Plasma dihydroxyphenylglycol for estimation of noradrenaline neuronal re-uptake in the sympathetic nervous system in vivo

1. Neuronal re-uptake is the primary means for terminating the actions of endogenously released noradrenaline. A portion of the recaptured noradrenaline is deaminated to form dihydroxyphenylglycol. The present report describes a technique using plasma dihydroxyphenylglycol for estimation of the rate of neuronal reuptake of endogenous noradrenaline in vivo. 2. Neuronal re-uptake of noradrenaline in the sympathetic nervous system of the rat was estimated from the effects of neuronal uptake blockade with desipramine on three variables: (i) the plasma clearance of intravenously infused 3H-labelled noradrenaline, (ii) the plasma concentration of endogenous dihydroxyphenylglycol, and (iii) the plasma concentration of 3H-labelled dihydroxyphenylglycol formed from infused 3H-labelled noradrenaline. 3. Desipramine decreased plasma dihydroxyphenylglycol by 36%, this representing the fraction of dihydroxyphenylglycol in plasma that was derived from recaptured noradrenaline. After desipramine, the decrease in the rate of neuronal uptake of 3H-labelled noradrenaline was 9.7 times that of the decrease in the plasma spillover of 3H-labelled dihydroxyphenylglycol. Since the appearances in plasma of dihydroxyphenylglycol from unlabelled and 3H-labelled noradrenaline were similar, the neuronal re-uptake of endogenous noradrenaline could be assumed to be 9.7 times as much as the plasma spillover of dihydroxyphenylglycol that was derived from recaptured noradrenaline (0.15 nmol min-1 kg-1). 4. The rate of neuronal re-uptake of endogenous noradrenaline was estimated to be 1.45 nmol min-1 kg-1, whereas the plasma spillover of noradrenaline was 0.127 nmol min-1 kg-1. Thus, only a small fraction (less than 9%) of the noradrenaline released into the synaptic cleft spills over into the circulation.     

Plasma noradrenaline in cirrhosis: a study of kinetics and temporal relationship to ascites formation

The kinetics of plasma noradrenaline (NA) were studied in 14 patients with cirrhosis and ascites and 13 normal subjects. [3H]noradrenaline ([3H] NA) was infused intravenously to steady state and the spillover of NA into plasma and its clearance from plasma calculated. The increase in plasma NA in the cirrhotic patients was due to an increase in NA spillover (14.5 vs 3.9 nmol min-1m-2; P less than 0.001). NA plasma clearance was also increased in the cirrhotic patients (3.5 vs 2.11 min-1m-2; P less than 0.01). Plasma NA and dihydroxyphenylglycol (DHPG), a metabolite of NA of which a portion is formed after re-uptake of NA into sympathetic nerve endings, were then measured in 23 patients with cirrhosis and ascites, 17 patients with cirrhosis who had never had ascites, and 34 normal subjects. Both plasma NA and DHPG were significantly increased in the patients with ascites (NA 4.7, DHPG 14.7 nmol l-1 and in the patients with cirrhosis but no ascites (NA 3.8, DHPG 12.0 nmol l-1) compared with normal subjects (NA 1.9, DHPG 8.8 nmol 1-1). Therefore, the increase in plasma NA in cirrhosis is due to increased activity of the sympathetic nervous system rather than interference with the metabolism of NA or impaired neuronal uptake of NA. This increase appears to precede the development of ascites.     

Effect of the dopamine D2 receptor agonist quinpirole on renal sympathetic nerve activity and renal norepinephrine spillover in anesthetized rabbits.

Cardiovascular and sympathetic nervous system effects of the dopamine D2 receptor-selective agonist quinpirole were studied in anesthetized rabbits. Sodium nitroprusside was administered for comparison. The animals received a tracer infusion of [3H] norepinephrine i.v. Arterial and renal venous concentrations of endogenous norepinephrine and epinephrine and [3H]norepinephrine, the firing rate of the renal sympathetic nerves and renal blood flow were determined. Quinpirole (100 micrograms kg-1 + 5 micrograms kg-1 min-1 i.v.) lowered blood pressure and renal vascular resistance. The firing rate of the renal sympathetic nerves was increased, but there was no reflex tachycardia. Despite the increase in renal sympathetic firing, the renal spillover of norepinephrine into blood was decreased. The increase in total body norepinephrine spillover during quinpirole-induced hypotension was less than expected from baroreflex activation. Effects of quinpirole were antagonized by domperidone (1000 micrograms kg-1 + 200 micrograms kg-1 h-1). The distinguishing feature of this study is the simultaneous measurement of sympathetic firing and norepinephrine spillover in the same organ, the kidney, under conditions of intact sympathetic impulse traffic. Quinpirole activated presynaptic D2 receptors and thus reduced the released norepinephrine per action potential. Consequences of the presynaptic inhibition were reductions of blood pressure and renal vascular resistance and absence of reflex tachycardia.     

Effect of yohimbine on renal sympathetic nerve activity and renal norepinephrine spillover in anesthetized rabbits.

The function of presynaptic alpha-2 adrenergic autoinhibition of norepinephrine release was studied in anesthetized rabbits (alfadolone + alfaxalone) with uninterrupted sympathetic impulse traffic. The animals received a tracer infusion of [3H]norepinephrine i.v. Arterial and renal venous concentrations of endogenous norepinephrine and [3H]norepinephrine, the firing rate of the renal sympathetic nerves and renal blood flow were determined. The results were used to calculate the renal fractional [3H]norepinephrine extraction, the renal removal and spillover of norepinephrine, the total body [3H]norepinephrine clearance and total body norepinephrine spillover. Sodium nitroprusside (10-80 micrograms kg-1 min-1 i.v.), which was infused to modulate sympathetic activity through the baroreceptors, caused hypotension and increased the renal sympathetic firing rate and the renal as well as total body norepinephrine spillover. Increases of total body norepinephrine spillover were much higher than increases of renal spillover. Yohimbine (1 mg kg-1 + 0.2 mg kg-1 hr-1 i.v.) caused slight central sympathoexcitation. In addition, it enhanced the renal and total body spillover of norepinephrine at any given firing rate of the renal sympathetic nerves. The distinguishing feature of this study is the measurement of sympathetic firing rate and norepinephrine spillover in one and the same organ, the kidney. The results demonstrate that the alpha-2 adrenergic autoinhibition of norepinephrine release normally operates in the kidney with intact sympathetic impulse traffic. They also suggest its operation in other peripheral sympathetically innervated tissues.     

Increased plasma dihydroxyphenylalanine during sympathetic activation in humans is related to increased norepinephrine turnover

Plasma concentrations of dihydroxyphenylalanine (DOPA) were measured before and during isometric handgrip exercise or mental stress and after coffee drinking or intravenous infusion of desipramine to examine the influence of sympathetic nervous activity on DOPA formation. Sympathetic activity was assessed by the spillover of norepinephrine into plasma. Turnover of norepinephrine was assessed by the plasma concentration of its intraneuronal metabolite, dihydroxyphenylglycol (DHPG). In normal subjects the resting plasma concentration of DOPA was 6.05 +/- 0.16 nmol/L (n = 42). Plasma DOPA level was increased by stimulation of the sympathetic nervous system; handgrip exercise caused a 0.49 +/- 0.07 nmol/L increase (n = 15), mental stress a 0.25 +/- 0.10 nmol/L increase (n = 34), and coffee drinking a 0.85 +/- 0.19 nmol/L increase (n = 9). Desipramine decreased plasma DOPA level by 0.25 +/- 0.06 nmol/L (n = 23). The small but consistent changes in plasma DOPA level during manipulations of sympathetic activity were positively correlated with changes in norepinephrine spillover (r = 0.55, n = 81) and plasma DHPG level (r = 0.66, n = 81). Percentage increases in plasma DOPA level during sympathetic activation were similar to those in plasma DHPG but were a sixth of the percentage increases in norepinephrine spillover. The similar increases in plasma DOPA and DHPG levels indicated that production of DOPA was related to the turnover of norepinephrine in sympathetic nerves. The smaller percentage increases in plasma DOPA (smaller than those in norepinephrine spillover) were consistent with the partial contribution of exocytotic neurotransmitter release to the turnover of norepinephrine in sympathetic nerves.     

Cardiac and whole-body [3H]noradrenaline kinetics during adrenaline infusion in man.

1. To investigate the possible role of adrenaline as a modulator of noradrenaline release from the sympathetic nervous system, the responses of cardiac and whole-body noradrenaline kinetics to intravenous infusions of adrenaline (30 ng min-1 kg-1) and matching saline placebo were determined at rest and during supine bicycle exercise in 16 patients undergoing cardiac catheterization, in whom beta-adrenoceptor antagonists had been discontinued for 72 h. 2. At rest and compared with placebo, infusion of adrenaline was associated with a small increase in arterial plasma noradrenaline from 211 +/- 29 pg/ml to 245 +/- 29 pg/ml (P less than 0.05). Increases in whole-body noradrenaline spillover to arterial plasma were larger (from 282 +/- 40 ng min-1 m-2 to 358 +/- 41 ng min-1 m-2, P less than 0.01) and there was a trend towards an increase in whole-body noradrenaline clearance. Cardiac noradrenaline clearance was modestly increased during adrenaline infusion, but cardiac noradrenaline spillover was not altered despite increases in heart rate and coronary sinus plasma flow. Adrenaline infusion was associated with symptomatic myocardial ischaemia in four of 14 patients with coronary heart disease. 3. Supine bicycle exercise was associated with significant increases in peripheral noradrenaline concentrations and in cardiac and whole-body noradrenaline spillover. The increases on exercise were not significantly different for these variables during saline and adrenaline infusions. 4. Infusion of adrenaline to produce 'physiological' increases in plasma adrenaline concentration was associated with an increase in total noradrenaline release, as assessed by whole-body noradrenaline spillover to plasma.(ABSTRACT TRUNCATED AT 250 WORDS)     

Pressor effect of arginine vasopressin in progressive autonomic failure

The blood pressure (BP) and heart rate (HR) responses to 5 min incremental intravenous infusions of noradrenaline (NA) and arginine vasopressin (AVP) were investigated both in patients with progressive autonomic failure (PAF) and in normal volunteers. Stepwise infusion of NA at rates of 300-3000 pmol min-1 kg-1 produced a bradycardia and a dose related increase in BP in normal subjects. In subjects with PAF there was no significant HR response but the dose-BP response was shifted to the left with significant pressor responses at infusion rates of 60-300 pmol min-1 kg-1. Stepwise infusion of AVP at 0.2-5.0 pmol min-1 kg-1 caused transient bradycardia but no pressor response in seven normal volunteers. Further increases in AVP infusion in three other subjects achieved plasma AVP levels as high as 3000-4000 pmol/l, and still no significant pressor response was observed. Stepwise infusion of AVP at 0.05-2.0 pmol min-1 kg-1 in the eight subjects with PAF resulted in a pressor response without any change in HR. During this infusion plasma AVP increased from 0.8 +/- 0.2 (mean +/- SEM) to 30 +/- 2 pmol/l. A significant pressor response was already apparent at a plasma AVP level of 5.5 +/- 1.8 pmol/l.     

The immediate pressor response to saralasin in man: evidence against sympathetic activation and for intrinsic angiotensin II-like myotropism

The cardiovascular and hormonal effects of intravenous saralasin (0.5, 1 and 5 micrograms min-1 kg-1) were assessed in nine tetraplegic patients (with complete cervical spinal cord transaction above the sympathetic outflow) and in six normal subjects. In the tetraplegic patients, saralasin caused an immediate transient pressor response which was not dose-dependent and substantially greater than the pressor response in normal subjects. The pressor response in the tetraplegic patients was not accompanied by a rise in levels of plasma noradrenaline. In the tetraplegic patients, after alpha-adrenoceptor blockade with thymoxamine (1 mg kg-1 h-1), twice the dose of intravenous noradrenaline was needed to induce the same pressor response. The pressor response to saralasin (5 micrograms kg-1 min-1), however, was unaffected by thymoxamine. Saralasin caused minimal changes in levels of plasma renin activity and plasma aldosterone in both groups. There was no relationship between basal plasma renin activity and the pressor response in either group. We therefore conclude that the immediate transient pressor response to saralasin in man is not due to central sympathetic stimulation, is unlikely to be due to peripheral sympathetic activation and is probably the result of intrinsic angiotensin II-like myotropism.     

Captopril enhances vascular and adrenal responsiveness to angiotensin II in essential hypertension

The converting-enzyme inhibitor captopril (25-50 mg orally every 6 h for 66 h) was used to dissociate the circulating levels of angiotensin II (ANG II) from changes in sodium balance in 11 patients with normal renin essential hypertension on 10 mmol of sodium/day intake. Pressor, renal vascular and adrenal responses to graded infusions of ANG II (0.3, 1 and 3 pmol kg-1 min-1) were measured before and after captopril administration. Systemic vascular responses were assessed by measuring diastolic blood pressure (DBP), renovascular responses by measuring p-aminohippurate (PAH) clearance and adrenal responses by measuring plasma aldosterone. After receiving captopril for 66 h the hypertensive subjects showed a significantly (P less than 0.004) enhanced blood pressure response to the infused ANG II but not to noradrenaline when compared with the response before captopril. ANG II (3 pmol kg-1 min-1) also produced a significantly (P less than 0.03) greater reduction in PAH clearance after (-194 +/- 40 ml/min) compared with before (-104 +/- 15 ml/min) captopril. These results suggest that the responsiveness to ANG II in these two target tissues is determined by the circulating ANG II level. In the adrenal gland the aldosterone responses to ANG II also were significantly greater after (P less than 0.01) than before captopril (increment at 3 pmol kg-1 min-1: 660 +/- 88 vs 381 +/- 94 pmol/l). These results are in distinct contrast with the responses previously reported for normotensive subjects and support the hypothesis that the regulation of aldosterone secretion is altered in subjects with essential hypertension.     

Cerebrospinal fluid levels of catechols in patients with neurogenic orthostatic hypotension

In multiple system atrophy (MSA) and pure autonomic failure (PAF), orthostatic hypotension (OH) results from deficient noradrenaline release from sympathetic nerves during standing. Post-mortem findings have indicated loss of central noradrenergic cells in both diseases. The present study sought in vivo neurochemical evidence for central noradrenergic deficiency in patients with OH due to MSA or PAF. A total of 28 patients with OH (18 with MSA; 10 with PAF) had cerebrospinal fluid and blood sampled for levels of noradrenaline and its neuronal metabolite dihydroxyphenylglycol. A control group of 44 subjects included 10 elderly normal volunteers, 10 patients with Alzheimer's disease, 18 patients with dysautonomia (postural tachycardia syndrome or neurocardiogenic syncope) and six patients with MSA in the absence of OH. Patients with OH had lower cerebrospinal fluid concentrations of noradrenaline (0.53+/-0.07 nmol/l) and dihydroxyphenylglycol (6.52+/-0.46 nmol/l) than did control subjects (0.90+/-0.09 and 9.64+/-0.46 nmol/l respectively; P =0.0001). The MSA+OH group had higher plasma levels of both catechols (noradrenaline, 1.31+/-0.16 nmol/l; dihydroxyphenylglycol, 5.08+/-0.43 nmol/l) than did the PAF group (noradrenaline, 0.38+/-0.08 nmol/l; dihydroxyphenylglycol, 2.53+/-0.30 nmol/l; P <0.001), despite similarly low cerebrospinal fluid levels. Among MSA patients, those with OH had lower cerebrospinal fluid levels of noradrenaline and dihydroxyphenylglycol than those without OH (noradrenaline, 1.71+/-0.64 nmol/l; dihydroxyphenylglycol, 10.41+/-1.77 nmol/l respectively; P =0.006). The findings are consistent with central noradrenergic deficiency in both MSA+OH and PAF. In MSA, central noradrenergic deficiency seems to relate specifically to OH.     

Comparison of two indices for forearm noradrenaline release in humans

Although there is as yet no method which measures directly the neuronal release of noradrenaline in humans in vivo, the isotope dilution technique with [(3)H]noradrenaline has been applied to estimate forearm neuronal noradrenaline release into plasma. Two different equations have been developed for this purpose: one to estimate the spillover of noradrenaline into the venous effluent, and a modified formula (often referred to as the appearance rate) which may reflect more closely changes in the neuronal release of noradrenaline into the synaptic cleft, particularly during interventions that alter forearm blood flow. The present study was performed to compare the effects of two interventions known to exert contrasting actions on neuronal forearm noradrenaline release and forearm blood flow. Intra-arterial infusion of sodium nitroprusside at doses without systemic effect increases forearm blood flow, but not neuronal noradrenaline release. In contrast, lower-body negative pressure at -25 mm Hg causes forearm vasoconstriction by stimulating neuronal noradrenaline release. During sodium nitroprusside infusion, forearm noradrenaline spillover increased from 1.1+/-0.3 to 2.2+/-1.0 pmol x min(-1) x 100 ml(-1) (P<0.05), whereas the forearm noradrenaline appearance rate was unchanged. Lower-body negative pressure did not affect the forearm noradrenaline spillover rate, but increased the forearm noradrenaline appearance rate from 3.4+/-0.4 pmol x min(-1) x 100 ml(-1) at baseline to 5.0+/-0.9 pmol x min(-1) x 100 ml(-1) (P<0.05). These results indicate that the noradrenaline appearance rate provides the better approximation of changes in forearm neuronal noradrenaline release in response to stimuli which alter local blood flow.     

Neurology (53)

Sympathetic innervation and function in reflex sympathetic dystrophy. (National Institutes of Health, Bethesda, MD) Ann Neurol 2000;48:49–59. This study examined sympathetic neurocirculatory function and the role of sympathetic postganglionic nerve traffic in maintaining the pain in 30 patients with reflex sympathetic dystrophy. Most had had the condition for more then 1 year, and 14 had undergone sympathectomy for the pain. Positron emission tomographic scanning after administration of ¹³N‐ammonia was used to assess local perfusion, and 6‐[¹⁸F]fluorodopamine was used to assess sympathetic innervation. Rates of entry of norepinephrine in the regional venous drainage (spillovers) and regional plasma levels of L‐dihydroxyphenylalanine (the immediate product of the rate‐limiting enzymatic step in norepinephrine biosynthesis) and dihydroxyphenylglycol (the main neuronal metabolite of norepinephrine) were measured with and without intravenous trimethaphan for ganglion blockade. ¹³N‐ammonia‐derived radioactivity was less on the affected side than on the unaffected side, whereas 6‐[¹⁸F]fluorodopamine‐derived radioactivity was symmetrical. Thus, perfusion‐adjusted 6‐[¹⁸F]fluorodopamine‐derived radioactivity was higher on the affected side. Norepinephrine spillover and smaller arteriovenous increments in plasma levels of L‐dihydroxyphenylalanine and dihydroxyphenylglycol did not differ significantly between affected and unaffected limbs, although 4 patients had noticeably less norepinephrine spillover and smaller arteriovenous increments in plasma dihydroxyphenylglycol on the affected side. Trimethaphan decreased the pain in only 2 of 12 nonsympathectomized patients. The results indicate that patients with chronic unilateral reflex sympathetic dystrophy have decreased perfusion of the affected limb, symmetrical sympathetic innervation and norepinephrine synthesis, variably decreased release and turnover of norepinephrine in the affected limb, and failure of ganglion blockade to improve the pain in most cases. These findings suggest augmented vasoconstriction, intact sympathetic terminal innervation, possibly impaired sympathetic neurotransmission, and pain usually independent of sympathetic neurocirculatory outflows.     

Glutamine: a major gluconeogenic precursor and vehicle for interorgan carbon transport in man.

To compare glutamine and alanine as gluconeogenic precursors, we simultaneously measured their systemic turnovers, clearances, and incorporation into plasma glucose, their skeletal muscle uptake and release, and the proportion of their appearance in plasma directly due to their release from protein in postabsorptive normal volunteers. We infused the volunteers with [U-14C] glutamine, [3-13C] alanine, [2H5] phenylalanine, and [6-3H] glucose to isotopic steady state and used the forearm balance technique. We found that glutamine appearance in plasma exceeded that of alanine (5.76 +/- 0.26 vs. 4.40 +/- 0.33 mumol.kg-1.min-1, P < 0.001), while alanine clearance exceeded glutamine clearance (14.7 +/- 1.3 vs. 9.3 +/- 0.8 ml.kg-1.min-1, P < 0.001). Glutamine appearance in plasma directly due to its release from protein was more than double that of alanine (2.45 +/- 0.25 vs. 1.16 +/- 0.12 mumol.kg-1.min-1, P < 0.001). Although overall carbon transfer to glucose from glutamine and alanine was comparable (3.53 +/- 0.24 vs 3.47 +/- 0.32 atoms.kg-1.min-1), nearly twice as much glucose carbon came from protein derived glutamine than alanine (1.48 +/- 0.15 vs 0.88 +/- 0.09 atoms.kg-1.min-1, P < 0.01). Finally, forearm muscle released more glutamine than alanine (0.88 +/- 0.05 vs 0.48 +/- 0.05 mumol.100 ml-1.min-1, P < 0.01). We conclude that in postabsorptive humans glutamine is quantitatively more important than alanine for transporting protein-derived carbon through plasma and adding these carbons to the glucose pool.     

Effects of pancreatic polypeptide on motilin and circulating metabolites in man

Pancreatic polypeptide was infused intravenously in healthy fasting subjects at 1 pmol kg-1 (n = 7) and 4 pmol kg-1 min-1 (n = 10) producing plasma PP concentrations of 223 +/- 37 pmol/l (mean +/- SEM) and 891 +/- 64 pmol/l respectively. These levels are similar to and four-fold higher than those seen after a normal mixed breakfast in healthy young adults. In a separate study five healthy subjects ingested a small breakfast during infusion of PP on different days at 1 pmol kg-1 min-1 and 2 pmol kg-1 min-1 respectively. PP at 1 pmol kg-1 min-1 caused a marked reduction in fasting plasma motilin concentrations to 20% of the basal level (p less than 0.001). There were, however, no significant changes in plasma concentrations of insulin, glucagon, gastrin, secretin, enteroglucagon, gastric inhibitory peptide or neurotensin. Despite previous reports possibly implicating PP in metabolism, there were no significant effects on blood levels of glucose, alanine lactate, 3-hydroxybutyrate, glycerol or non-esterified fatty acids, either in the fasting state or after the ingestion of food. Although it seems unlikely that PP is a major hormonal regulator of intermediary metabolism in man, its ability to suppress motilin at physiological concentrations suggests the possibility of an indirect influence on digestive motor function.     

Dopamine1 receptor agonist and alpha-2 adrenoceptor antagonist effects of fenoldopam in rabbits

Neurochemical and circulatory effects of fenoldopam were studied in pithed rabbits with electrically stimulated sympathetic outflow and in strips of the rabbit pulmonary artery. In pithed rabbits, fenoldopam (1-30 micrograms/kg/min) decreased the arterial blood pressure. Fenoldopam (3-30 microgram/kg/min) also increased the norepinephrine spillover rate (the rate at which endogenous norepinephrine enters into the plasma after having been released from postganglionic sympathetic nerves) and decreased the [3H]norepinephrine plasma clearance. The selective dopamine (DA)1 antagonist SCH 23390 (bolus injection of 10 micrograms/kg followed by infusion of 2 micrograms/kg/hr) antagonized markedly and the DA2-selective antagonist domperidone (bolus injection of 200 micrograms/kg followed by infusion of 50 micrograms/kg/hr) antagonized slightly the hypotensive effect. The increase in the norepinephrine spillover rate was enhanced after treatment with desipramine. Clonidine (0.3 microgram/kg/min) reduced the spillover of norepinephrine, and this effect was abolished by fenoldopam (30 micrograms/kg/min). In pulmonary artery strips preincubated with [3H]norepinephrine, fenoldopam (10(-7) and 10(-6) M) increased the electrically evoked overflow of tritium. The effect of fenoldopam (10(-6) M) was prevented in the presence of a supramaximal concentration of clonidine (10(-5) M). The results suggest that fenoldopam lowers blood pressure mainly by activation of vascular smooth muscle DA1 receptors. In addition, however, it blocks prejunctional alpha-2 autoreceptors at postganglionic sympathetic axons.     

Dose-response study of the redistribution of intravascular volume by angiotensin II in man.

1. The response of systemic and regional haemodynamic indices to increasing infusion rates of angiotensin II (1, 3 or 10 ng min-1 kg-1) or placebo [5% (w/v) D-glucose] was studied in eight normal male subjects. 2. As compared with placebo, angiotensin II infusion caused an incremental rise in the serum angiotensin II level [14.5 +/- 7.7 (placebo) to 187.2 +/- 36.1 (10 ng of angiotensin II min-1 kg-1) pmol/l; mean +/- 95% confidence interval] associated with a stepwise increase in total peripheral resistance [880 +/- 42 (placebo) to 1284 +/- 58 (10 ng of angiotensin II min-1 kg-1) dyn s cm-5] and a progressive reduction in cardiac output [8.3 +/- 0.4 (placebo) to 7.0 +/- 0.4 (10 ng of angiotensin II min-1 kg-1) litres/min]. 3. A stepwise fall in renal blood flow was observed with increasing angiotensin II infusion rate [1302 +/- 65 (placebo) to 913 +/- 64 (10 ng of angiotensin II min-1 kg-1) ml/min]. In contrast, calf blood flow was unaffected by 1 ng or 3 ng of angiotensin II min-1 kg-1 and was significantly increased by 10 ng of angiotensin II min-1 kg-1 (P less than 0.01). 4. Calf venous capacitance was uninfluenced by 1 ng of angiotensin II min-1 kg-1, but was significantly increased by both 3 ng (P less than 0.005) and 10 ng (P less than 0.001) of angiotensin II min-1 kg-1.(ABSTRACT TRUNCATED AT 250 WORDS)     

Adrenergic responses to sustained handgrip in patients with juvenile-onset-type diabetes mellitus.

1. The response of plasma noradrenaline, arterial blood pressure and heart rate to sustained handgrip at 30% of maximal voluntary contraction was studied in patients with long-term juvenile-onset-type diabetes millitus and healthy subjects of comparable age. 2. There was no significant difference between the intensity and duration of handgrip in diabetic patients and healthy subjects. 3. Sustained handgrip produced an increase in plasma concentration of noradrenaline both in diabetic and healthy subjects but the response in the diabetic subjects was significantly less. 4. The increase in systolic blood pressure during handgrip was significantly greater in diabetic subjects than in normal subjects. The increases in diastolic and mean blood pressure did not differ significantky. 5. The increase in heart rate during handgrip was greater in healthy subjects than in diabetic subjects. The response was smaller in diabetic patients with retinopathy than in the patients without retinopathy. 6. The sustained handgrip test may be useful for the diagnosis of abnormal sympathetic nervous system and haemodnynamic responsiveness in diabetic patients.     

Renal haemodynamic, hormonal and excretory effects of low-dose atrial natriuretic factor infusion in renal transplant recipients.

1. In experimental studies, activation of renal sympathetic nerves attenuates the natriuretic response to atrial natriuretic factor. We therefore investigated the response to low-dose infusion of atrial natriuretic factor in renal transplant recipients. 2. Eight male cyclosporin-treated renal transplant recipients received human-alpha atrial natriuretic factor (1-28) at a dose of 1.2 pmol min-1 kg-1 or placebo for 2 h in a placebo-controlled, randomized, cross-over study. The plasma atrial natriuretic factor concentration rose from 18.5 to 49.2 pmol/l in association with an immediate natriuresis (a rise of 49.1 mumol/min in the first 30 min, P less than 0.05; peaking at a 61% increase from baseline, P less than 0.01), diuresis (from 3.37 to 7.46 ml/min) and a threefold rise in urinary cyclic GMP excretion. 3. In response to infusion of atrial natriuretic factor, the packed cell volume rose by 4.2% (P less than 0.001) and the filtration fraction by 5% (from 22 to 27%, P less than 0.05), but there was no significant change in renal plasma flow, glomerular filtration rate or mean arterial blood pressure. Likewise, the plasma catecholamine concentrations, plasma renin activity and serum erythropoietin concentration remained unchanged. 4. The sensitivity of the renal allograft to plasma atrial natriuretic factor concentrations in the high physiological range suggests a role for endogenous atrial natriuretic factor in the modulation of graft function. Furthermore, the immediate natriuretic response to atrial natriuretic factor in the effectively denervated transplant kidney, in contrast to the delayed response seen in normal subjects, may imply that sympathetic nerves have an inhibitory effect on the renal response to atrial natriuretic factor in normal man.(ABSTRACT TRUNCATED AT 250 WORDS)     

Plasma clearance of noradrenaline does not change with age in normal subjects

Summary. Noradrenaline kinetics (plasma concentrations, plasma clearance and appearance rates) were investigated in seven elderly healthy subjects and in six young healthy subjects. Forearm venous plasma noradrenaline concentrations were higher in the elderly subjects compared with the young subjects. Plasma clearance of noradrenaline was identical in the two groups. The increase in plasma noradrenaline concentration, with age, probably reflects an increased sympathetic nervous activity.     

Loss of hepatic autoregulation after carbohydrate overfeeding in normal man.

To determine the effect of increased glycogen stores on hepatic carbohydrate metabolism, 15 nondiabetic volunteers were studied before and after 4 d of progressive overfeeding. Glucose production and gluconeogenesis were assessed with [2-3H] glucose and [6-14C] glucose (Study I, n = 6) or [3-3H] glucose and [U-14C]-alanine (Study II, n = 9) and substrate oxidation was determined by indirect calorimetry. Overfeeding was associated with significant (P < 0.01) increases in plasma glucose (4.97 +/- 0.10 to 5.09 +/- 0.11 mmol/liter), insulin (18.8 +/- 1.5 to 46.6 +/- 10.0 pmol/liter) and carbohydrate oxidation (4.7 +/- 1.4 to 18.0 +/- 1.5 mumol.kg-1.min-1) and a decrease in lipid oxidation (1.2 +/- 0.2 to 0.3 +/- 0.1 mumol.kg-1.min-1). Hepatic glucose output (HGO) increased in Study I (10.2 +/- 0.5 to 13.1 +/- 0.9 mumol.kg-1.min-1, P < 0.01) and Study II (11.17 +/- 0.67 to 13.33 +/- 0.83 mumol.kg-1.min-1, P < 0.01), and gluconeogenesis decreased (57.6 +/- 6.4 to 33.4 +/- 4.9 mumol/min, P < 0.01), indicating an increase in glycogenolysis. The increase in glycogenolysis was only partly compensated by an increase in glucose cycle activity (2.2 +/- 0.2 to 3.4 +/- 0.4 mumol.kg-1.min-1, P < 0.01) and the fall in gluconeogenesis, thus resulting in increased HGO. The suppression of gluconeogenesis despite increased lactate and alanine (glycerol was decreased) was associated with decreased free fatty acid (FFA) oxidation and negligible FFA enhanced gluconeogenesis. These studies suggest that increased liver glycogen stores alone can overwhelm normal intrahepatic mechanisms regulating carbohydrate metabolism resulting in increased HGO in nondiabetic man.