Down-regulation of alpha 2 adrenoceptors in ventrolateral medulla of spontaneously hypertensive rats.

The binding of [3H]idazoxan [correction of idaxazon] to imidazole sites and [3H]rauwolscine to alpha 2 adrenoceptors of neuronal membranes prepared from cerebral cortex and ventrolateral medulla of 10 week old spontaneously hypertensive (SHR) and normotensive Wistar-Kyoto (WKY) rats was determined. [3H]idazoxan [correction of idaxazon] bound to the membranes of cerebral cortex and ventrolateral medulla at a single high affinity site. The binding of [3H]idazoxan [correction of idaxazon] in ventrolateral medulla and cerebral cortex was found to be similar in SHR and WKY rats. [3H]Rauwolscine bound to the membranes of cerebral cortex and ventrolateral medulla at a single high affinity site. The binding of [3H]rauwolscine in the cerebral cortex was found to be similar in SHR and WKY rats. However, in the ventrolateral medulla [3H]rauwolscine binding was found to be significantly lower in SHR as compared to WKY rats. The decreased binding was due a decrease (32%) in the Bmax value in SHR rats as compared to WKY rats. The Kd values were similar in SHR and WKY rats. It is concluded that imidazole binding sites are not affected while, alpha 2 adrenergic binding sites are decreased in the ventrolateral medulla of SHR rats and may be contributing to the regulation of blood pressure.     

Ontogeny of endothelin and its receptors in rat brain.

The ontogeny of endothelin (ET) system in rats was studied in preterm (18 days of gestation), term (21 days of gestation) and 1 week post term rats. Brains were dissected out and (1) processed for the estimation of endogenous ET-1 by RIA and (2) membranes were prepared for radioreceptor binding. Receptor characteristics, affinity (Kd) and density (Bmax) were determined using [125I] ET-1 and [125I] SRT 6b (which is structurally similar to ET) and cold ET-1 or SRT 6b as displacer. ET levels were found to be 25.66 +/- 3.18 pg/g protein in preterm, 47.37 +/- 5.31 pg/g protein in term and 48.30 +/- 1.90 pg/g protein in post term rats. ET levels were significantly lower in preterm as compared to term and post term rats. Preterm, term and post term rats showed single high affinity binding site for both [125I] ET-1 and [125I] SRT 6b. The Kd values for [125I] ET-1 and [125I] SRT 6b binding were similar in preterm, term and post term rats. The Bmax values of both [125I] ET-1 and [125I] SRT 6b binding were found to be similar in preterm and term rats while they were significantly higher in post term rats. In adult (4 month old) rats the Kd values were similar to neonatal rats while the Bmax values were significantly lower than the post term neonatal rats. It is concluded that ET and its receptors are developmentally regulated and there is a possibility that endogenous ET is involved in the regulation of ET receptor density.     

Characteristics of central binding sites for [3H] DAMGO in spontaneously hypertensive rats

The binding of [3H] DAMGO, a highly selective ligand for mu-opiate receptors, to membranes of discrete brain regions and spinal cord of 10 week old spontaneously hypertensive (SHR) and normotensive Wistar-Kyoto (WKY) rats was determined. The brain regions examined were hypothalamus, amygdala, hippocampus, corpus striatum, pons and medulla, midbrain and cortex. [3H] DAMGO bound to membranes of brain regions and spinal cord at a single high affinity site. The receptor density (Bmax value) and apparent dissociation constant (Kd value) of [3H] DAMGO to bind to membranes of hippocampus, corpus striatum, pons and medulla, cortex and spinal cord of WKY and SHR rats did not differ. The Bmax value of [3H] DAMGO in membranes of hypothalamus and midbrain of SHR rats was significantly higher than in WKY rats but the Kd values in the two strains did not differ. On the other hand, the Bmax value of [3H] DAMGO in membranes of amygdala of SHR rats was lower than that of WKY rats but the Kd values in the two strains were similar. It is concluded that SHR rats have higher density of mu-opiate receptors in hypothalamus and midbrain but lower density in amygdala in comparison with WKY rats, and that such differences in the distribution of mu-opiate receptors may be related to the elevated blood pressure in SHR rats.     

Proliferation of thyrotropin releasing hormone receptors in specific brain regions during the development of hypertension in spontaneously hypertensive rats

The binding of [3H] [3-MeHis2] thyrotropin releasing hormone [( 3H]MeTRH) to brain membranes prepared from 8 week old spontaneously hypertensive (SHR) and normotensive Wistar-Kyoto (WKY) rats was determined. [3H]MeTRH bound specifically to rat brain membranes at a single high affinity site. The density (Bmax value) of [3H]MeTRH binding sites was significantly greater (28%) in SHR rats compared to WKY rats. The apparent dissociation constants (Kd values) for the binding of [3H]MeTRH in SHR and WKY rats did not differ. Binding in the various brain regions revealed that the density of [3H]MeTRH was highest in the hypothalamus followed in decreasing order by pons + medulla, midbrain, cortex and striatum. The binding of [3H]MeTRH was approximately 25% greater in cortex, hypothalamus and striatum of SHR rats in comparison to WKY rats. The binding in pons + medulla, midbrain and pituitary of SHR and WKY rats did not differ. To assess the significance of increased binding sites for [3H]MeTRH in some brain regions of SHR rats, the binding studies were carried out during normotensive and hypertensive stages of postnatal age in the two strains. In 3 and 4 week old SHR rats there was neither an increase in blood pressure nor any increase in [3H]MeTRH binding in the hypothalamus and striatum as compared to age matched WKY rats. With the development of elevated blood pressure at 6 weeks, an increase in [3H]MeTRH binding in the hypothalamus and striatum of SHR rats in comparison to the tissues from WKY rats was observed. The results provide, for the first time, evidence for a parallel increase in the density of brain TRH receptors with elevation of blood pressure, and suggest that brain TRH receptors may play an important role in the pathophysiology of hypertension.     

Opiate antagonist binding sites in discrete brain regions of spontaneously hypertensive and normotensive Wistar-Kyoto rats

The binding of 3H-naltrexone, an opiate receptor antagonist, to membranes of discrete brain regions and spinal cord of 10 week old spontaneously hypertensive (SHR) and normotensive Wistar-Kyoto (WKY) rats was determined. The brain regions examined were hypothalamus, amygdala, hippocampus, corpus striatum, pons and medulla, midbrain and cortex. 3H-Naltrexone bound to membranes of brain regions and spinal cord at a single high affinity site with an apparent dissociation constant value of 3 nM. The highest density of 3H-naltrexone binding sites were in hippocampus and lowest in the cerebral cortex. The receptor density (Bmax value) and apparent dissociation constant (Kd value) values of 3H-naltrexone to bind to opiate receptors on the membranes of amygdala, hippocampus, corpus striatum, pons and medulla, midbrain, cortex and spinal cord of WKY and SHR rats did not differ. The Bmax value of 3H-naltrexone binding to membranes of hypothalamus of SHR rats was 518% higher than WKY rats but the Kd values in the two strains did not differ. It is concluded that SHR rats have higher density of opiate receptors labeled with 3H-naltrexone in the hypothalamus only, in comparison with WKY rats, and that such a difference in the density of opiate receptors may be related to the elevated blood pressure in SHR rats.     

Atrial natriuretic peptide and angiotensin II binding sites in cerebral capillaries of spontaneously hypertensive rats

1. We carried out investigations on specific atrial natriuretic peptide (ANP) and angiotensin II (ANG) binding sites in capillaries isolated from the cerebral cortex of spontaneously hypertensive rats (SHR), an animal model of human essential hypertension, and also from Wistar Kyoto rats (WKY). 2. In an equilibrium binding study done in the presence of increasing concentrations of the radiolabeled ligands, the binding of 125I-rat alpha-ANP (1-28) [ANF-(99-126)] (125I-rANP) and 125I-ANG (5-L-isoleucine) (125I-ANG) to the cerebral capillaries was single and of a high affinity. 3. The maximum binding capacity (Bmax) and dissociation constant (Kd) in the 125I-rANP binding of 20-week-old, hypertensive SHR was significantly lower than in age-matched, normotensive WKY. Conversely, a significant increase in the Bmax of 125I-ANG binding of adult SHR was observed, with a significant decrease in the Kd. 4. There was no differences in the Bmax of 125I-rANP and 125I-ANG binding between 4-week-old, prehypertensive SHR and age-matched WKY. However, there was a significant decrease in the Kd of 125I-rANP binding of SHR. 5. As a dramatic change in the binding kinetics of 125I-rANP and 125I-ANG was noted in the cerebral capillaries of adult sustained-hypertensive SHR, the possibility that ANP and ANG play a role in the etiology of dysfunction of the blood-brain barrier complicated with hypertension, by interacting with specific receptors, would have to be considered.     

Upregulation of endothelin-1 binding in tissues of salt-loaded stroke-prone spontaneously hypertensive rats

Upon maintained on a 1% NaCl drinking solution beginning at 7 weeks of age, the stroke-prone spontaneously hypertensive rat (SHRsp) developed severe hypertension and stroke; most died by 16 weeks. The mechanism by which these diseases evolve remains unclear. Endothelin-1 (ET-1) is a potent, peptidic vasoconstrictor and is implicated in the pathogenesis of various cardiovascular, renal, and central nervous system diseases. The purpose of the present study was to compare the binding of [125I]ET-1 to the brain, heart, kidney, liver, and spleen membrane preparations of 16-week-old SHRsp and age-matched normotensive Wistar-Kyoto rats (WKY). The KD values for [125I]ET-1 binding to the corresponding tissues of the two strains were not significantly different, except in the brain (SHRsp: 17 +/- 1 pM; WKY: 24 +/- 1 pM). In contrast, the Bmax values measured in the brain, heart, kidney, and liver of SHRsp were 1.5- to 2.1-fold greater than those of their WKY counterparts. Competition of [125I]ET-1 binding to the membrane preparations by the specific ETA receptor antagonist BQ-123 or the specific ETB receptor agonist sarafotoxin S6c revealed a similar proportion of ETA and ETB receptor subtypes in the corresponding tissues of the two rat strains. These results indicate that ET-1 binding is upregulated in SHRsp and suggest that ET-1 may play a pathophysiological role in this animal model of genetic hypertension.     

Differential changes in atrial natriuretic peptide and vasopressin receptor bindings in kidney of spontaneously hypertensive rat

To elucidate the role of atrial natriuretic peptide (ANP) and vasopressin (VP) in a hypertensive state, ANP and VP receptor bindings in spontaneously hypertensive rat (SHR) kidney were analyzed using the radiolabeled receptor assay (RRA) technique. Systolic blood pressure of SHR aged 12 weeks was statistically higher than that of age-matched Wistar Kyoto (WKY) rats. Maximum binding capacity (Bmax) of [125I]-ANP binding to the SHR kidney membrane preparations was statistically lower than that of WKY rats, but dissociation constant (Kd) was not significantly different. On the other hand, Bmax of [3H]-VP binding to the SHR kidney membrane preparations was statistically higher than that of WKY rats, but Kd were similar. Since the physiological action of ANP is natriuresis and VP is the most important antidiuretic hormone in mammalia, these opposite changes of ANP and VP receptor bindings in SHR kidney suggested that these peptides may play an important role in the pathophysiology of the hypertensive state, although it has not been confirmed as yet.     

Cocaine-induced changes in 3H-naloxone binding in brain membranes isolated from spontaneously hypertensive and Wistar-Kyoto rats

Effects of sub-acute cocaine treatment on 3H-naloxone binding to 6 brain regions were examined in spontaneously hypertensive (SHR) and Wistar-Kyoto (WKY) rats. Cocaine hydrochloride (3 mg/kg, i.v.) was given by bolus injection daily for five days. Rats were decapitated 24 hr following the final injection and crude membrane fractions prepared from the cortex (CT), hippocampus (HI), striatum (ST), hypothalamus (HY), midbrain (MB) and medulla/pons (MD). Binding of 3H-naloxone was consistent with a single site model in CT, HI, HY, MB and MD from vehicle-treated SHR and WKY. Cocaine treatment of SHR significantly decreased the maximal binding capacity (Bmax) of 3H-naloxone in the HI, ST and HY and the binding affinity was increased in HI. In contrast, a significant increase in Bmax was noted in CT and HI membranes isolated from cocaine-treated WKY. The binding affinity of 3H-naloxone to MB membranes of WKY was significantly decreased by cocaine treatment. The binding characteristics of 3H-naloxone in MD membranes were not different following cocaine treatment or between strains. Scatchard analysis indicated biphasic binding of 3H-naloxone binding to ST membranes from both SHR and WKY. Our results indicate that cocaine produces complex and differential changes in opiate receptors and, presumably, opioid peptide neuronal function in SHR and WKY.     

Repeated Idazoxan Increases Brain Imidazoline Receptors in Normotensive (WKY) but Not in Hypertensive (SHR) Rats

The specific binding of [3H]idazoxan in the presence of 10(-6) M (-)-adrenaline was used to evaluate the density of imidazoline receptors in the brain of spontaneously hypertensive (SHR) rats and sex- and age-matched normotensive Wistar-Kyoto (WKY) rats. In SHR rats the density of imidazoline receptors (cerebral cortex, hypothalamus, and medulla oblongata) was not different from that in normotensive (WKY) rats. However, repeated treatment with idazoxan consistently increased (23-80%) the density of imidazoline receptors in the various brain regions of WKY rats but not in SHR rats. In normotensive Sprague-Dawley rats, repeated treatment with the imidazoline drugs idazoxan and cirazoline also increased (33-37%) the density of imidazoline receptors in the cerebral cortex. The lack of regulation by idazoxan of the density of imidazoline receptors in the brain of SHR rats might reflect the existence of a relevant abnormality of these receptors in this genetic model of hypertension.     

Decreased angiotensin II binding affinity and binding capacity in the anterior pituitary gland of adult spontaneously hypertensive rats

Angiotensin II (ANG) binding sites were quantified in single pituitary glands from 4-week-old and 14-week-old male spontaneously hypertensive rats (SHR) and age-matched male normotensive Wistar-Kyoto (WKY) control rats after incubation with 125I-[Sar1]-ANG, autoradiography with computerized densitometry, and comparison to 125I-standards. The maximum binding capacity (Bmax) decreased while the dissociation constant (Kd) for ANG increased in 14-week-old SHR when compared to age-matched WKY control rats (Bmax: 265 +/- 9 and 224 +/- 4 fmol/mg protein; Kd: 0.79 +/- 0.04 and 1.14 +/- 0.08 10(-9) M in WKY and SHR, respectively). Conversely, no difference between rat strains was found in 4-week-old animals. Our results suggest that pituitary ANG binding sites may play a role in the pathophysiology of established genetic hypertension.     

A reversible radioligand specific for the ETB receptor: [125I]Tyr13-Suc-[Glu9,Ala11,15]-endothelin-1(8- 21), [125I]IRL 1620.

Suc-[Glu9,Ala11,15]-endothelin(ET)-1(8-21), IRL 1620, is a linear ET-analog specific for the ET-isopeptide-nonselective ETB receptor. The radio-iodinated analog, [125I]IRL 1620, showed a single class of saturable binding to the ETB receptors in porcine lung membranes with a Kd of 18 pM and a Bmax of 930 fmol/mg protein, which are almost comparable to the values obtained with [125I]ET-3 (6 pM and 900 fmol/mg protein). In competitive binding assays with [125I]IRL 1620, unlabeled ET-1, ET-3, IRL 1620 and [monoiodo-Tyr13]-IRL 1620 showed almost identical displacement curves with Ki of 8 to 16 pM. However, [125I]IRL 1620 was dissociated from the binding sites by addition of an excess amount (100 nM) of any of these unlabeled peptides, each with the same t1/2 of 100 min. This was in marked contrast to [125I]ET-3 which was hardly dissociated from the binding sites.     

Binding sites for atrial natriuretic factor (ANF) in kidneys and adrenal glands of spontaneously hypertensive (SHR) rats

Binding sites for atrial natriuretic factor (ANF) were studied in kidneys and adrenal glands of 17 week old male spontaneously hypertensive (SHR) and Wistar-Kyoto (WKY) normotensive rats by quantitative autoradiography using 125I-ANF-28. In kidney, 125I-ANF-28 binding sites were found in high concentrations in glomeruli and in much lower concentrations in the renal papilla. In adrenal gland, 125I-ANF-28 binding sites were highly localized to the zona glomerulosa and were of moderate density in the inner cortical regions. ANF binding sites did not occur in the adrenal medulla. The maximum binding capacity (Bmax) of 125I-ANF-28 was reduced by 50% in the kidney glomeruli of SHRs compared to WKY controls. In contrast, the affinity constant (Ka) for 125I-ANF-28 was elevated by 100% in kidney glomeruli of SHRs. There were no significant strain differences in values for Bmax or Ka for 125I-ANF-28 binding in the adrenal zona glomerulosa. These findings suggest that the natriuretic and diuretic actions of ANF within kidney glomeruli may be compromised in adult SHR rats and these alterations may contribute to the development and maintenance of hypertension in rats of this strain.     

Kinetic analyses demonstrate that the equilibrium assumption does not apply to [125I]endothelin-1 binding data.

The kinetics of [125I]Endothelin-1 ([125I]ET-1) binding were studied using membranes from rat heart, rat lung, rat brain, and porcine vascular smooth muscle at 37 degrees C in 0.05M Tris-HCl buffer (pH = 7.4). The dissociation half-life (t1/2, diss.) for bound [125I]ET-1 was in excess of 30 hours for each tissue studied. Equilibrium-time requirements for proper Scatchard analysis of [125I]ET-1 were also far in excess of 30 hours for each tissue. These data suggest that determination of dissociation constants, Kd, and receptor concentrations, Bmax, by conventional Scatchard analysis is not feasible with [125I]ET-1. Kinetic analyses may provide a more accurate means for determining [125I-ET-1] binding characteristics including Kd and Bmax.     

Myocardial meta-[125l]iodobenzylguanidine uptake in awake genetically hypertensive rats at different ages: an autoradiographic study.

The purpose of this work was to evaluate changes in myocardial meta-[125I]iodobenzylguanidine ([125I]MIBG) uptake and distribution with age in awake spontaneously hypertensive rats (SHR) with respect to Wistar-Kyoto (WKY) rats. Rats were randomly divided into two groups, one for measuring myocardial [125I]MIBG uptake and distribution 4 h after its injection and the second for evaluating myocardial catecholamine concentrations. Mean arterial blood pressure, cardiac hypertrophy index (heart/body weight ratio), and heart rate were significantly higher with increasing age in SHR compared with matched WKY rats. Myocardial catecholamine concentrations and turnover did not differ between the two strains and were significantly decreased with increasing age. Myocardial [125I]MIBG uptake determined by gamma counting was similar in WKY rats and SHR and did not vary significantly with age when expressed as uptake density. However, in both strains of rats, [125I]MIBG uptake determined by autoradiography was significantly greater at the base of the heart than at the apex and midventricular levels, and the uptake values of young rats were significantly higher than those of older rats. In 21-week-old WKY rats and SHR, the highest [125I]MIBG uptake values were found in the right ventricle. Thus, quantitative autoradiography allowed detection of significant changes in myocardial [125I]MIBG uptake and showed its heterogeneous distribution in the rat heart.     

Reduction in brain immunoreactive corticotropin-releasing factor (CRF) in spontaneously hypertensive rats

The brain CRF concentration of spontaneously hypertensive rats (SHR) and normotensive Wistar Kyoto rats (WKY) was examined by rat CRF radioimmunoassay. Anti-CRF serum was developed by immunizing rabbits with synthetic rat CRF. Synthetic rat CRF was also used as tracer and standard. The displacement of 125I-rat CRF by serially diluted extracts of male Wistar rats hypothalamus, thalamus, midbrain, pons, medulla oblongata, cerebral cortex, cerebellum and neurointermediate lobe was parallel to the displacement of synthetic rat CRF. In both WKY and SHR the highest levels of CRF immunoreactivity were shown by the hypothalamus and neuro-intermediate lobe, and considerable CRF immunoreactivity was also detected in other brain regions. The CRF immunoreactivity in the hypothalamus, neurointermediate lobe, midbrain, medulla oblongata and cerebral cortex was significantly reduced in SHR and it may suggest that CRF abnormality may be implicated in the reported abnormalities in the pituitary-adrenal axis, autonomic response and behavior of SHR.     

Vascular reactivity, tissue levels, and binding sites for endothelin: a comparison in the spontaneously hypertensive and Wistar-Kyoto rats.

The role of endothelin (ET-1) in mediating the development of blood pressure was investigated in the spontaneously hypertensive (SHR) rat using the Wistar-Kyoto (WKY) rat as the normotensive control. The following were characterized in both rat strains: age-dependent changes in mean arterial blood pressure (MAP), tissue (blood, lung, heart, and kidney) levels of immunoreactive ET-1 like related peptides (ET-1RP), aortic ring responses to ET-1, and specific high-affinity tissue (lung, atrium, ventricle, aorta, and kidney) binding sites for 125I-labelled ET-1. Commencing at age 10 weeks through to 12 weeks, SHR rats but not WKY rats developed a significant increase in MAP (from 152 +/- 7 to 189 +/- 3 mmHg) (1 mmHg = 133.32 Pa). However, in both WKY and SHR rats immunoreactive levels of ET-1RP increased (100 and 80%, respectively) throughout the same measurement period. The potency of ET-1 to contract aortic rings from SHR rats was slightly but not significantly greater than that for aortic rings from WKY rats, although aortic rings from SHR rats contracted in the presence of 0.5 nM ET-1, while those from WKY rats did not. The levels of immunoreactive ET-1RP were significantly reduced (32%) in the kidney and unchanged in the heart and lung of SHR rats compared with WKY rats. Specific 125I-labelled ET-1 binding sites displayed an increase and a significant decrease (24%) of density in the atrium and ventricle, respectively, a significant increase (31%) of affinity in the lung, and were unchanged in the kidney and aorta of SHR rats compared with WKY rats following the development of hypertension. The lack of a correlation between circulating levels of immunoreactive ET-1RP and the development of hypertension coupled with a lack of significant differences in vascular reactivity suggest that ET-1 is not the sole mediator of hypertension in this animal model. However, the tissue-specific changes in immunoreactive ET-1RP and 125I-labelled ET-1 binding sites suggest that ET-1 may be a partial mediator of hypertension and is subject to compensatory changes in response to the increased total peripheral resistance in SHR rats.     

Comparison of [125I]Iodolysergic Acid Diethylamide Binding in Human Frontal Cortex and Platelet Tissue

The human platelet contains a functional 5-hydroxytryptamine (5-HT) receptor that appears to resemble the 5-HT2 subtype. In this study, we have used the iodinated derivative [125I]iodolysergic acid diethylamide ([125I]iodoLSD) in an attempt to label 5-HT receptors in human platelet and frontal cortex membranes under identical assay conditions to compare the sites labelled in these two tissues. In human frontal cortex, [125I]iodoLSD labelled a single high-affinity site (KD = 0.35 +/- 0.02 nM). Displacement of specific [125I]iodoLSD binding indicated a typical 5-HT2 receptor inhibition profile, which demonstrated a significant linear correlation (r = 0.97, p less than 0.001, n = 17) with that observed using [3H]ketanserin. However, [125I]iodoLSD (Bmax = 136 +/- 7 fmol/mg of protein) labelled significantly fewer sites than [3H]ketanserin (Bmax = 258 +/- 19 fmol/mg of protein) (p less than 0.001, n = 6). In human platelet membranes, [125I]iodoLSD labelled a single site with affinity (KD = 0.37 +/- 0.03 nM) similar to that in frontal cortex. The inhibition profile in the platelet showed significant correlation with that in frontal cortex (r = 0.96, p less than 0.001, n = 16). We conclude that the site labelled by [125I]iodoLSD in human platelet membranes is biochemically similar to that in frontal cortex and most closely resembles the 5-HT2 receptor subtype, although the discrepancy in binding capacities of [125I]iodoLSD and [3H]ketanserin raises a question about the absolute nature of this receptor.     

Changes in renal, platelet and cardiac nitrobenzylthioinosine binding in spontaneously hypertensive rats

In an attempt to investigate the role of nucleoside transporter function in the hypertensive state, we have compared the binding of [3H]nitrobenzylthioinosine ([3H]NBMPR), a nucleoside transporter probe, in membranes prepared from platelet, renal, pulmonary, cardiac and brain tissues of spontaneously hypertensive rats (SHR) to those of age-matched Wistar-Kyoto (WKY) controls. At 4 weeks of age, [( 3H]NBMPR) binding sites (Bmax) increased in the kidney of SHR but decreased in platelets, whereas no changes were found in the heart, lung or brain. At 18 weeks of age, [3H]NBMPR binding sites (Bmax) remained increased in the kidney and decreased in platelets with no changes in the other tissues. The only change in apparent binding affinity (KD) was an increase in the heart of SHR at 4 weeks. Age-dependent decreases were also observed in the heart and platelets of both SHR and WKY at 18 weeks. The results indicate that the changes in binding characteristics may be due to a combination of the pharmacodynamic differences between the strains, age, as well as to the pathogenesis of hypertension. Consequently, it cannot be concluded that the altered binding characteristics are the result of the elevated blood pressure.     

Quantitative in vitro autoradiographic characterization of [125I]angiotensin III binding sites in rat adrenal gland

A single class of high-affinity binding sites for [125I]angiotensin III and [125I]angiotensin II were found in rat adrenal medulla and zona glomerulosa by quantitative autoradiography. In the medulla, Kd were 1.46 and 1.16 nM, and Bmax 1700 and 1700 fmol/mg protein, for [125I]angiotensin II and [125I]angiotensin III, respectively. In the zona glomerulosa, Kd were 0.86 and 0.90 nM, and Bmax 790 and 560 fmol/mg protein, for [125I]angiotensin II and [125I]angiotensin III, respectively. Unlabeled angiotensin III and angiotensin II displaced [125I]angiotensin III with similar potency in both adrenal zona glomerulosa and medulla. Our findings suggest that angiotensin III and angiotensin II might share the same binding sites in adrenal gland and support the hypothesis of a role for angiotensin III in the adrenal medulla and zona glomerulosa.