Do patients choose physicians of their own race?

This study seeks to determine whether minority Americans tend to see physicians of their own race as a matter of choice or simply because minority physicians are more conveniently located within predominantly minority communities. Using data from the Commonwealth Fund 1994 National Comparative Survey of Minority Health Care, we found that black and Hispanic Americans sought care from physicians of their own race because of personal preference and language, not solely because of geographic accessibility. As minority populations continue to grow, the demand for minority physicians is likely to increase. Keeping up with this demand will require medical school admissions policies and physician workforce planning to include explicit strategies to increase the supply of underrepresented minority physicians.

Patient-physician racial concordance and the perceived quality and use of health care.

BACKGROUND: Patients from racial and ethnic minority groups use fewer health care services and are less satisfied with their care than patients from the majority white population. These disparities may be attributable in part to racial or cultural differences between patients and their physicians. OBJECTIVE: To determine whether racial concordance between patients and physicians affects patients' satisfaction with and use of health care. METHODS: We analyzed data from the 1994 Commonwealth Fund's Minority Health Survey, a nationwide, telephone survey of noninstitutionalized adults. For the 2201 white, black, and Hispanic respondents who reported having a regular physician, we examined the association between patient-physician racial concordance and patients' ratings of their physicians, satisfaction with health care, reported receipt of preventive care, and reported receipt of needed medical care. RESULTS: Black respondents with black physicians were more likely than those with nonblack physicians to rate their physicians as excellent (adjusted odds ratio [OR], 2.40; 95% confidence interval [CI], 1.55-3.72) and to report receiving preventive care (adjusted OR, 1.74; 95% CI, 1.01-2.98) and all needed medical care (adjusted OR, 2.94; 95% CI, 1.10-7.87) during the previous year. Hispanics with Hispanic physicians were more likely than those with non-Hispanic physicians to be very satisfied with their health care overall (adjusted OR, 1.74; 95% CI, 1.01-2.99). CONCLUSIONS: Our findings confirm the importance of racial and cultural factors in the patient-physician relationship and reaffirm the role of black and Hispanic physicians in caring for black and Hispanic patients. Improving cultural competence among physicians may enhance the quality of health care for minority populations. In the meantime, by reducing the number of underrepresented minorities entering the US physician workforce, the reversal of affirmative action policies may adversely affect the delivery of health care to black and Hispanic Americans.

Accelerated lipoprotein uptake by transplantable hepatomas that express hepatic lipase.

To test the hypothesis that hepatic lipase plays a key role in lipoprotein removal in vivo, a novel system was used. Hepatoma cells (HTC 7288c) were transfected with a cDNA encoding hepatic lipase in culture and grown as solid tumors in vivo. In culture, transfected cells degraded chylomicron remnants and low density lipoprotein (LDL) somewhat more efficiently than untransfected cells. Tumors from the transplanted cells produced hepatic lipase localized to the surface of tumors from transfected cells but not tumors from non-transfected cells, grown in the same rat. The tumors from transfected cells removed, per gm of tissue, 34% (P < 0.001) more 125I-labeled LDL than tumors from non-transfected cells in the same animal. The uptake of chylomicron remnants (by tumors from transfected cells) was also modestly enhanced (15 +/- 6%, P < 0.005). There were no differences in the uptake of 125I-labeled albumin or 125I-labeled asialoglycoprotein. Compared to the liver, the untransfected tumors took up 12%, and the transfected tumors took up about 18% as much LDL per gram of tissue. The uptake of chylomicron remnants compared to liver was far lower. Both types of tumors had about twice as much LDL receptor related protein as the liver. Wild-type tumors had the highest level of LDL receptor, twice hepatic lipase-secreting tumors, and six times that of the liver. Using the novel approach of transfecting transplantable tumor cells with hepatic lipase, the ability of hepatic lipase to facilitate the removal of apoB-containing lipoproteins was demonstrated. The liver still removes low density lipoprotein and especially chylomicron remnants more rapidly than the tumors, suggesting factors in addition to hepatic lipase and LDL receptor level play a major role in hepatic lipoprotein removal.

Unmet mental health needs of women in public-sector gynecologic clinics.

OBJECTIVE: We examined the mental health needs of poor young women seen in public-sector gynecologic settings. STUDY DESIGN: Participants were 205 ethnically diverse women, mean age 29 years, seen by gynecologists at San Francisco General Hospital, all either uninsured or receiving public medical assistance. An interview with an instrument designed to diagnose mood, anxiety, alcohol, and eating disorders in medical patients, the Prime-MD, was used to assess current mental disorders. Any history of sexual or other physical assault was recorded. Receipt of primary care was scored for comprehensiveness. RESULTS: The rates of current psychiatric disorders were extremely high; 21.5% had current major depression. The prevalence of anxiety disorders was also elevated among these women. Many had a history of sexual trauma, and 28% had been the victims of unwanted intercourse. Finally, many reported behaviors that pose serious health risks. For example, 32% smoked and 2% used illicit drugs. Fewer than half had access to comprehensive primary medical care. CONCLUSIONS: Young, poor women who seek care in public-sector gynecologic clinics would benefit from comprehensive medical care addressing their psychosocial needs.

Overexpression of hormone-sensitive lipase in Chinese hamster ovary cells leads to abnormalities in cholesterol homeostasis.

Hormone-sensitive lipase (HSL) is an intracellular enzyme that functions as both a neutral triglyceride and cholesteryl ester hydrolase. In order to explore the effects of HSL on cholesterol homeostasis, Chinese hamster ovary (CHO) cells were transfected with rat HSL and several different stable cell lines that overexpress HSL mRNA, HSL protein, and HSL activity approximately 600-fold were isolated. Cells transfected with HSL contained less cholesteryl esters and unesterified cholesterol than control cells. HSL transfectants expressed 20-60% fewer LDL receptors than control cells when grown in lipid-depleted media or in the presence of mevinolin, as assessed by binding and degradation of LDL and immunoblotting of LDL receptors. In contrast, the rate of cholesterol synthesis and the activity of 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase were increased 3- to 14-fold in HSL transfectants grown in sterol replete media. The rate of cholesterol synthesis and the activity of HMG-CoA reductase increased when cells were grown in lipid-depleted media, and remained markedly elevated compared to control cells. These results show that the regulation of LDL receptor expression and cholesterol synthesis can be dissociated through the actions of HSL and suggest multiple control mechanisms for sterol-responsive genes.

Primary care and patient perceptions of access to care.

BACKGROUND: Although much is known about how insurance affects access to care, it is unclear whether good primary care contributes to access. The purpose of this study was to determine how optimal primary care given by providers at a regular place of care, defined in terms of continuity, comprehensiveness, communication, and availability, contributed to perceptions of access to care in a large population-based probability sample of adults. METHODS: Data were from a cross-sectional survey of 6674 English- and Spanish-speaking adults 18 to 64 years of age, randomly sampled from 41 urban California communities with a range of levels of access to care. RESULTS: Following adjustment for sociodemographics and need for care, we found that having "optimal" primary care contributed independently to improved self-rated access, as did having health insurance, a regular place, and a regular provider. The largest difference n access was between having any health insurance and not having insurance. Once insurance was available, each additional element contributed in a cumulative manner to self-rated access. For those with insurance and a regular place, adding optimal primary care improved self-rated access to an extent similar to adding a regular provider. CONCLUSIONS: We conclude that although providing insurance to the uninsured is the most effective means of improving self-rated access, the other elements each improve access as well. Once insurance and a regular place are provided, good primary care at that place may be equivalent to having a regular provider in terms of perceived access. Results support promotion of primary care as a model of health care that encourages good access.

Chinese hamster ovary cells expressing a cell surface-anchored form of hepatic lipase. Characterization of low density lipoprotein and chylomicron remnant uptake and selective uptake of high density lipoprotein-cholesteryl ester.

The enzyme hepatic lipase may play several roles in lipoprotein metabolism. Recent investigation has suggested a role for the enzyme in lipoprotein and/or lipoprotein lipid uptake. To study this, a simple isolated system that mimics the in vivo system would be desirable. The enzyme is secreted by the hepatic parenchymal cell but exists, and presumably exerts its effects, while bound to capillary endothelial cells in the liver, adrenal gland, and the ovary. We constructed a cDNA that encodes the expression of a chimeric protein composed of rat hepatic lipase and the signal sequence for the addition of the glycophosphatidylinositol (GPI) anchor from human decay-accelerating factor. When transfected into Chinese hamster ovary (CHO) cells this gave rise to a cell population that had immunoreactive hepatic lipase on the cell surface. Cloning of the transfected cells produced several cell lines that expressed the chimeric protein bound to the cell surface by a GPI anchor. This was documented by demonstrating incorporation of [3H]ethanolamine into anti-hepatic lipase immunoprecipitable material; in addition, hepatic lipase was released from the cells by phosphatidylinositol-specific phospholipase C but not by heparin. Phosphatidylinositol-phospholipase C treatment of cells expressing the anchored lipase released material that comigrated with hepatic lipase on SDS-polyacrylamide gel electrophoresis and was immunoreactive with antibody to the cross-reacting determinant of GPI anchors. Cell lysates containing the anchored protein contained salt-resistant lipase activity, a known feature of the secreted hepatic lipase; thus it appears that these cells have a surface-anchored hepatic lipase molecule. Although it was not possible to demonstrate lipolysis by the enzyme while it was on the cell surface for technical reasons, the protein produced by these cells was active when studied in cell membranes. The ability of the cells to take up lipoproteins was studied. The cells demonstrated an increased affinity for low density lipoprotein (LDL) receptor mediated uptake of LDL. They did not, however, demonstrate any enhanced binding or removal of chylomicron remnants. With respect to LDL and remnants, the cells expressing anchored lipase behaved similarly to CHO cell that expressed secreted hepatic lipase. The cells expressing anchored hepatic lipase had a marked increase in the uptake of high density lipoprotein and high density lipoprotein cholesteryl ester when compared to that seen with CHO cells secreting hepatic lipase. This increase occurred primarily via the selective pathway, and was not reduced by addition of anti-LDL receptor or anti-hepatic lipase antibodies or the receptor-associated protein. Together the results suggest that hepatic lipase, when bound to the cell surface by a GPI anchor, plays a role in enhancing lipoprotein uptake. For LDL this may involve the provision of a second foot for particle binding, thus enhancing affinity for the LDL receptor. For chylomicron remnants an additional molecule or molecules are necessary to mediate this effect. For HDL, the enzyme facilitates uptake of cholesteryl ester primarily by the selective pathway.

Physician practice style and rates of hospitalization for chronic medical conditions.

Hospitalization rates for chronic medical conditions vary across small areas and are associated inversely with community income. The authors studied whether variation in hospitalization rates can be attributed to differences in physician practice style. Using census and hospital discharge data, hospitalization rates were calculated for asthma, congestive heart failure, and diabetes in 40 medical service areas in California. The authors surveyed a random sample of 1,530 emergency physicians, general internists, and family and general practitioners in these areas, and measured clinical admission threshold by asking physicians whether they would hospitalize patients presented in 15 vignettes of graded severity. The authors measured social admission predisposition by asking how physicians' admission decisions would be influenced by social characteristics that increase patients' vulnerability to illness, including homelessness and drug use; 1,090 physicians responded (71%). There was significant variation across areas in both the clinical (P < 0.0001) and social (P < 0.001) admission scores. Variation in hospitalization rates correlated with physicians' clinical (r = .34, P = 0.03) and social (r = .36, P = 0.02) admission scores. However, in a multiple linear regression analysis that included community sociodemographic factors, physician practice style was not associated significantly with hospitalization rates. Physician practice style varies across areas, but does not explain variation in admission rates for chronic medical conditions after adjusting for community sociodemographic factors. Using methods such as practice guidelines or utilization review to re-set physicians' threshold for admission may not be effective in reducing hospitalizations for chronic medical conditions.

The role of black and Hispanic physicians in providing health care for underserved populations.

BACKGROUND: Patients who are members of minority groups may be more likely than others to consult physicians of the same race or ethnic group, but little is known about the relation between patients' race or ethnic group and the supply of physicians or the likelihood that minority-group physicians will care for poor or black and Hispanic patients. METHODS: We analyzed data on physicians' practice locations and the racial and ethnic makeup and socioeconomic status of communities in California in 1990. We also surveyed 718 primary care physicians from 51 California communities in 1993 to examine the relation between the physicians' race or ethnic group and the characteristics of the patients they served. RESULTS: Communities with high proportions of black and Hispanic residents were four times as likely as others to have a shortage of physicians, regardless of community income. Black physicians practiced in areas where the percentage of black residents was nearly five times as high, on average, as in areas where other physicians practiced. Hispanic physicians practiced in areas where the percentage of Hispanic residents was twice as high as in areas where other physicians practiced. After we controlled for the racial and ethnic makeup of the community, black physicians cared for significantly more black patients (absolute difference, 25 percentage points; P < 0.001) and Hispanic physicians for significantly more Hispanic patients (absolute difference, 21 percentage points; P < 0.001) than did other physicians. Black physicians cared for more patients covered by Medicaid (P = 0.001) and Hispanic physicians for more uninsured patients (P = 0.03) than did other physicians. CONCLUSIONS: Black and Hispanic physicians have a unique and important role in caring for poor, black, and Hispanic patients in California. Dismantling affirmative-action programs as is currently proposed, may threaten health care for both poor people and members of minority groups.

Isoproterenol decreases LDL receptor expression in rat adipose cells: activation of cyclic AMP-dependent proteolysis.

The low density lipoprotein (LDL) receptor is part of a family of proteins that mediate the uptake of lipoproteins into cells. In this paper we have demonstrated the over-expression in E. coli of a rat LDL receptor fusion protein that contains the region of the receptor sharing homology with the EGF precursor. The fusion protein was utilized to immunize rabbits and successfully generate antibodies that recognize the intact LDL receptor. These anti-LDL receptor/fusion protein antibodies were used to examine the effects of cyclic AMP on the expression of LDL receptors in isolated rat adipocytes. Incubation of adipocytes with isoproterenol caused a dose-dependent diminution in intact LDL receptors in the plasma membrane with the concomitant appearance of smaller immunoreactive proteins. Pulse-chase experiments demonstrated that isoproterenol rapidly shortened the initial half-life of intact, immunoprecipitable LDL receptors in the plasma membrane. The effects of isoproterenol on LDL receptor expression were mimicked by forskolin, by an analog of cyclic AMP, and by ACTH. In contrast, incubation with propranolol blocked the effects of isoproterenol on LDL receptor expression. While antioxidants and several different protease inhibitors had no effects, N-acetyl-leucine-leucine-methionine (ALLM) was able to prevent the isoproterenol-induced effects on LDL receptors. Thus, it appears that agents acting via cyclic AMP cause a rapid decrease in LDL receptors in the plasma membranes of isolated adipose cells due to the apparent stimulation of an ALLM-sensitive protease that degrades the LDL receptor. These results suggest a novel mechanism for the posttranscriptional regulation of LDL receptor expression in adipocytes.

Relative roles of the LDL receptor, the LDL receptor-like protein, and hepatic lipase in chylomicron remnant removal by the liver.

Studies were carried out in mice utilizing inhibitors of several cell surface molecules to evaluate their relative roles in chylomicron remnant removal. Anti-LDL receptor antibody inhibited approximately 45% of rapid remnant removal from plasma, prolonged their half life (63 s to 115 s) and reduced hepatic uptake by 45%. Receptor-associated protein (RAP) (1 mg/mouse), a high affinity inhibitor of the LDL receptor-related protein (LRP) and a low affinity inhibitor of the LDL receptor decreased remnant removal approximately 55%, prolonged the half life from 63 s to 230 s, and reduced hepatic uptake by 70%. RAP, but not anti-LDL receptor antibody, inhibited splenic uptake. With both injected together, an incremental effect was seen; plasma removal decreased 60%, T1/2 increased to 290 s, and hepatic uptake decreased by 80%. Thus, it is likely that virtually all of the very rapid removal of remnants from the plasma by the liver requires the presence of at least one of these members of the LDL receptor family. Anti-hepatic lipase antibody caused a small but significant delay in remnant removal from plasma and a larger decrease in hepatic uptake (22.5%). It doubled adrenal uptake. The anti-hepatic lipase antibody was not additive with either the anti-LDL receptor antibody or RAP. Anti-rat hepatic lipase antibody did not inhibit lipolysis by mouse hepatic lipase, suggesting that lipolysis is not the way hepatic lipase enhances remnant uptake. Hepatic lipase bound to remnants to a greater degree than it bound to other lipoproteins. Together these data suggest that hepatic lipase may serve as a binding site for chylomicron remnants, thereby enhancing their affinity for the liver surface, and thus removal by the proteins of the LDL receptor family. Other molecules may also play a role in removal from the circulation under conditions where the LDL receptor family receptors are absent or occupied.

Location and regulation of low-density lipoprotein receptors in intestinal epithelium.

The expression, distribution, and some aspects of the regulation of low-density lipoprotein (LDL) receptors in rat intestinal epithelial cells were examined. Cells prepared by a perfusion technique provided a pure preparation of epithelial cells and could be manipulated to produce crypt-villus units or villi alone. On a total protein basis, the abundance of LDL receptors in villus cell membranes was half that in hepatic membranes. The level of receptors in both tissues was reduced by feeding an atherogenic diet but was increased only in the liver by ethinyl estradiol-induced hypocholesterolemia. The level of LDL receptor mRNA in intestinal epithelial cells was somewhat lower than in liver. Regulation of LDL receptor mRNA was similar to that of protein. Judged by the ratio of mRNA in villus cells to the villus-crypt unit and nuclear run-on assay for LDL receptor gene transcription, we conclude that LDL receptor mRNA is produced in the villus cells. The effect of fat feeding was regulated at the level of transcription. Expression in villus cells in ileum was severalfold higher than in jejunum and higher than in the liver. Together the results suggest serum cholesterol level is not the prime determinant of LDL receptor level in intestine, but LDL degradation in this organ may be regulated by factors in the lumen.

Preventable hospitalizations and access to health care.

OBJECTIVE: To examine whether the higher hospital admission rates for chronic medical conditions such as asthma, hypertension, congestive heart failure, chronic obstructive pulmonary disease, and diabetes in low-income communities resulted from community differences in access to care, prevalence of the diseases, propensity to seek care, or physician admitting style. DESIGN: Analysis of California hospital discharge data. We calculated the hospitalization rates for these five chronic conditions for the 250 ZIP code clusters that define urban California. We performed a random-digit telephone survey among adults residing in a random sample of 41 of these urban ZIP code clusters stratified by admission rates and a mailed survey of generalist and emergency physicians who practiced in the same 41 areas. SETTING: Community based. PARTICIPANTS: A total of 6674 English- and Spanish-speaking adults aged 18 through 64 years residing in the 41 areas were asked about their access to care, their chronic medical conditions, and their propensity to seek health care. Physician admitting style was measured with written clinical vignettes among 723 generalist and emergency physicians practicing in the same communities. MAIN OUTCOME MEASURES: We compared respondents' reports of access to medical care in an area with the area's cumulative admission rate for these five chronic conditions. We then tested whether access to medical care remained independently associated with preventable hospitalization rates after controlling for the prevalence of the conditions, health care seeking, and physician practice style. RESULTS: Access to care was inversely associated with the hospitalization rates for the five chronic medical conditions (R2 = 0.50; P < .001). In a multivariate analysis that included a measure of access, the prevalence of conditions, health care seeking, and physician practice style to predict cumulative hospitalization rates for chronic medical conditions, both self-rated access to care (P < .002) and the prevalence of the conditions (P < .03) remained independent predictors. CONCLUSION: Communities where people perceive poor access to medical care have higher rates of hospitalization for chronic diseases. Improving access to care is more likely than changing patients' propensity to seek health care or eliminating variation in physician practice style to reduce hospitalization rates for chronic conditions.

Site-directed mutagenesis using thermostable enzymes.

The two-primer method for site-directed mutagenesis facilitates the mutation of targets in double-stranded DNA. We have encountered difficulties using the original method for the mutagenesis of DNA cloned into pBluescript vectors, which is possibly due to the presence of regions of secondary structure that cannot be efficiently copied by the enzymes used. We report a modification of the two-primer method using the thermostable VentR DNA polymerase and Thermus aquaticus ligase, allowing an increase in reaction temperatures. The modified method is functional with the pBluescript family of vectors.

Overexpression of hormone-sensitive lipase prevents triglyceride accumulation in adipocytes.

Hormone-sensitive lipase (HSL) is a cytosolic neutral lipase that hydrolyzes intracellular stores of triglycerides within adipocytes and is thought to be the rate limiting enzyme in lipolysis; however, direct evidence to prove this concept has been lacking. The present study was designed to establish the function of HSL in adipocytes. A 2360-bp fragment containing the entire HSL coding region was cloned into the vector pCEP4 and was used to transfect the 3T3-F442A adipogenic cell line. Nondifferentiated, transfected cells were screened for HSL overexpression by indirect immunofluorescence microscopy and confirmed by immunoblotting cell extracts with anti-HSL/fusion protein antibodies and by Northern blots for HSL mRNA. Stable transfectants overexpressing HSL were obtained and cloned. Compared with undifferentiated 3T3-F442A cells transfected with pCEP4 not containing the insert (vector alone) where HSL expression was very low, undifferentiated HSL transfectants had up to a 100-fold increase in HSL activity. Likewise, immunoreactive HSL protein and HSL mRNA levels were increased up to 100-fold in HSL transfectants. When confluent cells were allowed to differentiate by exposure to insulin, HSL expression increased in vector alone transfected cells, but remained below that observed in HSL transfectants. A similar degree of differentiation was seen in both vector alone and HSL transfectants when based on the induction of lipoprotein lipase. Cellular triglyceride content increased dramatically in the vector alone transfected cells while triglyceride content was markedly reduced in the HSL transfectants. The expression of late markers of adipocyte differentiation, such as aP2 and GPDH, was diminished and appeared to vary with the degree to which HSL was overexpressed and the cellular triglyceride content was reduced. Thus, the overexpression of HSL in 3T3-F442A cells prevents differentiated adipocytes from taking on the appearance of fat cells, i.e., accumulating triglyceride. Furthermore, the overexpression of HSL directly or indirectly attenuates the expression of several genes that appear during late adipocyte differentiation.

California physicians' willingness to care for the poor.

Although generalist physicians appear to be more likely than specialists to provide care for poor adult patients, they may still perceive financial and nonfinancial barriers to caring for these patients. We studied generalist physicians' attitudes toward caring for poor patients using focus groups and used the results to design a survey that tested the generalizability of the focus group findings. The focus groups included a total of 24 physicians in 4 California communities; the survey was administered to a random sample of 177 California general internists, family physicians, and general practitioners. The response rate was 70%. Of respondents, 77% accepted new patients with private insurance; 31% accepted new Medicaid patients, and 43% accepted new uninsured patients. Nonwhite physicians were more likely to care for uninsured and Medicaid patients than were white physicians. In addition to reimbursement, nonfinancial factors played an important role in physicians' decisions not to care for Medicaid or uninsured patients. The perception of an increased risk of being sued was cited by 57% of physicians as important in the decision not to care for Medicaid patients and by 49% for uninsured patients. Patient characteristics such as psychosocial problems, being ungrateful for care, and noncompliance were also important. Poor reimbursement was cited by 88% of physicians as an important reason not to care for Medicaid patients and by 77% for uninsured patients. Policy changes such as universal health insurance coverage and increasing the supply of generalist physicians may not adequately improve access to care unless accompanied by changes that address generalist physicians' financial and nonfinancial concerns about providing care for poor patients.

Generation of antibodies against a human lipoprotein lipase fusion protein.

Antibodies generated against specific proteins are useful tools for studying the physiology and cell biology of the protein of interest. Although antibodies have been successfully generated against lipoprotein lipase (LPL) and used to elucidate many aspects of its biology, there have been problems with the specificity, affinity and availability of these antibodies. To circumvent these problems, we have expressed a portion of human LPL as a bacterial fusion protein. The human LPL bacterial fusion protein was utilized to generate polyclonal antibodies in rabbits that recognize intact human, rat and bovine LPL. Using these antibodies, it was possible to demonstrate a direct correlation between LPL mass and LPL activity from different samples of human post-heparin plasma. In addition, these antibodies were used to develop an ELISA for the measurement of LPL in tissue or plasma. This is a useful means for obtaining polyclonal antibodies to LPL in sufficient quantity and without contaminating mammalian proteins.

Transcriptional regulation of lipoprotein lipase in the heart during development in the rat.

Lipoprotein lipase (LPL) is differentially expressed in fat and heart under a variety of physiological conditions, particularly during development. LPL activity, protein and mRNA levels have been shown to rise dramatically during the first three weeks of life. The mechanism responsible for these changes in LPL in the heart during development are not fully understood. In order to address the changes in LPL in the heart during development, we measured steady state levels of LPL mRNA and the rate of LPL transcription during development. Northern blot analysis of LPL mRNA in the heart of rats from 5-120 days of age showed no changes in transcript size; however, steady state levels of LPL mRNA increased approximately 10-fold by day 20 and remained elevated thereafter. The rate of LPL transcription increased dramatically between day 5-20 and remained elevated thereafter. Thus, as opposed to other settings where posttranscriptional and posttranslational mechanisms can be important, the increased expression of LPL in rat heart that occurs during development appears to be largely due to the transcriptional activation of the gene.

Acceleration of uptake of LDL but not chylomicrons or chylomicron remnants by cells that secrete apoE and hepatic lipase.

ApoE is a ligand for the low density lipoprotein (LDL) receptor as well as for the LDL receptor-related protein (LRP). The enzyme hepatic lipase (HL) may also affect the uptake of lipoproteins by modifying their composition. We have tested the hypothesis that hepatic lipase and apoE can function as co-factors to alter the rate of lipoprotein uptake. Chinese hamster ovary (CHO) cells were transfected with cDNAs for rat hepatic lipase, human apoE or both HL and apoE. The secreted recombinant proteins were thoroughly characterized and had properties identical to the native proteins. Hepatic lipase and apoE were secreted at 0.17 and 1.25 micrograms/mg cell protein per hour, rates comparable to those in normal liver. 125I-labeled LDL, chylomicron remnants, or chylomicrons were added to media at concentrations near their Kd. In cells that secreted either apoE or hepatic lipase, or both apoE and hepatic lipase, LDL binding was significantly greater than with control cells (2.2-, 2-, 2-fold greater, respectively). Similar enhancement of LDL degradation was observed. In the presence of anti-LDL receptor antibodies, these values were reduced to control levels; thus, the enhanced uptake was mediated by the LDL receptor and not the LRP. The amount of LDL receptor protein, as judged by Western blotting, was similar in the various cell types. Incubation of control CHO cells with media from secreting transfected cells also increased the uptake of 125I-labeled LDL. Kinetic studies indicated that, in apoE-secreting cells, increased LDL binding is associated with a lower Kd and an unchanged Vmax as compared to the control cells; furthermore, when LDL were reisolated by column chromatography (but not by ultracentrifugation) from the incubations where apoE was being secreted, apoE was identified adherent to the LDL particles. Together, these results suggest that the effect is due to alteration of the lipoprotein and not the cell. In contrast, the uptake of 125I-labeled chylomicron remnants, and 125I-labeled chylomicrons was not greater in the transfected cells. Thus, in the amounts secreted by these cells, hepatic lipase and apoE do not convert chylomicrons to chylomicron remnants or alter the uptake of chylomicron remnants by either the LDL receptor or the LRP. The enhancement of LDL removal in cells that secrete hepatic lipase or apoE may help determine the amount of LDL removed by a particular tissue.

Early induction of LDL receptor gene during rat liver regeneration.

After partial hepatectomy in the rat, there is substantial lipid accumulation in the liver. No information is available on the possible role of receptor-mediated endocytosis in this process. Since the low density lipoprotein (LDL) receptor is stimulated as a part of an early growth response in cell culture (Ellsworth et al.: Biochem. J. 279:175-187, 1991), the metabolism of this receptor during liver regeneration was studied. The mRNA and membrane protein level of the receptor were measured in the liver and in the adrenal glands at different times after partial hepatectomy, corresponding to different phases of the cell cycle. A discontinuous pattern of receptor expression is detectable in the regenerating liver; a large increase of mRNA and membrane protein occurs at an early time (2-4 h), suggesting that there is induction of LDL receptor gene transcription shortly after partial hepatectomy. This response seems specific for the liver following injury since the adrenal receptor does not show a different pattern in partially hepatectomized rats and sham-operated controls. After returning to control levels, the LDL receptor again increases slightly above control at 24 h, a time when cell replication begins.