Metabolic and hormonal adjustments during hemorrhage in cats after interference with the sympatho-adrenal system

Determinants of Fasting Hyperglucagonemia in Patients with Type 2 Diabetes and Nondiabetic Control Subjects

BACKGROUND

Fasting hyperglucagonemia can be detrimental to glucose metabolism in patients with type 2 diabetes (T2D) and may contribute to metabolic disturbances in obese and/or prediabetic subjects. However, the mechanisms underlying fasting hyperglucagonemia remain elusive.

METHODS

We evaluated the interrelationship between fasting hyperglucagonemia and demographic and biochemical parameters in 106 patients with T2D (31% female, age: 57 ± 9 years [mean ± standard deviation; body mass index (BMI): 30.1 ± 4.4 kg/m²; fasting plasma glucose (FPG): 9.61 ± 2.39 mM; hemoglobin A1c (HbA1c): 57.1 ± 13.1 mmol/mol] and 163 nondiabetic control subjects (29% female; age: 45 ± 17 years; BMI: 25.8 ± 4.1 kg/m²; FPG: 5.2 ± 0.4 mM; and HbA1c: 35.4 ± 3.8 mmol/mol). Multiple linear regression analysis was applied using a stepwise approach with fasting plasma glucagon as dependent parameter and BMI, waist-to-hip ratio (WHR), blood pressure, hemoglobin A1c, FPG, and insulin concentrations as independent parameters.

RESULTS

Fasting plasma glucagon concentrations were significantly higher among patients with T2D (13.5 ± 6.3 vs. 8.5 ± 3.8 mM, P < 0.001) together with HbA1c (P < 0.001), FPG (P < 0.001), and insulin (84.9 ± 56.4 vs. 57.7 ± 35.3 mM, P < 0.001). When adjusted for T2D, HbA1c and insulin were significantly positive determinants for fasting plasma glucagon concentrations. Furthermore, WHR comprised a significant positive determinant.

CONCLUSIONS

We confirm that fasting plasma glucagon concentrations are abnormally high in patients with T2D, and show that fasting plasma glucagon concentrations are influenced by WHR (in addition to glycemic control and fasting plasma insulin concentrations), which may point to visceral fat deposition as an important determinant of increased fasting plasma glucagon concentrations.

Acute hemorrhage causes hepatic insulin sensitizing substance (HISS)-dependent insulin resistance

Hepatic insulin sensitizing substance (HISS) has been shown to account for 55% of the action of insulin in the fed state. HISS blockade leads to HISS-dependent insulin resistance (HDIR). The objective of this study was to test the hypothesis that insulin resistance produced by hemorrhage was HDIR. Insulin sensitivity was measured using the rapid insulin sensitivity test (RIST), which can identify HISS-dependent and independent components. Hemorrhage was performed in anesthetized rats by removing blood to reduce mean arterial pressure to 50 mmHg. Subsequent to blood removal, a RIST was performed. The results show that hemorrhage caused complete HDIR as subsequent administration of atropine failed to further reduce insulin sensitivity. However, the post-hemorrhage RIST was reduced by 34% and not the anticipated 55%. The lesser reduction of the RIST index by hemorrhage was related to reduced apparent volume of distribution and clearance of insulin, since occlusion of the superior mesenteric artery, which caused a similar decrease in portal venous flow as did hemorrhage, resulted in a similar degree of reduction of insulin clearance. The response to administered insulin was confounded by the impact of reduced hepatic blood flow on insulin metabolism that resulted in an increase in the HISS independent (direct) action of injected insulin against a background of complete HDIR. HDIR represents a useful hormonal response to assure a hyperglycemic response to hemorrhage.

The influence of gender in the evaluation of platelet and plasma catecholamines

The platelet and plasma levels of catecholamines (CA) were simultaneously studied in a group of normal subjects in order to find possible sex-related changes in the distribution of CA in these two compartments. No significant differences between males and females were observed, but a marked platelet noradrenaline increase was found in the luteal phase as compared to the follicular phase. Furthermore, the platelet and plasma CA levels were strongly correlated in the male group but not in the female group. These results, while confirming the existence of a menstrual-related variability in noradrenergic activity, suggest a sex-related difference in the dynamic balance between platelet and plasma CA levels. The simultaneous assay of platelet and plasma CA enabled this phenomenon to be revealed, whereas the separate evaluation of platelet or plasma CA levels would not have done so.

Free plasma catecholamine levels in healthy subjects: a basal and dynamic study. The influence of age

We studied the levels of free plasma noradrenaline (norepinephrine, NE), adrenaline (epinephrine, E), and dopamine (DA) in 143 normal subjects, either basally or, in a part of them, in response to four tests stimulating the sympathoadrenomedullary activity: the tilt-table test (TTT), the cold-pressor test (CPT), the mental-arithmetic test (MAT), and the insulin tolerance test (ITT). In both cases we evaluated the influence of age, which is considered the main physiological variable affecting the peripheral sympathetic activity. A normal distribution of values was observed, in the basal study, only for NE, while E and particularly, DA levels were distributed in an non-homogeneous fashion; a direct correlation was observed between age of subjects and NE levels, while neither E, nor DA levels showed any correlation with the aging process; sex did not influence any of the catecholamines. In the dynamic study, CPT, ITT and, above all, TTT elicited a significant rise in NE levels, while the E release was greatly stimulated by the insulin-induced hypoglycaemia. Neither NE, nor E levels rose after the MAT stimulation. Also in this case, the elderly showed an increased noradrenergic responsiveness when compared with the young subjects, confirming the existence of an 'up-regulation' of the peripheral sympathetic tone in old people.

Neural control of islet function by norepinephrine and sympathetic neuropeptides

It is clear that the sympathoadrenal system has a role in the regulation of endocrine pancreatic function and that the sympathetic nerves of the pancreas can change pancreatic hormone secretion to increase the availability of metabolic fuels. It seems likely that the classical sympathetic neurotransmitter, NE, acts in concert with peptide co-transmitters, such as galanin and NPY. Each is released during the stimulation of pancreatic sympathetic nerves and each is capable of influencing either islet function or pancreatic blood flow. There is considerable indirect evidence that the sympathetic innervation of the pancreas is activated during acute stress and influences the endocrine pancreas. However, proving such a physiologic role is difficult because of redundant mechanisms that influence the secretion of the metabolically-crucial hormones, insulin and glucagon. Such definitive proof therefore awaits the development of new techniques to dissect and dissociate these mechanisms.

The sources of plasma catecholamines in the American eel, Anguilla rostrata

The origin of the catecholamines (CAs) in the systemic blood of the American eel, Anguilla rostrata, was studied by three approaches: (1) determination of the CA content of tissues suspected to release large quantities of dopamine, norepinephrine, and/or epinephrine into the circulation; (2) measurement of local CA titers in selected regions of the cardiovascular system; and (3) removal of tissues with high CA concentrations, followed by determination of its impact on stimulated CA release. Large quantities of all three CAs were found in the walls of the posterior cardinal veins, from their caudal origin within the opisthonephric kidney to their termination in the ductus Cuvieri. Near the ductus Cuvieri, the CA concentration was 1-3 orders of magnitude above that in other tissues. In this region, which contains the presumed adrenal medulla equivalent, occur the highest plasma levels of the CAs. Strong CA release also in the opisthonephric kidney region raises the question if these CAs affect locally the kidney functions, and/or via the hepatic portal vein (which originates in this region), the liver. Other organs (especially brain and heart) contain CA concentrations high enough to potentially affect the CA level in the systemic blood, if instantly released. However, neither partial removal of the brain nor hypophysectomy, "adrenomedullectomy," Stanniectomy, or urophysectomy had an appreciable impact on stimulated CA release. Together with previous data, these findings show that in the eel (a) the region of the presumed adrenal medulla equivalent is the most important source of all three CAs in systemic plasma; (b) that strong CA-stimulated CA release also occurs outside this region; and (c) that the pituitary, forebrain, and midbrain are not necessary for the CA-stimulated CA release.

Effects of physiological increases in plasma noradrenaline on the human endocrine pancreas

The effect of plasma noradrenaline concentrations within the physiological range (less than 5-6 nM) on the endocrine pancreas was investigated in 9 nondiabetic volunteers. Noradrenaline significantly inhibited plasma insulin levels but did not change plasma glucagon and somatostatin concentrations.

Endogenous renal dopamine and control of blood pressure

Activation of specific receptors for dopamine in the renal vasculature and tubules leads to increases in glomerular filtration, and to diuresis and natriuresis. There is evidence for intrarenal production and release of dopamine, which may originate from two sources: tubular decarboxylation of plasma l-DOPA and a population of dopaminergic sympathetic neurons that innervate the renal cortex. Studies of plasma and urinary catecholamine levels indicate that dopamine is released within the kidney in response to sodium loading and to activation of sensory pathways related to nociception and chemoreception. There is also evidence for deficient renal release of dopamine in patients with renovascular or essential hypertension. Collectively, the available data suggest that intrarenal dopamine has a physiological function in control of blood volume and blood pressure, and that defects in this control may be implicated in the aetiology of some hypertensive states.

Effect of rate of hemorrhage on sympathoadrenal catecholamine release in cats

The effect of rate of blood loss on catecholamine release and cardiovascular compensation to hemorrhage (H) was assessed in alpha-chloralose-urethane anesthetized cats. Arterial blood was withdrawn at a rapid rate (10% measured blood vol/min) or at a slow rate (2%/min), and responses were compared across three volumes of hemorrhage (10, 20, or 30% of total blood vol). Plasma epinephrine did not increase after 10% H, but increased modestly after rapid (199 +/- 25 pg/ml) or slow 20% H (359 +/- 92 pg/ml). In contrast, rapid 30% H evoked a significantly (P less than 0.01) greater increase in epinephrine than slow 30% H (1,827 +/- 274 vs. 630 +/- 165 pg/ml). The rate of hemorrhage had no differential effect on hemorrhage-evoked plasma norepinephrine, but a graded increase was seen with increasing volume of hemorrhage. Similarly, hemorrhage-evoked plasma glucose was proportional to the volume of hemorrhage and was not affected by rate of hemorrhage. Volume of hemorrhage was a good indicator of norepinephrine release after rapid or slow rate of hemorrhage, whereas epinephrine release was well correlated with the mean changes in blood pressure during the posthemorrhage sampling period after rapid or slow rate of hemorrhage. The data indicate that hemorrhage-evoked release of epinephrine depends on the rate of blood loss, but only after large (30%) volumes of hemorrhage. Norepinephrine released into the peripheral circulation demonstrates no dependency on rate of hemorrhage, but is well correlated with volume of hemorrhage.(ABSTRACT TRUNCATED AT 250 WORDS)

Central hemodynamic effects of adrenaline with special reference to beta 2-adrenergic influence on heart rate and cardiac afterload in anesthetized cats

Central hemodynamic responses evoked by i.v. infusions of adrenaline and noradrenaline were studied in normovolemic anesthetized cats with intact adrenoceptors, after selective beta 2-blockade (ICI 118,551), and after nonselective beta-blockade propranolol). The results demonstrated the presence of an important beta 2-adrenergic component in the integrated response to 'physiological' doses of adrenaline contributing to increased cardiac output, decreased total peripheral resistance and virtually unchanged mean arterial blood pressure. Corresponding beta 2-adrenergic effects of noradrenaline were small. The beta 2-adrenergic effects of adrenaline on the heart seemed to be both direct and indirect. A moderate direct chronotropic response mediated by beta 2-adrenoceptors apparently was present but there was no evidence of a direct beta 2-adrenergic inotropic effect. An indirect, quite marked effect on the heart was accomplished by a beta 2-adrenergic vasodilator interaction with the alpha-adrenergic vasoconstrictor influence on the systemic resistance vessels. This caused a net decrease in total peripheral resistance, thereby preventing an undue increase in cardiac afterload (arterial pressure) which seemed to be essential for evoking 'optimal' increases in cardiac output. It is suggested that such adrenaline evoked indirect, beta 2-adrenergic improvement of cardiac performance is of functional importance in reflex sympatho-adrenal circulatory control.

Sympathetic nervous system and adrenal medullary responses to ischemic injury in mice

Acute, severe injury is frequently attended by hypotension, hypothermia, and decreased metabolic rate despite elevated urine and plasma catecholamine levels. Because the combination of sympathetic nervous system (SNS) suppression and adrenal medullary stimulation documented in several other situations could account for these observations, SNS and adrenal medullary function were examined independently in mice in the hindlimb ischemia model of acute injury. SNS activity was assessed by the measurement of [3H]norepinephrine (NE) turnover in heart and adrenal medullary secretion by depletion of adrenal catecholamine content. In nine separate experiments during the first 10 h after termination of a 2.5-h period of hindlimb ischemia, cardiac NE turnover was reduced an average of 23% (P less than 0.05) in injured mice. At the same time, adrenal catecholamine content fell 37% (P less than 0.05) in injured animals but not in controls. In contrast to the acute reaction, SNS activity in mice surviving 3 days was 59% greater than in controls. Thus, the reduction in NE turnover and depletion of adrenal catecholamine content suggest that SNS suppression and adrenal medullary stimulation constitute the acute sympathoadrenal response in this model of severe injury. Because survival within the first 24 h after injury was decreased in adrenalectomized mice despite glucocorticoid treatment, adrenal medullary catecholamines may contribute to survival in severely injured animals. Furthermore, because the SNS plays an important role in the regulation of blood pressure and heat production, the diminution in SNS activity in the hours after injury may contribute to posttraumatic hypotension and hypometabolism.

Effects of adrenergic blockade on the release of insulin, glucagon and somatostatin from the pancreas in response to splanchnic nerve stimulation in cats

The effects of alpha-, beta- or alpha + beta-adrenergic blockade on arterial plasma concentrations of insulin, glucagon and somatostatin in response to splanchnic nerve stimulation were studied in anesthetized cats. In control experiments splanchnic nerve stimulation caused a marked rise in plasma glucose and glucagon concentrations and a marked fall in insulin but somatostatin was unaffected. Pretreatment with phentolamine significantly increased basal plasma insulin concentration but the response pattern to splanchnic nerve stimulation was not altered. Propranolol attenuated both the glucose and insulin responses. Combined alpha-and beta-blockade abolished the hyperglycemia and hypoinsulinemia induced by splanchnic nerve stimulation, whereas the rise in plasma glucagon was not affected. It is concluded that insulin release from the pancreas and glucose release from the liver is controlled by adrenergic mechanisms whereas pancreatic glucagon and somatostatin secretion is relatively insensitive to splanchnic nerve stimulation in cats.