BACKGROUND AND PURPOSEIntroducing the calcineurin inhibitors cyclosporin (CsA) and tacrolimus (Tac) has improved the outcome of organ transplants, but complications such as new onset diabetes mellitus after transplantation (NODAT) decrease survival rates. EXPERIMENTAL APPROACHWe sought, in a beta-cell culture model, to elucidate the pathogenic mechanisms behind NODAT and the relative contribution of the calcineurin inhibitors. INS-1E cells were incubated at basal and stimulatory glucose concentrations, while exposed to pharmacologically relevant doses of CsA, Tac and vehicle for 6 or 24 h. RESULTSTac inhibited basal (P < 0.05), but not glucose-stimulated insulin secretion (GSIS) after 6 h of exposure. After 24 h, both agents inhibited basal and GSIS (P < 0.05). Calcineurin phosphatase activity was decreased by both drugs during all conditions. Apoptosis was only seen with CsA treatment, which also induced a slight suppression of calcineurin and insulin mRNA, as well as increased levels of the sterol receptor element binding protein (SREBP)-1c, a transcription factor thought to suppress genes essential for beta-cell function and induce insulin resistance. Expression levels of nuclear factor of activated T-cells (NFAT)-c1, -c2, -c3 and -c4 were not decreased notably by either drug. CONCLUSIONS AND IMPLICATIONSTac had acute inhibitory effects on basal insulin secretion, but prolonged exposure (24 h) to Tac or CsA revealed similar suppression of insulin secretion. These prolonged effects were mirrored by a total inhibition of calcineurin activity in beta-cells. CsA showed greater inhibition of beta-cell survival and transcriptional markers, essential for beta-cell function. AbbreviationsBax, Bcl-2 associated X protein; Bcl-2, B-cell leukaemia/lymphoma 2; CaN, calcineurin phosphatase; GSIS, glucose-stimulated insulin secretion; IRS-2, insulin receptor substrate 2; NFATc, nuclear factor of activated T-cells cytoplasmic; NODAT, new onset diabetes mellitus after transplantation; PDX1, pancreatic and duodenal homebox factor 1; SREBP-1c, sterol receptor element binding protein 1c

The effect of a continuous infusion of human brain natriuretic peptide (BNP) was studied in 48 healthy men. The study was randomized, placebo controlled, and single blind. BNP was given in doses of 1, 2, or 4 pmol ⋅ kg−1 ⋅ min−1for 60 min, and peak values of BNP in plasma were 38, 85, and 199 pmol/l, giving increments in plasma as seen in heart or renal failure. BNP infusion increased the urinary flow rate and the excretion of sodium in a dose-dependent way. The maximal effects were +65 and +156%, respectively. GFR increased and RPF decreased, the latter in a dose-dependent manner. Blood pressure, heart rate, angiotensin II, and aldosterone were all unaffected by infusion of BNP, whereas a direct inhibition of renin secretion was seen. With the use of the lithium clearance technique, we concluded that the tubular site of action is in both the proximal and distal segments, and the major effect on sodium handling is in the distal parts of the nephron.

A new, fast and reliable radioimmunoassay for measurement of brain natriuretic peptide (BNP) in human plasma has been developed and its application is reported in healthy subjects and in patients with congestive heart failure, chronic renal failure, liver cirrhosis and essential hypertension. The antibody was raised in rabbits, the tracer was made by the iodogen method and polyethylene glycol was used for separation of free and bound tracer. BNP was extracted from plasma using Sep-Pak C18 cartridges. The recovery of unlabelled BNP added to plasma was 77.5 +/- 6.2% (mean +/- SD). The detection limit in plasma was 0.55 pmol l-1. No cross-reactivity existed with the natriuretic peptides ANP, CNP or urodilatin. In 124 healthy subjects the mean BNP was 1.8 +/- 1.0 pmol l-1 (SD), range 0.6-5.5. BNP increased slightly with age, was higher in women than men and had no circadian rhythm. In eight patients with congestive heart failure the median BNP level was 30.5 pmol l-1, range 3.9-65.3. In 14 patients with chronic renal failure the median BNP level was 50.5 pmol l-1, range 10.9-219.8 before dialysis, and 38.0 pmol l-1, range 9.4-180.0 immediately following dialysis. In 25 patients with liver cirrhosis the median BNP value was 7.8 pmol l-1, range 1.2-43.1. There was no difference between patients with or without ascites. In 18 medically treated patients with essential hypertension the median BNP level was 5.0 pmol l-1, range 1.2-45.5 pmol l-1.

The effect of a continuous infusion of human brain natriuretic peptide, 2 pmol.min-1.kg-1, during 60 min was studied in nine patients with congestive heart failure and in 10 healthy control subjects. Brain natriuretic peptide increased from 1.6 to 101 pmol/l in control subjects and from 25 to 173 pmol/l in congestive heart failure during infusion. Urinary sodium excretion increased significantly in both congestive heart failure (60%) and control subjects (71%), but the absolute increase was significantly lower in congestive heart failure (27 micromol/min) than in control subjects (190 micromol/min). Urinary flow rate did not change. The lithium clearance technique was used to evaluate the segmental tubular function; the distal fractional reabsorption of sodium decreased significantly less in congestive heart failure (DFRNa: -0.8%) than in control subjects (DFRNa: -3.7%). Baseline values for glomerular filtration rate and renal plasma flow were reduced in congestive heart failure, but brain natriuretic peptide induced no significant changes between congestive heart failure and control subjects. Brain natriuretic peptide induced the same absolute increase in secondary messenger cGMP in plasma and urine in both patients and healthy subjects. It is concluded that the natriuretic response to brain natriuretic peptide infusion was impaired in patients with congestive heart failure compared with healthy subjects, and it is likely that the impaired natriuretic response was caused by a reduced responsiveness in the distal part of the nephron.

WHAT IS ALREADY KNOWN ABOUT THIS SUBJECT• New onset diabetes after transplantation is related to treatment with immunosuppressive medications. Clinical studies have shown that risk of new onset diabetes is greater with tacrolimus compared with ciclosporin. The diabetogenicity of ciclosporin and tacrolimus has been attributed to both beta cell dysfunction and impaired insulin sensitivity. WHAT THIS STUDY ADDS• This is the first trial to investigate beta cell function and insulin sensitivity using gold standard methodology in healthy human volunteers treated with clinically relevant doses of ciclosporin and tacrolimus. We document that both drugs acutely increase insulin sensitivity, while first phase and pulsatile insulin secretion remain unaffected. This study demonstrates that ciclosporin and tacrolimus have similar acute effects on glucose metabolism in healthy humans. AIMThe introduction of calcineurin inhibitors (CNIs) ciclosporin (CsA) and tacrolimus (Tac) has improved the outcome of organ transplants, but complications such as new onset diabetes mellitus after transplantation (NODAT) cause impairment of survival rates. The relative contribution of each CNI to the pathogenesis and development of NODAT remains unclear. We sought to compare the impact of CsA and Tac on glucose metabolism in human subjects. METHODSTen healthy men underwent 5 h infusions of CsA, Tac and saline in a randomized, double-blind, crossover study. During infusion glucose metabolism was investigated using following methods: a hyperinsulinaemic-euglycemic clamp, an intravenous glucose tolerance test (i.v.GTT), glucose-stimulated insulin concentration-time series and indirect calorimetry. RESULTSClamp derived insulin sensitivity was increased by 25% during CsA (P < 0.0001) and 13% during Tac administration (P = 0.047), whereas first phase and pulsatile insulin secretion were unaffected. Coinciding with the CNI induced improved insulin sensitivity, glucose oxidation rates increased, while insulin clearance rates decreased, only non-significantly. Tac singularly lowered hsCRP concentrations, otherwise no changes were observed in circulating glucagon, FFA or adiponectin concentrations. Mean blood concentrations of CNIs were 486.9 Ϯ 23.5 mg l -1 for CsA and 12.8 Ϯ 0.5 mg l -1 for Tac. CONCLUSIONSAcute effects of i.v. CsA, and to a lesser degree Tac infusions, in healthy volunteers include increased insulin sensitivity, without any effect on first phase or pulsatile insulin secretion.