Epinephrine plasma metabolic clearance rates and physiologic thresholds for metabolic and hemodynamic actions in man

Catecholamine physiology in ovine fetus. II. Metabolic clearance rate of epinephrine

This study measured the metabolic clearance rate (MCR) of epinephrine (E) in 13 chronically catheterized fetal lambs between 120 and 145 days gestation. The E-MCR was determined by a constant infusion method at an E infusion rate of 0.1 microgram/kg estimated fetal wt. Fetal and maternal arterial blood samples were taken for measurements of catecholamine levels, pH, blood gases, and glucose. There was a significant positive correlation between gestational age and E-MCR (r = 0.87, P less than 0.001). The E production rate in fetuses less than 132 days (n = 6) (1,234 +/- 301 pg/min) was not significantly different from fetuses greater than or equal to 132 days (n = 7) (1,195 +/- 242). Catecholamine infusion resulted in a decrease in pH from a control value of 7.37 +/- 0.01 to 7.31 +/- 0.01 by 15 min of infusion, but there were no significant changes in fetal heart rate or blood pressure. The mean fetal plasma glucose concentration increased 45% above base line at 15 and 20 min and 65% above base line by 30 min of catecholamine infusion. After 60 min of infusion plasma norepinephrine (NE) increased from 380 +/- 60 to 520 +/- 75 pg/ml and plasma dopamine from 100 +/- 20 to 240 +/- 50 pg/ml (both P less than 0.05). These results indicate that E-MCR increases with maturation in the absence of a change in basal E production.

The effects of acute or chronic ingestion of propranolol or metoprolol on the metabolic and hormonal responses to prolonged, submaximal exercise in hypertensive men

We have studied the effects of single oral doses of, and of 28 days treatment with, placebo, propranolol or metoprolol, on the metabolic and hormonal responses to prolonged exercise in hypertensive men. Blood glucose levels fell during exercise on all occasions. No additional effects of the beta-adrenoceptor antagonists, compared to placebo, were observed. The exercise-induced increase in plasma potassium was enhanced after a single dose of propranolol or metoprolol, and also after chronic treatment with propranolol. Chronic treatment with either drug led to an increase in plasma potassium levels at rest. The growth hormone response to exercise was potentiated by a single dose of metoprolol or propranolol, and after chronic treatment with the drugs. A single dose of propranolol (but not metoprolol) was associated with a marked increase in plasma cortisol and adrenaline levels during exercise. After chronic treatment no such increase occurred. In both the acute and chronic phases of the study, blood lactate levels were higher during exercise in the presence of either propranolol or metoprolol compared to placebo, whereas non-esterified fatty acid levels were lower. A single dose of metoprolol produced a significantly greater reduction in blood glycerol levels during exercise than a single dose of propranolol. After chronic treatment, both propranolol and metoprolol produced similar reductions in blood glycerol levels during exercise. After a single dose, both drugs significantly augmented the increase in plasma noradrenaline levels during exercise. A similar effect was seen after chronic treatment.

Decreased plasma epinephrine concentrations after glucose ingestion in humans

Plasma levels of norepinephrine (NE), epinephrine (E), immunoreactive insulin (IRI), and glucose were measured in six healthy volunteers after glucose consumption and in six volunteers after a water solution. Ingestion of the glucose (100 g) solution significantly decreased E levels from 46.7 +/- 8.0 to 20.8 +/- 1.9 pg/mL (P less than 0.01). Three hours after the glucose ingestion, plasma E levels nearly returned to basal values. Plasma IRI and glucose levels peaked at 45 minutes after glucose consumption (P less than 0.01), then declined toward basal values. Plasma NE levels were unaffected by glucose consumption. There were no changes in glucose, IRI, NE, or E levels in the control group. These results suggest that E behaves as a counter-regulatory hormone to insulin under stimulation by glucose.

Epinephrine supports the postabsorptive plasma glucose concentration and prevents hypoglycemia when glucagon secretion is deficient in man

We hypothesized that adrenergic mechanisms support the postabsorptive plasma glucose concentration, and prevent hypoglycemia when glucagon secretion is deficient. Accordingly, we assessed the impact of glucagon deficiency, produced by infusion of somatostatin with insulin, without and with pharmacologic alpha- and beta-adrenergic blockade on the postabsorptive plasma glucose concentration and glucose kinetics in normal human subjects. During somatostatin with insulin alone mean glucose production fell from 1.5 +/- 0.05 to 0.7 +/- 0.2 mg/kg per min and mean plasma glucose declined from 93 +/- 3 to 67 +/- 4 mg/dl over 1 h; glucose production then increased to base-line rates and plasma glucose plateaued at 64-67 mg/dl over 2 h. This plateau was associated with, and is best attributed to, an eightfold increase in mean plasma epinephrine. It did not occur when adrenergic blockade was added; glucose production remained low and mean plasma glucose declined progressively to a hypoglycemic level of 45 +/- 4 mg/dl, significantly (P less than 0.001) lower than the final value during somatostatin with insulin alone. These data provide further support for the concept that maintenance of the postabsorptive plasma glucose concentration is a function of insulin and glucagon, not of insulin alone, and that adrenergic mechanisms do not normally play a critical role. They indicate, however, that an endogenous adrenergic agonist, likely adrenomedullary epinephrine, compensates for deficient glucagon secretion and prevents hypoglycemia in the postabsorptive state in humans. Thus, postabsorptive hypoglycemia occurs when both glucagon and epinephrine are deficient, but not when either glucagon or epinephrine alone is deficient, and insulin is present.

Adrenaline and hypertension

In man, circulating adrenaline has little or no direct effect on the control of blood pressure. A small proportion of adrenaline secreted by the adrenal medulla is accumulated in sympathetic nerve endings and may be re-released by sympathetic nerve stimulation. Recent pharmacological studies have suggested that adrenaline acts on a presynaptic beta-receptor on sympathetic nerve endings to facilitate noradrenaline release, and it has been proposed that adrenaline re-released from these nerve endings is therefore a functionally important "co-transmitter". Intermittently elevated secretion of adrenaline from the adrenal medulla could therefore lead indirectly to a sustained increase in neuronal release of noradrenaline and hence to hypertension.

Hypokalemia from beta2-receptor stimulation by circulating epinephrine

To determine whether epinephrine-induced hypokalemia is due to beta2-adrenoceptor stimulation, and whether hypokalemia can occur at physiologic concentrations of the agonist, epinephrine was infused into six normal volunteers at a rate of 0.1 microgram per kilogram of body weight per minute. The circulating epinephrine concentration was increased to 1.74 +/- 0.65 ng per milliliter, plasma potassium was reduced by 0.82 +/- 0.19 meq per liter, plasma insulin fell by 12 +/- 4 mU per liter, plasma renin activity was elevated, and tachycardia occurred. Isoproterenol infused at 0.02 micrograms per kilogram per minute caused similar tachycardia (25 beats per minute) and elevation in plasma renin activity (6.0 to 6.5 ng per milliliter per hour), but no hypokalemia. The difference in responses to the two catecholamines was ascribed to the relative beta2-selectivity of epinephrine. This hypothesis was tested in six subjects given infusions of epinephrine (0.05 micrograms per kilogram per minute) after administration of either 2.5 or 5 mg of ICI 118551--a selective beta2-receptor antagonist--or placebo. After placebo, epinephrine infusion elevated the circulating epinephrine concentration and reduced plasma potassium; hypokalemia was prevented by the beta2-antagonist. This drug only partially inhibited the rises in plasma renin and glucose and the shortening of systolic time intervals; there was no tachycardia. Fifteen-fold to 30-fold increases in circulating epinephrine concentration appear to cause hypokalemia by a specific beta2-receptor effect distinct from other actions of epinephrine. This phenomenon may be of physiologic importance after severe myocardial infarction, when similar increases in plasma epinephrine have occurred.

Exercise-induced increments in plasma levels of propranolol and noradrenaline

Exercise-induced changes in the plasma levels of propranolol and noradrenaline were determined in nine volunteers. Total plasma propranolol levels were increased during submaximal treadmill exercise, with exercise-induced increments of 13 +/- 4% at 4 h after the last dose, 18 +/- 7% at 9 h and 41 +/- 5% at 16 h. Exercise-induced increments in plasma propranolol were observed after single as well as repeated doses. During exercise, increments in plasma propranolol were correlated temporally with changes in plasma noradrenaline. Exercise-induced increments in plasma noradrenaline were greater during propranolol administration than during placebo periods. The changes in plasma propranolol concentration during exercise may reflect a redistribution of propranolol at its site(s) of action.

Changes in cardiac transcapillary exchange with metabolic coronary vasodilation in the intact dog

The effects of metabolic coronary vasodilation on transcapillary exchange in the heart were examined in anesthetized dogs by use of the multiple indicator dilution technique. Animals were studied under basal conditions and during coronary sinus pacing. To obviate adrenal medullary stimulation, catheters were placed in coronary artery and coronary sinus in a closed chest preparation. Plasma catecholamine concentrations were determined to provide an index of the level of sympathetic tone. Labeled albumin and sucrose were injected into the coronary artery, and outflow dilution curves were secured. Analysis of these, with a model incorporating throughput and returning components, and heterogeneity of capillary transit times, provided parameters reflecting flow, permeability-surface product for sucrose, and capillary heterogeneity. Coronary sinus pacing increased both heart rate and plasma norepinephrine values; in response, myocardial oxygen consumption increased, metabolic vasodilation occurred, and coronary flow increased. The capillary permeability-surface product for sucrose increased with the flow but tended to plateau at higher values, showing a saturation phenomenon. Capillary heterogeneity, present in control animals with low sympathetic tone, was grossly decreased during cardiac metabolic activation. The Crone-Renkin approximation formula for the permeability-surface product yielded values that were too low at low flows and values approaching those from the complete model at high flows. The findings indicate an integrated pattern of circulatory response to cardiac metabolic activation characterized by decreased resistance, increased flow, increased permeability-surface product, and reduced heterogeneity. The last two effects amplify the capacity of increased flow to deliver substrates to heart muscle cells.

Direct alpha-adrenergic stimulation of hepatic glucose production in human subjects

Six normal humans each underwent infusions of 1) saline; 2) propranolol; 3) somatostatin; 4) somatostatin with propranolol; and 5) somatostatin with propranolol plus phentolamine on separate occasions. Propranolol alone had no effect on glucose production or plasma glucose. Somatostatin alone produced the expected initial decrease followed by an increase in both hepatic glucose production and plasma glucose. beta-Adrenergic blockade with propranolol displaced the glucose production (MANOVA, P = 0.0220) and plasma glucose (MANOVA, P = 0.0057) somatostatin response curves to higher levels, whereas alpha-adrenergic blockade with phentolamine combined with beta-adrenergic blockade displaced the glucose production (MANOVA, P = 0.0281) and plasma glucose (MANOVA, P = 0.0134) somatostatin response curves to lower levels. Because plasma insulin, C-peptide, and glucagon were suppressed comparably under all three conditions and plasma glucose concentrations were comparable initially, this represents direct alpha-adrenergic stimulation of hepatic glucose production in postabsorptive humans demonstrable when the primary glucoregulatory hormones are withdrawn and beta-adrenergic mechanisms are blocked. It is best attributed to sympathetic neural norepinephrine release.

Epinephrine sensitivity with respect to metabolic rate and other variables in women

A test for determination of epinephrine sensitivity has been worked out using six healthy young women. Variables considered were metabolic rate, heart rate, respiratory frequency, blood pressure, blood glucose, plasma insulin, glycerol, free fatty acids, and lactate. After established basal conditions, epinephrine was infused at rates of 0.01, 0.03, and 0.1 microgram X kg fat-free mass-1 X min-1. Most variables responded to epinephrine in a dose-dependent manner. Physiological threshold plasma concentrations of epinephrine ranged from 95 to 250 pg/ml for different variables. Calculated maximal responses ranged from approximately -15% to +900% of basal values and infusion rates giving half-maximal responses from approximately 15 to 190 ng X kg fat-free mass-1 X min-1. On an average, metabolic rate increased by 8, 16, and 29%, respectively, at the three infusion rates, and the maximal metabolic response was calculated to be approximately 35%. The error in determining epinephrine-induced increments in metabolic rate was 7% of the response. As calculated from nonprotein RQ, carbohydrate oxidation increased and lipid oxidation decreased rapidly during the first 10 min of epinephrine infusion. Later, fat oxidation became more important. Results on epinephrine plasma metabolic clearance rate agreed with earlier results in the literature.

Behavioral and physiological effects of ethanol in high-risk and control children: a pilot study

Blood and breath acetaldehyde levels were measured following ethanol ingestion (0.5 ml/kg) in 11 boys familially at risk for alcoholism and 11 age-matched controls. No significant differences were found between groups for acetaldehyde, objective, or subjective measures of intoxication. Previous reports of acetaldehyde as a marker of risk for alcoholism were not confirmed. Baseline behavioral state predicted response to alcohol. Children tended to have a subjective response in a direction opposite from the baseline mood state.

Insulin resistance in alloxan-diabetic dogs: evidence for reversal following insulin therapy

Hepatic glucose production and peripheral glucose utilization were measured basally and during infusion of insulin (25 and 40 m U X kg-1 X h-1) in normal dogs and in insulin-deficient diabetic dogs, before and after a 10-14 day period of insulin treatment. Basal hepatic glucose production was significantly raised in the diabetic dogs (21.4 +/- 2.5 mumol X kg-1. min-1; p less than 0.005) compared with normal dogs (11.9 +/- 2.5 mumol X kg-1 X min-1) and fell by 20% in diabetic dogs following insulin treatment (17.4 +/- 3.0 mumol X kg-1 X min-1). However, in all groups, hepatic glucose production suppressed equally well during the low dose insulin infusions, suggesting that the raised hepatic glucose production of diabetes is due to insulin deficiency and not hepatic insulin resistance. In addition, a marked defect of glucose utilization was found in the diabetic dogs (25 +/- 5 mumol X kg-1 X min-1; p less than 0.001) compared with normal dogs (99 +/- 15 mumol X kg-1 X min-1) during matched hyperinsulinaemia and hyperglycaemia. This defect of glucose utilization, as defined by euglycaemic insulin dose-response curves employing insulin infusion rates between 40-600 mU X kg-1 X h-1, demonstrated a marked reduction of glucose disposal in diabetic dogs. The severity of the insulin resistance closely paralleled the degree of hyperglycaemia. In contrast, following 10-14 days of insulin treatment, an improvement of glucose disposal was seen in all diabetic dogs. It is concluded that insulin deficiency leads to (a) increased hepatic glucose production, and (b) the development of marked peripheral insulin resistance, which is reversed by insulin treatment.

Elevated plasma catecholamines in hypertensives with primary glomerular diseases

Supine plasma concentration of norepinephrine (PNE), epinephrine (PE), and aldosterone (PA), plasma renin activity (PRA), and blood volume (BV) were measured in 25 normotensive and 11 hypertensive patients with biopsy-proven glomerulonephritis who had serum creatinine concentrations of less than 1.6 mg/dl, and in 20 normotensive control subjects. PNE and PE were measured according to the trihydroxyindol method using high pressure liquid chromatography. Renal clearances of p-aminohippurate (CPAH) and endogenous creatinine (Ccr) were also determined. Age, BV, and 24-hour urinary excretion of sodium were not significantly different in the three groups. Although all the measured variables were comparable between the control subjects and the normotensive nephritic patients, blood pressure, PNE, PE, PRA, and PA were significantly higher and CPAH and Ccr were significantly lower in the hypertensive nephritic patients than in the normotensive nephritic patients or the control subjects. In the pooled nephritic patients, mean blood pressure was significantly correlated with PNE (r = 0.76, p less than 0.001), PE (r = 0.34, p less than 0.05), PRA (r = 0.33, p less than 0.05), PA (r = 0.40, p less than 0.05) and CPAH (r = -0.51, p less than 0.01). Highly significant positive correlation was also observed between PNE and systolic pressure (r = 0.63, p less than 0.001) or diastolic blood pressure (r = 0.78, p less than 0.001). The results suggest that deterioration of renal function is an important factor in the development of hypertension even in non-azotemic patients with glomerulonephritis, and that increased activities of the sympathetic nervous system and the renin-aldosterone system participate, in part, in elevating blood pressure in the hypertensive nephritic patients. Mechanisms involved in the elevation of plasma concentrations of catecholamines and renal effects on the plasma catecholamines remain to be elucidated.

Mechanisms of postprandial glucose counterregulation in man. Physiologic roles of glucagon and epinephrine vis-a-vis insulin in the prevention of hypoglycemia late after glucose ingestion

The transition from exogenous glucose delivery to endogenous glucose production late after glucose ingestion is not solely attributable to dissipation of insulin and, therefore, must also involve factors that actively raise the plasma glucose concentration--glucose counterregulatory factors. We have shown that the secretion of two of these, glucagon and epinephrine, is specific for glucose ingestion and temporally related to the glucose counterregulatory process. To determine the physiologic roles of glucagon and epinephrine in postprandial glucose counterregulation, we produced pharmacologic interventions that resulted in endogenous glucagon deficiency with and without exogenous glucagon replacement, adrenergic blockade, and adrenergic blockade coupled with glucagon deficiency starting 225 min after the ingestion of 75 g of glucose in normal subjects. Also, we assessed the effect of endogenous epinephrine deficiency alone and in combination with glucagon deficiency late after glucose ingestion in bilaterally adrenalectomized subjects. Glucagon deficiency resulted in nadir plasma glucose concentrations that were approximately 30% lower (P less than 0.01) than control values, but did not cause hypoglycemia late after glucose ingestion. This effect was prevented by glucagon replacement. Neither adrenergic blockade nor epinephrine deficiency alone impaired the glucose counterregulatory process. However, combined glucagon and epinephrine deficiencies resulted in a progressive fall in mean plasma glucose to a hypoglycemic level late after glucose ingestion; the final glucose concentration was 40% lower (P less than 0.02) than the control (epinephrine deficient) value in these patients, and was nearly 50% lower (P less than 0.001) than the control value and approximately 30% lower (P less than 0.05) than the glucagon-deficient value in normal subjects. We conclude (a) the transition from exogenous glucose delivery to endogenous glucose production late after glucose ingestion is the result of the coordinated diminution of insulin secretion and the resumption of glucagon secretion. (b) Epinephrine does not normally play a critical role in this process, but enhanced epinephrine secretion compensates largely and prevents hypoglycemia when glucagon secretion is deficient.

Neuroendocrine responses to glucose ingestion in man. Specificity, temporal relationships, and quantitative aspects

The mechanisms of postprandial glucose counterregulation-those that blunt late decrements in plasma glucose, prevent hypoglycemia, and restore euglycemia-have not been fully defined. To begin to clarify these mechanisms, we measured neuroendocrine and metabolic responses to the ingestion of glucose (75 g), xylose (62.5 g), mannitol (20 g), and water in ten normal human subjects to determine for each response the magnitude, temporal relationships, and specificity for glucose ingestion. Measurements were made at 10-min intervals over 5 h. By multivariate analysis of variance, the plasma glucose (P < 0.0001), insulin (P < 0.0001), glucagon (P < 0.03), epinephrine (P < 0.0004), and growth hormone (P < 0.01) curves, as well as the blood lactate (P < 0.0001), glycerol (P < 0.001), and beta-hydroxybutyrate (P < 0.0001) curves following glucose ingestion differed significantly from those following water ingestion. However, the growth hormone curves did not differ after correction for differences at base line. In contrast, the plasma norepinephrine (P < 0.31) and cortisol (P < 0.24) curves were similar after ingestion of all four test solutions, although early and sustained increments in norepinephrine occurred after all four test solutions. Thus, among the potentially important glucose regulatory factors, only transient increments in insulin, transient decrements in glucagon, and late increments in epinephrine are specific for glucose ingestion. They do not follow ingestion of water, xylose, or mannitol. Following glucose ingestion, plasma glucose rose to peak levels of 156+/-6 mg/dl at 46+/-4 min, returned to base line at 177+/-4 min, reached nadirs of 63+/-3 mg/dl at 232+/-12 min, and rose to levels comparable to base line at 305 min, which was the final sampling point. Plasma insulin rose to peak levels of 150+/-17 muU/ml (P < 0.001) at 67+/-8 min. At the time glucose returned to base line, insulin levels (49+/-12 muU/ml) remained fourfold higher than base line (P < 0.01); thereafter they declined but never fell below base line. Plasma glucagon decreased from 95+/-14 pg/ml to nadirs of 67+/-11 pg/ml (P < 0.001) at 84+/-9 min and then rose progressively to peak levels of 114+/-17 pg/ml (P < 0.001 vs. nadirs) at 265+/-12 min. Plasma epinephrine, which was 18+/-4 pg/ml at base line, did not change initially and then rose to peak levels of 119+/-20 pg/ml (P < 0.001) at 271+/-13 min. These data indicate that the glucose counterregulatory process late after glucose ingestion is not solely due to the dissipation of insulin and that sympathetic neural norepinephrine, growth hormone, and cortisol do not play critical roles. They are consistent with, but do not establish, physiologic roles for the counterregulatory hormones-glucagon, epinephrine, or both-in that process.

Identification of type I diabetic patients at increased risk for hypoglycemia during intensive therapy

During intravenous insulin infusions (40 mU per kilogram of body weight per hour for up to 100 minutes), 9 of 22 patients with insulin-requiring diabetes mellitus had neurologic signs or symptoms of hypoglycemia, plasma glucose concentrations that were below 35 mg per deciliter (1.9 mmol per liter) and continued to decline, or both. This inadequate glucose counterregulation resulted from the combined effect of deficient glucagon and epinephrine responses. In 8 of the 9 patients with inadequate counterregulation severe hypoglycemia developed during subsequent intensive therapy, whereas such episodes occurred in only 1 of 13 patients with adequate counterregulation. Thus, an intravenous insulin-infusion test can prospectively identify patients who are at increased risk for recurrent severe hypoglycemia during intensive therapy for diabetes.

Epinephrine is a hypophosphatemic hormone in man. Physiological effects of circulating epinephrine on plasma calcium, magnesium, phosphorus, parathyroid hormone, and calcitonin

The physiologic effects of epinephrine on mineral metabolism are not known. In six healthy men, insulin-induced hypoglycemia, a potent stimulus to endogenous epinephrine secretion, resulted in a decrement of 0.9+/-0.1 mg/dl (mean+/-SE, P < 0.001) in serum inorganic phosphorus and smaller increments in magnesium and total and ionized calcium. Plasma immunoreactive parathyroid hormone (iPTH) decreased and plasma immunoreactive calcitonin (iCT) increased appropriately with the increments in calcium and magnesium. We wished to determine to what extent these changes in mineral metabolism might be attributable to epinephrine. Therefore, in the same protocol, we infused the hormone over 60 min in these six men, in doses that resulted in steady-state plasma epinephrine concentrations ranging from 52 to 945 pg/ml (levels that span the physiologic range), for a total of 25 studies. Serum ionized calcium, iPTH, and iCT concentrations were unaltered by these physiologic elevations of plasma epinephrine. However, epinephrine resulted in dose-dependent decrements in serum inorganic phosphorus of 0.6+/-0.1 mg/dl (P < 0.005) for the highest epinephrine infusion rate. The plasma epinephrine concentration threshold for this hypophosphatemic effect was approximately 50-100 pg/ml. Thus, the sensitivity of the hypophosphatemic response to epinephrine is comparable to that of the cardiac chronotropic, systolic pressor, and lipolytic responses to epinephrine, and considerably greater than that of the diastolic depressor, glycogenolytic, glycolytic, and ketogenic responses to the hormone in human beings. In view of its rapidity, the hypophosphatemic effect of epinephrine is probably the result of a net shift of phosphate from the extracellular compartment to intracellular compartments. We suggest that it is a direct effect of epinephrine, in that it is not mediated by changes in availability of the primary regulatory hormones PTH and CT, although indirect effects mediated by changes in other hormones, such as insulin, cannot be excluded. The hypophosphatemic response is also not attributable to increments in plasma calcium. These data indicate that epinephrine in physiologic concentrations is a hypophosphatemic hormone in man.

Increased plasma norepinephrine accompanies persistent tachycardia after hydralazine

To determine the role of the peripheral sympathetic nervous system in the persistent tachycardia caused by the antihypertensive drug hydralazine, we examined the temporal relationships between the changes in heart rate and plasma norepinephrine concentration and the reduction in blood pressure produced by a range of doses of hydralazine administered intravenously to five hypertensive patients. Significant linear correlations were found between the increases in heart rate and plasma norepinephrine concentration and the reduction in blood pressure at 15 and 30 minutes after injection. However, at 240 minutes after injection, changes in heart rate and plasma norepinephrine were not correlated with changes in blood pressure and were disproportionately elevated relative to the reduction in blood pressure. A significant linear correlation between changes in heart rate and plasma norepinephrine concentration was noted at 15, 30, and 240 minutes after injection. The temporal discordance of the changes of both heart rate and plasma norepinephrine relative to the reduction in blood pressure and the significant linear correlation between the increases in heart rate and plasma norepinephrine concentration suggest that continued activation of the peripheral sympathetic nervous system contributes to the persistent tachycardia seen after the administration of hydralazine.

Catecholamine release during and after cross clamping of descending thoracic aorta

During graft replacement of descending thoracic and thoracoabdominal aneurysms, aortic cross clamping without the use of bypass or shunts is accompanied by underperfusion of distal vascular beds. This study, comprising 10 patients, was based on the hypothesis that ischemia of the lower spinal cord and adrenal glands might precipitate release of catecholamines. Arterial blood samples, obtained before (control), during, and after arterial cross clamping, were analyzed for epinephrine (E) and norepinephrine (NE). The E/NE ratio was used as an index of ischemic sympathoadrenal activation. During cross clamping, mean E and E/NE increased by a factor of 4.5 (P = 0.03) and 2.4 (P = 0.001), respectively. The greatest increases were observed in the 5 min postclamp sample: relative to control, mean E increased 22-fold (P = 0.011), NE 3-fold (P = 0.009), and E/NE 8.4-fold (P = 0.013). During the immediate postclamp period, mean E/NE fell exponentially with an average "half-life" of 12.05 +/- 5.83 min (SD). A second-order polynomial related (P = 0.004) log E/NE in first postclamp sample to the ratio between clamp time and mean proximal arterial pressure during clamping (T/AP). Left-ventricular-minute-work-function correlations: (1) positive with log E during clamping (P = 0.043); and (2) none with log E (P = 0.563) or log (E + NE) (P = 0.641) 5 min post-clamp; (3) positive with log (E + NE) 30 min post-clamp (P = 0.016). It is concluded that (1) distal ischemia caused by cross clamping the descending thoracic aorta without bypass or shunts, results in distal regional sympathoadrenal activation, independent of known central reflex mechanisms; (2) this activation leads to marked increases of E/NE and is, in part, dependent upon T/AP during clamping; (3) the activation is probably transitory; (4) by indirect evidence, cardiodepressant factor(s) may transiently be present following declamping; (5) by its magnitude, sympathoadrenal activation is likely to provide compensation for deleterious factors that may affect cardiovascular functions during cross clamping and after declamping; alternatively, it might contribute to postoperative hypertension and cardiac complications such as myocardial ischemia and arrhythmias.

Different norepinephrine disappearance rate in venous and arterial plasma in man

The disappearance of norepinephrine in both arterial (radial) and venous (antecubital) plasma was studied in five patients with mild essential hypertension following isometric exercise and norepinephrine infusion. Arterial levels of epinephrine throughout the study and of norepinephrine during norepinephrine infusion were consistently higher than venous levels, indicating that both amines are removed by passage through the forearm. Following infusion the disappearance rate of norepinephrine from arterial plasma was faster than from venous plasma. After isometric exercise there was a delay in fall of venous levels, consistent with a delayed efflux of norepinephrine from local tissues. Arterial plasma levels probably reflect total body contribution whereas venous plasma levels presumably reflect additional local removal and/or release from the forearm.

Effect of intravenous aminophylline on plasma levels of catecholamines and related cardiovascular and metabolic responses in man

Theophylline is thought to act by inhibiting the activity of phosphodiesterase, with a resultant increase in intracellular cyclic AMP. However, this concept is largely based on in vitro studies using concentrations of theophylline which greatly exceed therapeutic plasma concentrations. To investigate the relationship of the cardiovascular and metabolic effects of theophylline to activation of the sympathetic nervous system, i.v. aminophylline was administered to six healthy males under basal conditions. Each subject received four infusions. Mean theophylline concentrations (+/- SEM) of 4.5 +/- 0.2, 10.0 +/- 0.5, 14.0 +/- 0.5 and 20.0 +/- 1.2 micrograms/ml were achieved. Plasma epinephrine increased 262% (from 29 +/- 4 to 105 +/- 14 pg/ml, p less than 0.01) and plasma norepinephrine increased 64% (from 190 +/- 18 to 312 +/- 51 pg/ml, p less than 0.05) during the high-dose infusion. The increases in circulating catecholamines were dose-related (p less than 0.001 by analysis of variance). Dose-related increases in heart rate, systolic blood pressure, plasma glucose, free fatty acids and insulin were also observed (p less than 0.001 by analysis of variance). Although the duration of total electromechanical systole (QS2) and left ventricular ejection time adjusted for heart rate fell during the aminophylline infusions, this positive inotropic response was not influenced by dose, except possibly the high dose. Echocardiographic ejection fraction was not changed by the aminophylline infusions. We conclude that the acute cardiovascular and metabolic effects of theophylline may be mediated in part by stimulation of the sympathetic nervous system.

Glucose and insulin effects on the novo amino acid synthesis in young men: studies with stable isotope labeled alanine, glycine, leucine, and lysine

We have explored interrelationships between te dynamic aspects of whole body glucose and alanine and glycine metabolism in adult humans. Using a primed, continuous intravenous infusion of [1-13C] leucine or lysine given simultaneously with [2H3] or [15N]alanine or [15N]glycine, respectively, whole body alanine and glycine fluxes and their rates of de novo synthesis were determined in three experiments with healthy young men. Subjects were studied in the post-absorptive state and during a 150 min period of an intravenous infusion with unlabeled glucose, at a rate of 4 mg.kg-1 min-1. In one experiment, insulin was given together with the glucose infusion to maintain normoglycemia. In the other two studies, subjects received glucose alone. For the post-absorptive state, alanine flux (mean +/- SEM) was 381 +/- 26 and 317 +/- 18 mumole.kg-1 hr-1 in two separate experiments and glycine flux was 240 +/- 22 mumole.kg-1 hr-1. De novo synthesis of alanine and glycine accounted for 75%-81% and 81% of flux, respectively. Infusion with glucose alone raised plasma glucose to a mean level of 152 mg/dl and increased alanine flux, due to a rise in alanine synthesis of 98 mumole.kg-1 hr-1 (p less than 0.01). Glycine flux and synthesis rate were unaffected by the glucose infusion. When insulin was given with glucose to maintain normoglycemia, the rate of alanine synthesis was unchanged. Because glucose uptake rate, measured with [6,6-2H2] glucose was the same whether glucose was infused along or with exogenous insulin, these results support the view that the circulating plasma glucose level itself may affect alanine synthesis and that the hyperglycemic state is an important factor in regulating interorgan nitrogen transfer, via alanine, in various pathophysiologic states.

Elevated plasma noradrenaline in response to beta-adrenoceptor stimulation in man

1 Dose-dependent increments of plasma noradrenaline were observed during graded infusions of (±)isoprenaline (3.5-35 ng kg^-1 min^-1 i.v.) in seven normal subjects and in ten subjects with borderline hypertension. At the highest dose of isoprenaline, noradrenaline rose by 166 ± 16 pg/ml in normals and by 169 ± 34 pg/ml in hypertensives (mean ± s.e. mean).

2 In the subjects with borderline hypertension isoprenaline infusions were repeated after 7 days of treatment with (±)propranolol (320 mg/day, divided into 4 doses) and subsequently after 7 days of treatment with (±)atenolol (100 mg/day) 2-3 h after the morning dose of β-adrenoceptor blocker. The dose-response curve for plasma noradrenaline was shifted to higher doses of isoprenaline by a factor of 4 by atenolol and the heart rate response was similarly shifted. The heart rate response was shifted by a factor of 16 by propranolol, but plasma noradrenaline did not change after isoprenaline under propranolol treatment, even when isoprenaline was given at doses high enough to induce increments of heart rate similar to those without β-adrenoceptor blocker treatment.

3 In the subjects with borderline hypertension mean and diastolic intra-arterial pressures fell at the highest dose of isoprenaline by 9 ± 2 and 13 ± 2 mm Hg respectively. These effects were antagonized by propranolol and not by atenolol.

4 The observed rise in plasma noradrenaline after isoprenaline might have been caused by baro-reflex-stimulation of central sympathetic outflow. The isoprenaline-induced decrease in mean arterial pressure, however, was small. Moreover pulse pressure rose and this tends to suppress rather than stimulate baroreflex-mediated sympathetic activity. Activation of presynaptic β-adrenoceptors, allegedly of the β₂-subtype, is known to facilitate noradrenaline release upon nerve stimulation of isolated tissues. Our results lend support to the hypothesis that such a facilitatory mechanism is also operative in intact man.

Concentration effect relationships of infused histamine in normal volunteers

Histamine was infused in six normal volunteers at rates of 16, 32, 64 and 96 ng/kg/min increasing at 5-min intervals followed by 128 ng/kg/min for 45 min. Heart rate increased, diastolic blood pressure decreased and skin temperature increased in a dose-dependent fashion. Mean heart rate increased by 15.6 +/- 5.7 beats/min, mean diastolic pressure fell by 8.8 +/- e.2 mmHg and mean skin temperature increased by 1.2 +/- 0.3 degrees C at the highest infusion rate. Mean plasma histamine rose from a basal level of 0.20 +/- 0.03 ng/ml to 1.97 +/- 0.25 ng/ml at the end of the highest infusion rate. The threshold infusion rate for physiological effects was 64-96 ng/kg/min corresponding to 0.77-0.97 ng/ml. Salivary flow was stimulated by 21% after 30 min at the highest dose infusion (P = 0.05). Plasma adrenaline increased 132% but plasma noradrenaline was unchanged. There was a linear decline in heart rate after terminating the histamine infusion with a half time of 82 sec. The half life of infused histamine in the plasma was 102 sec. The clearance of histamine from the plasma was 6.1 %/- 0.2 l/min or 83 ml/kg/min. These concentration effect relationships in normals throw doubt on some of the high endogenous plasma histamine values in the literature.

Beta-adrenoceptor blockade in stress due to oral surgery

1 The effects of a single oral dose of 5 mg pindolol (P) and 100 mg metoprolol (M) were assessed in a double-blind study in 30 patients undergoing oral surgery. 2 Systolic and diastolic blood pressures and heart rate were reduced 90 min after oral medication and did not exceed initial values at rest during the procedure. 3 Noradrenaline, adrenaline and c-AMP concentrations did not differ at any time from the control values at rest after P, but were increased after local anaesthesia and during oral surgery after M as were the metabolic responses reflected by plasma concentrations of glucose and free-fatty acids. 4 Plasma levels of ACTH and cortisol showed the typical increase during the procedure, being independent of beta-adrenoceptor blockade. In contrast to the cardioselective antagonist M, prophylactic administration of the non-selective drug P prevented the sympathetic and metabolic responses to the stress of oral surgery. 5 Hypothalamic and adrenal stimulation were not reduced by either selective or non-selective beta-adrenoceptor blockade.

Arterial plasma epinephrine concentrations and hemodynamic responses after dental injection of local anesthetic with epinephrine

The effect of dental injection of local anesthetic on arterial plasma epinephrine concentrations and cardiovascular functions was assessed in patients having a maxillary third molar extracted. After three and five minutes, arterial plasma epinephrine concentrations were more than two times higher than baseline values in patients who were given an injection of a standard Carpule (1.8 ml) of 2% lidocaine with 1/100,000 epinephrine (18 micrograms). The heart rate and pressure-rate product increased slightly above baseline control values, and the mean arterial pressure declined slightly (P less than .05) after five minutes. Patients who received an injection of lidocaine alone had no significant change of plasma epinephrine or of the cardiovascular parameters measured. Although the hemodynamic responses to lidocaine plus epinephrine in these healthy young adults were small, the significant increase of systemic plasma epinephrine concentrations suggests that high-risk patients who receive this type of anesthesia should be monitored carefully.

Importance of glucagon in mediating epinephrine-induced hyperglycemia in alloxan-diabetic dogs

In normal dogs epinephrine stimulates glucose production (Ra) independently of glucagon. To investigate the role of this interaction in diabetes, epinephrine (0.1 micrograms . kg-1 . min-1) was infused for 90 min in five alloxan-diabetic dogs in the presence or absence of somatostatin (0.1 micrograms . kg-1 . min-1). In response to epinephrine, glycemia rose by 40% reflecting a near maximal (122%) increase in Ra. Plasma glucagon (IRG) rose to 953 pg/ml, whereas insulin (IRI) increased minimally. When somatostatin was infused with epinephrine to prevent the rise of IRG and IRI, there was only a marginal increase of glucose concentration (12%) and production (38%). The effect of somatostatin was reversed by infusing glucagon (10 ng . kg-1 . min-1) together with epinephrine and somatostatin into five additional alloxan-diabetic dogs. Increments in IRG, glycemia, and Ra were fully reestablished. A 100% FFA increase was observed in all three groups, indicating that the lipolytic effect of epinephrine was independent of glucagon. In conclusion, in diabetic dogs, in contrast to normal dogs, epinephrine induced a marked and prolonged increase in glucose concentration and production mostly through a stimulation of IRG secretion.

Epinephrine plasma thresholds for lipolytic effects in man: measurements of fatty acid transport with [l-13C]palmitic acid

To determine the plasma epinephrine thresholds for its lipolytic effect, 60-min epinephrine infusions at nominal rates of 0.1, 0.5, 1.0, 2.5, and 5.0 micrograms/min were performed in each of four normal young adult men while they also received a simultaneous infusion of [1-13C]palmitic acid to estimate inflow transport of plasma free fatty acids. These 20 infusions resulted in steady-state plasma epinephrine concentrations ranging from 12 to 870 pg/ml. Plasma epinephrine thresholds for changes in blood glucose, lactate, and beta-hydroxybutyrate were in the 150--200-pg/ml range reported by us previously (Clutter, W. E., D. M. Bier, S. D. Shah, and P. E. Cryer. 1980. J. Clin. Invest. 66: 94--101.). Increments in plasma glycerol and free fatty acids and in the inflow and outflow transport of palmitate, however, occurred at lower plasma epinephrine thresholds in the range of 75 to 125 pg/ml. Palmitate clearance was unaffected at any steady-state epinephrine level produced. These data indicate that (a) the lipolytic effects of epinephrine occur at plasma levels approximately threefold basal values and (b) lipolysis is more sensitive than glycogenolysis to increments in plasma epinephrine.

Tolerance to the humoral and hemodynamic effects of caffeine in man

Acute caffeine in subjects who do not normally ingest methylxanthines leads to increases in blood pressure, heart rate, plasma epinephrine, plasma norepinephrine, plasma renin activity, and urinary catecholamines. Using a double-blind design, the effects of chronic caffeine administration on these same variables were assessed. Near complete tolerance, in terms of both humoral and hemodynamic variables, developed over the first 1-4 d of caffeine. No long-term effects of caffeine on blood pressure, heart rate, plasma renin activity, plasma catecholamines, or urinary catecholamines could be demonstrated. Discontinuation of caffeine ingestion after 7 d of administration did not result in a detectable withdrawal phenomenon relating to any of the variables assessed.

Epinephrine and norepinephrine are cleared through beta-adrenergic, but not alpha-adrenergic, mechanisms in man

Although catecholamines are rapidly removed from the extracellular fluid, the role of adrenergic mechanisms in the clearance of epinephrine and norepinephrine has not been defined. In five normal human subjects, mean (+/- SE) plasma epinephrine concentrations did not change during control infusions, rose from 21 +/- 6 pg/ml to 834 +/- 84 pg/ml during the infusion of epinephrine (50 ng/kg/min) over 180 min and to 853 +/- 112 pg/ml during the infusion of epinephrine plus phentolamine (500 micrograms/min after a 5.0 mg loading dose infused over 2 min), but to 2400 +/- 104 pg/ml during the infusion of epinephrine plus propranolol (80 micrograms/min after a 5.0 mg loading dose infused over 2 min), indicating that beta-adrenergic blockade sharply reduces the clearance of epinephrine in man. In separate studies in seven subjects, similar increments in plasma epinephrine occurred during the infusion of epinephrine alone and the clearance of epinephrine was comparably reduced during the infusion of epinephrine plus propranolol and during the infusion of epinephrine plus propranolol plus phentolamine, suggesting that the reduction of epinephrine clearance produced by beta-adrenergic blockade during epinephrine infusion is not mediated by an alpha-adrenergic reduction of blood flow to organs of epinephrine clearance. Endogenous plasma norepinephrine concentrations doubled during the infusion of phentolamine without propranolol but rose to nearly fourfold higher values during the infusion of phentolamine with propranolol indicating that beta-adrenergic blockade reduces the clearance of norepinephrine as well as that of epinephrine. These findings indicate that epinephrine and norepinephrine are cleared through beta-adrenergic, but not alpha-adrenergic, mechanisms in man.