An epidemiological test of the hyperinsulinemia-hypertension hypothesis

Anesthetic challenges in the obese patient

Obesity seems to be the modern concern to society. An increasing number of obese patients present annually to surgical wards to undergo surgical procedures. As morbid obesity affects most of the vital organs, the anesthesiologist must be prepared to deal with several challenges. These include the preoperative evaluation of the consequences of obesity, particularly on cardiac, respiratory, and metabolic systems; airway management; different pharmacokinetic and pharmacodynamic drug regimen; and perioperative management (i.e., hemodynamic, respiratory, and hyperglycemic). This paper reviews and assesses the most important anesthetic issues in managing obese patients.

Insulin resistance and risk of incident hypertension among men

J Clin Hypertens (Greenwich). 2009;11:483-490. (c) 2009 Wiley Periodicals, Inc.The independent association between insulin resistance and the development of hypertension remains in doubt because insulin resistance correlates with other metabolic factors also proposed to be associated with hypertension. The authors examined the association between the insulin sensitivity index and incident hypertension in a prospective nested case-control study among 1453 men (mean age, 61 years) who participated in the Health Professionals' Follow-up Study. The authors computed the insulin sensitivity index for each man in the study based on fasting insulin and triglyceride levels. Logistic regression was performed conditioned on age and adjusted for standard hypertension risk factors as well as renal function, cholesterol, and uric acid. The insulin sensitivity index was 6% lower in the cases compared with the controls (P<.001). The multivariable odds ratio for hypertension comparing the lowest with highest quartile of insulin sensitivity index was 1.09 (0.71-1.65) among the entire sample. However, the association between the insulin sensitivity index and incident hypertension differed significantly by age (P interaction <.001). Among men younger than 60 years, the multivariable odds ratio for the lowest compared with highest quartile was 1.93 (1.01-3.71) but was 0.67 (0.37-1.24) among older men. Insulin resistance is independently associated with incident hypertension among younger men.

Physical activity, insulin sensitivity, and hypertension among US adults: findings from the Insulin Resistance Atherosclerosis Study

Although regular physical activity is associated with less hypertension and improved insulin sensitivity, there is debate regarding the role of insulin sensitivity in hypertension. Thus, in this cross-sectional study, the authors investigated whether physical activity and insulin sensitivity were associated with hypertension. The sample consisted of 1,599 persons aged 40-69 years who participated in the Insulin Resistance Atherosclerosis Study. The outcome measure was hypertension as measured by a standard protocol. Energy expended in vigorous physical activity was calculated from a recall interview on past-year physical activity. Descriptive statistics revealed that 590 (37%) participants had prevalent hypertension. In adjusted logistic regression analysis, participants expending >or=150 kcal/day in vigorous physical activity had an odds ratio for hypertension of 0.73 (95% confidence interval (CI): 0.55, 0.98) in comparison with participants who were sedentary. Further adjustment for insulin sensitivity resulted in attenuation of the effect of vigorous physical activity on hypertension (odds ratio = 0.97, 95% CI: 0.71, 1.33), while the effect of insulin sensitivity was significant (odds ratio = 0.33, 95% CI: 0.26, 0.41). These results suggest that longitudinal studies are warranted to determine whether insulin sensitivity is a mediator of the relation between physical activity and hypertension.

Clustering of cardiovascular risk factors associated with the insulin resistance syndrome: assessment by principal component analysis in young hyperandrogenic women

OBJECTIVE

Hyperinsulinemia is often associated with several metabolic abnormalities and increased blood pressure, which are risk factors for cardiovascular disease. It has been hypothesized that insulin resistance may underlie all these features. However, recent data suggest that some links between insulin resistance and these alterations may be indirect. The aim of our study was to further investigate this issue in a sample of young hyperandrogenic women, who often show insulin resistance and other metabolic abnormalities typical of the insulin resistance syndrome.

RESEARCH DESIGN AND METHODS

We tested the hypothesis of a single factor underlying these features by principal component analysis, which should recognize one component if a single mechanism explains this association. The analysis was carried out in a sample of 255 young nondiabetic hyperandrogenic women. Variables selected for this analysis included the basic features of the insulin resistance syndrome and some endocrine parameters related to hyperandrogenism.

RESULTS

Principal component analysis identified four separate factors, explaining 64.5% of the total variance in the data: the first included fasting and postchallenge insulin levels, BMI, triglycerides, HDL cholesterol, and uric acid; the second, BMI, blood pressure, and serum free testosterone; the third, fasting plasma glucose, postchallenge glucose and insulin levels, serum triglycerides, and free testosterone; and the fourth, postchallenge plasma insulin, serum free testosterone, and gonadotropin-releasing hormone agonist-stimulated 17-hydroxyprogesterone.

CONCLUSIONS

These results support the hypothesis of multiple determinants in the clustering of abnormalities in the so-called insulin resistance syndrome.

Pathogenesis and prevalence of hypertension in acromegaly

Hypertension is an important complication of acromegaly, contributing to the increased morbidity and mortality of this condition. Prevalence of hypertension in acromegalic patients is about 35%, ranging from 18 to 60% in different clinical series, and the incidence is higher than in the general population. The lowering of blood pressure observed concomitantly with the reduction in GH levels after successful therapy for acromegaly suggests a relationship between GH and/or IGF-I excess and hypertension. The exact mechanisms underlying the development of hypertension in acromegaly are still not clear but may include several factors depending on the chronic exposure to GH and/or IGF-I excess. Experimental and clinical studies suggest that the anti-natriuretic action of GH (due to direct renal action of GH or IGF-I and/or to indirect, systemic GH or IGF-I-mediated mechanisms) may play a role in the pathogenesis of hypertension. Acromegaly is frequently associated with insulin resistance and hyperinsulinaemia which may induce hypertension by stimulating renal sodium absorption and sympathetic nervous activity. Whether sympathetic tone is altered in acromegalic hypertensive patients remains a matter of debate. Recent studies indicate that an increased sympathetic tone and/or abnormalities in the circadian activity of sympathetic system could play an important role in development and/or maintenance of elevated blood pressure in acromegaly, and may partially account for the increased risk of cardiovascular complications. Acromegalic cardiomiopathy may also concur to elevate blood pressure and can be aggravated by the coexistence of hypertension. Finally, a role of GH and IGF-I as vascular growth factors cannot be excluded. In conclusion, acromegaly is associated with hypertension, but there is still no real consensus in the literature on the mechanisms behind the development of the high blood pressure.

Midpregnancy serum C-peptide concentration and subsequent pregnancy-induced hypertension

OBJECTIVE

To test the hypothesis that elevated midpregnancy serum insulin (IRI) and C-peptide (CP) concentrations are associated with later development of pregnancy-induced hypertension (PIH), independent of prepregnancy obesity and midpregnancy blood pressure.

RESEARCH DESIGN AND METHODS

In this prospective study, a cohort of normotensive women, ages > or = years performed a 50-g glucose challenge test at 24-30 weeks' gestational age. Blood samples were collected after an overnight fast and 1 h after glucose ingestion. Serum IRI and CP concentrations were measured in each sample. Maternal height, blood pressure and proteinuria were measured at the time of glucose challenge testing and after 36 weeks' gestational age.

RESULTS

Of 320 subjects enrolled 44 women (13.8%) had subsequent PIH. Crude odds ratios (ORs) for devevelopment of PIH associated with each 1 U rise in log fasting IRI, log lasting CP. and glucosed-induced increase in CP (expressed as log [postprandial CP/fasting CP]) were 2.0 (95% CI 1.3-3.3), 1.8 (CI 1.2-2.7), and 2.3 (CI 1.1-4.9) respectively. After controlling for prepregnancy BMI, gestational age, and midpregnancy mean arterial pressure, adjusted ORs corresponding to log fastig IRI and CP for the development of PIH were 1.3 (95% CI 0.7-2.3) and 1.7 (CI 1.1-2.7) respectively, and, afterq adjustment for fasting CP, the adjusted OR of the glucose-induced rise in log CP was 3.7 (CI 1.5-9.3).

CONCLUSIONS

Mid-pregnancy tasting and postoral glucose CP levels are associated with subsequent development of PIH, independent of maternal obesity and midpregnancy baseline blood pressure. These findings many reflect an amplified beta3-cell response to glycemic stimulus, similar to that found in states of insulin resistance, that appears to be independently associated with PIH.

Does impaired glucose tolerance predict hypertension? A prospective analysis

This study evaluates prospectively the relationship between impaired glucose tolerance (IGT) and blood pressure. From a population of 1376 men and women aged 40-59 years, all those with IGT (n = 54) plus 133 age- weight- and sex-matched normoglycaemic control subjects were selected after excluding treated hypertensive patients. Blood pressure, fasting and postload blood glucose and plasma insulin were measured. At 11.5 years after the first visit 76% of the IGT patients and 80% of the control subjects were re-examined. At baseline blood pressure was significantly higher in IGT patients than in control subjects (systolic 135.5 +/- 2.3 vs 127.9 +/- 1.4 mmHg, p < 0.001; and diastolic 88.0 +/- 1.5 vs 84.7 +/- 0.7 mm Hg, p < 0.05) independent of age, gender, weight, antihypertensive medication and insulinaemia. Accordingly, hypertension was more frequent in subjects with IGT (odds ratio 2.1, 95% confidence, interval (CI) 0.9-4.9). Postload insulin was significantly associated with hypertension--both at univariate and multivariate analysis--in normoglycaemic subjects, but not in those with IGT. At follow-up systolic blood pressure increased in both groups; the increase was smaller in patients with IGT (6.0 +/- 2.4 vs 12.3 +/- 1.6 mm Hg p < 0.05). Likewise, the 11.5 years' cumulative incidence of hypertension was not significantly different in subjects with baseline IGT or normoglycaemia; if anything it was lower in the IGT group (odds ratio 0.36, 95% CI 0.1-1.2). In multivariate analysis incidence of hypertension was associated positively with baseline blood pressure (p < 0.0003) and negatively with IGT status p < 0.03), while no significant association was found with insulin. In conclusion, the findings of this study question IGT as a risk factor for hypertension. Furthermore, these data do not indicate a major role for hyperglycaemia and hyperinsulinaemia per se in the aetiology of hypertension and suggest that IGT and hypertension share one or more pathogenetic factor(s) (i.e., insulin resistance, hyperactivity of the sympathetic nervous system, etc.), which induce deterioration of blood pressure control first, and hyperglycaemia later.

Multivariate analysis of the insulin resistance syndrome in women

The insulin resistance syndrome (IRS) is characterized by a constellation of interrelated coronary heart disease (CHD) risk factors, including dyslipidemia, obesity, central obesity, elevated systolic blood pressure, and hyperinsulinemia. Factor analysis was used to investigate the clustering of these risk factors in individuals by examining the correlational structure among these variables. Data from 281 genetically unrelated nondiabetic women who participated in exam 2 (1979 to 1980) of the Kaiser Permanente Women Twins Study were used. Factor analysis reduced 10 correlated risk factors to 3 uncorrelated factors, each reflecting a different aspect of the IRS: factor 1 (increased body weight, waist circumference, fasting insulin, and glucose), factor 2 (increased postload and fasting glucose and insulin and systolic blood pressure), and factor 3 (larger low-density lipoprotein particles, decreased plasma triglycerides, and increased high-density lipoprotein). Together, the factors explained nearly 66% of the total variance in the data. Thus, factor analysis defined three distinct aspects of the IRS in this sample of nondiabetic women. These factors may reflect separate underlying mechanisms of the syndrome, each of which may also be involved in CHD risk.