Insulin sensitivity and atherosclerosis. The Insulin Resistance Atherosclerosis Study (IRAS) Investigators

BACKGROUND

Reduced insulin sensitivity has been proposed as an important risk factor in the development of atherosclerosis. However, insulin sensitivity is related to many other cardiovascular risk factors, including plasma insulin levels, and it is unclear whether an independent role of insulin sensitivity exists. Large epidemiological studies that measure insulin sensitivity directly have not been conducted.

METHODS AND RESULTS

The Insulin Resistance Atherosclerosis Study (IRAS) evaluated insulin sensitivity (SI) by the frequently sampled intravenous glucose tolerance test with analysis by the minimal model of Bergman. IRAS measured intimal-medial thickness (IMT) of the carotid artery as an index of atherosclerosis by use of noninvasive B-mode ultrasonography. These measures, as well as factors that may potentially confound or mediate the relationship between insulin sensitivity and atherosclerosis, were available in relation to 398 black, 457 Hispanic, and 542 non-Hispanic white IRAS participants. There was a significant negative association between SI and the IMT of the carotid artery both in Hispanics and in non-Hispanic whites. This effect was reduced but not totally explained by adjustment for traditional cardiovascular disease risk factors, glucose tolerance, measures of adiposity, and fasting insulin levels. There was no association between SI and the IMT of the carotid artery in blacks. The association between SI and the IMT was stronger for the internal carotid artery than for the common carotid artery in all ethnic groups.

CONCLUSIONS

Higher levels of insulin sensitivity are associated with less atherosclerosis in Hispanics and non-Hispanic whites but not in blacks. This effect is partially mediated by traditional cardiovascular risk factors.

Re-engineering: managing radical change

Faced with both a move to a new facility and the need for radical, cost-saving organizational change, the Ontario Cancer Institute/Princess Margaret Hospital turned to the principles of re-engineering. With the help of a consulting firm, the organization overhauled sufficiently to save $7.5 million, enough to finance the move, the transition and even the expansion of some services.

Characterization and regulation of angiotensin II receptors in rat adipose tissue. Angiotensin receptors in adipose tissue

Characterization and regulation of angiotensin II (AII) receptor binding sites was performed in rat membrane preparations from nonadipose (liver, lung) and adipose (interscapular (ISBAT) and periaortic (PA) brown adipose tissue; epididymal (EF) and retroperitoneal (RPF) white adipose tissue). In membrane preparations from brown and white adipose sources, [125I]AII saturation binding revealed a single, high affinity (Kd range of 0.3 -0.6 nM) binding site with a modest AII receptor density (Bmax range of 17-120 fmol/mg protein) comparable to rat lung (130 fmol/mg protein). White adipose tissue contained a greater number of AII receptor sites than brown adipose tissue. Competition displacement studies demonstrated the AT1 receptor is the only angiotensin receptor subtype localized in adipose tissue, with the rank order for competition of [125I]AII binding in all adipose tissues examined AIII > AII > losartan > angiotensin I (AI) > PD123319. The AT2 specific receptor antagonist, PD123319, was ineffective at displacing [125I]AII binding in all adipose tissues examined. Since components of the renin-angiotensin system are regulated in adipose tissue, we determined if the AII receptor is also regulated in the obese state. AII receptor binding characteristics were determined in liver, lung, ISBAT and EF membrane preparations from adult Zucker obese (fa/fa) and lean (Fa/?) rats. AII receptor density was decreased in liver from obese rats. In contrast, the affinity for [125I]AII binding was not altered in tissues from obese rats. In a separate group of obese and lean rats, regulation of the AII receptor by phenobarbital (PB) was examined. Administration of PB restored AII receptor density in liver from obese rats to levels obtained in lean rats. In summary, these results demonstrate the presence of AT1 receptor sites in brown and white adipose tissue. Moreover, AII receptor density is decreased in tissues from obese rats, with restoration of receptor density by administration of PB. Future studies will determine if PB regulates the AT1 receptor at the level of gene expression.

Tobacco and the law: the state of the art

Litigation has become a major weapon in the conflict between those who seek to control tobacco and the tobacco industry. Apart from the cases arising from the high proportion of fires caused by cigarettes (including, in the UK, the disastrous fire at the Bradford football stadium and the fire at Kings Cross railway station, both of which were caused by discarded cigarette butts), in the last few years there have been and are continuing major lawsuits against the tobacco manufacturers both in the USA and in the UK. In Australia, a Court has ruled that the tobacco industry's claims that passive smoke had not been proven to cause a variety of diseases were false and misleading. A Quebec judge ruled as unconstitutional a Canadian law which had banned tobacco advertising. A product liability suit was filed against cigarette manufacturers by airline flight attendants whose health, they alleged, was impaired by exposure to passive smoke. To date, attempts to win damages from the manufacturers for injuries caused by smoking have failed, but several group actions are pending in the courts in England and the USA. The cases to date demonstrate the range and importance of tobacco control issues now being considered by the Courts.

Distribution and correlates of plasma fibrinogen in middle-aged women. Initial findings of the Postmenopausal Estrogen/Progestin Interventions (PEPI) study

Fibrinogen levels have been reported in cohort and case-control studies to be positively related to the development of coronary heart disease. This report presents the distribution and determinants of fibrinogen in women enrolling in a 3-year randomized trial of hormone replacement therapy (HRT), the Postmenopausal Estrogen/Progestin Interventions (PEPI) trial. Fasting plasma fibrinogen levels were measured in 874 postmenopausal women, aged 45 to 65 years, who had not used HRT for at least 3.5 months. Mean (+/- SD) fibrinogen level was 2.83 +/- 0.45 g/L. There was a significant positive association between fibrinogen and age (P = .03). Significantly higher (P < .005) fibrinogen levels were seen in current smokers versus nonsmokers (2.94 versus 2.81 g/L), in women who reported consuming fewer than 12 alcoholic drinks in the 12 months before the baseline visit versus higher consumption (2.90 versus 2.79 g/L), and in women who reported never versus ever having used HRT (2.90 versus 2.77 g/L). Self-reported leisure time physical activity (LTPA) was negatively associated (P = .0001) with fibrinogen levels as follows: inactive (2.84 g/L), light (2.89 g/L), moderate (2.80 g/L), and heavy (2.60 g/L), with significantly (P = .0001) lower levels in women who reported heavy LTPA versus each of the other categories and in women reporting moderate versus light LTPA. A strong positive correlation was found between fibrinogen and body mass index (BMI) (r = .32; P < .0001). In a model that included age, smoking, alcohol intake, prior HRT, LTPA, and BMI, LTPA was no longer a statistically significant predictor of fibrinogen level, while associations with other variables remained significant.(ABSTRACT TRUNCATED AT 250 WORDS)

The insulin resistance atherosclerosis study (IRAS) objectives, design, and recruitment results

The Insulin Resistance Atherosclerosis Study (IRAS) is the first epidemiologic study designed to assess the relationships between insulin resistance, insulinemia, glycemia, other components of the insulin resistance syndrome, and prevalent cardiovascular disease (CVD) in a large multiethnic cohort. Over 1600 men and women were recruited from four geographic areas to represent a range of glucose tolerance (normal, impaired, and diabetic) and ethnicity (hispanic, non-Hispanic white, and African-American). Insulin resistance was assessed directly using the frequently sampled intravenous glucose tolerance test with minimal model analysis. Intimal-medial carotid artery wall thickness, an indicator of atherosclerosis, was measured using B-mode ultrasonography. Prevalent CVD was assessed by questionnaire and resting electrocardiography. This report describes the design of the study and provides the recruitment results. Forthcoming cross-sectional analyses will help to disentangle the association between insulin resistance and CVD, apart from the concomitant hyperinsulinemia and related CVD risk factors.

Role of social class in excess black stroke mortality

BACKGROUND AND PURPOSE

It has been suggested that a substantial proportion of the excess stroke mortality among black Americans may be attributable to relatively lower socioeconomic status (SES) in this group. In this report we provide the first quantitative estimates of the proportion of excess black stroke mortality attributable to SES for a large population-based cohort.

METHODS

We used data from the National Longitudinal Mortality Study for persons 45 years and older (73,400 white men, 87,528 white women, 6522 black men, and 8816 black women). Sex-specific proportional hazards model were used to estimate excess black stroke mortality with and without adjustment for education and income (measures of SES). The contribution of SES to the excess black stroke risk was estimated from the difference in regression coefficients for race in these models.

RESULTS

In men, low SES was associated with increased stroke mortality (P < or = .0001) and accounted for 14% to 46% of the excess black stroke risk (P < .05). However, we could find no association between SES and stroke mortality in women, and SES did not account for a significant proportion of the excess stroke mortality in black women.

CONCLUSIONS

Although SES proved to account for a statistically significant proportion of excess male black stroke mortality, overall SES explained less than one quarter of the observed excess between ages 45 and 65. In women, SES did not significantly reduce the estimated excess black stroke mortality. Although SES may be playing a role in excess black stroke mortality, a substantial proportion of the excess appears attributable to other sources, including cerebrovascular risk factors that are unrelated to SES, unmeasured lifestyle influences, social resources, and genetic factors.

Genetic influences on bone density: physiological correlates of vitamin D receptor gene alleles in premenopausal women

Common vitamin D receptor (VDR) gene alleles have recently been shown to contribute to the genetic variability in bone mass and bone turnover, however, the physiological mechanisms involved are unknown. To examine this, the response to 7 days of 2 micrograms oral 1,25-dihydroxyvitamin D[1,25-(OH)2D] (calcitriol) stimulation was assessed in 21 premenopausal women, homozygous for one or other of the common VDR alleles (bb, n = 11; BB, n = 10). Indices of bone turnover and calcium homeostasis were measured during 2 weeks. Baseline osteocalcin, 1,25-(OH)2D, type I collagen carboxyterminal telopeptide, and inorganic phosphate levels were significantly higher and spinal bone mineral density was significantly lower in the BB allelic group. After calcitriol administration, similar levels of 1,25-(OH)2D were attained throughout the study in both genotypic groups. The increase in serum osteocalcin levels in the BB group was significantly less than that in the bb group (11% vs. 32%, P = 0.01). The genotype-related baseline difference in osteocalcin levels was not apparent at the similar serum 1,25-(OH)2D levels. By contrast, the baseline differences in phosphate and type I collagen carboxyterminal telopeptide persisted throughout the study. Serum ionized calcium levels did not differ between genotypes, nor did it move out of normal range values. However, parathyroid hormone was less suppressed in the low bone density group (38% vs. 11%, P = 0.01). These data indicate that the VDR alleles are associated with differences in the vitamin D endocrine system and may have important implications in relation to the pathophysiology of osteoporosis.

Is the stroke belt disappearing? An analysis of racial, temporal, and age effects

BACKGROUND AND PURPOSE

The stroke risk among white residents of the coastal plain of North Carolina, South Carolina, and Georgia (the "Stroke Belt") has been reported to be between 1.3 and 2.0 times the national average. In this study we examined (1) whether a similar excess risk exists for blacks in this region, (2) whether this regional excess stroke risk has decreased over time, and (3) whether the regional excess risk is consistent across ages from 45 to more than 85 years.

METHODS

Using data from the Compressed Mortality File, we estimated the annual relative stroke mortality risk for black and white men and women in a region of 153 coastal plain counties and compared these rates to those for the remainder of the United States.

RESULTS

The relative geographic excess risk of stroke death was similar for black residents and white residents of the Stroke Belt for both men and women. Despite the decline in stroke mortality, the relative increased risk of stroke death in the region has remained constant from 1968 to 1991; however, the pattern of excess risk across age differed significantly between race/sex groups.

CONCLUSIONS

These data show that the Stroke Belt continues to exist for blacks and whites and for men and women. Although the specific causes of the Stroke Belt remain unknown, the public health impact is staggering, with a greater than 40% excess risk of stroke mortality and more than 1200 excess stroke deaths annually.

Arterial wall thickness is associated with prevalent cardiovascular disease in middle-aged adults. The Atherosclerosis Risk in Communities (ARIC) Study

BACKGROUND AND PURPOSE

This study was done to assess the relationship between prevalent cardiovascular disease and arterial wall thickness in middle-aged US adults.

METHODS

The association of preexisting coronary heart disease, cerebrovascular disease, and peripheral vascular disease with carotid and popliteal intimal-medial thickness (IMT) (measured by B-mode ultrasound) was assessed in 13,870 black and white men and women, aged 45 to 64, during the Atherosclerosis Risk in Communities (ARIC) Study baseline examination (1987 through 1989). Prevalent disease was determined according to both participant self-report and measurements at the baseline examination (including electrocardiogram, fasting blood glucose, and medication use).

RESULTS

Across four race and gender strata, mean carotid far wall IMT was consistently greater in participants with prevalent clinical cardiovascular disease than in disease-free subjects. Similarly, the prevalence of cardiovascular disease was consistently greater in participants with progressively thicker IMT. The greatest differences in carotid IMT associated with prevalent disease were observed for reported symptomatic peripheral vascular disease (0.09 to 0.22 mm greater IMT in the four race-gender groups).

CONCLUSIONS

These data document the substantially greater arterial wall thickness observed in middle-aged adults with prevalent cardiovascular disease. Both carotid and popliteal arterial IMT were related to clinically manifest cardiovascular disease affecting distant vascular beds, such as the cerebral, peripheral, and coronary artery vascular beds.

The relationship of active and passive smoking to carotid atherosclerosis 12-14 years later

BACKGROUND

Active and passive smoking have been found to be associated with clinical atherosclerotic disease. To explore the effects of smoking on atherogenesis, we investigated the relationship of past and current active and passive smoking to carotid atherosclerosis in middle-aged adults.

METHODS

The study population consisted of 2,073 middle-aged residents of Washington County, Maryland. Information on active smoking and exposure to environmental tobacco smoke (ETS) was obtained from a 1975 census and from the baseline visit of the Atherosclerosis Risk in Communities (ARIC) Study in 1987-1989. Carotid artery intimal-medial wall thickness, measured by B-mode ultrasound methods in 1987-1989, was used as an indicator of carotid atherosclerosis. Mean intimal-medial wall thickness (IMT) was adjusted for age, gender, cardiovascular risk factors, and education using multiple linear regression.

RESULTS

The lowest mean IMT was found among never smokers who had never been exposed to ETS (mean +/- standard error: 0.706 +/- 0.013 mm). Exposure to ETS in one or both time periods was associated with increased IMT among never smokers (ETS in 1975 only: 0.731 +/- 0.022; ETS in 1987-1989 only: 0.738 +/- 0.011; ETS in both periods: 0.734 +/- 0.012). Active smoking in 1975 was also associated with increased IMT. The greatest mean intimal-medial wall thickness was found among persons who were current smokers in both time periods (0.807 +/- 0.009).

CONCLUSIONS

Both past and current passive and active smoking are associated with increased carotid intimal-medial wall thickness.

Ethnic differences in stroke mortality between non-Hispanic whites, Hispanic whites, and blacks. The National Longitudinal Mortality Study

BACKGROUND AND PURPOSE

Although US blacks are known to have an excess stroke mortality compared with US whites, little is known about the stroke burden of the Hispanic white population. This report will provide estimates of the relative burden of stroke mortality in the US black and Hispanic population relative to the white population and examine the consistency of this relation across age.

METHODS

Data were from participants aged > 45 years from the National Longitudinal Mortality Study. There were 1844 stroke deaths among 239,734 non-Hispanic whites, 46 deaths among 12,527 Hispanic whites, and 234 deaths among 23,468 black participants. Standard statistical methods were used to examine the ethnic differences in stroke mortality.

RESULTS

The hazard ratios for black men and women (relative to non-Hispanic whites) were nearly identical, at > 4.0 at age 45 but marginally < 1.0 by age 85. For both Hispanic men and women, the hazard ratios (relative to non-Hispanic whites) were approximately 1.0 at age 45 but were marginally significantly < 1.0 at older ages. The ethnic differences in stroke death rates reveal differences in age distributions of age at fatal stroke between these groups. Approximately 6% of fatal strokes for non-Hispanic whites occurred before age 60, whereas > 15% occurred in both Hispanic whites and blacks.

CONCLUSIONS

These results suggest that (1) for Hispanics, stroke risk is similar to that for non-Hispanic whites at young ages but is marginally lower at older ages, (2) the excess stroke mortality in blacks mainly occurs at younger ages (between 45 and 55 years), and (3) the relation between stroke risk for blacks and Hispanics relative to whites is similar by sex. The impact of age on relative stroke mortality would argue against simple age adjustment for describing ethnic differences in stroke mortality. Finally, proportionally, more strokes occur at older ages in non-Hispanic whites than in either US blacks or Hispanic whites.

Spatial distribution of carotid intimal-medial thickness as measured by B-mode ultrasonography

BACKGROUND AND PURPOSE

Measurements of intimal-medial thickness (IMT) of the carotid artery by B-mode ultrasonography are widely used as markers of atherosclerosis. This report describes empirical features of these measurements to characterize their distribution within arterial wall segments, to explore their potential as study outcome measures, and to examine their links with traditional risk factors for cardiovascular disease.

METHODS

Sequential transverse measurements of IMT in the carotid arteries were made in 899 participants from the Asymptomatic Carotid Artery Progression Study (ACAPS) at baseline. Data from 17 intrasegment sites in each of 12 arterial wall segments were used to describe patterns of thickness and visualization and to characterize cross-sectional area, severity, and roughness/irregularity by the intrasegment averages, maxima, and SDs of IMT, respectively.

RESULTS

Serial correlations of IMT measurements indicated localized and diffuse features of disease. The spatial distribution of IMT had two dominant features: overall mass and mass relative to roughness. The validity of these features was demonstrated by their correlation to known risk factors for carotid atherosclerosis: body mass index, age, high-density lipoprotein cholesterol, systolic blood pressure, smoking, and sex.

CONCLUSIONS

Both the mean and maxima of intrasegment measurements appear to be good candidates for use in clinical studies. B-mode ultrasonography has validity for the description of IMT roughness and shape. Both of these features are linked to cardiovascular risk factors, which supports the multifaceted nature of atherosclerosis.

Galanin: a novel intraovarian regulatory peptide

Galanin is a 29-amino acid peptide that acts as a neuropeptide in many tissues. To date, galanin action and the hormonal regulation of galanin gene expression have not been described in the ovary of any species. To study possible ovarian expression and regulation of galanin, immature gonadotropin-primed rats were given hCG (10 IU), and their ovaries were collected 0, 4, 8, 12, and 20 h after hCG treatment for determination of galanin messenger RNA (mRNA) concentration by solution hybridization. Galanin mRNA levels progressively increased after hCG administration, peaking at 12 h (2.4-fold increase vs. 0 h), with a subsequent return to 0 h levels at 20 h. To determine a possible ovarian role for galanin, rats were killed 48 h after gonadotropin administration, their ovaries were removed, and granulosa cells were harvested. These cells and the ovarian tissue remaining after granulosa cell collection (i.e. "shells") were each cultured for 24 h with increasing concentrations of galanin (0, 10, 100, and 1000 nM) in the presence or absence of LH. The medium was examined for steroid production and metalloproteinase inhibitor activity. In granulosa cell cultures, galanin increased the levels of estradiol by 26% and had no effect on progesterone, but decreased metalloproteinase inhibitor activity by 61% in the conditioned medium. In the shell cultures, galanin increased estradiol, progesterone, and androstenedione in the medium, suggesting that galanin acts on cells other than granulosa cells or that galanin action requires a paracrine interaction between granulosa and thecal cells. Our data demonstrate that galanin message is increased by hCG, and that galanin acts to amplify ovarian steroidogenesis while decreasing metalloproteinase inhibitor activity. These findings establish that ovarian galanin mRNA is hormonally stimulated and that galanin acts as an intraovarian regulatory peptide.

Relations of intimal-medial thickness among sites within the carotid artery as evaluated by B-mode ultrasound. ARIC Investigators. Atherosclerosis Risk in Communities

BACKGROUND AND PURPOSE

B-mode ultrasound is a widely used technique for the clinical and epidemiological assessment of carotid atherosclerosis. This article describes the relation between arterial intimal-medial thickness (IMT) at different sites within the extracranial carotid artery.

METHODS

IMT was measured by B-mode real-time ultrasound as an index of atherosclerotic involvement in the extracranial carotid arteries as part of the population-based Atherosclerosis Risk in Communities (ARIC) study. The relation between IMT at different sites was described by correlation coefficients and percentile regression techniques based on between 4034 and 9386 pairs of measurements (variation in sample size depending on the paired sites).

RESULTS

Increased IMT at one site was associated with increased IMT at other sites. The correlation between right and left IMT at the same anatomic location in the carotid artery ranged from .34 to .49; the correlation at different anatomic locations in the carotid artery on the same side ranged from .25 to .43. The distribution of IMT, described by the percentiles of IMT at the inference site as a function of IMT at the index site, showed constricted percentiles of IMT at the inference site for small IMT at the index site and an increase in the spread of percentiles with increasing IMT.

CONCLUSIONS

Although increased carotid IMT at one site is positively associated with thickened walls at other carotid sites, the ability to accurately predict wall thickness at a site given the wall thickness at other sites is modest. The general association between sites supports the systemic nature of atherosclerosis, while the lack of tight agreement between sites supports the focal nature of the atherosclerotic process.