Differences in insulin sensitivity and risk markers due to gender and age in hypertensives.

Men run a higher risk for cardiovascular disease than women, even if hypertensive. This has been attributed to a more pronounced central (abdominal) fat distribution in men as well as menopausal state in women. The hypothesis to be tested in hypertensives was that men have more pronounced insulin resistance and other cardiovascular risk factors than pre-menopausal, but not post-menopausal, women. We carried out a cross-sectional observation study of middle-aged hypertensives of both sexes, divided into two age groups, below or over 50 years of age. The study was performed in untreated out-patients, visiting a hypertension policlinic, in Uppsala, Sweden. Three hundred men and 170 women with a mean age of 57 years were investigated. Measurements were taken by: physical examination (body mass index, waist-to-hip ratio, blood pressure); intravenous glucose tolerance test (IVGTT); euglycaemic hyperinsulinaemic clamp; and blood sampling for lipoprotein lipid fractions, uric acid, and free fatty acids. The results were that pre-menopausal women showed a higher insulin-mediated glucose disposal (7.6 vs5.8 mg/kg/min; P < 0. 01), and lower fasting glucose (4.9 vs 5.2 mmol/l; P < 0.05) than men, as well as a more advantageous lipoprotein profile. However, in post menopausal women insulin sensitivity decreased and the lipoprotein profile deteriorated. Women still showed higher levels of high-density lipoprotein (HDL)-cholesterol, and men a higher waist-to-hip ratio and levels of uric acid, in both age groups. It was concluded that post-menopausal hypertensive women are relatively more insulin resistant than pre-menopausal ones in comparison with men in the same age group and with the same degree of overall obesity. Journal of Human Hypertension (2000) 14, 51-56.

Effects of hydrochlorothiazide and captopril on lipoprotein lipid composition in patients with essential hypertension.

OBJECTIVE: Effective antihypertensive agents may differ in their capacity to reduce cardiovascular risk because they induce potentially atherogenic alterations in lipoprotein composition. PATIENTS: To assess this possibility, the effects of five months' treatment with either hydrochlorothiazide (HCTZ) or the converting enzyme inhibitor captopril (CAPT) on lipoprotein lipid composition were compared in thirty normolipidaemic patients with essential hypertension (EH). RESULTS: The sixteen patients treated with HCTZ showed the expected directional alterations in plasma TG (+31%), HDL2-C (-16%), and CHOL (+7.6%); in contrast TG and CHOL were unchanged after captopril in fourteen patients and their HDL2-C declined (-16%). Neither drug altered lipoprotein core lipid composition, but small increases were observed in the HDL2 sphingomyelin/lecithin ratio after both agents. The plasma free (unesterified) cholesterol (FC) lecithin (L) ratio, a new index of cardiovascular risk, was abnormally increased before treatment and was not altered by either drug. CONCLUSION: These findings indicate that HCTZ and CAPT treatment have small, but demonstrable effects on lipoprotein surface lipid composition in patients with EH that are confined to the HDL2 subfraction.

Abnormal lipoprotein phospholipid composition in patients with essential hypertension.

Vascular cell membranes from patients with essential hypertension (EH) and animals with genetic forms of hypertension have been found to have alterations in the content of free cholesterol and negatively charged phospholipids that may modify their function. Since membrane and lipoprotein lipids exchange freely, the lipid composition of lipoproteins may be an indirect measure of the content of vascular and other cells. To determine whether abnormalities are present in the lipid and phospholipid composition of lipoproteins from patients with EH, 30 EH (11 women; 19 men) and 20 normotensive control subjects were studied. Since significant gender differences were present in a number of parameters of lipoprotein composition, male and female data were examined separately. The EH group of both sexes tended to have higher plasma TG and VLDL + LDL and HDL2 lipid levels than their respective controls. Not only were the calcium-binding phospholipids phosphatidylinositol (PI) + phosphatidylserine (PS), and the membrane fluidizer phosphatidylethanolamine (PE) were significantly reduced in their VLDL + LDL, but all phospholipids (L, sphingomyelin (SPH), PI + PS, and PE) were significantly reduced in their neutral lipid content in both the HDL2 and HDL3 subfractions. These directional changes in lipoprotein FC and phospholipid in the EH women significantly increased the EH FC/PC (mol/mol) ratio in their plasma, a new cardiovascular risk factor, (EH 1.08 +/- 0.22 vs. control 0.86 +/0 0.08; P < 0.01) and lowered the SPH/PC ratio HDL2 and HDL3 in EH patients of both sexes. These findings showed that lipoproteins in normolipidemic EH women are relatively enriched in FC and in EH patients of both sexes depleted in certain phospholipids lacking in lipoproteins, their functional properties could be altered and vascular tone increased.

Increased level of hemoglobin A1c, but not impaired insulin sensitivity, found in hypertensive and normotensive smokers.

Smoking is associated with an abnormal plasma lipoprotein pattern. Recently, both insulin resistance and normal insulin action have been reported in smokers. In a total of 191 hypertensive and normotensive subjects recruited from a health survey, serum lipoprotein lipids, glucose tolerance (by intravenous glucose tolerance test (IVGTT), insulin secretion, and insulin sensitivity (euglycemic insulin clamp) were compared in the 41 smokers and 150 nonsmokers. Subjects were examined in the morning during a fasting state and after abstinence from smoking for 10 to 12 hours. Smokers showed a higher level of hemoglobin A1c (HbA1c) as compared with nonsmokers, 4.9% versus 4.7% (P < .05). There were no significant differences in fasting glucose, insulin, or insulin-mediated glucose disposal. However, a number of indices of insulin sensitivity tended to show enhanced insulin action among smokers. Only lower glucose and insulin values during the late phase (40 to 90 minutes) of the IVGTT reached statistical significance. Compared with nonsmokers, smokers had an expected higher level of serum triglycerides (2.1 v 1.8 mmol/L, P < .05) and an increased low-density lipoprotein (LDL) to high-density lipoprotein (HDL) cholesterol ratio (4.5 v 3.9, P < .05). These differences between smokers and nonsmokers were similar in both hypertensives and normotensives. In conclusion, smokers examined in the abstinence phase showed no signs of impaired insulin action. Lipoprotein abnormalities and elevated HbA1c may be caused in part by the insulin resistance induced during acute smoking and therefore may be quantitatively related to the time exposed to smoking. The effect on insulin sensitivity appears to be reversible over 10 to 12 hours.

Metabolic effects of anti-hypertensive treatment with nifedipine or furosemide: a double-blind, cross-over study.

To evaluate the metabolic effects of two anti-hypertensive agents with different actions, nifedipine 20 mg twice daily and furosemide 60 mg twice daily, 23 patients with untreated essential hypertension performed a double-blind, cross-over study in treatment periods of 5 months. Metabolic effects were evaluated by serum lipoprotein determinations, the intravenous glucose tolerance test and the hyperinsulinaemic euglycaemic clamp technique. Nifedipine and furosemide reduced blood pressure to the same extent (-14 to -15 mm Hg for supine SBP and -9 to -10 mm Hg for supine DBP, both P < 0.0001). Whereas both drugs significantly increased the levels of glycolysated haemoglobin (HbA1c, +0.24%, P < 0.005 for nifedipine and +0.43%, P < 0.001 for furosemide), only furosemide increased fasting blood glucose (+0.3 mmol/L, P < 0.01) and fasting insulin (+2.2 mU/L, P < 0.05) but impaired the early insulin response to i.v. glucose (-15 mU/L, P < 0.05). Insulin sensitivity on the other hand was significantly impaired by nifedipine treatment only (-1.6 mg/kg/min, P < 0.01). Whereas treatment with nifedipine did not change serum lipids, furosemide caused an increase in serum cholesterol (+0.2 mmol/L, P < 0.05) because of a rise in the LDL fraction (+0.32 mmol/L, P < 0.001). The insignificant change in heart rate induced by nifedipine treatment correlated with the change in HbA1c (r = 0.50, P = 0.05) and was inversely related to the change in insulin sensitivity (r = -0.56, P < 0.05). In conclusion, both furosemide and nifedipine caused abnormalities in glucose metabolism. In the nifedipine group the effects on glucose metabolism were related to the occurrence of tachycardia suggesting that sympathetic nerve activation could be involved in the metabolic impairments.

Long-term metabolic effects of antihypertensive drugs.

In short-term studies (4 to 6 months) we have reported that antihypertensive treatment with beta-adrenergic blockade and thiazide diuretics induced insulin resistance, hyperinsulinemia, and a deranged lipid profile; the ACE inhibitor captopril increased insulin sensitivity without affecting serum lipids. In the present study, 65 of the original 149 patients with essential hypertension included in the short-term studies were reexamined after treatment for 2 to 3 years. The hyperinsulinemic euglycemic clamp method showed that the significant decrease in insulin sensitivity (p < 0.01) induced by treatment with pindolol, propanolol, metoprolol, atenolol, or hydrochlorothiazide after 4 to 6 months persisted after 2 to 3 years of treatment. Furthermore, the increase in insulin sensitivity reported for captopril after 6 months (p < 0.05) was not significantly altered during long-term treatment. Also, the raised levels of very low-density lipoprotein triglycerides (p < 0.01) and reduced levels of high-density lipoprotein cholesterol (p < 0.01) induced by most of the beta-adrenergic blockade without intrinsic sympathomimetic activity and hydrochlorothiazide persisted. Captopril, on the other hand, did not significantly affect the lipids during prolonged treatment. In conclusion, the magnitude of the metabolic effects induced by antihypertensive treatment during short-term studies was of the same order after long-term treatment over 2 to 3 years and were not significantly different from the results in the short-term studies.

Metabolic effects of isradipine as monotherapy or in combination with pindolol during long-term antihypertensive treatment.

OBJECTIVES: To evaluate the effects of isradipine alone and in combination with pindolol on glucose and lipid metabolism during long-term antihypertensive therapy. DESIGN: Open long-term study with parallel groups. SETTING: Kungsgärdet Geriatric Hospital, Uppsala, a tertiary referral hospital. SUBJECTS: Twenty-six untreated hypertensive subjects. INTERVENTIONS: After 4 weeks on placebo, isradipine was titrated up to 10 mg daily to achieve appropriate blood pressure control (n = 11). If this failed, 5-10 mg pindolol was added. The treatments were continued for 2 years. MAIN OUTCOME MEASURES: Blood pressure, lipoprotein measurements, intravenous glucose tolerance test, hyperinsulinaemic euglycaemic clamp, HbA1c, body weight. RESULTS: Treatment with isradipine alone caused a sustained reduction in blood pressure (-22/-10 mm Hg, P < 0.01), but an increase in body weight (+2.2 kg, P < 0.05) and HbA1c (+1.5%; P < 0.001) were also noted. Addition of pindolol resulted in a similar degree of blood pressure reduction and weight gain, whilst HbA1c was less affected (+1.0%; P < 0.05, compared to isradipine alone). Insulin sensitivity became impaired in both groups (-1.2 to -1.5 mg kg-1 min-1; P < 0.01 for M-value at hyperinsulinaemic clamp) but after adjustment for the change in body weight the impairment was only significant (P < 0.01) in the group with combined treatment. The combined treatment also resulted in an increase in very-low-density-lipoprotein (VLDL) triglycerides (+ 0.37 mmol L-1; P < 0.05). CONCLUSIONS: The hypotensive effect of isradipine was sustained during long-term use but was associated with weight gain and an impaired glucose control. When isradipine was combined with pindolol there was also a reduction in insulin sensitivity and an increase in VLDL triglycerides, possibly as effects of the beta-adrenergic blockade.

On the interplay between insulin secretion and sensitivity as determinants of glucose tolerance.

Both insulin secretion and sensitivity have been claimed to be the main characteristics in the determination of future deterioration in glucose tolerance. In this cross-sectional study insulin secretion and insulin sensiturity were determined in 228 subjects with varying degrees of glucose tolerance. Insulin secretion was measured in an intravenous glucose tolerance test (IVGTT) and insulin sensitivity by the hyperinsulinaemic euglycaemic clamp test. Both the early insulin response in the IVGTT (increment) and the glucose disposal rate in the clamp test (M-value) were found to be related hyperbolically to fasting glucose (r = -0.63 and -0.66, respectively; both P < 0.0001) and in a second-order polynomial manner to the glucose disappearance rate (k-value) in the IVGTT (r = 0.53 and 0.48, respectively; both P < 0.0001). Multiple regression analysis showed the insulin increment in the IVGTT and the M-value in the clamp test to be equally important determinants of glucose tolerance, together explaining about 50% of the variation in fasting glucose and the k-value in the IVGTT. In conclusion, in this cross-sectional study insulin secretion and sensitivity studied over a broad range of glucose tolerance were found to be of almost equal importance in the determination of glucose tolerance. However, low levels of insulin increment in the IVGTT were more often associated with glucose intolerance than was a low insulin sensitivity.

Influences of different antihypertensive treatments on indices of systemic mineral metabolism.

A negative calcium balance has previously been described in human hypertension with low levels of plasma ionized calcium (Ca2+) and an increased urinary excretion of calcium. The cause of this disturbance in mineral metabolism is not known, nor is it known if this derangement could be abolished if blood pressure is reduced by antihypertensive treatment. In the present investigation, the effects of antihypertensive monotherapy on serum and fasting urinary electrolytes were studied. For 3 to 6 months, 319 hypertensive patients entered 17 study groups, each group using one of the following antihypertensive drugs: dilevalol, metoprolol, antenolol, pindolol, propranolol, hydrochlorothiazide, bendrofluomethiazide, furosemide, spironolactone, doxazocine, prazocine, diltiazem, verapamil, nifedipine, isradipine, captopril, or lisinopril. Treatment with different beta-blockers, as well as diuretics, reduced the fasting urinary calcium excretion (P < .001). However, while the beta-blockers increased the proportion of the ionized form of calcium in blood (Ca2+) (P < .001), Ca2+ was further decreased by diuretic treatment (P < .05). Angiotensin converting enzyme inhibitors caused no major changes in mineral metabolism while of the calcium antagonists studied only verapamil raised the levels of Ca2+ (P < .01). No significant relationship between the changes in mineral metabolism and the reduction in blood pressure was observed in any of the treatment groups. Of the antihypertensive drugs used in the present study, beta-blockers appeared to reverse the basic abnormality with regard to calcium balance, suggesting that the activity of the sympathetic nerve system is involved in the disturbed calcium metabolism seen in hypertensive patients.

Is it hyperinsulinemia or insulin resistance that is related to hypertension and other metabolic cardiovascular risk factors?

AIM OF STUDY: Epidemiologic and clinical studies have shown a close association between hypertension, hyperlipidemia and glucose intolerance. A metabolic imbalance has been proposed. As both hyperinsulinemia and insulin resistance appear to be of pathogenetic importance in this metabolic syndrome, we studied these features in hypertensive and normotensive subjects. METHODS: Glucose disposal under a hyperinsulinemic clamp was measured and different indices of hyperinsulinemia were obtained with the intravenous glucose tolerance test. The results were evaluated in relation to different cardiovascular risk factors assessed in 194 adult subjects selected from a health screening. RESULTS: Both hyperinsulinemia and the glucose disposal (clamped) value were significantly correlated with blood pressure (r = 0.36 and -0.42, respectively; both P < 0.0001), free fatty acids (r = 0.20 and -0.29, respectively; both P < 0.0005), serum triglycerides (r = 0.33 and -0.39, respectively; both P < 0.0001), high-density lipoprotein (HDL) cholesterol (r = -0.31 and 0.41, respectively; both P < 0.001) and fasting glucose (r = 0.45 and -0.44, respectively; both P < 0.0001). Multiple regression analysis with age, sex and obesity as confounding variables showed that insulin resistance was superior to hyperinsulinemia in the relationships with blood pressure and indices of hyperlipidemia (elevated free fatty acids, serum triglycerides and low HDL cholesterol), but both insulin sensitivity and hyperinsulinemia were significantly related to fasting glucose. CONCLUSIONS: Insulin sensitivity was more closely related to blood pressure, serum triglycerides and HDL cholesterol than hyperinsulinemia, but both insulin sensitivity and the insulin levels were associated with fasting glucose. Thus, insulin resistance is more important than hyperinsulinemia as a determinant of the constellation of cardiovascular risk factors comprising hypertension, glucose intolerance and hyperlipidemia.

On the relationships between mineral metabolism, obesity and fat distribution.

Alterations in calcium metabolism have been associated with cardiovascular risk factors. An altered binding of calcium to plasma proteins and raised levels of parathyroid hormone (PTH) have been described in morbid obesity. In the present study, indices of mineral metabolism were related to obesity (body mass index, BMI) and fat distribution (waist to hip ratio, w/h) in 194 subjects with a wide range of BMI and w/h. The ratio of total serum calcium to plasma ionized calcium (Ca2+) was found to be significantly correlated to both BMI (r = 0.20, P < 0.02) and w/h (r = 0.22, P < 0.005). Serum phosphate was also correlated to both of the indices of obesity in an inverse way (r = -0.24, P < 0.0008 for BMI and r = -0.33, P < 0.0001 for w/h). These relationships were still significant when the influences of age, sex and serum creatinine were included in the multiple regression analysis. This kind of analysis also disclosed that w/h was superior to BMI as a determinant of serum phosphate and the total calcium/Ca2+ ratio in serum. PTH was not significantly correlated to any of the indices of obesity. In conclusion, fat distribution rather than obesity per se was found to be associated with an altered mineral metabolism.

Calcium metabolism and sodium sensitivity in hypertensive subjects.

A pattern of negative calcium balanced with lowered levels of serum ionized calcium (Ca2+) and increased urinary excretion of calcium has been reported in hypertensive men. In the present study, ten untreated hypertensive subjects were salt loaded (20 g NaCl) for one week after a week on a low salt diet (< 3 g). The change in mean blood pressure (MBP) at the end of the high compared with the low salt diet was called salt sensitivity and was related to indexes of mineral metabolism. It was found that salt sensitivity was significantly correlated with both plasma ionized calcium (Ca2+) and serum calcium concentrations (both r = 0.64, P < 0.05) on the different diets. These relationships were strongest when sodium sensitivity was measured in the standing position during the low salt intake suggesting a role for an increased sympathetic tone. Salt loading increased the urinary excretion of calcium by 95% and also induced reductions in haemoglobin, serum albumin and serum calcium (P < 0.001). Ca2+, on the other hand, remained constant after salt loading. In conclusion, low levels of plasma ionized calcium and serum calcium were mainly found in hypertensive subjects with a low sensitivity to salt. Salt loading induced an increased calciuresis, haemodilution and possibly a shift of calcium from its protein-bound to its ionized form. The findings support the view that calcium metabolism is related to the regulation of BP.

Fasting insulin, calcium metabolism and the electrocardiogram in hypertensive subjects.

Changes in both calcium and insulin metabolism have been described in essential hypertension. Low levels of plasma ionized calcium (Ca2+) and high levels of insulin have previously been associated with vascular complications and coronary heart disease. In the present study, indices of calcium metabolism and fasting serum insulin were related to electrocardiographic (ECG) variables in 58 patients with untreated hypertension. Fasting insulin was found to be related to heart rate (r = 0.47, P < 0.001), diastolic interval (r = -0.39, P < 0.004) and electrical axis (r = -0.29, P < 0.03) while Ca2+ was found to be correlated with the QRS amplitude (r = -0.32, P < 0.03) and diastolic interval (r = 0.37, P < 0.02). Furthermore, non-ionized serum calcium was correlated with the QRS duration (r = 0.36, P < 0.02), ST-segment interval (r = -0.49, P < 0.002) and QT interval (QoT, r = -0.42, P < 0.008). These correlations were still significant when the influences of age, sex, obesity, blood pressure and heart rate were taken into account in the multiple regression analysis. In conclusion, the present study demonstrates that calcium and insulin metabolism are related to several basic characteristic functions of the heart, such as the systolic and diastolic function, as well as to signs of left ventricular hypertrophy.

Supplementation with n-3 fatty acids reduces triglycerides but increases PAI-1 in non-insulin-dependent diabetes mellitus.

The effects of dietary supplementation with n-3 fatty acids on lipid and glucose metabolism and on fibrinolysis were evaluated in 14 non-insulin-dependent diabetic patients who were given 10 g of MaxEPA (3 g n-3 fatty acids) or placebo (olive oil) per day in a randomized double-blind cross-over study during two consecutive 8-week periods. The serum triglyceride (TG) concentrations decreased by 27% (P < 0.01) after addition of MaxEPA with a reduction of VLDL TG by 36% (P < 0.05) while LDL cholesterol increased by 6% (P = 0.05). The fasting blood sugar and HbA1c concentrations increased significantly after addition of MaxEPA but the changes were not significantly different from those during the placebo period. The highest glucose concentrations at fasting and after an i.v. glucose injection were seen after MaxEPA while the serum insulin concentrations were unchanged. The peripheral insulin sensitivity, as measured by a euglycaemic, hyperinsulinaemic clamp technique, did not change during the study. The mean plasminogen inhibitor-1 (PAI-1) activity of the patients was elevated compared with healthy controls. In spite of the reduction of the triglyceride concentrations and unchanged insulin levels, there was a significant increase of the activity of PAI-1 (+21%, P < 0.01) after MaxEPA suggesting a possible impairment of the fibrinolytic capacity. In many situations there seems to be a reduction of PAI-1 when the triglycerides are lowered. In the diabetic patients given n-3 fatty acids this was not the case.

The sympathetic response to euglycaemic hyperinsulinaemia. Evidence from microelectrode nerve recordings in healthy subjects.

Sympathetic nervous system activation by insulin has been suggested as a mechanism explaining the association between insulin resistance and hypertension. We further examined the effect of insulin by direct microneurographic muscle and skin nerve sympathetic activity recordings during euglycaemic insulin clamps in healthy subjects. The mean plasma insulin level was elevated from 5.3 +/- 0.7 to 92.2 +/- 2.2 mU/l in seven subjects during a 90-min one-step clamp. In six other subjects plasma insulin was further raised from 85.7 +/- 4.0 mU/l to 747 +/- 53 mU/l between 45-90 min (two-step clamp). Four of the latter subjects received a sham clamp with NaCl infusions only on a second recording session. At the low dose of insulin muscle nerve sympathetic activity increased from a resting level of 22.7 +/- 5.0 bursts per min to 27.7 +/- 5.0 bursts per min at 15 min (p less than 0.05). The increases in muscle nerve sympathetic activity were significant (p less than 0.001; ANOVA) throughout insulin infusion, with a slight further increase (from 29.2 +/- 1.6 to 32.3 +/- 1.9 bursts per min) at the supraphysiological insulin concentration. During sham clamps muscle nerve sympathetic activity did not increase. Both insulin clamps induced minor, but significant, increases in forearm venous plasma noradrenaline concentrations. Skin nerve sympathetic activity (n = 3) did not change during insulin infusions. Heart rate increased slightly but significantly (p less than 0.005), during the insulin clamps. Blood pressure was not notably affected. In conclusion, hyperinsulinaemia was associated with increased vasoconstrictor nerve activity to skeletal muscle and with no change of sympathetic outflow to skin.

Metabolic cardiovascular risk factors and sodium sensitivity in hypertensive subjects.

Hypertension has previously been suggested to be a part of a metabolic syndrome also involving hyperlipidemia, hyperinsulinemia, and decreased insulin sensitivity. In the present study, 10 untreated hypertensive subjects were challenged with a high-salt diet (20 g NaCl) for 1 week after 7 days on a low-salt diet (less than 3 g). The difference in mean blood pressure (MBP) at the end of the high-salt diet v the low-salt diet was denoted salt sensitivity. We related the salt sensitivity to indices of glucose and lipid metabolism and studied the effect of salt deprivation on these metabolic variables. Salt sensitivity was found to be significantly correlated to HDL cholesterol (r = 0.79, P less than .007), insulin sensitivity (M value at the euglycemic clamp, r = 0.68, P less than .003), and fasting serum insulin (r = 0.69, P less than .04). Salt deprivation induced an increase in fasting insulin (P less than .03), but did not significantly affect any other indices of glucose and lipid metabolism. In conclusion, our study shows that hyperinsulinemia, decreased sensitivity to insulin, and low levels of HDL cholesterol were most commonly seen in hypertensive subjects with a low sodium sensitivity. A putative mechanism might be an increased activity in pressor systems also affecting glucose and lipid metabolism.

Metabolic effects of pindolol and propranolol in a double-blind cross-over study in hypertensive patients.

Metabolic effects of pindolol and propranolol were investigated in a randomised study of double-blind, double-dummy design in 39 Caucasians with newly detected hypertension. Each active treatment period was 6 months long. A euglycaemic hyperinsulinaemic clamp test was done to measure insulin sensitivity, and i.v. glucose tolerance was investigated with insulin determinations. Lipoprotein concentrations were quantified and lipoprotein lipase activities were determined in muscle and adipose tissue and in plasma after heparin injection. The blood pressure was significantly reduced by both regimes. The insulin sensitivity index was decreased by 34% during propranolol treatment and by 17% during pindolol treatment. The insulin concentrations in plasma were elevated at the end of the i.v. glucose tolerance test but were not high enough to compensate for the insulin resistance, so HbA1c and glucose concentrations were increased. A significant reduction of lipoprotein lipase activity in skeletal muscle during propranolol treatment probably explains the pronounced increase in serum triglyceride concentration during propranolol treatment despite lower free fatty acids and higher lipoprotein lipase activity in adipose tissue. These changes of lipoprotein lipase activity were not correlated to the changes in insulin sensitivity. In summary, the metabolic effects were significantly less pronounced with pindolol than with propranolol, which probably can be ascribed to the agonistic effect of pindolol on beta 2 adrenoceptors.

The metabolic and circulatory response to beta-blockade in hypertensive men is correlated to muscle capillary density.

Both haemodynamic and metabolic variables have been shown to be related to the fibre composition and capillary density of skeletal muscle in man. In the present study, the change of several metabolic variables during beta-blockade was investigated and related to muscle fibre composition and capillary density in 28 men with essential hypertension. They had been given atenolol (50 mg/day) or metoprolol (200 mg/day) or propranolol (160 mg/day) for 4-12 months. Serum triglycerides increased during treatment and individual changes were significantly inversely correlated with capillary density. Insulin concentrations in the fasting state and at the end of an i.v. glucose tolerance test were significantly higher during beta-blockade, and individual changes were inversely correlated with capillary density. Furthermore, body weight increased and heart rate decreased, changes that were also correlated with capillary density. It is concluded that many of the previously but poorly understood large interindividual differences in response to beta-blocker treatment may be explained by the degree of development of the capillary net in muscle tissue. Obesity, physical training as well as genetic factors are known determinants of capillary density.

Effects of antihypertensive treatment on insulin sensitivity with special reference to ACE inhibitors.

In 1984, the suspicion that pharmacological treatment may worsen the insulin resistance and associated metabolic abnormalities in lipid and carbohydrate metabolism and contribute to the relative failure of antihypertensive treatment to produce more than marginal reductions in cardiovascular morbidity and mortality led us to start a series of trials aimed at elucidating how antihypertensive drugs affect insulin sensitivity. These trials, which included assessment of insulin sensitivity by the euglycemic insulin clamp, showed that beta-adrenergic blockade and thiazide diuretic treatment (hydrochlorothiazide) increase insulin resistance and basal plasma insulin, whereas Ca(2+)-channel antagonists (verapamil and diltiazem), with the exception of the negative effect of nifedipine, are metabolically neutral. alpha-Adrenergic blockade with prazosin and angiotensin-converting enzyme (ACE) inhibition with captopril enhance insulin sensitivity. The mechanisms underlying the positive effects of ACE inhibition and beta-adrenergic blockade are largely unknown, but hemodynamic factors (vasodilation) may contribute by improving the access of glucose and insulin to skeletal muscle. The drugs, which were favorable or neutral with respect to insulin sensitivity, caused no changes in lipids or glucose homeostasis. In contrast, beta-blockers, except pindolol, had negative effects on triglycerides and high-density lipoprotein cholesterol, and thiazide diuretics caused adverse effects on total serum cholesterol, low-density lipoprotein cholesterol, and total and very-low-density lipoprotein triglyceride. The metabolic action of antihypertensive drugs is an important factor to consider in the choice of a proper treatment strategy in both diabetic and nondiabetic patients with hypertension.

Lipoprotein lipase activity in skeletal muscle is related to insulin sensitivity.

The relative effects of obesity, alone or in combination with insulin resistance and hyperinsulinemia (with or without diabetes), on lipoprotein concentrations, blood pressure, and other risk factors for cardiovascular disease were investigated in 28 men (mean age, 63 years). Special attention was given to lipoprotein lipase (LPL) activity in tissues and to postheparin plasma LPL activity and hepatic lipase activity and their relation to insulin resistance. The 28 men fulfilled the entrance criteria of the study so that they could be allocated to one of the four groups (seven in each group): 1) normal body weight, normal fasting insulin level, and normal glucose tolerance (controls); 2) the same as in group 1 but with moderate obesity; 3) the same as in group 2 but with fasting hyperinsulinemia; 4) the same as in group 3 but with non-insulin-dependent diabetes mellitus. Glucose infusion rate for the control group was 8.1 +/- 2.1 mg/kg body wt/min (mean +/- SD) at an insulin infusion rate of 56 milliunits/m2/min. The average values in groups 2, 3, and 4 were 6.0 +/- 0.7, 3.2 +/- 0.5, and 1.9 +/- 1.0 mg/kg body wt/min, respectively. Concentrations of very low density lipoproteins as well as blood pressure and urate concentrations were highest and those of high density lipoproteins were lowest in the two hyperinsulinemic groups (groups 3 and 4). Skeletal muscle LPL activity was 46 +/- 23, 41 +/- 25, 23 +/- 6, and 31 +/- 13 milliunits/g wet wt (mean +/- SD) in the four groups, respectively. There was a positive correlation between glucose infusion rate and muscle LPL activity (r = 0.58, p less than 0.0001). The hepatic lipase activity was positively correlated with the insulin area under the curve of the intravenous glucose tolerance test (r = 0.35, p = 0.02). Furthermore, blood pressure, free fatty acid concentration, liver enzymes, and urate concentrations were significantly correlated with glucose infusion rate at the clamp test. These data give further support for insulin resistance as an important factor behind the observed lipoprotein abnormalities and blood pressure elevations as part of the insulin resistance syndrome characteristic for obese and diabetic patients.