Glucagon and hepatic glucose production: modulation by low-dose bradykinin infusion

The effect of bradykinin on the oxidative state of rats with acute hyperglycaemia

Many clinical and experimental studies have established the beneficial effect of kinins in hypertension, heart failure and ischaemia-reperfusion syndrome, but little attention has been given to the role of kinins in hyperglycaemic conditions. The purpose of the present study was to determine the influence of bradykinin on the levels of glucose, insulin, malondialdehyde and hydrogen peroxide, as well as antioxidative enzyme activity in rats with streptozotocin (STZ)-induced acute hyperglycaemia. In STZ-induced hyperglycaemic rats the levels of glucose, hydrogen peroxide and malondialdehyde were increased by 256% (from 6.0+/-0.3 to 21.4+/-1.3 mmol/l, P<0.001), 33% (from 1.9+/-0.1 to 5.6+/-0.3 mmol H(2)O(2)/ml, P<0.001) and 19% (from 3.7+/-0.3 to 4.9+/-0.2 nmol/l, P<0.001) respectively. The activity of superoxide dismutase, catalase and glutathione peroxidase and the level of insulin were decreased by 46% (from 1367+/-73 to 737+/-59 U/g Hb, P<0.001), 36% (from 2.3+/-0.3 to 1.4+/-0.1 U Bergmayera/g Hb, P<0.001), 31% (from 236+/-19 to 163+/-24 U/g Hb, P<0.001) and 91% (from 47.5+/-1.7 to 2.4+/-0.5 mU/l, P<0.001) respectively in rats treated with streptozotocin. The administration of bradykinin caused the decrease in glucose, hydrogen peroxide and malondi-aldehyde levels by 38% (from 21.4+/-1.3 to 13.3+/-1.0 mmol/l, P<0.001), 37% (from 5.6+/-0.3 to 4.3+/-0.2 mmol H2O2/ml, P<0.001), 39% (from 4.9+/-0.2 to 3.0+/-0.2 nmol/l, P<0.001) respectively and the increase in insulin level and superoxide dismutase, catalase and glutathione peroxidase activity by 62% (from 2.4+/-0.5 to 4.0+/-0.4 mU/l, P<0.001), 23% (from 736.8+/-58.5 to 906.7+/-47.8 U/g Hb, P<0.001), 23% (from 1.4+/-0.1 to 1.9+/-0.1 U Bergmayera/g Hb, P<0.01) and 19% (from 163.1+/-23.6 to 202.3+/-11.7 U/g Hb, P<0.001) respectively in rats with hyperglycaemia. Thus, bradykinin is able to reduce oxidative stress in hyperglycaemic conditions.

ACE inhibition but not angiotensin II antagonism reduces plasma fibrinogen and insulin resistance in overweight hypertensive patients

The aim of this study was to compare the effects of the angiotensin-converting enzyme (ACE) inhibitor perindopril and the angiotensin II antagonist losartan on insulin sensitivity and plasma fibrinogen in overweight hypertensive patients. Twenty-eight overweight mild to moderate [diastolic blood pressure (DBP) >90 and <110 mm Hg] hypertensives aged 43-64 years, after a 4-week placebo period, were randomized to perindopril, 4 mg o.d., or losartan, 50 mg o.d., for 6 weeks. Then, after a new placebo period, patients were crossed to the alternative regimen for further 6 weeks. At the end of the placebo and of the treatment periods, blood pressure was measured, plasma fibrinogen was evaluated, and insulin sensitivity was assessed by the euglycemic, hyperinsulinemic clamp technique. Glucose infusion rate (GIR) during the last 30 min of clamp and total glucose requirement (TGR) were evaluated. Both perindopril and losartan reduced SBP (by a mean of 20.2 mm Hg, p < 0.001 vs. placebo; and 15.8 mm Hg, p = 0.002 vs. placebo, respectively) and DBP (by a mean of 15.2 mm Hg, p = 0.001 vs. placebo, and 11.8 mm Hg, p = 0.01 vs. placebo respectively), with no difference between the two treatments. GIR was significantly increased by perindopril (+2.91 mg/min/kg, p = 0.042 vs. placebo), but not by losartan (+0.28 mg/min/kg, NS). TGR was not modified by losartan but was increased by perindopril (+9.3 g, p = 0.042 vs. placebo). Plasma fibrinogen levels were reduced by perindopril (-53.4 mg/dl, p = 0.022 vs. placebo) but not by losartan (-16.8 mg/dl, NS). The perindopril-induced decrease in fibrinogen was correlated with the increase in GIR (r = 0.39; p < 0.01). These findings suggest that fibrinogen decrease produced by the ACE inhibitor is related to its action on insulin sensitivity, which seems to be dependent not on angiotensin II blockade but rather on other mechanisms.

Bradykinin decreases T-kininogen synthesis in a rat hepatoma cell line: evidence of bradykinin B2-type receptors

Using the rat H4-II-E-C3 hepatoma cell line, we investigated the presence of [125I][Tyr8]BK binding sites and the direct modulation of T-kininogen synthesis, an acute phase protein of inflammation, by bradykinin (BK) analogues. H4-II-E-C3 membrane preparations exhibited [125I][Tyr8]BK binding sites with a Kd of 4 nM and a Bmax of 120 fmol/mg of protein. Des-Arg9-BK showed no affinity (Ki > 10(-4) M) for these sites. The B2 metabolism-resistant and selective agonist [Phe8 psi (CH2-NH)Arg9]BK decreased the T-kininogen concentration in H4-II-E-C3 medium by 23% (p < 0.05). This effect was reversed by coincubation with the B2 antagonist HOE140. The B1 agonist Sar[D-Phe8]des-Arg9-BK and the B1 antagonist Lys[Leu8]des-Arg9-BK did not modify T-kininogen concentrations. The interaction between cytokines and kinins in the modulation of T-kininogen synthesis was also studied. Preincubation of hepatoma cells for 1 h with interleukin-1 alpha (IL-1 alpha) alone reduced T-kininogen concentrations by 37%, and this effect was blocked by co-addition of HOE140. Preincubation with interleukin-6 (IL-6) increased T-kininogen levels by threefold. Coincubation in the presence of the B2 agonist decreased this augmentation by 24%. The latter effect was reversed by co-addition of HOE140. None of the cytokines tested induced a response to the B1 agonist or antagonist under the experimental conditions studied. Overall, these results support the presence of a functional B2 receptor on H4-II-E-C3 cells that modulates T-kininogen synthesis. We suggest that the receptor is involved in vivo in a retroaction loop between kinins and T-kininogen production during inflammation. We speculate that BK could be a mediator in the modulation of acute phase protein synthesis by the cytokines IL-1 alpha and IL-6.

Decreased hepatic glucose production in rats with carbon tetrachloride-induced cirrhosis

Energy metabolism was studied in fed and fasted rats with carbon tetrachloride (CCl4)-induced cirrhosis. In situ liver perfusion experiments were performed under basal conditions (no substrate added to the perfusate) and after stimulation with glucagon (2 nM) and L-alanine (20 mM). Under basal conditions, oxygen consumption per gram of liver was reduced in cirrhotic rats irrespective of the metabolic state. After addition of glucagon/L-alanine to the perfusate, oxygen consumption increased significantly in fed and fasted control and cirrhotic rats. Under basal conditions, glucose production was reduced by 76% in cirrhotic rats, averaging 0.75 +/- 0.19 vs. 0.18 +/- 0.15 mumol.g liver-1.min-1 in control and cirrhotic livers, respectively (means +/- S.E.M., P < 0.05). After addition of glucagon/L-alanine to the perfusate, glucose production increased in both groups and was reduced by 65% in fed cirrhotic as compared with fed control rats, averaging 3.63 +/- 0.27 vs. 1.27 +/- 0.17 mumol.g liver-1.min-1 in control and cirrhotic rats, respectively (P < 0.05). Stimulated glucose production was linearly correlated with the fractional aminopyrine elimination rate constant (ABT-k), a measure of hepatic function in vivo. After 12 h of fasting, stimulated glucose production was decreased by 15% in control and by 65% in fed cirrhotic rats compared with the fed state, averaging 3.07 +/- 0.22 vs. 0.33 +/- 0.03 mumol.g liver-1.min-1 in control and cirrhotic rats, respectively (P < 0.05). After 24 h of starvation, glucose production was not significantly different between control and cirrhotic rats.(ABSTRACT TRUNCATED AT 250 WORDS)

The role of the renin-angiotensin system in insulin sensitivity in normotensive subjects

Nonobese patients with essential hypertension have been reported to be insulin resistant. Because blockade of the renin-angiotensin system has been demonstrated to improve insulin sensitivity in hypertensive patients, the authors evaluated the effects of angiotensin-II administration and of angiotensin-converting enzyme inhibition with enalapril on insulin-mediated glucose uptake in normotensive men. The results showed no change in insulin sensitivity with either 0.3 ng/kg/min or 1 ng/kg/min angiotensin-II administration or with enalapril therapy. The authors conclude that neither physiologic amounts of angiotensin-II nor converting enzyme inhibition alter insulin sensitivity in normotensive men.

Bradykinin attenuates glucagon-induced leucine oxidation in humans

Trauma and injury are associated with accelerated protein loss. Counterregulatory hormones are possible mediators of this response. In the present study, the effect of glucagon and glucagon plus bradykinin on leucine and urea kinetics was examined in nine normal volunteers during somatostatin infusion and basal insulin replacement. Bradykinin was given because of its prostaglandin-stimulating qualities and the potential anabolic action of prostaglandins. Physiological hyperglucagonemia elicited a small but significant reduction of total leucine flux and rate of urea synthesis. Simultaneously, leucine oxidation increased by 70%. The simultaneous infusion of bradykinin did not alter glucagon-related changes in urea or leucine kinetics. Bradykinin, however, significantly attenuated the stimulation of leucine oxidation by glucagon. These results suggest that glucagon and tissue factors are involved in controlling leucine metabolism in humans.

The phospholipid/arachidonic acid second messenger system: its possible role in physiology and pathophysiology of metabolism

The phospholipid/arachidonic acid second messenger system is a signaling system by which systemic regulators (hormones) and local mediators (tissue factors) control certain aspects of tissue metabolism. In vivo and in vitro evidence indicates that these effectors activate phospholipolytic enzymes in cellular membranes. The products of these enzymatic reactions (such as inositol phosphates or arachidonic acid metabolites) can serve as second messengers that can potentially influence glucose, lipid and protein metabolism at the cellular level. Alterations in this second messenger system could be involved in metabolic changes associated with some pathologic conditions as well as certain drug treatments, and thus, a better understanding of the system could reveal new possibilities for therapeutic interventions.