William A. Pettinger

Reversible renal insufficiency due to angiotensin converting enzyme inhibitors in hypertensive nephrosclerosis

OBJECTIVE To review the incidence of reversible renal insufficiency in patients with hypertensive nephrosclerosis undergoing antihypertensive therapy. DESIGN Retrospective analysis of 73 patients in a long-term blood pressure control study that compared the effects of an angiotensin converting enzyme (ACE) inhibitor plus conventional antihypertensive agents compared with placebo plus antihypertensive agents. SETTING Hospital-based outpatient treatment center. INTERVENTIONS Patients were divided into group 1, which received enalapril plus conventional antihypertensives, and group 2, which received placebo plus conventional antihypertensives. MEASUREMENTS Blood pressure and serum creatinine levels were measured, and imaging studies of the main renal arteries were done. MAIN RESULTS In group 1, eight of 42 patients (19%, 95% CI, 9% to 34%) developed reversible renal insufficiency, defined as an unexpected increase in serum creatinine of 88 mumol/L or higher. Six episodes of reversible renal insufficiency occurred during July and August when temperatures were 32.2 degrees C to 37.8 degrees C (90 degrees F to 100 degrees F). Renal artery stenosis was excluded by renal arteriogram or ultrasonic duplex scanning. All eight group-1 patients had a significant decrease in mean arterial pressure below their baseline level during reversible renal insufficiency (mean change, -28 +/- 10 mm Hg, P less than 0.001). The increase in the serum creatinine level was inversely correlated with the decrease in the mean arterial pressure (r = -0.68, P less than 0.01). Reversible renal insufficiency was successfully managed by withdrawing or reducing enalapril as well as other antihypertensive agents. Subsequently, enalapril was tolerated by seven of the eight patients without recurrence of renal insufficiency. In contrast, none of 31 (CI, 0% to 11%) patients in group 2 developed reversible renal insufficiency despite the fact that both the incidence of decreases in mean arterial pressure in 6 of 31 patients (19%) and the magnitude of the decreases in mean arterial pressure (mean change, -33 +/- 16 mm Hg) were similar to those observed in group 1. CONCLUSIONS Reversible renal insufficiency in hypertensive nephrosclerosis associated with ACE inhibitor therapy correlates with relative hypotension, is not dependent on renal artery stenosis, and can usually be managed by dose reduction.

Enhanced release of endothelium-derived relaxing factor in mineralocorticoid hypertension

Ring segments of superior mesenteric arteries studied in vitro were used to determine the role of the vascular endothelium in regulating vascular contractile and relaxant sensitivity in deoxycorticosterone acetate (DOCA)-salt hypertension. Wistar rats were given DOCA (20 mg/kg s.c. twice per week) and 1% NaCl drinking water for 5 weeks. In ring segments containing endothelium, there was a decrease in contractile sensitivity to arginine vasopressin, no change in contractile sensitivity to norepinephrine and KCl, and no change in relaxant sensitivity to acetylcholine or isoproterenol in arteries from hypertensive rats compared with normotensive controls. Removal of the vascular endothelium by rubbing had no effect on the contractile response to arginine vasopressin and KCl or the relaxant response to isoproterenol in control arteries. In arteries without endothelium, DOCA-salt hypertension caused a threefold increase in contractile sensitivity for arginine vasopressin, norepinephrine, and KCl; a 50% reduction in maximal relaxation to isoproterenol; and a threefold decrease in relaxant sensitivity to sodium nitroprusside. Indomethacin (10 microM) had no effect on contraction or relaxation. However, N-monomethyl L-arginine unmasked altered contractile sensitivity to norepinephrine in arteries from DOCA-salt hypertensive rats. These data show that the endothelium compensates for increased contractile and reduced relaxant responses of vascular muscle in DOCA-salt hypertension by increasing the release of endothelium-derived relaxing factor. These data suggest that altered vascular responsiveness is masked by the endothelium, thus preventing these alterations from contributing to increased peripheral resistance during the development of DOCA-salt hypertension.

Sex influence on renal alpha 2-adrenergic receptor density in the spontaneously hypertensive rat.

Male spontaneously hypertensive rats (SHR) have higher blood pressure than females. We compared renal alpha 2-adrenergic receptor density among intact SHR and Wistar-Kyoto (WKY) rats of both sexes, male and female SHR gonadectomized at 4 weeks of age, and gonadectomized SHR supplemented with testosterone. Additional groups of SHR were treated with enalapril (30 mg/kg per day), an angiotensin-converting enzyme inhibitor, from 5 to 14 weeks of age. Renal alpha 2-adrenergic receptor density was higher in males than females in both SHR and WKY rats. Female SHR and WKY rats had identical low renal alpha 2-adrenergic receptor density. Castration of male SHR reduced the male-female differences in blood pressure and renal alpha 2-adrenergic receptor density by 60%. Treatment with testosterone raised blood pressure and renal alpha 2-adrenergic receptor density to the intact male levels in both gonadectomized males and females. Treatment with enalapril decreased blood pressure but not renal alpha 2-adrenergic receptor density in both male and female SHR. We conclude that (1) both renal alpha 2-adrenergic receptor density and blood pressure are influenced by sex in SHR and WKY, (2) renal alpha 2-adrenergic receptor density like blood pressure is regulated by androgens, and (3) increased renal alpha 2-adrenergic receptor density is not a consequence of high blood pressure in male SHR.

The frequency of α2-adrenoceptor restriction fragment length polymorphisms in normotensive and hypertensive humans

OBJECTIVE To examine the frequency of distribution of allelic polymorphisms of the alpha 2-adrenoceptor gene in normotensive and hypertensive humans. DESIGN The frequency of alpha 2-adrenoceptor genotypes was compared in the two groups using the chi 2-test. SETTING The Midwest Hypertension Research Center Outpatient Clinic of Creighton University School of Medicine. STUDY PARTICIPANTS History was taken from and physical examination performed on each of the 60 hypertensive and 47 normotensive adults. METHODS DNA was extracted from leukocytes from each participants. Twenty restriction endonucleases were used and one restriction fragment length polymorphism (RFLP) was found using a 950-bp restriction fragment from the coding region of the human platelet alpha 2-adrenoceptor gene (ADRA2R) and Bsu36I restriction endonuclease. This probe and Bsu36I restriction endonuclease, in addition to another restriction endonuclease (Dra I), were then used in the study. RESULTS Three genotype patterns were found. Homozygotes for the Bsu36I RFLP have either a unique 12-kb or a unique 5.8-kb band. Heterozygotes have both bands. The frequency of this alpha 2-adrenoceptor RFLP was calculated. In hypertensives the frequencies of the 12- and 5.8-kb alleles were 0.52 and 0.48, compared with 0.45 and 0.55, respectively, in normotensive, a difference that was not statistically significant. CONCLUSIONS The frequency of the Bsu36I RFLP involving an alpha 2-adrenoceptor gene in hypertensives did not differ significantly from that in normotensives. A genetic linkage study is now under way to test for an association of the Bsu36I RFLP of the alpha 2-adrenoceptor gene with essential hypertension in families.

Cosegregation of the renin gene with an increase in mean arterial blood pressure in the F2 rats of SHR-WKY cross

Using the restriction endonuclease, BgI I, Samani et al. found a restriction fragment length polymorphism (RFLP) for the renin gene in spontaneously hypertensive rats (SHR) and its normotensive control Wistar-Kyoto (WKY) rats. This RFLP was confirmed in our laboratory in SHR and WKY rats using a rat renin cDNA probe. The correlation of blood pressure and the renin RFLP was examined in 106 F2 rats produced from F1 rats, the offspring of a cross between SHR males and WKY females. Systolic blood pressure was measured by the tail cuff method at 12 weeks of age. Mean arterial blood pressure of anesthetized rats was measured by cannulation of the femoral artery prior to sacrifice. The frequency of renin genotype showed a typical 1:2:1 Mendelian ratio in F2 rats of SHR and WKY cross. The mean arterial blood pressure of F2 rats homozygous with the SHR allele was significantly higher than F2 rats that were heterozygous or homozygous for the WKY allele. No significant difference in systolic blood pressure was observed in these F2 rats. Thus, the renin gene RFLP cosegregates with an increase in mean arterial blood pressure in the F2 rats of SHR and WKY cross.

Vasopressin response in collecting ducts of rats resistant to mineralocorticoid hypertension.

In previous studies we found that vasopressin stimulation of both cyclic AMP (cAMP) formation in cortical collecting tubules (CCT) and sodium reabsorption in isolated perfused kidneys was markedly exaggerated in rats with mineralocorticoid hypertension. In the present study, we tested the response (cAMP accumulation) of cortical and outer medullary collecting tubules (OMCT) to vasopressin in two rat models that are resistant to deoxycorticosterone acetate (DOCA)-induced hypertension, the Wistar-Furth strain and NaCl-deficient rats. The blood pressure of normal outbred Wistar rats rose to hypertensive levels (systolic pressure more than 165 mm Hg) during a 5-week treatment with DOCA (10 mg/week) and 1% saline to drink. Significant hypertrophy of the heart and kidneys was also observed. Vasopressin (10(-8) M)-induced cAMP formation was enhanced 3.4-fold in the CCT (OMCT unchanged) of hypertensive rats compared with normotensive controls. Significant hypertrophy (as indexed by tubule diameter) of the CCT but not the OMCT was also observed in DOCA-salt hypertensive rats. Restriction of dietary NaCl (0.13% in chow, tap water to drink) completely prevented DOCA-induced hypertension, organ and CCT hypertrophy, and enhancement of vasopressin-stimulated cAMP formation in the CCT. In Wistar-Furth rats, DOCA-salt treatment did not alter blood pressure or cause significant organ hypertrophy. However, DOCA-salt treatment enhanced vasopressin-stimulated cAMP formation by 4.1-fold in CCT of Wistar-Furth rats, with significant tubular hypertrophy in the CCT but not the OMCT. We conclude that DOCA-induced hypertension and changes in CCT function are dependent on excess dietary NaCl.(ABSTRACT TRUNCATED AT 250 WORDS)

Northern blot and ribonuclease protection study of α2-adrenoceptor subtypes in cultured cell lines

Northern blot and ribonuclease protection assay were used to identify alpha 2-adrenoceptor subtypes in human colonic adenocarcinoma (HT29), neuroblastoma x glioma rat-mouse hybrid NG108-15 (NG108) and opossum kidney (OK) cell lines. Radioligand binding studies showed that the alpha 2-adrenoceptor expressed in HT29, NG108 and OK cells represent the pharmacological alpha 2A, alpha 2B and alpha 2C subtypes respectively. In our Northern blot analysis, hybridization of poly(A)+ RNA from HT29, NG108 and OK cells with human kidney alpha 2-adrenoceptor cDNA probe (alpha 2-C4) identified a single band of 4.4, 4.2 and 4.4 kb respectively in each cell line. Hybridization with a human platelet alpha 2-adrenoceptor genomic probe (alpha 2-C10) resulted in two bands for HT29 cells with the size of 4.4 kb and 3.9 kb. No bands were seen for HT29, NG108 and OK cells when hybridized with a third alpha 2-adrenoceptor human genomic DNA probe which is localized in chromosome 2 (alpha 2-C2). For the HT29 cells, the 3.9 kb band was seen only when using the alpha 2-C10 probe. Thus, this band probably represents alpha 2-C10 mRNA. To further characterize the alpha 2-adrenoceptor mRNA expressed in HT29, NG108 and OK cells, the sensitive ribonuclease protection assay was performed. A single band about 900 bp was protected when the poly(A)+ RNA from NG108 and OK cells was hybridized with an alpha 2-C4 RNA probe and digested with RNAases. Hybridization of mRNA from HT29 cells with alpha 2-C10 RNA probe and digestion with RNAases protected a 500 bp fragment.(ABSTRACT TRUNCATED AT 250 WORDS)

The distorted α2-adrenoceptor genotype distribution in F2 populations of dahl salt sensitive and resistant rats cross

To examine the role of the alpha 2-adrenoceptor gene in the development of genetic hypertensive rats, we tested Dahl salt sensitive (S) and resistant rats (R) for the presence of a restriction fragment length polymorphism (RFLP) in that gene. An RFLP was found between the S and R rats with a human kidney cDNA alpha 2-adrenoceptor probe (alpha 2-C4) and Msp I restriction endonuclease. The alpha 2-C4 probe detected two alleles, S and R, of 3.0 and 2.8 kb in size. The two strains of rats were each homozygous for their corresponding allele. The inheritance of the alleles was investigated by crossbreeding S and R rats and subsequent brother/sister mating of F1 rats. Two hundred and fifteen F2 rats were produced by breeding 14 pairs of F1 rats. An atypical distribution of alpha 2-adrenoceptor genotypes was observed. We found a reduced number of the SS genotype in both males and females of the F2 generation. To investigate the mechanism of this distorted alpha 2-adrenoceptor genotype distribution in the F2 rats of S and R cross, we backcrossed the F1 rats to their S and R parents. The litter size and gender distribution were counted for each breeding colony. Analysis by chi-square test showed that there was no sex difference among the backcrosses. Also, there was no significant decrease in litter size. This excludes the possibilities of fetal demise of S homozygotes and intrauterine selection. Therefore the deficiency of SS genotype may be due to gene recombination or may not be due to the alpha 2-adrenoceptor gene itself, but to the effect of other genes closely linked to the alpha 2-adrenoceptor.

Reticulo-Endothelial Blockade and Capillary Resistance Response to Cortisone and STH.

Summary It is shown that blocking the RE system with India ink diminishes or abolishes capillary resistance response to cortisone and STH. That large doses of cortisone can overcome the block suggests that the RE system functions by increasing sensitivity of tissues to cortisone.