Glucagon secretion is essential for aminoacid-induced hyperfiltration in man

Incretin and glucagon receptor polypharmacology in chronic kidney disease

Chronic kidney disease is a debilitating condition associated with significant morbidity and mortality. In recent years, the kidney effects of incretin-based therapies, particularly glucagon-like peptide-1 receptor agonists (GLP-1RAs), have garnered substantial interest in the management of type 2 diabetes and obesity. This review delves into the intricate interactions between the kidney, GLP-1RAs, and glucagon, shedding light on their mechanisms of action and potential kidney benefits. Both GLP-1 and glucagon, known for their opposing roles in regulating glucose homeostasis, improve systemic risk factors affecting the kidney, including adiposity, inflammation, oxidative stress, and endothelial function. Additionally, these hormones and their pharmaceutical mimetics may have a direct impact on the kidney. Clinical studies have provided evidence that incretins, including those incorporating glucagon receptor agonism, are likely to exhibit improved kidney outcomes. Although further research is necessary, receptor polypharmacology holds promise for preserving kidney function through eliciting vasodilatory effects, influencing volume and electrolyte handling, and improving systemic risk factors.

Efficacy and safety of cotadutide, a dual glucagon-like peptide-1 and glucagon receptor agonist, in a randomized phase 2a study of patients with type 2 diabetes and chronic kidney disease

AIM

To assess the efficacy, safety and tolerability of cotadutide in patients with type 2 diabetes mellitus and chronic kidney disease.

MATERIALS AND METHODS

In this phase 2a study (NCT03550378), patients with body mass index 25-45 kg/m² , estimated glomerular filtration rate 30-59 ml/min/1.73 m² and type 2 diabetes [glycated haemoglobin 6.5-10.5% (48-91 mmol/mol)] controlled with insulin and/or oral therapy combination, were randomized 1:1 to once-daily subcutaneous cotadutide (50-300 μg) or placebo for 32 days. The primary endpoint was plasma glucose concentration assessed using a mixed-meal tolerance test.

RESULTS

Participants receiving cotadutide (n = 21) had significant reductions in the mixed-meal tolerance test area under the glucose concentration-time curve (-26.71% vs. +3.68%, p < .001), more time in target glucose range on continuous glucose monitoring (+14.79% vs. -21.23%, p = .001) and significant reductions in absolute bodyweight (-3.41 kg vs. -0.13 kg, p < .001) versus placebo (n = 20). In patients with baseline micro- or macroalbuminuria (n = 18), urinary albumin-to-creatinine ratios decreased by 51% at day 32 with cotadutide versus placebo (p = .0504). No statistically significant difference was observed in mean change in estimated glomerular filtration rate between treatments. Mild/moderate adverse events occurred in 71.4% of participants receiving cotadutide and 35.0% receiving placebo.

CONCLUSIONS

We established the efficacy of cotadutide in this patient population, with significantly improved postprandial glucose control and reduced bodyweight versus placebo. Reductions in urinary albumin-to-creatinine ratios suggest potential benefits of cotadutide on kidney function, supporting further evaluation in larger, longer-term clinical trials.

Renal functional reserve: from physiological phenomenon to clinical biomarker and beyond

Glomerular filtration rate (GFR) is acutely increased following a high-protein meal or systemic infusion of amino acids. The mechanisms underlying this renal functional response remain to be fully elucidated. Nevertheless, they appear to culminate in preglomerular vasodilation. Inhibition of the tubuloglomerular feedback signal appears critical. However, nitric oxide, vasodilator prostaglandins, and glucagon also appear important. The increase in GFR during amino acid infusion reveals a "renal reserve," which can be utilized when the physiological demand for single nephron GFR increases. This has led to the concept that in subclinical renal disease, before basal GFR begins to reduce, renal functional reserve can be recruited in a manner that preserves renal function. The extension of this concept is that once a decline in basal GFR can be detected, renal disease is already well progressed. This concept likely applies both in the contexts of chronic kidney disease and acute kidney injury. Critically, its corollary is that deficits in renal functional reserve have the potential to provide early detection of renal dysfunction before basal GFR is reduced. There is growing evidence that the renal response to infusion of amino acids can be used to identify patients at risk of developing either chronic kidney disease or acute kidney injury and as a treatment target for acute kidney injury. However, large multicenter clinical trials are required to test these propositions. A renewed effort to understand the renal physiology underlying the response to amino acid infusion is also warranted.

Differential Impact of Dietary Branched Chain and Aromatic Amino Acids on Chronic Kidney Disease Progression in Rats

The metabolism of dietary proteins generates waste products that are excreted by the kidney, in particular nitrogen-containing urea, uric acid, ammonia, creatinine, and other metabolites such as phosphates, sulfates, and protons. Kidney adaptation includes an increase in renal plasma flow (RPF) and glomerular filtration rate (GFR) and represents a burden for diseased kidneys increasing the progression rate of CKD. The present study aimed at identifying potential differences between amino acid (AA) groups constituting dietary proteins regarding their impact on RPF, GFR, and CKD progression. We utilized the well-established 5/6 nephrectomy (5/6 Nx) CKD model in rats and submitted the animals for 5 weeks to either the control diet (18% casein protein) or to diets containing 8% casein supplemented with 10% of a mix of free amino acids, representing all or only a subset of the amino acids contained in casein. Whereas the RPF and GFR measured in free moving animals remained stable during the course of the diet in rats receiving the control mix, these parameters decreased in animals receiving the branched chain amino acid (BCAA) supplementation and increased in the ones receiving the aromatic amino acids (AAAs). In animals receiving essential amino acids (EAAs) containing both BCAAs and AAAs, there was only a small increase in RPF. The kidneys of the 5/6 Nx rats receiving the BCAA diet showed the strongest increase in smooth muscle actin and collagen mRNA expression as a result of higher level of inflammation and fibrosis. These animals receiving BCAAs also showed an increase in plasma free fatty acids pointing to a problem at the level of energy metabolism. In contrast, the animals under AAA diet showed an activation of AMPK and STAT3. Taken together, our results demonstrate that subsets of EAAs contained in dietary proteins, specifically BCAAs and AAAs, exert contrasting effects on kidney functional parameters and CKD progression.

Glucagon revisited: Coordinated actions on the liver and kidney

Glucagon secretion is stimulated by a low plasma glucose concentration. By activating glycogenolysis and gluconeogenesis in the liver, glucagon contributes to maintain a normal glycemia. Glucagon secretion is also stimulated by the intake of proteins, and glucagon contributes to amino acid metabolism and nitrogen excretion. Amino acids are used for gluconeogenesis and ureagenesis, two metabolic pathways that are closely associated. Intriguingly, cyclic AMP, the second messenger of glucagon action in the liver, is released into the bloodstream becoming an extracellular messenger. These effects depend not only on glucagon itself but on the actual glucagon/insulin ratio because insulin counteracts glucagon action on the liver. This review revisits the role of glucagon in nitrogen metabolism and in disposal of nitrogen wastes. This role involves coordinated actions of glucagon on the liver and kidney. Glucagon influences the transport of fluid and solutes in the distal tubule and collecting duct, and extracellular cAMP influences proximal tubule reabsorption. These combined effects increase the fractional excretion of urea, sodium, potassium and phosphates. Moreover, the simultaneous actions of glucagon and extracellular cAMP are responsible, at least in part, for the protein-induced rise in glomerular filtration rate that contributes to a more efficient excretion of protein-derived end products.

Protein- and diabetes-induced glomerular hyperfiltration: role of glucagon, vasopressin, and urea

A single protein-rich meal (or an infusion of amino acids) is known to increase the glomerular filtration rate (GFR) for a few hours, a phenomenon known as “hyperfiltration.” It is important to understand the factors that initiate this upregulation because it becomes maladaptive in the long term. Several mediators and paracrine factors have been shown to participate in this upregulation, but they are not directly triggered by protein intake. Here, we explain how a rise in glucagon and in vasopressin secretion, directly induced by protein ingestion, might be the initial factors triggering the hepatic and renal events leading to an increase in the GFR. Their effects include metabolic actions in the liver and stimulation of sodium chloride reabsorption in the thick ascending limb. Glucagon is not only a glucoregulatory hormone. It is also important for the excretion of nitrogen end products by stimulating both urea synthesis in the liver (along with gluconeogenesis from amino acids) and urea excretion by the kidney. Vasopressin allows the concentration of nitrogenous end products (urea, ammonia, etc.) and other protein-associated wastes in a hyperosmotic urine, thus allowing a very significant water economy characteristic of all terrestrial mammals. No hyperfiltration occurs in the absence of one or the other hormone. Experimental results suggest that the combined actions of these two hormones, along with the complex intrarenal handling of urea, lead to alter the composition of the tubular fluid at the macula densa and to reduce the intensity of the signal activating the tubuloglomerular feedback control of GFR, thus allowing GFR to raise. Altogether, glucagon, vasopressin, and urea contribute to set up the best compromise between efficient urea excretion and water economy.

Active urea transport in lower vertebrates and mammals

Some unicellular organisms can take up urea from the surrounding fluids by an uphill pumping mechanism. Several active (energy-dependent) urea transporters (AUTs) have been cloned in these organisms. Functional studies show that active urea transport also occurs in elasmobranchs, amphibians, and mammals. In the two former groups, active urea transport may serve to conserve urea in body fluids in order to balance external high ambient osmolarity or prevent desiccation. In mammals, active urea transport may be associated with the need to either store and/or reuse nitrogen in the case of low nitrogen supply, or to excrete nitrogen efficiently in the case of excess nitrogen intake. There are probably two different families of AUTs, one with a high capacity able to establish only a relatively modest transepithelial concentration difference (renal tubule of some frogs, pars recta of the mammalian kidney, early inner medullary collecting duct in some mammals eating protein-poor diets) and others with a low capacity but able to maintain a high transepithelial concentration difference that has been created by another mechanism or in another organ (elasmobranch gills, ventral skin of some toads, and maybe mammalian urinary bladder). Functional characterization of these transporters shows that some are coupled to sodium (symports or antiports) while others are sodium-independent. In humans, only one genetic anomaly, with a mild phenotype (familial azotemia), is suspected to concern one of these transporters. In spite of abundant functional evidence for such transporters in higher organisms, none have been molecularly identified yet.

Normal renal function 8 to 13 years after cyclosporin A therapy in 285 diabetic patients

BACKGROUND

Cyclosporin A (CyA) may induce acute nephrotoxicity. The question has been raised of the possible long-term unfavorable course of CyA-induced lesions. Advantage was taken of a large cohort of diabetic patients treated for several months using moderate CyA dosage to evaluate the long-term evolution of renal function in such patients.

METHODS

Two hundred and eighty five recently diagnosed type 1 diabetic patients having received CyA for a mean of 19.9 months were monitored for 13 years, in parallel with 100 similar patients treated with insulin alone.

RESULTS

In the CyA-treated group, a transient increase in creatininemia levels occurred during the first 18 months of treatment associated with a transient increase in renal vascular resistance. Both effects disappeared later on: creatininemia levels then remained normal. Inulin and p-aminohippurate (PAH) clearances remained normal throughout follow-up. Neither permanent renal failure nor progressive deterioration of renal function occurred in either group or in individual patients. A 10 to 12% increase in inulin and PAH clearance was elicited by IV amino acid infusion at 7 to 10 years, a finding consistent with a normal renal functional reserve. Patients with moderate kidney lesions on biopsy at 1 year had normal and stable clearance values at 7 to 13 years. The prevalence of arterial hypertension and retinopathy was lower in the CyA-treated group than in the control group, possibly because of the tighter metabolic control obtained in the CyA group.

CONCLUSION

These results suggest that low-dose CyA treatment combined with thorough monitoring does not result in long-term renal dysfunction.

Extracellular cAMP inhibits proximal reabsorption: are plasma membrane cAMP receptors involved?

Glucagon binding to hepatocytes has been known for a long time to not only stimulate intracellular cAMP accumulation but also, intriguingly, induce a significant release of liver-borne cAMP in the blood. Recent experiments have shown that the well-documented but ill-understood natriuretic and phosphaturic actions of glucagon are actually mediated by this extracellular cAMP, which inhibits the reabsorption of sodium and phosphate in the renal proximal tubule. The existence of this "pancreato-hepatorenal cascade" indicates that proximal tubular reabsorption is permanently influenced by extracellular cAMP, the concentration of which is most probably largely dependent on the insulin-to-glucagon ratio. The possibility that renal cAMP receptors may be involved in this process is supported by the fact that cAMP has been shown to bind to brush-border membrane vesicles. In other cell types (i.e., adipocytes, erythrocytes, glial cells, cardiomyocytes), cAMP eggress and/or cAMP binding have also been shown to occur, suggesting additional paracrine effects of this nucleotide. Although not yet identified in mammals, cAMP receptors (cARs) are already well characterized in lower eukaryotes. The amoeba Dictyostelium discoideum expresses four different cARs during its development into a multicellular organism. cARs belong to the superfamily of seven transmembrane domain G protein-coupled receptors and exhibit a modest homology with the secretin receptor family (which includes PTH receptors). However, the existence of specific cAMP receptors in mammals remains to be demonstrated. Disturbances in the pancreato-hepatorenal cascade provide an adequate pathophysiological understanding of several unexplained observations, including the association of hyperinsulinemia and hypertension, the hepatorenal syndrome, and the hyperfiltration of diabetes mellitus. The observations reviewed in this paper show that cAMP should no longer be regarded only as an intracellular second messenger but also as a first messenger responsible for coordinated hepatorenal functions, and possibly for paracrine regulations in several other tissues.

Effects of amino acids and glucagon on renal hemodynamics in type 1 diabetes

Increased dietary protein and circulating amino acids raise glomerular filtration rate (GFR) and pressure. In diabetes, this glomerular hyperfiltration response is augmented. The purpose of this study was to determine whether glucagon mediates the augmented GFR response to amino acids in diabetes and whether the responses to amino acids and glucagon depend on prostaglandins. Patients with type 1 diabetes mellitus (n = 12) and normal control subjects (n = 12) were studied in a series of six experiments, each on different occasions. Baseline GFR was not significantly increased, but filtration fraction was higher in diabetes. In response to amino acid infusion, GFR increased more and filtration fraction was greater among those with diabetes. Their augmented GFR response to amino acids was not inhibited by octreotide or indomethacin. Participants with diabetes also had enhanced GFR and renal plasma flow responses to glucagon infusion, both of which were inhibited by indomethacin. Glomerular hyperfiltration responses induced by amino acids or glucagon occur by divergent pathways in diabetes; only the response to glucagon is prostaglandin dependent.

Cyclic AMP is a hepatorenal link influencing natriuresis and contributing to glucagon-induced hyperfiltration in rats

The effects of glucagon (G) on proximal tubule reabsorption (PTR) and GFR seem to depend on a prior action of this hormone on the liver resulting in the liberation of a mediator and/or of a compound derived from amino acid metabolism. This study investigates in anesthetized rats the possible contribution of cAMP and urea, alone and in combination with a low dose of G, on phosphate excretion (known to depend mostly on PTR) and GFR. After a 60-min control period, cAMP (5 nmol/min x 100 grams of body weight [BW]) or urea (2.5 micromol/min x 100 grams BW) was infused intravenously for 200 min with or without G (1.2 ng/min x 100 grams BW, a physiological dose which, alone, does not influence PTR or GFR). cAMP increased markedly the excretion of phosphate and sodium (+303 and +221%, respectively, P < 0.01 for each) but did not alter GFR. Coinfusion of cAMP and G induced the same tubular effects but also induced a 20% rise in GFR (P < 0.05). Infusion of urea, with or without G, did not induce significant effects on PTR or GFR. After G infusion at increasing doses, the increase in fractional excretion of phosphate was correlated with a simultaneous rise in plasma cAMP concentration and reached a maximum for doubling of plasma cAMP. These results suggest that cAMP, normally released by the liver into the blood under the action of G, (a) is probably an essential hepatorenal link regulating the intensity of PTR, and (b) contributes, in conjunction with specific effects of G on the nephron, to the regulation of GFR.

Renal handling of drugs and amino acids after impairment of kidney or liver function--influences of maturity and protective treatment

Renal tubular cells are involved both in secretion and in reabsorption processes within the kidney. Normally, most xenobiotics are secreted into the urine at the basolateral membrane of the tubular cell, whereas amino acids are reabsorbed quantitatively at the luminal side. Under different pathological or experimental circumstances, these transport steps may be changed, e.g., they may be reduced by renal impairment (reduction of kidney mass, renal ischemia, administration of nephrotoxins) or they may be enhanced after stimulation of transport carriers. Furthermore, a distinct interrelationship exists between excretory functions of the kidney and the liver. That means liver injury can influence renal transport systems also (hepato-renal syndrome). In this review, the following aspects were included: based upon general information concerning different transport pathways for xenobiotics and amino acids within kidney cells and upon a brief characterization of methods for testing impairment of kidney function, the maturation of renal transport and its stimulation are described. Similarities and differences between the postnatal development of kidney function and the increase of renal transport capacity after suitable stimulatory treatment by, for example, various hormones or xenobiotics are reviewed. Especially, renal transport in acute renal failure is described for individuals of different ages. Depending upon the maturity of kidney function, age differences in susceptibility to kidney injury occur: if energy-requiring processes are involved in the transport of the respective substance, then adults, in general, are more susceptible to renal failure than young individuals, because in immature organisms, anaerobic energy production predominates within the kidney. On the other hand, adult animals can better compensate for the loss of renal tissue (partial nephrectomy). With respect to stimulation of renal transport capacity after repeated pretreatment with suitable substances, age differences also exist: most stimulatory schedules are more effective in young, developing individuals than in mature animals. Therefore, the consequences of the stimulation of renal transport can be different in animals of different ages and are discussed in detail. Furthermore, the extent of stimulation is different for the transporters located at the basolateral and at the luminal membranes: obviously the tubular secretion at the contraluminal membrane can be stimulated more effectively than reabsorption processes at the luminal side.

Renal functional reserve in patients with IgA glomerulopathy

Seven patients with histologically proven IgA nephropathy and modest impairment of renal function, and 2 patients with IgA nephropathy and nephrotic syndrome were investigated, compared to a control group of 9 healthy individuals, to study the effects of amino acids on glomerular and tubular function, and to evaluate renal functional reserve in IgA nephropathy with different clinical course. Inulin and PAH clearances were used to evaluate glomerular filtration rate (GFR) and effective renal plasma flow (ERPF); proximal and distal tubular fluid delivery and reabsorption were measured by lithium clearance, before and after submission of a standardized amino acid solution. GFR and ERPF increased significantly during amino acid load in healthy individuals and patients without nephrotic syndrome, while filtration fraction (GFR/ERPF) remained constant. Lithium clearance (CLi) and fractional lithium excretion (CLi/GFR) rose significantly in both groups, whereas the reabsorbed volume of fluid in the proximal tubule did not change. In the distal tubule, fractional volume excretion decreased significantly during amino acid load whereas the reabsorbed volume significantly increased. Baseline values of the two groups did not differ significantly. Two patients with nephrotic course of IgA nephropathy showed a distinct decrease in glomerular and tubular function, and a loss of renal functional reserve after amino acid load.

CONCLUSIONS

Despite distinct alterations in renal biopsy, IgA nephropathy without nephrotic course presents with a still adequately preserved kidney function and renal functional reserve. A single determination of renal function with noninvasive functional tests does not give valid prognostic information concerning glomerular and tubular function. Therefore, a repeated measurement of renal function at defined intervals might reveal clinical progression of renal disease. The results of the lithium clearance might indicate an increase in tubular function after amino acid load, indicating a tubular adaptation in state of hyperfiltration.

Preservation of renal haemodynamic response to an oral protein load in non-insulin-dependent diabetes mellitus

Glomerular Filtration Rate (GFR) and Effective Renal Plasma Flow (ERPF) were determined, for 2 h prior to and 3 h following the ingestion of a 1.2 g kg-1 meat meal, in seven normotensive normoalbuminuric Type 2 diabetic patients exhibiting good glycaemic control (fasting plasma glucose (mean +/- SD): 7.2 +/- 2.0 mmol l-1; glycosylated haemoglobin: 8.1 +/- 1.7%) and in nine normal subjects selected for similar basal GFR values. Baseline GFR and ERPF (corrected to 1.73 m2 surface area) were 83 +/- 10 and 410 +/- 76 ml min-1 for the Type 2 diabetic patients and 86 +/- 11 and 405 +/- 113 ml min-1 for the normals. GFR increased by 38 +/- 8 and 32 +/- 15% in the diabetic patients and normals, to 108 +/- 25 and 105 +/- 26 ml min-1 (p < 0.01 vs baseline). Peak ERPF was 501 +/- 127 and 476 +/- 119 ml min-1 for the two respective groups (p < 0.01 vs baseline). Filtration fractions at peak GFR and EPRF values were unchanged from baseline for either groups. Fractional clearance of albumin for the Type 2 diabetic patients was unaltered by protein ingestion. Therefore, protein ingestion in Type 2 diabetes, as in normals, results in an acute elevation of GFR. Absolute and incremental changes in GFR were identical for the two groups. These data demonstrate a preserved capacity for renal vasodilatation in Type 2 diabetic patients despite their greater chronological age.

Role of the renin-angiotensin system on the renal functional reserve in renal transplant recipients

To determine the renal functional reserve in renal transplant recipients, we measured the glomerular filtration rate by inulin clearance and the renal plasma flow by PAH clearance before and during an amino acid infusion (Totamine, 6 to 8 mg/kg/min for 90 to 120 min) in 18 transplanted patients with stable renal function. To test the role of the renin-angiotensin system on the renal functional reserve, we performed a crossover placebo-controlled randomized trial of acute blockade of the renin-angiotensin system by injection of perindoprilat (2 mg i.v.), an inhibitor of angiotensin converting enzyme before amino acid infusion, each patient being studied twice at seven day intervals. Amino acid infusion induced a time-dependent increase in the glomerular filtration rate (P = 0.04), whether or not the renin-angiotensin system was blocked. Maximal increases were from 49.1 +/- 4.1 to 58.9 +/- 5.4, mean +/- SE (18.5%), in control conditions and from 52.4 +/- 5.6 to 62.1 +/- 5.5 ml/min/1.73 m2 (19.7%) after perindoprilat. The increase in glomerular filtration rate was less pronounced in patients taking cyclosporin A than in patients treated with steroid and azathioprine. Amino acid infusion also induced a significant and time-dependent increase (15.2 to 20.2%) in the renal plasma flow (P < 0.01) whether or not perindoprilat had been given. Furthermore, perindoprilat alone increased renal plasma flow by 13.6%, and this effect seemed additive with that of amino acids. Perindoprilat injection decreased filtration fraction (from 0.20 +/- 0.01 to 0.19 +/- 0.01). This parameter returned to basal values after amino acid infusion (0.20 +/- 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of intravenous glucagon infusion on renal haemodynamics and renal tubular handling of sodium in healthy humans

The effects of a 2-h intravenous infusion of glucagon 5 ng kg-1 min-1 or placebo on glomerular filtration rate (GFR), renal plasma flow (RPF), tubular sodium handling as judged by the lithium clearance method, and plasma concentrations of angiotensin II (AngII), aldosterone (Aldo), and atrial natriuretic factor (ANF) were investigated in two groups of healthy human volunteers, glucagon group (n = 10), and placebo group (n = 10). Glucagon infusion resulted in a maximal increase in plasma concentrations of glucagon of 400%. GFR increased 5.9% (range 1.3-12.4, p < 0.001) through the whole infusion period, whereas RPF only increased transiently during the first hour of infusion 6.5% (range 2.6-15.3, p < 0.05). Whereas filtered load of sodium increased significantly in response to glucagon infusion (p < 0.001), urinary sodium excretion was unchanged. Neither of these variables were affected by placebo. As judged from assessments of tubular sodium handling derived from the renal clearance of lithium, the increased filtered load of sodium resulted in an increase in the output of sodium from the proximal tubules of a similar magnitude, and an increase in absolute reabsorption of sodium in the distal tubules totally counterbalancing this increased input to the distal tubules. These alterations in tubular sodium handling did not involve Ang II, Aldo, or ANF. We conclude that an increase in plasma concentration of glucagon within the physiological range is capable of inducing a small and sustained increase in GFR, whereas RPF increases only transiently.(ABSTRACT TRUNCATED AT 250 WORDS)

Renal reserve filtration capacity in growth hormone deficient subjects

In normal subjects, the glomerular filtration rate (GFR) and effective renal plasma flow (ERPF) acutely increase in response to infusion of amino acids and to low doses of dopamine. It is uncertain whether circulatory growth hormone (GH) is a permissive factor for these stimulatory effects. GFR and ERPF (constant infusion technique using 125I-iothalamate and 131I-hippuran, respectively) were measured before and during the infusion of dopamine and amino acids in 8 GH deficient subjects. The clearance study was repeated during concomitant administration of octreotide to investigate whether this somatostatin analogue would modify the amino acid and dopamine-induced renal haemodynamic changes. Dopamine increased baseline GFR from 89 +/- 3 (mean +/- SEM, n = 8) to 102 +/- 4 ml min-1 1.73 m-2 and ERPF from 352 +/- 19 to 476 +/- 26 ml min-1 1.73 m-2, P less than 0.001 for both. During amino acid infusion GFR and ERPF increased to 108 +/- 3 and 415 +/- 23 ml min-1 1.73 m-2, respectively, P less than 0.001 for both. Octreotide did not significantly decrease baseline and dopamine-stimulated renal haemodynamics but lowered the amino acid-stimulated GFR (98 +/- 4 ml min-1 1.73 m-2, P less than 0.05) and ERPF (381 +/- 18 ml min-1 1.73 m-2, P less than 0.05). Basal plasma glucagon concentrations were not suppressed by octreotide, whereas the amino acid-induced increments in plasma glucagon were partially inhibited. It is concluded that GH is not a necessary factor for the stimulatory effects of amino acids and dopamine on renal haemodynamics.(ABSTRACT TRUNCATED AT 250 WORDS)