Albumin permeability in isolated glomeruli in incipient experimental diabetes mellitus

AIMS/HYPOTHESIS

The pre-clinical phase of diabetic nephropathy is characterised by increased glomerular filtration rate and episodes of microalbuminuria. The cause of the microalbuminuria has been variably ascribed to alterations of the size or charge selective barriers of the glomerulus or both or as a consequence of the haemodynamic changes. Our aim was to investigate very early albumin permeability alterations in isolated glomeruli which were not subject to perfusion pressure.

METHODS

Isolated glomeruli were studied from 120 male Wistar rats, divided into three groups: streptozotocin-treated, streptozotocin-treated with insulin pellet implants, and controls. From each group ten animals were killed at 7, 14, 28, and 56 days after induction. Study variables included blood pressure, proteinuria, iopamidol clearance, albumin permeability and glomerular area. Subsequently, albumin permeability, proteinuria, and iopamidol clearance were determined in an additional group of 40 diabetic animals studied at 24, 72, 96, and 120 h after induction.

RESULTS

Albumin permeability increased steadily from induction in streptozotocin-treated animals, reaching a plateau at approximately 120 h. Glomerular filtration rate was shown to increase significantly at approximately 7 days and proteinuria correlated with it. Glomerular hypertrophy was observed both in streptozotocin-treated animals and in streptozotocin-treated rats with insulin pellet implants. Strict blood glucose control delayed the appearance of the permeability defect in isolated glomeruli and inhibited the increase in glomerular filtration in intact animals. It did not prevent glomerular hypertrophy.

CONCLUSION/INTERPRETATION

An albumin permeability defect exists early in isolated non-perfused glomeruli from streptozotocin-treated rats and seems to be independent of glomerular filtration rate alterations.

Control of glomerular hyperfiltration and renal hypertrophy by an angiotensin converting enzyme inhibitor prevents the progression of renal damage in hypertensive diabetic rats

OBJECTIVE

Glomerular hyperfiltration and renal hypertrophy are both considered important in the progression of diabetic nephropathy. The aim of this study was to compare the effects of an equivalent reduction in blood pressure produced by the angiotensin-converting enzyme (ACE) inhibitor spirapril (SPI) and an antihypertensive triple drug combination of hydralazine, reserpine and hydrochlorothiazide (HRH) on kidney function, proteinuria and renal structure in hypertensive diabetic rats.

DESIGN AND METHODS

Four groups of animals were evaluated in short-term and long-term studies. In both studies one group served as a non-diabetic hypertensive control (H). The other three groups were rendered diabetic and were allocated to one of the following groups: the first diabetic group received no specific therapy (HD), the second diabetic group was treated with SPI (HD-SPI) and the third diabetic group was treated with HRH (HD-HRH). In each of the two studies the systolic blood pressure (SBP), 24 h urinary total protein, glomerular filtration rate (GFR), glomerular area, proximal tubular area and glomerular sclerosis were evaluated.

RESULTS

The blood pressure reduction was equal in rats receiving either SPI or HRH. The GFR, proteinuria, glomerular area and tubular area were significantly increased in the HD group, both in the short-term and the long-term study. In the HD-SPI group the diabetic hyperfiltration and renal hypertrophy responses were prevented. In the HD-HRH group the GFR and proteinuria were slightly reduced in the later phases of diabetes, while the glomerular area and tubular area were not affected. Semiquantitative analysis of renal lesions showed that SPI was more effective than HRH in the prevention of the development of glomerulosclerosis.

CONCLUSIONS

The results of this study suggest that the control of early adaptive hyperfiltration and renal hypertrophy by SPI may be relevant in the prevention of glomerulosclerosis.

[Role of Doppler color ultrasonography and of flowmetric analysis in the diagnosis and follow-up of Grave's disease]

Hyperthyroidism in Graves' disease is caused by the presence of circulating autoantibodies to the THS receptors on the thyroid cells. Thyroid-suppression therapy prevents hormone production directly, without affecting the pathogenetic process. We performed color Doppler US of the thyroid gland and pulsed Doppler analysis of thyroid artery flow in 21 patients with Graves' disease before and during medical treatment. US results were compared with those of a control group of 40 healthy subjects and correlated with the values of thyroid hormones, TSH, and thyroid microsomal and thyroglobulin antibodies. The thyroid gland was hypovascularized in the control group. Pulsed Doppler examination of the thyroid arteries exhibited peak systolic velocity of PSV 20 +/- 4 cm/s, diastolic velocity of 8 +/- 1 cm/s, and resistive index of 0.60 +/- 0.04. The thyroid gland of Graves' disease patients was hypervascularized. Pulsed Doppler examination of the thyroid arteries exhibited peak systolic velocity (PSV = 51 +/- 12 cm/s), end diastolic velocity (VD = 15 +/- 4 cm/s), and resistive index (RI = 0.71 +/- 0.04) significantly higher than in normal subjects (p < 0.001). Circulating thyroid hormones and flow parameters normalized after 6-8 months of medical therapy (PSV = 20 +/- 6 cm/s, VD = 9 +/- 3 cm/s, RI = 0.58 +/- 0.07). Conversely, the color Doppler patterns normalized only in a patient with normal TSH and antibodies. Sampling of the thyroid arteries proved more repeatable than sampling of parenchymal vessels.

Effects of central alpha 2-adrenergic agonists on systemic haemodynamics and on baroreceptor reflex sensitivity in spontaneously hypertensive rats

Clonidine, an imidazoline derivative, is a widely used antihypertensive agent which acts by stimulating the alpha 2-adrenergic receptors at the central nervous system. Clonidine also seems to exert beneficial effects on baroreceptor reflex sensitivity which is usually altered by arterial systemic hypertension and arteriosclerosis. Aim of the study was to compare acute and chronic hypotensive response and the effects on baroreflex sensitivity of a newly synthesized central alpha 2-adrenergic agonist, guanfacine, with those induced by clonidine. The effects of acute and chronic treatment were studied by evaluating blood pressure modifications through intraarterial or sphygmomanometric detection. Baroreflex sensitivity was studied before and after acute treatment with the two drugs. Our results show that guanfacine and clonidine may induce comparable effects, both reducing arterial blood pressure levels and heart rate with an order of potency for guanfacine 10 times lower than clonidine. After chronic treatment the effect of guanfacine on blood pressure was more pronounced than that observed after clonidine administration. Both drugs may enhance baroreflex sensitivity, with a more evident effect of guanfacine than clonidine in response to a sudden decrease of blood pressure. This suggests that guanfacine could afford a more effective cardiovascular adaptation during acute hypotension (i.e. during orthostatic hypotension), particularly in the elderly hypertensive patients.