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Androgens regulate blood pressure and renal alpha 2-adrenergic receptors in a parallel fashion in the spontaneously hypertensive rat (SHR). The present studies investigated whether this regulation of renal alpha 2B-adrenergic receptors occurs at the mRNA level. Male and female SHR were gonadectomized at 4 weeks of age. The gonadectomized rats were implanted with or without testosterone propionate. Sham-gonadectomized rats served as controls. Total kidney RNA was purified, and alpha 2B-adrenergic receptor mRNA was quantified with a reverse transcriptase-polymerase chain reaction (RT-PCR) assay. The assay uses a mimic RNA added at known concentrations to the sample RNA. The mimic was constructed from the target sequence in the alpha 2B-adrenergic receptor mRNA plus a 20-bp insertion of a random nucleotide sequence. The amount of alpha 2B-adrenergic receptor mRNA present in each sample was obtained by determining the equivalence point between the amount of RT-PCR product formed in the target band versus the mimic band, which were resolved by gel electrophoresis. Intact males had more than two times as much alpha 2B-adrenergic receptor mRNA as intact females. Castration of males reduced the male-female difference by more than 60%. Ovariectomy slightly increased the alpha 2B-adrenergic receptor mRNA level compared with that of intact females. Treatment with testosterone elevated alpha 2B-adrenergic receptor mRNA levels of gonadectomized males and females to the level of intact males. The alpha 2B-adrenergic receptor mRNA levels correlated remarkably well with renal alpha 2-adrenergic receptor density. We conclude that testosterone regulates renal alpha 2B-adrenergic receptor gene expression at the mRNA level in the SHR.

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.

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.

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)

Chronic (3-day) treatment with prazosin causes an increase in renal alpha 2-adrenergic receptor density and the relocation of renal tubular alpha 2-adrenergic receptors from extrajunctional to postjunctional sites. We investigated whether chronic prazosin treatment (2 mg/kg, i.p.) caused a functional alteration of other renal alpha 2-adrenergic receptors, using the isolated perfused rat kidney. Prazosin significantly reduced blood pressure and increased heart rate during the 3-day treatment. Renal nerve stimulation (2-8 Hz, 10 V, 1 msec) caused a frequency-dependent increase in renovascular resistance, which was potently blocked by prazosin in vitro in both control and prazosin-treated rat kidneys. The vasoconstrictor response to the alpha 2-adrenergic receptor-selective agonist BHT 933 (3-300 microM) was significantly higher in kidneys from prazosin-treated rats. Yohimbine (3-300 nM) potentiated the response to renal nerve stimulation in both treatment groups. The increase in vascular resistance following renal nerve stimulation was lower in kidneys from prazosin-treated rats, but the response to the alpha 1-adrenergic receptor agonist methoxamine (0.3-1 microM) was unchanged. Further studies revealed that renal nerve stimulation-evoked norepinephrine release from prazosin-treated rat kidneys was significantly lower than release from untreated controls. This response could be normalized to control levels by a combination of cocaine (10 microM) and yohimbine (100 nM). Thus, chronic prazosin treatment caused enhanced alpha 2-adrenergic receptor-mediated vasoconstriction and facilitated renal prejunctional inhibitory mechanisms. We conclude that with chronic alpha 1 adrenergic receptor blockade there is increased alpha 2-adrenergic receptor function in at least two and possibly three sites in the kidney; these include postjunctional tubular, prejunctional vascular, and possibly extra-junctional vascular sites.

Renal sympathetic antidiuretic, antinatriuretic, and vasoconstrictor responses are mediated by alpha 1-adrenergic receptors in the normal rat. Since the renal nerve has been implicated in the pathogenesis of rat genetic hypertension, we investigated renal alpha 1-adrenergic receptor coupling to phosphoinositide turnover in spontaneously hypertensive rats (SHR) and Wistar-Kyoto rats (WKY). In cortical slices from adult (13-week-old) SHR and WKY, stimulation with norepinephrine (10(-7)-10(-3) M) caused a concentration-dependent increase in accumulation of [3H]inositol phosphates. However, dose-response curves for SHR characteristically displayed a depression of the maximum response as compared with those for WKY. Baseline accumulation of [3H]inositol phosphates was not different between strains (39.4 +/- 2.2 cpm/mg tissue/hr for WKY and 34.4 +/- 2.1 cpm/mg tissue/hr for SHR slices; n = 5 rats/group, determined in triplicate). Antagonist competition studies revealed that norepinephrine-stimulated (10(-4) M) [3H]inositol phosphate accumulation was mediated by alpha 1-adrenergic receptors (IC50) for prazosin: 65 +/- 11 nM for SHR and 64 +/- 5 nM for WKY). The reduction in norepinephrine-stimulated [3H]inositol phosphate accumulation in SHR cortex was not the result of the hypertension, since it was also present in cortical slices from young (4-week-old) SHR in which the blood pressure was not yet significantly different from that in WKY and since [3H]inositol phosphate accumulation was unchanged from control values in rats made hypertensive by treatment with deoxycorticosterone acetate. Scatchard analysis of [3H]prazosin binding in renal cortical membranes of young and adult SHR and WKY revealed no significant differences in alpha 1-adrenergic receptor density or affinity between strains at either age. Our results suggest that renal alpha 1-adrenergic receptor coupling to phospholipase C is less efficient in SHR than in WKY. This impaired response is not the result of hypertension or changes in receptor density; this defect may play a role in increased renal sympathetic nerve activity and in the development or maintenance of hypertension in SHR.

Renal alpha 1 and alpha 2-adrenergic receptors were quantified in Dahl salt-sensitive and salt-resistant rats, in Okamoto-Aoki spontaneously hypertensive rats (SHR), in Wistar Kyoto "normotensive" (WKY), and in Charles River rats made hypertensive by the Grollman ligature technique and by DOC-NaCl administration after unilateral nephrectomy. The effect of high dietary NaCl on renal alpha receptors was studied in Dahl, SHR, and WKY rats. Renal alpha 1 and alpha 2 receptor densities were higher (p less than 0.05) in SHR and in Dahl salt-sensitive rats than in their normotensive controls. High dietary sodium increased renal alpha 2 receptors and blood pressure in SHR, WKY and Dahl salt-sensitive, but not in resistant Dahl rats. A study of time relationships revealed that the increase in renal alpha 2 receptors preceded most of the blood pressure elevation due to high dietary sodium. Renal alpha-adrenergic receptor densities of surgical (Grollman) and endocrine (DOC-NaCl) forms of rat hypertension were not different from normotensive controls. Thus, renal alpha 2 receptor density and increase thereof by dietary sodium may be: 1) a biochemical marker for genetic forms of hypertension in the rat, and 2) closely linked to the basic mechanism of high blood pressure.

Vasodilating antihypertensive drugs have in common the capacity to activate the peripheral sympathetic nervous system through the carotid sinus baroreceptor reflex mechanism, thereby increasing heart rate, renin release, and sodium and water retention. They differ in their tendencies to augment cardiac output and to relieve or precipitate cardiac failure and arrhythmias. Vasodilating antihypertensive drugs can produce an array of side effects and toxicity including headache, facial changes, hair growth, varying degrees of sodium and water retention, and rarely systemic lupus erythematosus and allergic reactions. Detailed knowledge of these effects is a prerequisite to skillful individualization of antihypertensive regimens.

Activation of renal alpha-adrenergic receptors induces vasoconstriction, proximal tubular reabsorption of sodium, and inhibition of renal release. Excesses of these effects are present in varying degrees in animal models of, and in patients with, "essential" hypertension. Since essential hypertension is genetically determined, we sought abnormalities of renal alpha-adrenergic receptors in the Okamoto-Aoki strain of spontaneously hypertensive rats (sr-SHR) and their stroke-prone variant (sp-SHR). Total alpha-adrenergic receptor concentrations were determined by Scatchard analysis of [3H]dihydroergocryptine binding to a renal membrane fraction and were found to be increased (p less than 0.02) in male sr-SHR at 4, 16, and 32 weeks of age and in female sr-SHR at 16 weeks of age as compared to age- and sex-matched Wistar-Kyoto controls. They were also increased in 9-week-old sp-SHR renal membranes (p less than 0.005). Further studies revealed that this increase in renal alpha-adrenergic receptors was due entirely to an increase in alpha 2-receptors as measured by [3H]yohimbine binding rather than to an increase in alpha 1-receptors as quantitated by [3H]prazosin binding. No difference in binding affinities of the various radioligands could be demonstrated between any of the hypertensive and normotensive groups of rats. Plasma norepinephrine levels were elevated (p less than 0.01) in the 4-, 9- and 16-week-old SHR, but not in the 32-week-old hypertensive rats. Thus, high renal alpha 2-adrenergic receptor number is coupled with a significant increase in plasma norepinephrine concentrations during the development of hypertension in SHR. By mediating an enhanced receptor-coupled response, such as increased proximal tubular sodium reabsorption, this abnormality of renal alpha-adrenergic receptors may contribute to some or all of the pathophysiologic derangements leading to hypertension in SHR.

Renal nerve stimulation-induced antinatriuresis normally is mediated through post-synaptic alpha 1-adrenergic receptors; however, prazosin-induced alpha 1-adrenergic receptor blockade is associated clinically with sodium retention and not natriuresis. To study whether alpha 2-adrenergic receptors mediate renal nerve stimulation-induced antinatriuresis after chronic prazosin treatment, Sprague-Dawley rats were pretreated for 3 days with prazosin (3 mg/kg/day i.p. plus 0.15 mg/ml drinking water) or vehicle (untreated). In isolated perfused (Krebs-Henseleit; Ficoll, 3.5 g/dl, + albumin, 1.0 g/dl at 36 degrees C) kidneys from untreated rats, subpressor levels of renal nerve stimulation (approximately 1 Hz, 10 V, 1 msec) decreased (p less than 0.05) sodium (from 4.50 +/- 0.42 to 1.71 +/- .23 muEq/min) and urinary excretion rate (from 87.2 +/- 4.1 to 57.9 +/- 3.9 microliter/min). Adding prazosin (30 nM) to the perfusate completely (approximately 90%) reversed this effect (p less than 0.05), while alpha 2-adrenergic receptor blockade with yohimbine (300 nM) had no effect. In perfused kidneys from prazosin-treated rats, renal nerve stimulation decreased (p less than 0.05) sodium (from 3.24 +/- .40 to 1.32 +/- .27 muEq/min) and urinary excretion rate (from 78.7 +/- 5.0 to 54.1 +/- 5.3 microliter/min). However, adding prazosin (100 nM) to the perfusate produced only a slight, insignificant reversal of these effects; prazosin plus yohimbine were required to completely reverse the effects. These results suggest that renal nerve stimulation-induced sodium reabsorption was activated by alpha 1-adrenergic receptors in untreated rats and in part by alpha 2-adrenergic receptors in rats pretreated for 3 days with prazosin.(ABSTRACT TRUNCATED AT 250 WORDS)

Seventy-nine hypertensive nephrosclerosis patients entered a prospective randomized single-blind study to 1) establish the pattern of decay of renal function in this population and the variability therein and 2) to determine if strict diastolic blood pressure (DBP) control (less than or equal to 80 mm Hg) is more effective than conventional levels (90-95 mm Hg) in conserving renal function. Because of unexpected significant improvement in renal function in patients from both groups, which changed the perspectives on the course of this disease as described herein, this report is being published before completion of the trial. The selection criteria were 1) serum creatinine concentration of 1.6-7.0 mg/dl, 2) glomerular filtration rate of less than 70 ml/min/1.73 m2, and 3) absence of diseases (other than hypertension) known to destroy renal function. Renal function was assessed by glomerular filtration rate [( 125I]iothalamate clearance) and serum creatinine concentration. Before randomization, DBP was aggressively treated to reduce it to less than 80 mm Hg. Twenty-two subjects (14 in the strict DBP control group and eight in the conventional DBP control group) have been enrolled in the study for 36 months. In contrast to results from previous studies in humans and rats, renal function improved in both patient groups. Thus, irrevocable progression of renal damage after onset of renal failure from high blood pressure does not necessarily occur, and in fact, long-term improvement of renal function resulted from the effects of the study itself.(ABSTRACT TRUNCATED AT 250 WORDS)