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W B Jeffries

Publications and source records attributed to W B Jeffries.

32 records · Page 2Linked to original sources
PubMed1991

Regional distribution of alpha 1-adrenoceptor subtypes in rat kidney.

alpha 1-Adrenoceptors are expressed in high density in the rat kidney. Recent studies have shown that alpha 1-adrenoceptors are heterogeneous and can be subtyped based on their affinity for the antagonists WB 4101 (alpha 1A greater than alpha 1B) and chloroethylclonidine (alpha 1B-selective). We therefore investigated the distribution of alpha 1-adrenoceptor subtypes using [3H]prazosin binding in membranes prepared from cortex, the outer stripe of the outer medulla (OSOM), the inner stripe of the outer medulla (ISOM) and inner medulla dissected from rat kidney. [3H]Prazosin binding was detectable in each region with the following maximum binding site values for [3H]prazosin (femtomoles per milligram of protein): cortex, 186 +/- 20; OSOM, 76 +/- 14; ISOM, 34 +/- 2; and inner medulla, 8 +/- 2. Pretreatment of membranes with chloroethylclonidine (10 microM for 10 min) reduced maximum binding sites to 41 +/- 4% (75 +/- 9 fmol/mg) of control in cortex, 41 +/- 9% of control in OSOM (29 +/- 8 fmol/mg) and 15 +/- 3% of control in ISOM (5 +/- 1 fmol/mg). In competition studies, WB 4101 labeled both high and low affinity sites in cortex (respective pKi values = 10.01 +/- 0.3 and 8.23 +/- 0.1) and OSOM (pKi values = 9.6 + 0.3 and 8.3 +/- 0.5), but only low affinity sites in ISOM (pKi = 8.41 +/- 0.1). The relative prevalence of high:low affinity sites revealed by WB 4101 was 53:47 for cortex, 52:48 for OSOM and virtually all low affinity for ISOM. Prior treatment with chloroethylclonidine greatly reduced the low affinity component of the WB 4101 competition curve in cortex and OSOM. We conclude that: 1) the density of alpha 1-adrenoceptors is highest in the cortex and decreases from cortex to papilla and 2) the alpha 1A and alpha 1B subtypes are approximately equally distributed in the cortex and OSOM, but the alpha 1B subtype predominates in ISOM.

Adrenergic alpha-Antagonists↗
PubMed1991

Characterization of prazosin-sensitive alpha 2 B-adrenoceptors expressed by cultured rat IMCD cells.

alpha 2-Adrenoceptor subtype expression was investigated in cultured rat inner medullary collecting duct (IMCD) cells using radioligand binding studies, Northern blot analysis, and adenosine 3',5'-cyclic monophosphate (cAMP) assays. [3H]rauwolscine bound to a single class of alpha 2-adrenoceptors with high affinity [Kd = 1.7 +/- 0.3 nM, maximum binding (Bmax) = 45.2 +/- 10.8 fmol/mg protein]. alpha 2-Adrenoceptor ligands inhibited [3H]rauwolscine binding with a rank order of potency characteristic of interaction with the alpha 2B-adrenoceptor [inhibitory constant (Ki) values (in nM) rauwolscine (1.95) greater than ARC-239 (8.52) greater than prazosin (237) greater than oxymetazoline (30,000)]. Northern blot analysis was performed using poly(A)+ RNA isolated from 90% confluent rat IMCD cells and probes derived from alpha 2-adrenoceptor DNA sequences from the rat nonglycosylated alpha 2B-adrenoceptor and the human alpha 2A-adrenoceptor. The alpha 2B probe hybridized to a 4.2-kb band under high stringency conditions, but the alpha 2A-adrenoceptor probe did not hybridize to this band. In functional studies, the full alpha 2-adrenoceptor agonists epinephrine and UK-14,304 potently inhibited vasopressin-stimulated cAMP accumulation by 50 to 70% [half-maximal response (EC50) (in nM) epinephrine = 11.2, UK-14,304 = 6.4]. Guanabenz and clonidine were partial agonists, inhibiting cAMP accumulation by 30 to 40% and were less potent than the full agonists [EC50 (in nM) 56.0 guanabenz and 94.5 clonidine]. Epinephrine-induced inhibition of cAMP accumulation was blocked by rauwolscine, prazosin, and ARC-239 but not by the alpha 1-adrenoceptor antagonist corynanthine. We conclude that rat IMCD cells in primary culture express functional alpha 2-adrenoceptors of the alpha 2B-subtype.

Adrenergic alpha-Agonists↗
PubMed1991

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)

Animals↗
PubMed1989

Alpha 2-adrenoceptor regulation of parathyroid hormone function in the isolated perfused kidney.

We investigated physiological interactions between alpha 2-adrenoceptors and parathyroid hormone (PTH) in the isolated buffer-perfused kidney. PTH infusion (10nM) caused a rapid and significant rise in cAMP excretion which diminished despite continued hormone infusion. PTH also caused a delayed phosphaturia which peaked 20-30 minutes following the start of PTH infusion. alpha 2-Adrenoceptor stimulation with epinephrine (28nM) diminished PTH-stimulated cAMP accumulation by 68-71% (p less than 0.05) but had no effect on PTH-induced phosphaturia. None of the experimental interventions affected renal hemodynamics. In additional studies, we used lithium (1mM) as a marker of proximal tubular sodium transport. PTH caused a rapid rise in lithium excretion which was temporally distinct (maximum response in 0-10 minutes) from the phosphaturia. alpha 2-Adrenoceptor stimulation completely blocked the inhibitory effect of PTH on lithium reabsorption. These results suggest that alpha 2-adrenoceptors regulate the stimulatory effect of PTH at proximal tubular adenylate cyclase. However, alpha 2-adrenoceptors play no role in phosphate transport in this segment. alpha 2-Adrenoceptor stimulation reverses PTH-induced lithium excretion, suggesting physiological antagonism in the proximal tubule, most likely involving Na/H exchange.

Animals↗
PubMed1989

Adrenergic signal transduction in the kidney.

During signal transduction, renal adrenoceptors associate with (as in other tissues) specific members of a family of GTP-binding (G) proteins. Renal beta-adrenoceptors activate adenylate cyclase in glomeruli and distal nephrons via an interaction with the stimulatory G protein Gs. alpha 1-Adrenoceptors bind to an as yet uncharacterized G protein and activate phospholipase C to produce the putative second messengers 1,4,5-inositol trisphosphate and diacylglycerol. alpha 1-Adrenoceptors are found in most segments of the nephron where they regulate sodium reabsorption, and metabolic functions such as gluconeogenesis. Renal alpha 2-adrenoceptors which inhibit adenylate cyclase through the inhibitory G protein Gi are located mainly in the proximal convoluted tubule and the collecting ducts. Another population of alpha 2-adrenoceptors has been identified which enhances the sodium-hydrogen exchange across the luminal membrane of proximal tubules. Ongoing research is clarifying the locations and functions of these renal adrenoceptor subtypes.

Adenylyl Cyclases↗
PubMed1988

Enhanced vasopressin (V2-receptor)-induced sodium retention in mineralocorticoid hypertension.

The deoxycorticosterone acetate (DOCA)-Na model of hypertension requires the presence of vasopressin for expression of high blood pressure. In the present study, the effects of vasopressin V2-receptor stimulation were examined in kidneys from rats receiving 1 wk of DOCA-Na or control (olive oil-tap water) treatment. The dose response to vasopressin (10(-10) to 10(-6) M) was tested in microdissected cortical collecting tubule (CCT) segments and adenosine 3',5'-cyclic monophosphate (cAMP) accumulation was significantly increased in segments from DOCA-Na rats vs. controls, confirming our previous study. In other experiments, kidneys from DOCA-Na and control rats were perfused with a modified Krebs-Henseleit buffer (37 degrees C, pH 7.4) and treated with either vehicle or 0.21-2.1 pM 1-desamino-8-D-arginine vasopressin (DDAVP). DDAVP caused significant (P less than 0.05) dose-related reductions in urine excretion (UV) and urinary sodium excretion (UNaV) in both DOCA-Na and control kidneys in the absence of changes in renal hemodynamics. However, DDAVP produced earlier and significantly greater reductions in UV and UNaV in kidneys from DOCA-Na vs. control rats. Percent fractional excretion of sodium was reduced significantly only in the DOCA-Na group (2.1 pM DDAVP). A small degree of antikaluresis was seen with DDAVP in both groups. Thus, DOCA-Na treatment augmented cAMP accumulation in the CCT, accompanied by a significant enhancement of DDAVP-stimulated urinary sodium and water reabsorption at the level of the intact kidney.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1988

Tonic inhibition of renal response to vasopressin by a pertussis toxin substrate.

The putative role of the inhibitory guanine nucleotide binding protein (Gi) in modulating the renal response to vasopressin was investigated using islet activating protein (IAP). IAP treatment in rats in vivo abolished the capacity of alpha 2-adrenoceptors to reverse vasopressin-induced adenosine 3',5'-cyclic monophosphate (cAMP) accumulation in microdissected cortical collecting tubule (CCT) segments. IAP pretreatment also caused a marked upward shift in the dose-response curve of vasopressin (10(-10) to 10(-4) M)-induced cAMP accumulation. Augmentation of the response to vasopressin in rat CCT was dependent on the in vivo dose of IAP and paralleled the loss in alpha 2-adrenoceptor responsiveness. In the isolated perfused kidney the antinatriuretic and antidiuretic effects of the V2-receptor agonist desamino-8-D-arginine vasopressin (DDAVP) (1 pM) were enhanced following IAP pretreatment. alpha 2-Adrenoceptor stimulation (30 nM epinephrine) inhibited the renal effects of DDAVP (1 pM) in kidneys from control but not IAP-pretreated rats. Interestingly, IAP pretreatment alone caused increased urine flow rate and enhanced excretion of sodium and chloride without affecting potassium excretion or renal hemodynamics in vitro. Our results suggest that an IAP substrate, probably Gi, 1) is required for signal transduction by renal alpha 2-adrenoceptors, 2) may tonically modulate the response to vasopressin in the CCT but not of parathyroid hormone in the proximal convoluted tubule, and 3) participates in renal water and electrolyte reabsorption independent of exogenous adenylate cyclase stimulation.

Adenylate Cyclase Toxin↗
PubMed1988

Renal alpha 1-adrenergic receptor response coupling in spontaneously hypertensive rats.

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.

Angiotensin II↗
PubMed1987

Renal alpha 2-adrenoceptors and the adenylate cyclase-cAMP system: biochemical and physiological interactions.

alpha 2-Adrenoceptors were first described pharmacologically ten years ago. Within three years their capacity to inhibit adenylate cyclase had been demonstrated in many tissues. They were demonstrated biochemically in the kidneys in 1981 even before any renal physiological effects of their activation were known. They predominate numerically over alpha 1-adrenoceptors in renal membranes and their density is increased in genetic forms of rat hypertension. alpha 1-Adrenoceptors normally mediate the vasoconstriction and sodium- and water-retaining effects of sympathetic neuronally released norepinephrine. Norepinephrine or epinephrine must be infused to activate alpha 2-adrenoceptors, suggesting that renal alpha 2-adrenoceptors are extrajunctional, whereas alpha 1-adrenoceptors are postjunctional. When alpha 1-adrenoceptors are chronically blocked, renal alpha 2-adrenoceptor density increases and they assume a location at postjunctional sites, the otherwise exclusive domain of alpha 1-adrenoceptors. Results from microdissection studies have established that alpha 2-adrenoceptors are present on most segments of the nephron and that their activation can suppress adenosine 3,'5'-cyclic monophosphate (cAMP) accumulation induced by most renal hormones. However, failure of alpha 2-adrenoceptor activation to suppress cAMP accumulation in some tubular segments induced by certain hormones suggests compartmentalization of adenylate cyclase regulation that is hormone-function specific. In view of the potent inhibitory effects of alpha 2-adrenoceptor stimulation on hormone activated cAMP accumulation in several discrete areas of the nephron, we suggest that alpha 2-adrenoceptors fulfill important regulatory role(s) in renal function. To date, alpha 2-adrenoceptor activation has been shown to reverse vasopressin-induced sodium and water retention, and arachidonic acid- and furosemide-induced cAMP, sodium, and water excretion in the isolated perfused kidney. Thus the effects are qualitatively and quantitatively dependent in these studies on the hormone being infused and are therefore hormone-function specific. Physiological effects of alpha 2-adrenoceptor activation of thyrocalcitonin and on parathyroid hormone-induced effects have not been studied. alpha 2-Adrenoceptor activation can inhibit renin release in some model systems and can activate a sodium-hydrogen antiporter system in proximal tubules. The physiological roles of these actions are unknown.

Adenylyl Cyclases↗
PubMed1987

Prazosin-induced alterations in renal alpha-adrenergic receptor function.

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.

Adrenergic beta-Agonists↗
PubMed1986

Enhanced cAMP response to vasopressin in the CCT of DOCA-Na hypertensive rats.

We characterized altered adenosine 3',5'-cyclic monophosphate (cAMP) regulation in deoxycorticosterone acetate (DOCA)-Na hypertensive rats using endogenous cAMP accumulation in the intact cell system of microdissected renal tubule fragments. Increased cAMP accumulation in response to vasopressin (VP) in cortical collecting tubules (CCT) began on day 5 (67%) after exposure to DOCA-Na and increased by 320% on day 42. Increased blood pressure began after day 7 and polyuria after day 17. The increased response to VP was DOCA dependent and appears to be exaggerated by dietary NaCl. Anatomic and hormone specificity studies were done on days 21-30. These included cAMP responses to prostaglandin E2, parathyroid hormone, thyrocalcitonin, VP, and isoproterenol in the CCT. The cAMP response to VP was measured in the glomerulus, proximal convoluted tubule, thin descending limb of Henle, medullary thick ascending limb of Henle, cortical thick ascending limb of Henle, medullary collecting tubule, and CCT. The supersensitivity occurred only to VP and only in the CCT. Thus this alteration in the VP response is anatomic and hormone specific and does not appear to be an acute effect of DOCA, since it was not present on day 1 and on day 3 of DOCA exposure. DOCA-Na hypertension is VP dependent. A specific exaggerated cAMP response to this hormone in the CCT would be expected to cause increased sodium retention. Whether increased sodium retention at this site contributes to hypertension in the DOCA-Na rat is unknown.

Animals↗
PubMed1985

Withdrawal syndrome follows abrupt cessation of intracerebroventricular infusion of epinephrine in spontaneously hypertensive rats.

Aortic blood pressure and heart rate were measured directly during chronic (5-day) intracerebroventricular infusion of epinephrine in conscious, unrestrained spontaneously hypertensive rats (SHR), and following abrupt cessation of drug infusion. During the infusion period, no statistically significant differences in mean aortic pressures were observed between SHR that received vehicle and those which received epinephrine at 1.25, 2.5, or 5.0 micrograms (base) per hour for 5 days via osmotic minipumps. A significant reduction in heart rate was noted during some, but not all, days of the epinephrine infusion period; the onset of bradycardia appeared to be dose-related. Immediately following abrupt cessation of epinephrine (but not vehicle) infusion, a complex withdrawal syndrome was observed to include: a significant and sustained elevation of aortic blood pressure, tachycardia, increased water consumption, and several distinct behavioral effects. The reaction appeared maximal at about 2 hours, and lasted less than 24 hours.

Animals↗