Dopamine, the kidney and essential hypertension studies with gludopa

The formation and action of intrarenal dopamine is reviewed, as also is the evidence for the use of gamma-L-glutamyl-L-dopa as a relatively renally specific dopaminergic pro-drug. 'Salt sensitive' patients with essential hypertension may have a fault in the renal mobilisation of dopamine by sodium chloride. This failure of sodium to dopamine coupling may be particularly prevalent in the Negro race.

Molecular cloning and expression of neuroleukin, a neurotrophic factor for spinal and sensory neurons

A novel 56,000-dalton growth factor found in mouse salivary gland was purified, molecularly cloned, and expressed in monkey COS cells. The protein is a neurotrophic factor and also, surprisingly, a lymphokine product of lectin-stimulated T cells. The factor was therefore named neuroleukin. Neuroleukin promotes the survival in culture of a subpopulation of embryonic spinal neurons that probably includes skeletal motor neurons. Neuroleukin also supports the survival of cultured sensory neurons that are insensitive to nerve growth factor, but has no effect on sympathetic or parasympathetic neurons. The amino acid sequence of neuroleukin is partly homologous to a highly conserved region of the external envelope protein of HTLV-III/LAV, the retrovirus that causes acquired immune deficiency syndrome.

Domperidone treatment in man inhibits the fall in plasma renin activity induced by intravenous gamma-L-glutamyl-L-dopa

The dopamine pro-drug gamma-L-glutamyl-L-dopa (gludopa) was administered intravenously to six normal subjects at a dose of 12.5 micrograms min-1 kg-1, either with or without the dopamine antagonist domperidone. A control was provided by the intravenous infusion of domperidone and saline on a separate occasion. Intravenous gludopa produced a significant natriuresis, whether administered alone or in combination with domperidone. After gludopa infusion, there was a significant fall in plasma renin activity, an effect which was attenuated significantly by concomitant treatment with domperidone. These observations suggest that blockade of renal DA2 dopamine receptors has little or no effect on gludopa-induced natriuresis, but that at least part of the dopaminergic inhibition of renin release is mediated by renal DA2 receptors.

Studies with fenoldopam, a dopamine receptor DA1 agonist, in essential hypertension

A series of studies were undertaken to assess the effect of oral fenoldopam, a specific DA1 dopamine receptor agonist on blood pressure and renal function in patients with mild essential hypertension. Six patients with essential hypertension were entered into a dose-ranging study and received either placebo, 25, 50 or 100 mg fenoldopam. A significant, dose-related reduction in diastolic blood pressure, and increase in heart rate was demonstrated (both P less than 0.05), maximal at 45 min to 1 h. Fenoldopam increased plasma renin activity. In a double-blind study, seven patients received a single dose of fenoldopam 100 mg or placebo. Fenoldopam produced a significant fall in systolic (P less than 0.05) and diastolic (P less than 0.01) blood pressure and renal vascular resistance (P less than 0.01). Urine flow rate (P less than 0.05), sodium excretion (P less than 0.01), plasma renin activity (P less than 0.05) and plasma aldosterone (P less than 0.05) increased. Five patients underwent measurement of the above parameters following a single dose of fenoldopam 100 mg with a repeat of these measurements after they had taken fenoldopam 100 mg four times daily for 1 month. The acute response of blood pressure to the single dose appeared unchanged but tachyphylaxis was evident in the responses of heart rate, plasma renin activity and plasma aldosterone.

Patients with essential hypertension have an exaggerated natriuretic response to the dopamine pro-drug glutamyl-dopa

The relatively kidney-specific dopamine pro-drug, gamma-L-glutamyl-L-dopa (gludopa) was administered to eight normal subjects and eight patients with essential hypertension, control studies being provided by the infusion of saline on a separate occasion. There was a more marked natriuresis in the hypertensives than in the normal subjects, even though, in contrast to the normals, the hypertensives showed no significant change in effective renal plasma flow (ERPF) or glomerular filtration rate (GFR). A significant fall in plasma renin activity (PRA) occurred in both groups. These observations suggest that a part of the dopamine-induced natriuresis is due to stimulation of tubular receptors, and that there is up-regulation of these receptors in essential hypertension.

gamma-L-Glutamyl-L-dopa is a dopamine pro-drug, relatively specific for the kidney in normal subjects

gamma-L-Glutamyl-L-dopa was given by intravenous infusion to eight normal subjects at doses of 12.5 and 100 micrograms min-1 kg-1. Both doses of the dipeptide resulted in an increase in mean urinary sodium excretion. Mean effective renal plasma flow rose at both doses, but mean glomerular filtration rate increased only at the lower dose. There was a fall in mean plasma renin activity after the infusion of both 12.5 and 100 micrograms min-1 kg-1. Mean urine free dopamine excretion increased by 280- and 2500-fold at infusion rates of 12.5 and 100 micrograms min-1 kg-1 respectively. Mean plasma free dopamine rose at both doses but the increase at 12.5 micrograms min-1 kg-1 was not to a level previously associated with systemic effects of the catecholamine. On administration of the dipeptide at 12.5 micrograms min-1 kg-1 there were no changes in blood pressure or heart rate, but at the higher dose there was a fall in diastolic blood pressure. At a dose of 12.5 micrograms min-1 kg-1 in man, there is kidney specific conversion of gludopa to dopamine.

Failure of superoxide dismutase to alter equine arachidonic acid-induced platelet aggregation, in vitro or ex vivo

Superoxide dismutase (SOD), a free radical scavenger with anti-inflammatory activity, was administered IM to horses. Ex vivo platelet aggregation in response to arachidonic acid was monitored to determine whether exogenous SOD altered equine platelet prostaglandin metabolism. Preparations of platelet-rich plasma obtained before SOD administration were incubated with different concentrations of SOD and were aggregated with arachidonic acid. Superoxide dismutase did not exert a demonstrable effect, either ex vivo or in vitro. Aspirin abolished arachidonic acid-induced platelet aggregation in vitro. This indicates that SOD (in the resting state) does not exert an effect on platelet-derived free radicals that could alter the arachidonic acid pathway of equine platelets, that equine platelets do not release free radicals, or that equine platelets are insensitive to the products formed from free radicals by SOD.

The effect of oral fenoldopam (SKF 82526-J), a peripheral dopamine receptor agonist, on blood pressure and renal function in normal man

The effect of a single oral dose of 100 mg of fenoldopam on renal function and blood pressure was investigated in seven healthy male subjects in a double-blind placebo controlled study. Mean diastolic blood pressure fell by 10 mm Hg, 45 min after oral dosing and then gradually returned to baseline values. There was an increase in pulse rate and a delayed rise in systolic blood pressure. Measured from 30 to 120 min after drug ingestion, mean effective renal plasma flow increased to 158% of the value observed after placebo; mean glomerular filtration rate rose to 109% of the placebo value. Measured from 120 to 210 min after administration of the drug, effective renal plasma flow and glomerular filtration rate had returned to baseline values. Fenoldopam produced a small increase in the mean sodium excretion rate which was not significantly different from the fall after placebo. No change was detected in urine flow or potassium excretion rate. Mean plasma renin activity increased three-fold 1 h after oral dosing. Plasma aldosterone did not show a parallel increase although the plasma concentration at 1 h was significantly higher than after placebo. The results show a pronounced renal vasodilator effect lasting about 2 h. The findings are consistent with marked DA1 receptor agonist activity.

The spatial control of ganglionic neurite growth by the substrate-associated material from conditioned medium: an experimental model of haptotaxis

Techniques are described for forming on the culture substrate a narrow pathway of material derived from medium conditioned by embryonic non-neuronal cells. There is a precise correlation between the known location of the pathway and the spatial distribution of neurites extended from whole ciliary ganglia or dissociated neurons grown on the patterned substrate. When individual growth cones moving on the pathway contact one of its edges, they turn sharply so as to remain on the pathway. This turning response is not simply due to a physical barrier to movement across the edge, since growth cones can cross onto the pathway when entering from the adjacent untreated substrate. The strong preference for neurites to maintain contact with the pathway also is not simply a result of their inability to survive or elongate outside of the pathway, since neurites from whole ganglia elongate readily on other regions of the substrate, although their growth is then undirected. Direct contact with the pathway is required for these directive effects, and there is no indication that the material bound to the substrate diffuses off and exerts its effects at a distance. The neurite-guiding activity is found in partially purified fractions of conditioned medium which also contain a substrate-bound inducer of neurite outgrowth. It is possible that both activities may be due to the same components of conditioned medium. These results suggest that ciliary ganglion growth cones are able to detect specific components of conditioned medium on the substrate and respond to their presence by changing their direction of movement so as to remain in contact with these components.(ABSTRACT TRUNCATED AT 250 WORDS)

A paradoxical fall in urine dopamine output when patients with essential hypertension are given added dietary salt

The effect of dietary sodium on the urine dopamine excretion of eight hypertensive patients and six matched controls was studied under metabolic balance conditions over a 2 week period during which dietary sodium intake was increased from 20 to 220 mmol/day. The control group showed the expected increase in dopamine excretion in response to sodium but the hypertensive patients showed an initial fall followed by a return to baseline values. Neither group showed a rise in blood pressure but the hypertensive patients showed a greater weight gain on salt loading, although this change was not significant. The cumulative sodium balance was greater and more prolonged in the hypertensive patients, although this difference also did not attain statistical significance. This defect in dopamine mobilization may be important in relation to renal sodium handling by patients with essential hypertension.

Lack of effect of ibopamine, a dopamine pro-drug, on renal function in normal subjects

The effects of two single oral doses of ibopamine (150 and 600 mg) on heart rate, blood pressure, urine flow, sodium, potassium and creatinine excretion were studied in normal volunteers. No significant change was observed in urine flow, sodium, potassium or creatinine excretion at either dose. No significant change was observed in heart rate or blood pressure except that systolic blood pressure was transiently elevated after the 600 mg dose (P less than 0.05).

Recurrence of asthma following removal of a noradrenaline-secreting phaeochromocytoma

A patient with asthma and a phaeochromocytoma is described. At about the time she was first noted to be hypertensive her asthma resolved spontaneously but bronchospasm returned with some severity when the tumour was removed. The phaeochromocytoma was of the noradrenaline secreting variety. Possible mechanisms through which this catecholamine might have produced the observed alleviation of asthma are considered.

The protective effect of gamma-glutamyl L-dopa on the glycerol treated rat model of acute renal failure

gamma-Glutamyl L-dopa, a renal pro-drug for dopamine, was administered to rats before and after injection of glycerol, and to a control group which received water in place of glycerol. A third group of rats was given glycerol but no gamma-glutamyl L-dopa. The plasma creatinine in rats given gamma-glutamyl L-dopa and glycerol was significantly lower than in rats receiving glycerol alone. The fall in urine creatinine excretion, and polyuria, after glycerol was reduced by gamma-glutamyl L-dopa and the natriuresis abolished. gamma-Glutamyl L-dopa given alone caused a 4000-fold increase in urine dopamine excretion, associated with a natriuresis. The administration of gamma-glutamyl L-dopa reduces the severity of renal failure produced by glycerol.

Evidence for a hypothalamic disturbance in cyclical oedema

Fourteen women with cyclical oedema and six healthy female controls were investigated by use of a test in which thyrotrophin releasing hormone and luteinising hormone releasing hormone were given. Significant differences in the responses of prolactin, luteinising hormone, and follicle stimulating hormone were observed in the patients. These findings suggest that there may be a hitherto unrecognised hypothalamic defect in cyclical oedema that may account for some of the previously unexplained clinical features and lead to a more rational therapeutic approach in the management of the disorder.

Classification of human senile cataractous changes by the American Cooperative Cataract Research Group (CCRG) method. I. Instrumentation and technique

The American Cooperative Cataract Research Group (CCRG) has adopted a system of classifying human cataractous changes that is based on separate and independent photographic documentation of opacification and nuclear color. This system has been extremely useful to the laboratory scientist who wishes to know the significance of associations between laboratory data and the extent or type of cataractous change. It has been applied to the analysis of nearly 2500 cataracts since 1976. This study presents the details of the instrumentation and technique of this new system and the results of classifying 2231 intracapsularly-extracted cataracts.