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Abstract: Role of hepatic insulin degradation in modulating insulin delivery to peripheral circulation, in insulin-resistant hypertensive patients, is not yet fully understood. This issue was investigated here by a novel application to hypertension of a previously proposed minimal modelling of insulin and C-peptide data, using population values for insulin and C-peptide kinetics parameters. Data, from frequently sampled intravenous glucose tolerance test (FSIGTT), were analysed in ten normoglycemic, hypertensive patients (H-group), compared with eight normoglycemic, normotensive subjects (N-group), matched for age, gender and body mass index. Minimal modelling of C-peptide and insulin data provided β-cell responsiveness to glucose perturbation (first, Φ 1, second, Φ 2, and basal, Φ b , phase), insulin secretion rate, ISR(t) and total pre-hepatic insulin secretion, TIS, as well as insulin delivery rate, IDR(t), and total insulin delivery, TID, into plasma, over 5-h test. Instantaneous normalized hepatic insulin degradation rate was computed as HIDR(t)=1−[IDR(t)/ISR(t)]. In our H-group, insulin sensitivity, S I , assessed by minimal model of glucose kinetics, showed a 56% reduction, which confirmed deterioration of insulin action in hypertension. This was associated with significant increase in Φ 1 (105%), TIS (55%) and TID (62%). No significant alterations were observed in other characteristic parameters of secretion and hepatic degradation of insulin, such that no significant difference was observed in HIDR(t) between our H and N groups. In conclusion, an increase of first phase and total insulin secretion occurring, in our H-group, in the presence of no alteration of hepatic insulin degradation, resulted in up-regulation of total insulin delivered to plasma (TID) for insulin-resistance compensation. [Copyright &y& Elsevier]

The evolution with ageing of insulin resistance, body weight (BW) and mean arterial pressure (MAP) was studied in a group of Zucker fatty rats (ZFRs, n= 22), between 7 and 16 weeks of age, compared with an age-matched control group of Zucker lean rats (ZLRs, n= 22). The minimal model of glucose kinetics was applied to estimate glucose effectiveness, SG, and insulin sensitivity, SI, from insulinaemia and glycaemia measured during a 70 min intravenous glucose tolerance test. No correlation was found between SG and age in both ZFR and ZLR groups. No significant changes in mean SG between the two groups indicated no alteration of glucose-mediated glucose disposal. Estimates of SI from individual ZFRs were independent of age and, on average, showed 83% reduction ( P < 0.001) compared with the ZLR group. Despite the lack of alteration of SI with age, the ZFR group showed an age-related increase of MAP, which correlated with increasing BW (r = 0.71 and P < 0.001). These results support the hypothesis that in our ZFRs, as a suitable genetic model of obesity and hypertension, insulin resistance is fully established at the age of 7 weeks and remains practically unaltered until at least the sixteenth week. An age-related increase in arterial pressure, observed in this strain, relates more properly to increasing BW, rather than insulin resistance. Development of hypertension with increasing age and BW may result from an enhanced insulin-mediated activity of the sympathetic nervous system, as observed in our previously reported study. [ABSTRACT FROM AUTHOR]

Based on glucose kinetics minimal model (GKMM) interpretation of frequently sampled intravenous glucose tolerance test (FSIGTT), the aim was to broaden the characterization of insulin-mediated glucose disposal in hypertension by aid of a dynamic insulin sensitivity index, $$ S_{\text{I}}^{\text{D}} $$, and the related efficiency, $$ \eta = S_{\text{I}}^{\text{D}} /S_{\text{I}} , $$ of the metabolic system to convert the maximal individual response capacity, measured by S, into an effective insulin control on glucose. The C-peptide minimal model (CPMM) was used to interpret the role of β-cell function. Plasma glucose, insulin, and C-peptide concentrations were measured, during a 5-h FSIGTT, in eighteen normoglycemic individuals: ten hypertensive patients (H-group) and eight normotensive subjects (N-group) with no metabolic syndrome. Compared to our N-group, the H-group showed a significant ( P < 0.05) reduction of both S (56%) and $$ S_{\text{I}}^{\text{D}} $$ (50%), no significant change of η, a significant increase of both the first-phase β-cell responsiveness to glucose (105%) and total insulin secretion (55%), and no significant change in disposition indexes, defined as the product of insulin sensitivity (either S and $$ S_{\text{I}}^{\text{D}} $$) and β-cell responsiveness. These findings suggest that, in spite of no change of efficiency, insulin resistance in normoglycemic hypertensive patients is primarily compensated by an increase in first-phase insulin secretion to preserve glucose tolerance to intravenous glucose load. [ABSTRACT FROM AUTHOR]

Somatosympathetic reflexes were studied in young hyperinsulinemic, insulin-resistant (Zucker fatty) rats (ZFR) and a related control (Zucker lean) strain (ZLR). Glucose metabolism was characterized by minimal model analysis of intravenous glucose tolerance test data. Seven-week-old ZFR (n = 18) and ZLR (n = 17) were studied under pentobarbital anesthesia. Mean body weight and plasma glucose and insulin concentration were significantly greater (P < 0.05) in ZFR than in ZLR, whereas basal values of mean arterial pressure (MAP) and heart rate (HR) were not significantly different. Increments of MAP (ΔMAP) and HR (AHR) elicited by electrical stimulation of the sciatic nerve (5-s trains of 100 pulses, 0.5-ms pulse duration, 100- to 400-μA pulse intensity) were significantly higher (ANOVA, P < 0.05) in ZFR at each level of stimulus intensity. Regression analysis showed a linear increase in ΔMAP and AHR with increasing sciatic nerve stimulus intensity. Pressor responses to phenylephrine after ganglionic blockade demonstrated that vascular reactivity to adrenergic stimulation is not increased in ZFR compared with ZLR. Thus this factor does not contribute to enhancement of somatosympathetic reflexes observed in this strain. Insulin sensitivity in ZFR was one-fourth (P < 0.05) that in ZLR. These results suggest that stronger sympathetic nervous reactivity in ZFR is associated with a severe insulin-resistant state before the onset of hypertension and support the hypothesis that insulin-mediated stimulation of the sympathetic nervous system is involved in the development of cardiovascular diseases related to alterations of glucose metabolism. [ABSTRACT FROM AUTHOR]