Renal abnormalities in normotensive insulin-dependent diabetic offspring of hypertensive parents

Maternal but not paternal association of ambulatory blood pressure with albumin excretion in young offspring with type 1 diabetes

OBJECTIVE

Familial predisposition to hypertension has been associated with the development of diabetic nephropathy in adults, but there are limited data in adolescents. Our aim was to assess whether parental ambulatory blood pressure (ABP) was associated with ABP and albumin excretion in young offspring with type 1 diabetes.

RESEARCH DESIGN AND METHODS

Twenty-four-hour ABP monitoring was performed in 509 young offspring (mean +/- SD age 15.8 +/- 2.3 years) with type 1 diabetes, 311 fathers, and 444 mothers. Systolic (SBP) and diastolic blood pressure (DBP) measurements during 24 h, daytime, and nighttime were calculated. Three early morning urinary albumin-to-creatinine ratios (ACRs), A1C, and anthropometric parameters were available for the offspring.

RESULTS

All paternal ABP parameters, except for nighttime SBP, were independently related to the offspring's ABP (24-h SBP beta = 0.18, 24-h DBP beta = 0.22, daytime SBP beta = 0.25, daytime DBP beta = 0.23, and nighttime DBP beta = 0.18; all P < 0.01). Maternal 24-h DBP (beta = 0.19, P = 0.004), daytime DBP (beta = 0.09, P = 0.04), and nighttime SBP (beta = 0.24 P = 0.001) were related to the corresponding ABP parameter in the offspring. Significant associations were found between the offspring's logACR and maternal ABP. The association with 24-h DBP (beta = 0.16, P = 0.02), daytime DBP (beta = 0.16 P = 0.02), and nighttime DBP (beta = 0.15 P = 0.03) persisted even after adjustment for the offspring's ABP. Mothers of offspring with microalbuminuria had higher ABP than mothers of offspring without microalbuminuria (all P < 0.05).

CONCLUSIONS

In this cohort, parental ABP significantly influenced offspring blood pressure, therefore confirming familial influences on this trait. In addition, maternal ABP, particularly DBP, was closely related to ACR in the offspring, suggesting a dominant effect of maternal genes or an effect of the intrauterine environment on microalbuminuria risk.

The ocular hemodynamic response to nitric oxide synthase inhibition is unaltered in patients with early type I diabetes

BACKGROUND

An impaired ocular hemodynamic response to systemic nitric oxide synthesis inhibition has been demonstrated in patients with long-standing insulin-dependent diabetes mellitus. It is unclear whether this altered responsiveness is already detectable in early uncomplicated type I diabetes.

METHODS

The effect of the nitric oxide synthase inhibitor N(G)-monomethyl- l-arginine (L-NMMA) was studied in 10 male patients with early type I diabetes under euglycemic conditions and 10 healthy matched control subjects in a single (analyst) blinded cohort study design. Changes in ocular hemodynamics (fundus pulsation amplitude, mean flow velocity in the ophthalmic artery) and in pulse rate and mean blood pressure were measured in response to systemic intravenous doses of 1.5, 3, and 6 mg/kg L-NMMA.

RESULTS

L-NMMA dose-dependently and significantly decreased fundus pulsation amplitude (-21.0% vs -23.3% in diabetics and controls, respectively), mean flow velocity in the ophthalmic artery (-12.3% vs -10.8%) and pulse rate (-15.4% vs -16.6%) and increased mean arterial pressure (+19.5% vs +14.7%). The ocular and systemic hemodynamic effects of L-NMMA were not different between patients with diabetes and controls.

CONCLUSION

The responsiveness of the choroidal vasculature and the ophthalmic artery to L-NMMA is not altered in early type 1 diabetes. An impaired hemodynamic response to nitric oxide synthesis inhibition in diabetes is therefore not caused by a primary defect but rather due to altered vascular responsiveness secondary to long-standing disease.

Renal vascular responses to captopril and to candesartan in patients with type 1 diabetes mellitus

BACKGROUND

Enhanced renal vasodilator responses to angiotensin-converting enzyme (ACE) inhibition in diabetes mellitus despite a normal or low plasma renin activity level have suggested intrarenal activation of the renin-angiotensin system in this disease. There is, however, a continuing debate as to the mediators of the renal hemodynamic response to ACE inhibition-reduced angiotensin II formation or pathways involving kinins, prostaglandins, and nitric oxide.

METHODS

Twelve patients with type 1 diabetes mellitus of 18 +/- 3.2 (SEM) years of duration (7 females and 5 males, ages 17 to 50, 32 +/- 4.0 years) who were free of sustained microalbuminuria and on a high-salt diet were given the ACE inhibitor captopril (25 mg orally) on one day and the AT1 receptor blocker candesartan (16 mg orally) on another day. Renal plasma flow (RPF) and glomerular filtration rate were measured before and for four hours after administration.

RESULTS

Both drugs caused a significant increase in RPF (captopril 574 +/- 26 to 625 +/- 37 mL/min/1.73 m2, P = 0.008; candesartan 577 +/- 26 to 643 +/- 37, P = 0.004). There was a highly significant correlation between the responses to captopril and to candesartan (r = 0.86, P < 0.001). Seven subjects had an RPF response to captopril that was accentuated (90 +/- 13 mL/min/1.73 m2), while five had a response that was normal (-4 +/- 9). There was no significant change in glomerular filtration rate on either drug.

CONCLUSION

The remarkable rise in RPF in response to captopril and candesartan despite high-salt balance suggests the intrarenal activation of the renin-angiotensin system in diabetes that is not reflected in plasma renin levels. The high correlation between the renal hemodynamic response to captopril and to candesartan indicates that reduced angiotensin II formation is the main mechanism of action of the ACE inhibitor.

Metabolic features of newly established congenic diabetes-prone BB.SHR rat strains

The well-known association of hypertension and diabetes mellitus and the lack of suitable animal models to study diabetic hypertension prompted us to transfer 4 chromosomal regions with quantitative trait loci (QTLs) for blood pressure of the spontaneously hypertensive SHR rat onto the genetic background of the diabetes-prone and normotensive BB/OK rat. Four congenic strains developed are named as BB. Sa (Chr.1), BB.Bp2 (Chr.18), BB.1K (Chr.20) and BB.Xs (Chr.X). Because the systolic blood pressure is significantly elevated in all congenics, renal related traits were investigated in serum and urine. Comparing BB/OK and their congenic derivatives, significant differences were found in all serum and in 7 out of 8 urine constituents studied. Most significant differences were found between BB/OK and BB.Bp2 rats. Significant differences were also found between the different congenic strains indicating that each congenic strain has its own phenotype and that each chromosomal region contains most probably further QTLs for some of the traits studied.

Enhanced renal angiotensin II subtype 1 receptor responses in the spontaneously hypertensive rat

Results from renal transplantation experiments demonstrate that a renal defect is responsible for the development of hypertension in the spontaneously hypertensive rat (SHR). In addition, studies with inhibitors of the renin-angiotensin system have shown that angiotensin II (Ang II) is required for the development and maintenance of hypertension in the SHR. These observations prompted us to propose the hypothesis that hypertension in these rats is due to an enhanced renal responsiveness to Ang II. The purpose of the present study was to determine whether an enhanced renal responsiveness to Ang II exists in adult (12- to 14-week-old) SHR relative to Wistar-Kyoto control rats. To prevent hypertension-induced changes in renal function in SHR, we maintained both strains in the normotensive state from 4 weeks of age with long-term captopril treatment (100 mg/kg per day). Intrarenal Ang II infusions induced a significantly greater decrease in renal blood flow and glomerular filtration rate and a significantly greater increase in renal vascular resistance in SHR compared with Wistar-Kyoto rats. DuP 753 (Ang II subtype 1 [AT1] receptor antagonist), but not PD 123177 (Ang II subtype 2 receptor antagonist), blocked the renal responses to Ang II in SHR, suggesting that the enhanced renal responsiveness to Ang II was mediated solely by the AT1 receptor subtype. Unlike renal responses to Ang II, renal responses to periarterial renal nerve stimulation were similar in both strains, suggesting a selective renal hyperresponsiveness to Ang II in the SHR rather than a general hyperresponsiveness toward all vasoconstrictors. From these studies in chronically captopril-treated rats, we conclude that 1) SHR have a genetically determined, enhanced renal responsiveness to Ang II; 2) the enhanced renal responsiveness to Ang II is mediated by the AT1 receptor; and 3) renal responses to periarterial nerve stimulation are not significantly enhanced, suggesting a selective hyperresponsiveness to Ang II in the kidneys of SHR.