy over the higher temperature range was significantly lower in membranes from basal than from insulin-stimulated cells [27.7 +/- 5.0 kJ/mol (6.6 +/- 1.2 kcal/mol) and 45.3 +/- 2.1 kJ/mol (10.8 +/- 0.5 kcal/mol) respectively], giving rise to a larger relative response to insulin when transport was assayed at 37 degrees C as compared with 22 degrees C. The stimulation of transport activity at 22 degrees C was fully accounted for by an increase in the concentration of transporters measured by cytochalasin B binding, if a 5% contamination of plasma membranes with low-density microsomes was assumed. However, this 10-fold stimulation of transport activity contrasted with an only 2-fold increase in transporter immunoreactivity in membranes from insulin-stimulated cells. These data suggest that, in addition to stimulating the translocation of glucose transporters to the plasma membrane, insulin appears to induce a structural or conformational change in the transporter, manifested in an altered activation energy for plasma-membrane transport and possibly in an altered immunoreactivity as assessed by Western blotting.

Activity and phosphorylation state of glucose transporters in plasma membranes from insulin-, isoproterenol-, and phorbol ester-treated rat adipose cells

The counterregulatory action of catecholamines on insulin-stimulated glucose transport and its relation to glucose transporter phosphorylation were studied in isolated rat adipose cells. Plasma membranes exhibiting reduced glucose transport activity were prepared as described previously (Joost, H. G., Weber, T. M., Cushman, S. W., and Simpson, I. A. (1986) J. Biol. Chem. 261, 10033-10036) from cells treated with insulin, and subsequently with isoproterenol and adenosine deaminase. In these membranes, transporter affinity for cytochalasin B binding was significantly reduced (KD = 133.5 +/- 14 versus 89.8 +/- 11 nM, means +/- S.E.) with no change in number of sites or immunoreactivity of the transporter on Western blots. Reconstituted plasma membrane transport was significantly lower with isoproterenol treatment (0.50 +/- 0.12 versus 0.97 +/- 0.27 nmol/mg protein/10 s). In contrast, transport activity reconstituted from corresponding intracellular transporters (from low density microsomes) was unchanged (5.4 +/- 2.2 versus 6.9 +/- 1.2 nmol/mg protein/10 s). Thus, the intrinsic activity change of the transporter produced by catecholamines appears to reflect a structural modification that is confined to the plasma membrane and not recycled into the intracellular compartment. In cells equilibrated with [32P]phosphate, neither insulin nor isoproterenol induced [32P]phosphate incorporation into the glucose transporter immunoprecipitated from plasma membranes. Conversely, phorbol 12-myristate 13-acetate stimulated significant incorporation of [32P]phosphate into the glucose transporter in insulin-stimulated cells without any change in plasma membrane transport activity or transporter concentration. Thus, the phosphorylation state of the glucose transporter does not seem to be involved in either signaling transporter translocation or triggering changes in transporter intrinsic activity.

Insulin-stimulated glucose transport in rat adipose cells. Modulation of transporter intrinsic activity by isoproterenol and adenosine

The mechanism of modulation of insulin-stimulated glucose transport activity in isolated rat adipose cells by lipolytic and antilipolytic agents has been examined. We have measured glucose transport activity in intact cells with 3-O-methylglucose and in plasma membranes with D-glucose, and the concentration of glucose transporters in plasma membranes using a cytochalasin B binding assay. In intact cells, isoproterenol reduced insulin-stimulated transport activity by 60%. This effect was lost after cooling and washing the cells with homogenization buffer, and neither the concentration of glucose transporters nor transport activity in the plasma membranes differed from control. However, treatment of cells with KCN prior to homogenization preserved the isoproterenol effect through the fractionation procedure. Plasma membranes from these cells contained an unchanged number of transporters (31 +/- 7, mean +/- S.E., versus 31 +/- 4 pmol/mg of protein in controls) but transported glucose at a reduced rate (19 +/- 6 versus 48 +/- 9 pmol/mg of protein/s). Conversely, incubation of intact cells in the presence of adenosine stimulated plasma membrane glucose transport activity compared to that in the absence of adenosine (44 +/- 6 versus 36 +/- 6 pmol/mg of protein/s). Kinetic studies of isoproterenol-inhibited glucose transport in plasma membranes revealed a 60% decrease in Vmax (2900 +/- 350 versus 7200 +/- 1000 pmol/mg of protein/s) and a small increase in Km (15.1 +/- 1 versus 13.0 +/- 0.6 mM). These data indicate that modifications of glucose transport activity produced by lipolytic and antilipolytic agents in intact adipose cells can be fully retained in plasma membranes isolated under appropriate conditions. Furthermore, the effects of these agents occur through a modification of the glucose transporter intrinsic activity.

Characterization of a photosensitive glucose derivative. A photoaffinity reagent for the erythrocyte hexose transporter

The photosensitive reagent 6-N-(4-azido-2-hydroxy-3,5-diiodobenzoyl)-D-glucosamine has been assessed as a potential photoaffinity label for the hexose transporter. Under zero-trans conditions, transport experiments performed in the dark reveal that the reagent inhibits the uptake of D-glucose in resealed human erythrocyte ghosts. Increasing the concentration of glucose in the transport medium has a protective effect, reducing the inhibition. Kinetic analysis indicates that the probe acts as a competitive inhibitor with high affinity for the erythrocyte hexose transporter (Ki between 0.07 and 0.2 microM). Exposure to a 280 nm filtered high intensity mercury-vapor lamp results in a rapid and efficient photolysis. At low concentrations of the probe, specific labeling of membrane preparations was observed. Autoradiograms of 10% SDS gels revealed the specific labeling of bands 4.51 and 6. This labeling was concentration-dependent and protected by D-glucose (not the L-isomer) and phloretin in the medium. When subjected to multiple exposures of low concentration of the photoaffinity reagent, apparent saturation was achieved.