Intensive care management of a complex Medicaid population: a randomized evaluation

OBJECTIVES

Care management programs are employed by providers and payers to support high-risk patients and affect cost and utilization, with varied implementation. This study sought to evaluate the impact of an intensive care management program on utilization and cost among those with highest cost (top 5%) and highest utilization in a Medicaid accountable care organization (ACO) population.

STUDY DESIGN

Randomized controlled quality improvement trial of intensive care management, provided by a nonprofit care management vendor, for Medicaid ACO patients at 2 academic centers.

METHODS

Patients were identified using claims, chart review, and primary care validation, then randomly assigned 2:1 to intervention and control groups. Among 131 patients included in intent-to-treat analysis, 87 and 44 were randomly assigned to the intervention and control groups, respectively. Patients in the intervention group were eligible to receive intensive care management in the community/home setting and, in some cases, home-based primary care. Patients in the control group received standard of care, including practice-based care management. Prespecified primary outcome measures included total medical expense (TME), emergency department (ED) visits, and inpatient utilization.

RESULTS

Relative to controls, patients randomly assigned to receive intensive care management had a $1933 smaller increase per member per month in TME (P = .04) and directionally consistent but nonsignificant reductions in ED visits (17% fewer; P = .40) and inpatient admissions (34% fewer; P = .29) in the 12 months post randomization compared with the 12 months prerandomization.

CONCLUSIONS

Our study results support that targeted, intensive care management can favorably affect TME in a health system-based high-cost, high-risk Medicaid population. Further research is needed to evaluate the impact on additional clinical outcomes.

Detrimental conditions affecting Xestospongia muta across shallow and mesophotic coral reefs off the southwest coast of Puerto Rico

Sponges are fundamental components of coral reef communities and, unfortunately, like other major benthic members, they too have been impacted by epizootic and panzootic events. We report on the prevalence of disease-like conditions affecting populations of the giant barrel sponge Xestospongia muta across shallow and mesophotic coral reefs off La Parguera Natural Reserve (LPNR) and Mona Island Marine Reserve (MIMR) in Puerto Rico. Four different conditions affecting X. muta were observed during our surveys, of which 3 have been previously reported: cyclic spotted bleaching (CSB; apparently non-lethal), Xestospongia-tissue wasting disease (X-TWD; apparently lethal), and sponge orange band disease (SOB; sparsely associated with X-TWD infected individuals). Additionally, we describe a fourth condition, Xestospongia-tissue hardening condition (X-THC), a previously unreported disease recently observed along the insular shelf margin off LPNR and MIMR. Within LPNR, a total of 764 specimens of X. muta were inspected and measured. Of these, 590 sponges (72.2%) had CSB, 25 (3.27%) had signs of X-TWD, 7 (0.92%) had SOB, and the remaining 142 (18.6%) were apparently healthy. Three colonies inhabiting upper mesophotic depths on the LPNR insular shelf showed signs of CSB and X-TWD. At MIMR, video-transect surveys revealed a total of 514 colonies, of which 40 (7.78%) had signs of CSB and/or XTWD, 14 (2.72%) were affected by X-THC, while the remaining 460 (89.5%) showed no external signs of disease and appeared healthy. The presence of 4 concomitant disease-like conditions in barrel sponges of Puerto Rico is alarming, and indicative of the deteriorating status of Caribbean coral reefs.

Bending The Spending Curve By Altering Care Delivery Patterns: The Role Of Care Management Within A Pioneer ACO

Accountable care organizations (ACOs) appear to lower medical spending, but there is little information on how they do so. We examined the impact of patient participation in a Pioneer ACO and its care management program on rates of emergency department (ED) visits and hospitalizations and on Medicare spending. We used data for the period 2009-14, exploiting naturally staggered program entry to create concurrent controls to help isolate the program effects. The care management program (the ACO's primary intervention) targeted beneficiaries with elevated but modifiable risks for future spending. ACO participation had a modest effect on spending, in line with previous estimates. Participation in the care management program was associated with substantial reductions in rates for hospitalizations and both all and nonemergency ED visits, as well as Medicare spending, when compared to preparticipation levels and to rates and spending for a concurrent sample of beneficiaries who were eligible for but had not yet started the program. Rates of ED visits and hospitalizations were reduced by 6 percent and 8 percent, respectively, and Medicare spending was reduced by 6 percent. Targeting beneficiaries with modifiable high risks and shifting care away from the ED represent viable mechanisms for altering spending within ACOs.

Substantial Physician Turnover And Beneficiary 'Churn' In A Large Medicare Pioneer ACO

Alternative payment models, such as accountable care organizations (ACOs), attempt to stimulate improvements in care delivery by better alignment of payer and provider incentives. However, limited attention has been paid to the physicians who actually deliver the care. In a large Medicare Pioneer ACO, we found that the number of beneficiaries per physician was low (median of seventy beneficiaries per physician, or less than 5 percent of a typical panel). We also found substantial physician turnover: More than half of physicians either joined (41 percent) or left (18 percent) the ACO during the 2012-14 contract period studied. When physicians left the ACO, most of their attributed beneficiaries also left the ACO. Conversely, about half of the growth in the beneficiary population was because of new physicians affiliating with the ACO; the remainder joined after switching physicians. These findings may help explain the muted financial impact ACOs have had overall, and they raise the possibility of future gaming on the part of ACOs to artificially control spending. Policy refinements include coordinated and standardized risk-sharing parameters across payers to prevent any dilution of the payment incentives or confusion from a cacophony of incentives across payers.

Patient Population Loss At A Large Pioneer Accountable Care Organization And Implications For Refining The Program

There is an ongoing move toward payment models that hold providers increasingly accountable for the care of their patients. The success of these new models depends in part on the stability of patient populations. We investigated the amount of population turnover in a large Medicare Pioneer accountable care organization (ACO) in the period 2012-14. We found that substantial numbers of beneficiaries became part of or left the ACO population during that period. For example, nearly one-third of beneficiaries who entered in 2012 left before 2014. Some of this turnover reflected that of ACO physicians-that is, beneficiaries whose physicians left the ACO were more likely to leave than those whose physicians remained. Some of the turnover also reflected changes in care delivery. For example, beneficiaries who were active in a care management program were less likely to leave the ACO than similar beneficiaries who had not yet started such a program. We recommend policy changes to increase the stability of ACO beneficiary populations, such as permitting lower cost sharing for care received within an ACO and requiring all beneficiaries to identify their primary care physician before being linked to an ACO.

Development and Implementation of a Collaborative Team Care Model for Effective Insulin Use in an Academic Medical Center Primary Care Network

Improving glycemic control across a primary care diabetes population is challenging. This article describes the development, implementation, and outcomes of the Diabetes Care Collaborative Model (DCCM), a collaborative team care process focused on promoting effective insulin use targeting patients with hyperglycemia in a patient-centered medical home model. After a pilot, the DCCM was implemented in 18 primary care practices affiliated with an academic medical center. Its implementation was associated with improvements in glycemic control and increase in insulin prescription longitudinally and across the entire population, with a >1% reduction in the proportion of glycated hemoglobin >9% at 2 years after the implementation compared with the 2 years prior ( P < .001). Facilitating factors included diverse stakeholder engagement, institutional alignment of priorities, awarding various types of credits for participation and implementation to providers, and a strong theoretical foundation using the principles of the collaborative care model.

Implementing a hybrid approach to select patients for care management: variations across practices

OBJECTIVES

Appropriate selection of patients is key to the success of care management programs (CMPs). Hybrid patient selection approaches, in which large data assets are culled to develop a list of patients for more targeted clinical review, are increasingly common. We sought to describe the patient and practice characteristics associated with high-risk patient identification and selection for a CMP during clinical review, and to explore variation across primary care practices.

STUDY DESIGN

Retrospective cohort study.

METHODS

Standardized estimates of Medicare beneficiaries identified as high risk for poor outcomes and high medical expense, and appropriate for a CMP within a large Pioneer Accountable Care Organization, were developed using mixed effects logistic models. Study subjects were 2685 Medicare beneficiaries aged over 18 (includes individuals eligible for Medicare due to a disability) aligned to 35 primary care practices in 2013.

RESULTS

Independent predictors of patient identification as high risk include older age; higher risk score; recent increases in medical conditions; higher numbers of medical hospitalizations, skilled nursing facility days, and primary care physician visits; and shorter relationships with the primary care physician. Older age, and lower income, but no prior hospice use were independently associated with patient selection for a CMP among the subset of patients identified as being high risk. Adjusted predicted percents of high-risk patients varied significantly across practices overall and for 5 of the 6 patient characteristics that were independently associated with identification as high risk.

CONCLUSIONS

Inconsistency in high-risk patient identification and selection for a CMP may reflect differences in practice resources, but also highlight the need for continual training and feedback in order to protect against unintentional biases.

Impact of rapid screening for discontinuation of methicillin-resistant Staphylococcus aureus contact precautions

BACKGROUND

A history of methicillin-resistant Staphylococcus aureus (MRSA) is a determinant of inpatient bed assignment.

METHODS

We assessed outcomes associated with rapid testing and discontinuation of MRSA contact precautions (CP) in a prospective cohort study of polymerase chain reaction (PCR)-based screening in the Emergency Department (ED) of Massachusetts General Hospital. Eligible patients had a history of MRSA and were assessed and enrolled if documented off antibiotics with activity against MRSA and screened for nasal colonization (subject visit). PCR-negative subjects had CP discontinued; the primary outcome was CP discontinuation. We identified semiprivate rooms in which a bed was vacant owing to the CP status of the study subject, calculated the hours of vacancy, and compared idle bed-hours by PCR results. Program costs were compared with predicted revenue.

RESULTS

There were 2864 eligible patients, and 648 (22.6%) subject visits were enrolled. Of these, 65.1% (422/648) were PCR-negative and had CP discontinued. PCR-negative subjects had fewer idle bed-hours compared with PCR-positive subjects (28.6 ± 25.2 vs 75.3 ± 70.5; P < .001). The expected revenues from occupied idle beds and averted CP costs ranged from $214,160 to $268,340, and exceeded the program costs.

CONCLUSION

A program of targeted PCR-based screening for clearance of MRSA colonization resulted in expected revenues and decreased CP costs that outweighed programmatic costs.

Communicate, don't litigate: The Schwartz Center Connections Program

Little is known about effective educational approaches intended to reduce malpractice risk by improving communication with patients and among multidisciplinary teams in outpatient settings in order to prevent diagnostic delays and errors. This article discusses a prospective, controlled educational intervention that aimed to open lines of communication among teams in two disciplines: identifying how and why communication lapses occur between disciplines and with patients, and articulating strategies to avert them.

Extended geographic distribution of several Indo-Pacific coral reef diseases

Other than coral bleaching, few coral diseases or diseases of other reef organisms have been reported from Japan. This is the first report of lesions similar to Porites ulcerative white spots (PUWS), brown band disease (BrB), pigmentation response (PR), and crustose coralline white syndrome (CCWS) for this region. To assess the health status and disease prevalence, qualitative and quantitative surveys (3 belt transects of 100 m² each on each reef) were performed in March and September 2010 on 2 reefs of the Ginowan-Ooyama reef complex off Okinawa, and 2 protected reefs off Zamani Island, in the Kerama Islands 40 km west of Okinawa. Overall, mean (±SD) disease prevalence was higher in Ginowan-Ooyama (9.7 ± 7.9%) compared to Zamami (3.6 ± 4.6%). Porites lutea was most affected by PUWS at Ooyama (23.1 ± 10.4 vs. 4.5 ± 5.2%). White syndrome (WS) mostly affected Acropora cytherea (12. 5 ± 18.0%) in Zamami and Oxipora lacera (10.2 ± 10%) in Ooyama. Growth anomalies (GA) and BrB were only observed on A. cytherea (8.3 ± 6.2%) and A. nobilis (0.8%) at Zamami. Black band disease affected Pachyseris speciosa (6.0 ± 4.6%) in Ooyama only. Pigmentation responses (PR) were common in massive Porites in both localities (2.6 ± 1.9 and 5.6 ± 2.3% respectively). Crustose coralline white syndrome (CCWS) was observed in both localities. These results significantly expand the geographic distribution of PUWS, BrB, PR and CCWS in the Indo-Pacific, indicating that the northernmost coral reefs in the western Pacific are susceptible to a larger number of coral diseases than previously thought.

Are research ethics standards satisfied in pediatric journal publications?

BACKGROUND

The requirements for institutional review board (IRB) review and informed consent (IC) for research involving human subjects have existed for more than 2 decades. Although many studies document them poorly, most published research undergoes IRB review and has IC procedures. Less is known about research published in pediatric journals, and how child health research is determined to be exempt.

METHOD

All full-length articles published in the paper edition of 3 pediatric journals between January and December 2000 were examined. Articles were excluded if they were case studies, meta-analyses, lacked empirical data, or did not include at least 1 US researcher or US subjects. The remaining articles were examined to determine if they documented IRB review and IC mechanisms. If either or both of these features were missing, authors were asked to participate voluntarily in a survey. In addition, all exempt articles were examined to determine if the exemptions were in accordance with the federal regulations for the protection of human subjects.

RESULTS

Three hundred seventy-nine of 575 articles met inclusion criteria. One hundred ninety-seven (52.0%) documented IRB review, 164 (43.3%) documented IC, and 131 (34.6%) properly documented the presence of both IRB review and IC. Two hundred fifty-one researchers were surveyed to clarify IRB review and/or IC mechanisms. Approximately 13.5% of the research had not undergone IRB review, and 12.4% had not had their consent methods reviewed by an IRB. We found that between 26.9% and 39.8% of exempted research did not meet federal regulations requirements.

CONCLUSIONS

We found that most research underwent IRB review and had a consent mechanism despite the lack of documentation in the articles. We also found that most research that did not undergo IRB review would have been exempt under current guidelines. However, a significant number of IRB- and researcher-exempted research were inappropriately classified. Improving research ethics standards will require additional education for researchers and IRB members, and greater adherence of researchers (and editors) to the journals' guidelines on these issues.

A comparison of dermatologists' and primary care physicians' accuracy in diagnosing melanoma: a systematic review

OBJECTIVE

To compare the accuracy of dermatologists and primary care physicians (PCPs) in identifying pigmented lesions suggestive of melanoma and making the appropriate management decision to perform a biopsy or to refer the patient to a specialist.

DATA SOURCES

Studies published between January 1966 and October 1999 in the MEDLINE, EMBASE, and CancerLit databases; reference lists of identified studies; abstracts from recent conference proceedings; and direct contact with investigators. Medical subject headings included melanoma, diagnosis, screening, primary care, family practitioner, general practitioner, internal medicine, dermatologist, and skin specialist. Articles were restricted to those involving human subjects.

STUDY SELECTION

Studies that presented sufficient data to determine the sensitivity and specificity of dermatologists' or PCPs' ability to correctly diagnose lesions suggestive of melanoma and to perform biopsies on or refer patients with such lesions.

DATA EXTRACTION

Two reviewers independently abstracted data regarding the sensitivity and specificity of the dermatologists and PCPs for diagnostic and biopsy or referral accuracy. Disagreements were resolved by discussion. The quality of the studies was also evaluated.

DATA SYNTHESIS

Thirty-two studies met inclusion criteria; 10 were prospective studies. For diagnostic accuracy, sensitivity was 0.81 to 1.00 for dermatologists and 0.42 to 1.00 for PCPs. None of the studies reported specificity for dermatologists; one reported specificity for PCPs (0.98). For biopsy or referral accuracy, sensitivity ranged from 0.82 to 1.00 for dermatologists and 0.70 to 0.88 for PCPs; specificity, 0.70 to 0.89 for dermatologists and 0.70 to 0.87 for PCPs. Receiver operating characteristic curves for biopsy or referral ability were inconclusive.

CONCLUSIONS

The published data are inadequate to demonstrate differences in dermatologists' and PCPs' diagnostic and biopsy or referral accuracy of lesions suggestive of melanoma. We offer study design suggestions for future studies.

Quality of congestive heart failure treatment at a Canadian teaching hospital

BACKGROUND

Practice guidelines for the management of congestive heart failure (CHF) emphasize the need for assessment of left ventricular function and treatment with angiotensin-converting enzyme (ACE) inhibitors. However, previous studies have shown that many patients do not receive these tests or medications. The objective of this study was to evaluate the compliance of physicians at a large Canadian teaching hospital with published CHF management guidelines.

METHODS

We conducted a retrospective review of the charts of 200 patients admitted to Sunnybrook & Women's College Health Sciences Centre, Toronto, in 1997 for whom CHF was the diagnosis most responsible for the hospital admission. Quality of care was measured with 3 indicators: the use of left ventricular function testing to determine systolic versus diastolic dysfunction; the prescription of ACE inhibitors to appropriate patients (those with systolic dysfunction, no contraindications to ACE inhibitor therapy and no angiotensin II receptor blocker use); and the prescription of target doses of ACE inhibitors.

RESULTS

Of the 200 patients 177 (88.5%) received left ventricular function testing before or during their hospital stay; of the 177, 117 (66.1%) had systolic dysfunction. A total of 100 patients were considered to be ideal candidates for ACE inhibitor treatment. Of the 100, 89 (89.0%) received ACE inhibitors; however, only 23 (23.0%) were prescribed target doses.

INTERPRETATION

Most patients who had CHF at this Canadian hospital received left ventricular function testing and ACE inhibitor therapy. Future educational efforts should focus on the importance of adequate dosing of ACE inhibitors.

Examination of the Montastraea annularis Species Complex (Cnidaria: Scleractinia) Using ITS and COI Sequences

: The Caribbean coral Montastraea annularis has recently been proposed to be a complex of at least three sibling species. To test the validity of this proposal, we sequenced the ITS region of the nuclear ribosomal RNA gene family (ITS-1, 5.8S, and ITS-2), and a portion of the mitochondrial DNA gene cytochrome c oxidase subunit I (COI) from the three proposed species (M. annularis, M. faveolata, and M. franksi) from Florida reefs. The ITS fragment was 665 nucleotides long and had 19 variable sites, of which 6 were parsimony-informative sites. None of these sites was fixed within the proposed species. The COI fragment was 658 nucleotides long with only two sites variable in one individual. Thus, under both the biological species concept and the phylogenetic species concept, the molecular evidence gathered in this study indicates the Montastraea annularis species complex to be a single evolutionary entity as opposed to three distinct species. The three proposed Montastraea species can interbreed, ruling out prezygotic barriers to gene flow (biological species concept), and the criterion of monophyly is not satisfied if hybridization is occurring among taxa (phylogenetic species concept).

[Brief psychoanalytic point of view on assisted reproduction]

Some psychological mechanisms, regarding the new techniques of ART are reported in this work. A short overview of Freudian theory of psychosexual development of the child is given. The narcissistic wound induced by the diagnosis of sterility is quite important but quite different for men and women. It seems that oocyte donation may "cure" fantasmatically some female sterilities, given that this technique allows some women to get pregnant and to deliver a child, which was until then out of their biological "fate". Whether the anonymity of gamete donation is adapted to the psychic structure of recipients, donors, and medical teams is a question that should be considered. Very few works have been reported about the fantasies of the medical teams on this topic. The importance of infantile sexual theries is stressed again.

[Oocyte donation -- embryo donation]

From 1993 to 1995, 82 donors have permitted the retrieval of 810 oocytes allowing to obtain 411 embryos. 95 receiving couples have been included : 30 obtained a pregnancy, 7 abandoned and 38 are waiting for a transfer. The rate of pregnancies by transfer is superior to the one observed with the transfer of frozen embryos (40.5% versus 27%).

Salvage of extensively burned upper limbs by a pedicled latissimus dorsi flap

Very deep burns of the arm and elbow lead to soft tissue necrosis and infection with exposure of important structures. Aggressive debridement should be performed as early as possible to cut the vicious circle, and the defect, which may be extensive, should be covered by well-vascularized tissues. The reliability and versatility of the pedicled latissimus dorsi muscle or musculocutaneous flap make it our first choice in the management of this problem. A retrospective study of three patients for whom salvage of the upper limb has been achieved by the use of a pedicled latissimus dorsi flap is presented, illustrating the advantages of this technique.

Psychological aspects in anonymous and non-anonymous oocyte donation

A study, in which 110 patients were screened by a psychoanalyst, included 69 recipients who chose non-anonymous oocyte donation, i.e. they received oocytes from a known donor, most frequently a sister or a close relative. Another 41 recipients received anonymous oocytes, but had to bring a donor. Psychological motivations for either choice are reported, and significant topics such as attitudes towards confidentiality and links to the child are compared. No specific psychopathology is reported at this stage. An additional study on children born by these techniques is ongoing.

Sibling Species in Montastraea annularis, Coral Bleaching, and the Coral Climate Record

Measures of growth and skeletal isotopic ratios in the Caribbean coral Montastraea annularis are fundamental to many studies of paleoceanography, environmental degradation, and global climate change. This taxon is shown to consist of at least three sibling species in shallow waters. The two most commonly studied of these show highly significant differences in growth rate and oxygen isotopic ratios, parameters routinely used to estimate past climatic conditions; unusual coloration in the third may have confused research on coral bleaching. Interpretation or comparison of past and current studies can be jeopardized by ignoring these species boundaries.

Mechanism of insulin-induced activation of Na(+)-K(+)-ATPase in isolated rat soleus muscle

Insulin augments Na(+)-K(+)-ATPase activity in skeletal muscles. It has been proposed that the sequence of events is activation of Na(+)-H+ antiporter, increased intracellular Na+ concentration ( [Na+]i), and stimulation of Na(+)-K+ pump. We have used isolated rat soleus muscles to test this hypothesis. Insulin increased the ouabain-suppressible K+ uptake in a dose- and time-dependent manner. The maximal effect was observed at 50-100 mU/ml insulin. Stimulation of K+ uptake was accompanied by increased specific [3H]ouabain binding and lowered [Na+]i. The ionophore monensin, which promotes Na(+)-H+ exchange, also increased the rate of ouabain-suppressible K+ uptake in soleus muscle, with a maximal effect obtained at 10-100 microM ionophore. However, this increase was accompanied by an elevation of [Na+]i. In the presence of 10-100 microM monensin, addition of 100 mU/ml insulin further increased K+ uptake but reduced [Na+]i. The effect on K+ uptake was additive. Ouabain (10(-3) M) completely suppressed the effect of insulin on [Na+]i. Insulin had no effect on the magnitude or the time course of insulin stimulation of K+ uptake. Thus equal stimulation of Na(+)-K(+)-ATPase by insulin was observed when [Na+]i was elevated (under monensin) or lowered (under amiloride). These data suggest that activation of Na(+)-K(+)-ATPase in soleus muscle by insulin is not secondary to stimulation of Na(+)-H+ antiporter.

Ecological Effects of a Major Oil Spill on Panamanian Coastal Marine Communities

In 1986 more than 8 million liters of crude oil spilled into a complex region of mangroves, seagrasses, and coral reefs just east of the Caribbean entrance to the Panama Canal. This was the largest recorded spill into coastal habitats in the tropical Americas. Many population of plants and animals in both oiled and unoiled sites had been studied previously, thereby providing an unprecedented measure of ecological variation before the spill. Documenation of the spread of oil and its biological begun immediately. Intertidal mangroves, algae, and associated invertebrates were covered by oil and died soon after. More surprisingly, there was also extensive mortality of shallow subtidal reef corals and infauna of seagrass beds. After 1.5 years only some organisms in areas exposed to the open sea have recovered.

Fetal and adult human liver differ markedly in the fluidity and lipid composition of their microsomal membranes

The fluidity and lipid composition of the human hepatic microsomal membrane were studied in 11 livers from 16- to 21-week-old fetuses and in 5 adult livers, and compared with those of fetal and adult rat liver microsomes. Membrane fluidity was analyzed by measurement of fluorescence polarization using the fluorophore 1,6-diphenyl-1,3,5-hexatriene. The lipid apparent microviscosity (eta) of human fetal liver microsomes was 2.17 +/- 0.13 poise, as compared with 1.08 +/- 0.08 poise in adult liver (p less than 0.001). Similar differences in fluidity were found between fetal and adult rat liver microsomes. The more "fluid" adult microsomes had higher phospholipid/cholesterol and phosphatidylcholine/sphingomyelin molar ratios than those of the more "rigid" fetal microsomes. The degree of unsaturation of the adult microsomal lipids was much higher than that of the fetal lipids. The ratios of unsaturated/saturated fatty acids in microsomal lipids highly correlated with the eta values obtained for the combined group of fetal and adult human livers, suggesting that the developmental increase in degree of unsaturation of the microsomal lipids is a major determinant of the increased fluidity of adult as compared with fetal liver microsomes. These differences in fluidity and lipid composition between fetal and adult human liver microsomes may be a critical factor in the regulation of hepatic microsomal drug and carcinogen metabolizing enzyme activity, and could so determine the extent of toxicity and teratogenicity of drugs and/or their metabolites in the developing human fetus.

Glucocorticoids increase the fluidity of the fetal-rat liver microsomal membrane in the perinatal period

Dexamethasone, a synthetic glucocorticoid, was administered to pregnant rats during the last week of pregnancy in order to examine its effects on the fluidity of the developing fetal-rat liver microsomal membrane. This early prenatal exposure to dexamethasone, which preceded the natural appearance of fetal corticosteroids, markedly accelerated the normal perinatal course of fluidization of this membrane. The lipid apparent microviscosity, which was determined by measurement of fluorescence polarization, decreased in 21-days-old treated fetuses to values that were indistinguishable from those of untreated newborn rats. This dexamethasone-mediated acceleration of membrane fluidization was associated with an increase in the index of unsaturation of the fatty acyl moiety of microsomal lipids. Dexamethasone caused a significant increase in the microsomal content of polyunsaturated fatty acids (arachidonic and linoleic acid), which was accompanied by a decrease in content of monoenoic fatty acids (oleic and palmitoleic acid). This early exposure in utero to dexamethasone precociously induced the changes in fatty acid composition of fetal-rat liver microsomal lipids that normally occur between the last day of pregnancy and the first day of extra-uterine life. These results suggest that endogenous glucocorticoids play a major role in the perinatal fluidization of the rat liver microsomal membrane.