Cyclic AMP response to epinephrine and shock

Effect of esmolol on fluid therapy in normovolemia and hypovolemia

beta-Adrenergic agonists can enhance vascular volume expansion after a fluid bolus. The present study addresses how the beta-adrenergic antagonist esmolol influences volume expansion and fluid balance during normovolemia (series 1) and hypovolemia (series 2). Sheep were instrumented, and the spleen was removed. For series 1, continuous infusion of 50 to 100 microg.kg(-1).min(-1) esmolol (n = 6) or control (no drug; n = 6) was begun 30 min before administration of a 24-mL kg(-1) 20-min bolus of 0.9% NaCl. For series 2, anesthetized sheep were infused with 50 to 100 microg.kg(-1).min(-1) esmolol (n = 6) or control (no drug; n = 6) 30 min before a-20 mL kg(-1) hemorrhage. Fluid resuscitation (0.9% NaCl) was begun 30 min after hemorrhage. The 24-mL kg(-1) 20-min bolus was followed by titrated fluid therapy. Hemoglobin, fluid in, and urinary output were used to calculate changes in plasma volume (DeltaPV), extravascular volume (DeltaEVV = fluid in - urinary output - DeltaPV), volume expansion efficiency (VEE = fluid in / DeltaPV), and fluid distribution ratio (DeltaPV/DeltaEVV). Hemodynamics for both series were similar with the exception of heart rate. In series 1, peak DeltaPV was 9.1 +/- 1.0 mL kg(-1) in control and 3.7 +/- 1.0 mL kg(-1) at study end. Esmolol resulted in a lower peak DeltaPV (6.4 +/- 2.0 mL kg(-1)) and a negative DeltaPV (-0.4 +/- 0.6 mL kg(-1)) at study's end. Urinary output was lower, and EVV was greater with esmolol. In series 2, esmolol increased fluid requirements (67 +/- 7 mL kg(-1)) compared with control (54 +/- 5 mL kg(-1)). Esmolol reduced DeltaPV/DeltaEVV. These data suggest that esmolol impairs the vascular retention of fluid and may increase the amount of volume support during fluid resuscitation.

Administration of ATP-MgCl2 following hemorrhage and resuscitation increases hepatic phosphoenolpyruvate carboxykinase and decreases pyruvate kinase activities

Since administration of ATP-MgCl2 following trauma and hemorrhagic shock improves tissue perfusion as well as cell and organ function, the aim of this study was to determine whether this agent has any salutary effects on the hepatic rate-controlling enzymes specific for gluconeogenesis, such as phosphoenolpyruvate carboxykinase (PEPCK), and for glycolysis, such as pyruvate kinase (PK), under such conditions. To study this, rats underwent a 5-cm midline laparotomy (i.e., trauma-induced) and were bled to and maintained at a mean arterial pressure of 40 mm Hg until 40% of maximum bleed out volume was returned in the form of Ringer's lactate (RL). The animals were then resuscitated with 3 times the volume of shed blood with RL over 45 min, followed by 2 times RL with ATP-MgCl2 (50 micromol/kg body wt.) or an equivalent volume of normal saline over 95 min. Hepatic PEPCK, PK and glucokinase activities were determined 4 h after the completion of resuscitation. The mRNA levels of PEPCK and PK in the isolated hepatocytes were determined by Northern blot analysis. The results indicate that glucokinase activity was not significantly altered after hemorrhage, irrespective of ATP-MgCl2 treatment. Although the mRNA levels of PEPCK were similar in all groups, PEPCK activity decreased significantly after hemorrhage. ATP-MgCl2 treatment, however, restored PEPCK activity. Hemorrhage resulted in an increase in PK activity and its mRNA. ATP-MgCl2 treatment significantly decreased PK activity and the mRNA. Thus, up-regulation of the gluconeogenic enzyme, PEPCK, and down-regulation of the glycolytic enzyme, PK, by ATP-MgCl2 may be responsible, in part, for the beneficial effects of this agent following trauma-hemorrhage and resuscitation.

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

The relative contribution of the splanchnic sympathetic innervation and the adrenal medulla for metabolism and hormone secretion during two different levels of hemorrhagic hypotension was investigated in 3 groups of anesthetized cats, viz, intact, adrenalectomized and splanchnicotomized (adrenalectomy + cutting of splanchnic nerves). In intact cats, hemorrhage caused very marked elevations of arterial plasma glucose, adrenaline, noradrenaline, dopamine, lactate, cAMP, glycerol and glucagon concentrations whereas plasma insulin fell to only 20% of control values. Adrenalectomy attenuated the glucose, adrenaline, noradrenaline and cAMP responses whereas the normal insulin inhibition was abolished. Splanchnicotomy further reduced the hemorrhagic glucose and glycerol responses and, possibly, also that of glucagon. It is concluded that the adrenergic system as a whole is important for the adjustments of the release of glucose, cAMP, glycerol, insulin and glucagon that occur during hemorrhage in cats. The adrenal medulla seems to be of particular importance for the regulation of cAMP release.

The pathophysiology of shock

This is a very brief, superficial and biased discussion of the pathophysiologic changes in shock. It was designed to provide some insight into the very complex changes that occur, with particular attention to a few examples of the impaired cell metabolism, including changes in ATP, cAMP, and calcium. Although inadequate tissue perfusion through nutrietn capillaries is the main etiologic factor in most types of shock, it is not the primary problem in many patients, particularly those with early or hyperdynamic sepsis. The importantance of oxygen consumption and the possible benefits of higher hemoglobin levels are discussed to some extent because of their possible clinical application.

Plasma catecholamines, cyclic AMP and metabolic substrates in hemorrhagic shock of the rat. The effect of adrenal demedullation and 6-OH-dopamine treatment

Plasma catecholamines, cyclic AMP and metabolic substrates in hemorrhagic shock of rats was studied in 4 groups of animals: 1) Control rats, 2) rats with adrenal demedullation, 3) rats with 6-OH-dopamine induced chemical sympathectomy, and 4) rats with combined demedullation and sympathectomy. The rats were bled to a systemic blood pressure of 35 mmHg. The basal plasma level of noradrenaline (NA), adrenaline (A) and dopamine (DA) in control animals was each about 1 nmol/1. After hemorrhage for 1 h the A levels had reached 50 nmol/l and there was little further rise after 4 h. The rise was eliminated by demedullation but unaffected by sympathectomy. NA levels rose continuously in the control and in the sympathectomized rats. At 1 h the level was about 4 nmol/l and at 4 h about 20 nmol/l. The demedullated rats showed a 3-fold increase in circulating NA, while little or no change was seen in the combined demedullated and sympathectomized rats. DA levels did not change in any of the groups during the first hour, but were markedly elevated after 4 h of hypotension. Cyclic AMP and glucose levels in plasma showed a rapid increase 1 h after hemorrhage and thereafter returned to or below basal values. Demedullation largely prevented the increase, while sympathectomy had no effect. The increase in lactate and pyruvate levels were diminished but not eliminated by either sympathectomy or demedullation. Glycerol levels were unchanged and FFA decreased in all groups of rats. The results show that the adrenal medulla is the dominating source of plasma catecholamines in hemorrhagic shock in rats. The initial increase in plasma glucose and cyclic AMP appear to be largely mediated by adrenal A. The subsequent fall in these parameters and derangement of circulatory homeostasis are not, in the present shock model, primarily due to a failure of catecholamine secretion, but rather to a decreased responsiveness of peripheral tissues to catecholamine stimulation.

Mechanism of stress ulcer. Influence of alpha-adrenergic blockade on stress ulceration and gastric mucosal energy metabolism

In previous reports from this laboratory, it has been proposed that stress ulceration results from a severe gastric mucosal energy deficit due to shock-induced mucosal ischemia. In the experiments described in this report, the hypothesis was further tested by studying stress ulceration and gastric mucosal energy metabolism in rabbits subjected to hemorrhagic shock with or without the concomitant administration of an alpha-adrenergic blocking agent. Our data show that stress ulceration and gastric mucosal energy deficits are significantly less severe when shock is combined with alpha-adrenergic blockade.

Mechanism of plasma cyclic AMP response to hypoglycemia in man

The effect of insulin-induced hypoglycemia on plasma cyclic AMP levels was studied in normal volunteers, adrenalectomized, and sympathectomized subjects. Significant increases in plasma glucagon were observed in all groups. Normal subjects all had two- to threefold rises in plasma cAMP while no response was seen in any adrenalectomized or sympathectomized subject. These findings suggest that the mechanism for enhanced plasma cAMP release during insulin-induced hypoglycemia is catecholamine dependent. Glucagon does not contribute significantly to this response.

Alterations in splanchnic cyclic nucleotide levels in splanchnic artery occlusion shock and their modification by dexamethasone

The effects of dexamethasone sodium phosphate (DSP), 5 mg/kg, administration on the biochemical alterations in hepatic tissue subsequent to the production os splanchnic artery occlusion (SAO) shock was investigated. Following the induction of SAO shock, DSP-treated dogs exhibited a significantly improved cardiovascular status compared to placebo-treated shocked dogs, 2 hr after release of the occlusion, biopsies of the liver were taken and analyzed for beta-glucuronidase (BG), adenosine-3',5'-cyclic monophosphate (cAMP) and guanosine-3',5'-cyclic monophosphate (cGMP) content. SAO shock produced a significant increase in hepatic free BG activity which was reversed by DSP pretreatment. Additionally, SAO shock decreased hepatic cAMP levels, increased cGMP levels and significantly lowered the hepatic ratio of cAMP/cGMP. These changes in cyclic nucleotide levels were reversed by DSP administration and were found to be inversely related to changes in hepatic free BG activity. Thus, the ratio of cellular cAMP/cGMP may function as a regulatory mechanism for lysosomal enzyme release secondary to ischemia and hypoxia. Further, DSP may act to maintain lysosomal integrity in ischemic tissues by preservation of cAMP/cGMP ratios.