Glucagon and insulin secretion during acid-base alterations

Previously, we reported that change from the normal pH of 7.4 surrounding the islet cells to 7.8 results in a decreased B-cell response to 16.6 mM glucose, 10 mM arginine or 400 µg/ml tolbutamide. In the present report we studied the effect of modifications in the extracellular pH on glucose- and arginine-induced glucagon and insulin secretion by the perfused rat pancreas. It was found that at pH 7.8, arginine-induced glucagon secretion was significantly greater than at pH 7.4. On the other hand, the switch from pH 7.4 to 7.8 in a pancreas already stimulated by either low glucose or arginine, produced fast and transient glucagon release. Sequential extracellular pH changes from 7.4 to 7.8 and back to 7.4 in the presence of 8.3 mM glucose and a 5 mM arginine stimulus demonstrated that A- and B-cells rapidly modify their secretion in response to extracellular alkalosis in opposite directions. While glucagon output was enhanced (mean secretory rates at pH 7.4, 0.692 ± 0.042 ng/min and 0.948 ± 0.57 at pH 7.8), insulin secretion was clearly reduced (72.6 ± 6.2 ng/min and 35.7 ± 2.8 ng/min at pH 7.4 and 7.8, respectively). The above observations, together with our previously reported data, indicate that extracellular pH plays an important role in the regulation of glucagon and insulin release. Particularly, extracellular alkalosis enhances A-cell response to 2.3 mM glucose and 5 mM arginine while partially inhibiting B-cell secretion in the perfused rat pancreas.Centro de Endocrinología Experimental y Aplicad

Circadian variations of muscle metabolites

On the basis of several reports, it could be established that glycogen a and protein 2 metabolism in muscle has a very fast turnover and also that it is under hormonal control. Nevertheless, even when it is known that the levels of circulating hormones are far from being constant s-6, there is a scarcity of available data concerning the spontaneous variation of muscle metabolites concentration during the 24 h period. This information might provide important clues for the choice of any experimental design schedule. Therefore, we considered it important to establish whether the content of substances such as DNA, total protein and glycogen in muscle tissue vary or remain unchanged during the 24 h period. The results obtained are presented in this paper.Facultad de Ciencias Médica

Effect of Pioglitazone on the Fructose-Induced Abdominal Adipose Tissue Dysfunction

Aim. To test the potential role of PPARγ in the endocrine abdominal tissue dysfunction induced by feeding normal rats with a fructose rich diet (FRD) during three weeks. Methodology. Adult normal male rats received a standard commercial diet (CD) or FRD, (10% in drinking water) without or with pioglitazone (PIO) (i.p. 0.25mg/Kg BW/day; CD-PIO and FRD-PIO). Thereafter, we measured circulating metabolic, endocrine, and oxidative stress (OS) markers, abdominal adipose tissue (AAT) mass, leptin (LEP) and plasminogen activator inhibitor-1 (PAI-1) tissue content/expression, and leptin release by isolated adipocytes incubated with different concentrations of insulin. Results. Plasma glucose, insulin, triglyceride, TBARS, LEP, and PAI-1 levels were higher in FRD rats; PIO coadministration fully prevented all these increments. AAT adipocytes from FRD rats were larger, secreted a higher amount of LEP, and displayed decreased sensitivity to insulin stimulation; these effects were significantly ameliorated by PIO. Whereas AAT LEP and PAI-1 (mRNA) concentrations increased significantly in FRD rats, those of insulin-receptor-substrate- (IRS-) 1 and IRS-2 were reduced. PIO coadministration prevented FRD effects on LEP, PAI-1, and IRS-2 (fully) and IRS-1 (partially) mRNAs in AAT. Conclusion. PPARγ would play a relevant role in the development of the FRD-induced metabolicendocrine dysfunction.Facultad de Ciencias Médica

Effect of Pioglitazone on the Fructose-Induced Abdominal Adipose Tissue Dysfunction

Aim. To test the potential role of PPARγ in the endocrine abdominal tissue dysfunction induced by feeding normal rats with a fructose rich diet (FRD) during three weeks. Methodology. Adult normal male rats received a standard commercial diet (CD) or FRD, (10% in drinking water) without or with pioglitazone (PIO) (i.p. 0.25mg/Kg BW/day; CD-PIO and FRD-PIO). Thereafter, we measured circulating metabolic, endocrine, and oxidative stress (OS) markers, abdominal adipose tissue (AAT) mass, leptin (LEP) and plasminogen activator inhibitor-1 (PAI-1) tissue content/expression, and leptin release by isolated adipocytes incubated with different concentrations of insulin. Results. Plasma glucose, insulin, triglyceride, TBARS, LEP, and PAI-1 levels were higher in FRD rats; PIO coadministration fully prevented all these increments. AAT adipocytes from FRD rats were larger, secreted a higher amount of LEP, and displayed decreased sensitivity to insulin stimulation; these effects were significantly ameliorated by PIO. Whereas AAT LEP and PAI-1 (mRNA) concentrations increased significantly in FRD rats, those of insulin-receptor-substrate- (IRS-) 1 and IRS-2 were reduced. PIO coadministration prevented FRD effects on LEP, PAI-1, and IRS-2 (fully) and IRS-1 (partially) mRNAs in AAT. Conclusion. PPARγ would play a relevant role in the development of the FRD-induced metabolicendocrine dysfunction.Facultad de Ciencias Médica

Ultrastructural responses of pancreatic β cells to metabolic alkalosis

The ultrastructural changes in pancreatic β cells were studied following glucose-induced insulin secretion in vitro, at two different extracellular pH (7.4 and 7.8). The pancreata perfused at pH 7.4 exhibited a biphasic insulin response to glucose challenge together with signs of increased emiocytotic activity and numerous microtubules in the β cells. Conversely, the pancreata perfused at pH 7.8 showed a significant decrease in insulin secretion, and their β cells revealed scarce emiocytotic images and a marked increase of intracellular granulolysis. These results represent the ultrastructural correlate of the reduced insulin secretion produced by metabolic alkalosis in the perfused rat pancreas.Centro de Endocrinología Experimental y Aplicad

Regression of cardiomyocyte hypertrophy in SHR following chronic inhibition of the Na+/H+ exchanger

Objective: Experiments were performed to examine the effect of chronic inhibition of the Na+/H+ exchanger isoform-1 (NHE-1) on cardiac hypertrophy of spontaneously hypertensive rats (SHR). Methods: SHR were orally treated during 1 month with two different doses (0.3 and 3.0 mg/kg/day) of the NHE-1 inhibitor, cariporide, or nifedipine (10.0 mg/kg/day). Results: The two doses of cariporide did not differ in their effects after 1 month of treatment, since both induced a slight decrease in systolic blood pressure (SBP) of ∼6 mmHg and regression of the heart weight to body weight ratio (mg/g) from 3.28±0.05 to 3.04±0.05 (0.3 mg) and 2.99±0.10 (3.0 mg, P<0.05). Nifedipine, given for the same period, produced similar reduction in the hypertrophy index (3.03±0.05), but with a much greater decrease in arterial pressure (35.6±7.4 mmHg). Chronic treatment with cariporide induced a complete regression of the augmented cross sectional area of left ventricular myocytes without significant changes in collagen content, serum procollagen 1 propeptide levels or myocardial distensibility. Conclusions: NHE inhibition represents a novel approach to induce regression of pathological hypertrophy of the heart. The finding can be rationalized mechanistically by previous in vitro studies suggesting a role of the NHE in the development of myocardial hypertrophy.Facultad de Ciencias MédicasFacultad de Ciencias VeterinariasCentro de Investigaciones Cardiovasculare

Regression of cardiomyocyte hypertrophy in SHR following chronic inhibition of the Na+/H+ exchanger

Objective: Experiments were performed to examine the effect of chronic inhibition of the Na+/H+ exchanger isoform-1 (NHE-1) on cardiac hypertrophy of spontaneously hypertensive rats (SHR). Methods: SHR were orally treated during 1 month with two different doses (0.3 and 3.0 mg/kg/day) of the NHE-1 inhibitor, cariporide, or nifedipine (10.0 mg/kg/day). Results: The two doses of cariporide did not differ in their effects after 1 month of treatment, since both induced a slight decrease in systolic blood pressure (SBP) of ∼6 mmHg and regression of the heart weight to body weight ratio (mg/g) from 3.28±0.05 to 3.04±0.05 (0.3 mg) and 2.99±0.10 (3.0 mg, P<0.05). Nifedipine, given for the same period, produced similar reduction in the hypertrophy index (3.03±0.05), but with a much greater decrease in arterial pressure (35.6±7.4 mmHg). Chronic treatment with cariporide induced a complete regression of the augmented cross sectional area of left ventricular myocytes without significant changes in collagen content, serum procollagen 1 propeptide levels or myocardial distensibility. Conclusions: NHE inhibition represents a novel approach to induce regression of pathological hypertrophy of the heart. The finding can be rationalized mechanistically by previous in vitro studies suggesting a role of the NHE in the development of myocardial hypertrophy.Facultad de Ciencias MédicasFacultad de Ciencias VeterinariasCentro de Investigaciones Cardiovasculare

Regression of hypertensive myocardial fibrosis by Na+/H+ exchange inhibition

We have recently reported that the inhibition of the Na+/H+ exchanger (NHE) during 1 month in spontaneously hypertensive rats (SHR) is followed by regression of cardiomyocyte hypertrophy but not of myocardial fibrosis. The aim of this study was to evaluate whether a treatment of longer duration could reduce myocardial fibrosis and stiffness. SHR received 3.0 mg/kg per day of the specific NHE-1 inhibitor cariporide; the effect on cardiomyocyte cross-sectional area, myocardial collagen volume fraction, collagen synthesis, and myocardial stiffness (length-tension relation in left papillary muscles) was evaluated at several time points (after 1, 2, or 3 months). A slight decrease of ≈5 mm Hg in systolic blood pressure was observed after 1 month of treatment with no further changes. After 2 and 3 months of treatment, the size of cardiomyocytes remained within normal values and myocardial fibrosis progressively decreased to normal level. Accordingly, myocardial stiffness and the serum levels of the carboxyterminal propeptide of procollagen type I, a marker of collagen type I synthesis, were normalized after 3 months. Left ventricular weight decreased from 910±43 (in untreated SHR) to 781±21 mg (treated SHR) after 3 months of treatment. No difference in body weight between treated and untreated SHR was observed after this period of treatment. The present data allow us to conclude that in the SHR the administration of an NHE-1 inhibitor for 2 or 3 months leads to the normalization of collagen type I synthesis, myocardial collagen volume fraction, and stiffness.Facultad de Ciencias MédicasFacultad de Ciencias Veterinaria

Regression of hypertensive myocardial fibrosis by Na+/H+ exchange inhibition

We have recently reported that the inhibition of the Na+/H+ exchanger (NHE) during 1 month in spontaneously hypertensive rats (SHR) is followed by regression of cardiomyocyte hypertrophy but not of myocardial fibrosis. The aim of this study was to evaluate whether a treatment of longer duration could reduce myocardial fibrosis and stiffness. SHR received 3.0 mg/kg per day of the specific NHE-1 inhibitor cariporide; the effect on cardiomyocyte cross-sectional area, myocardial collagen volume fraction, collagen synthesis, and myocardial stiffness (length-tension relation in left papillary muscles) was evaluated at several time points (after 1, 2, or 3 months). A slight decrease of ≈5 mm Hg in systolic blood pressure was observed after 1 month of treatment with no further changes. After 2 and 3 months of treatment, the size of cardiomyocytes remained within normal values and myocardial fibrosis progressively decreased to normal level. Accordingly, myocardial stiffness and the serum levels of the carboxyterminal propeptide of procollagen type I, a marker of collagen type I synthesis, were normalized after 3 months. Left ventricular weight decreased from 910±43 (in untreated SHR) to 781±21 mg (treated SHR) after 3 months of treatment. No difference in body weight between treated and untreated SHR was observed after this period of treatment. The present data allow us to conclude that in the SHR the administration of an NHE-1 inhibitor for 2 or 3 months leads to the normalization of collagen type I synthesis, myocardial collagen volume fraction, and stiffness.Facultad de Ciencias MédicasFacultad de Ciencias Veterinaria

Serum carboxyl-terminal propeptide of procollagen type I in exercise-induced left ventricular hypertrophy

Background: Left ventricular hypertrophy (LVH) induced by exercise is considered to be a physiologic adaptive mechanism without fibrogenic hyperactivity, as occurs in pathologic hypertrophy. Hypothesis: This study investigated serum markers of collagen synthesis and echo parameters of left ventricular diastolic function (LVdf) in 22 male athletes. Methods: Twenty-two highly competitive male athletes (10 cyclists, 12 soccer players) were studied with full history, clinical examination, Doppler echocardiogram, and serum concentration of the carboxyl-terminal propeptide of collagen type I (PIP). They were divided into two groups: normal left ventricular mass (N) with left ventricular mass index (LVMI) &lt; 125 g/m2 (14 athletes) and LVH with LVMI &gt; 125 g/m2 (8 athletes). Results: Age, body surface area, blood pressure, heart rate, and systolic function were not different between the groups. Serum concentration of PIP (N: 163 ± 44.1 µg/l, LVH: 172.7 ± 61.2 µg/l—NS) and LVdf (early to atrial peak mitral flow velocity ratio: [E/A] N:1.77 ± 0.47, LVH: 1.98 ± 0.70—NS, and early to atrial peak mitral annulus velocity ratio: [Ea/Aa] N: 2.63 ± 0.70, LVMI: 2.55 ± 0.90 LV1.61—NS) were similar in both groups. Conclusions: Normal serum concentration of PIP in athletes with LVH in association with normal LVdf indicates the possibility that in this type of physiologic hypertrophy there is mainly an increase of myocyte size without interstitial fibrosis.Facultad de Ciencias Médica