Direct evidence of alpha-adrenoceptor binding in rat and human adrenal glands

In order to determine whether or not alpha-adrenoceptors are present in adrenal glands, radioligand receptor binding assay was performed in both Sprague-Dawley (SD) rat and human adrenal gland membranes. Radioligand binding assay using 3H-prazosin as an alpha 1-adrenoceptor ligand and 3H-yohimbine as an alpha 2-adrenoceptor ligand, clearly demonstrated alpha 1 and alpha 2 receptors present in both rat and human adrenal gland membranes. Maximal binding capacity (Bmax) and dissociation constant (Kd) of 3H-prazosin binding to the rat adrenal gland were 12.5 fmol/mg protein, and 0.11 nM, respectively. Those for the membrane preparations from adrenal cortex and medulla of the normal human were 16.3 fmol/mg protein, 0.34 nM and 16.3 fmol/mg protein, 0.27 nM, respectively. And those of the human pheochromocytoma were 25.6 fmol/mg protein, 0.15 nM, respectively. On the other hand, Bmax and Kd of 3H-yohimbine binding in the rat adrenal gland to were 22.9 fmol/mg protein, and 4.28 nM, respectively. Those for the membrane preparations from adrenal cortex and medulla of the normal human were 40.4 fmol/mg protein, 5.15 nM and 12.2 fmol/mg protein, 5.39 nM, respectively. And those of the human pheochromocytoma were 35.8 fmol/mg protein, and 1.08 nM, respectively. Bmax (35.8 fmol/mg protein) of 3H-yohimbine binding in the pheochromocytoma was significantly (p less than 0.01) greater than that (12.2 fmol/mg protein) in the human normal adrenal medulla, while Kd (1.08 nM) of this binding in the human pheochromocytoma was significantly (p less than 0.01) lower than that (5.39 nM) in the human normal adrenal medulla. Our data suggest that the alpha 2 receptor had greater affinity and binding site density to its agonist in the human pheochromocytoma than in the human normal adrenal medulla.     

Binding and functional properties of doxazosin in the human prostate adenoma and canine brain

The binding and functional properties of doxazosin were characterized in the canine brain and human prostate. 3H-Doxazosin binding sites were characterized in canine brain and human prostate homogenates using saturation experiments. The binding of 3H-doxazosin in the canine brain was consistently saturable and of high affinity. The mean equilibrium dissociation constant (Kd) and density (Bmax) of 3H-doxazosin binding sites in the canine brain were 0.19 nM and 2.17 fmol/mg wet wt, respectively. The binding of 3H-doxazosin in human prostate homogenates was not consistently linear owing to a relatively high proportion of nonspecific doxazosin binding sites. The mean Kd and Bmax of 3H-doxazosin binding sites in the prostate determined from the saturation experiments yielding linear Scatchard plots were 0.2 nM and 0.51 fmol/mg wet wt. The pharmacology of doxazosin binding sites was further characterized in the canine brain using competitive binding experiments. The rank order of IC50corr values for norepinephrine, clonidine, yohimbine, terazosin, and prazosin indicated that doxazosin binds selectively to alpha 1 and alpha 2 adrenergic binding sites. The relative affinity of unlabeled doxazosin for alpha 1 and alpha 2 binding sites in the human prostate was determined by displacing 125I-Heat or 3H-rauwolscine with varying concentrations of unlabeled doxazosin. The affinity of doxazosin for alpha 1 binding sites in the prostate adenoma was approximately 100-fold greater than its affinity for alpha 2 binding sites. The potency of doxazosin for inhibiting phenylephrine-induced contractions in the prostate indicated that prostate smooth muscle contraction is mediated by alpha 1 adrenoceptors.     

Characteristics of rat kidney dopamine receptors and the effects of renal denervation and dopamine infusion on these receptors

The characteristics of dopamine receptors, as well as the effects of denervation and dopamine infusion on dopamine receptors were studied using the radiolabeled receptor assay of [3H]-spiperone on rat kidney membrane preparations. The rat renal cortex was found to have a single class of [3H]-spiperone binding sites with a dissociation constant (Kd) of 13.5 +/- 2.2 nM. However, neither sulpiride nor serotonin strongly interacted with [3H]-spiperone binding, suggesting that DA1 receptors were predominant in the rat renal cortex. Denervation was performed by surgically stripping the nerves from the renal artery and coating them with 10% phenol. Chronic denervation had no significant effect on the affinity or maximum binding capacity of the renal dopamine receptors, although diuresis and the disappearance of catecholamine fluorophores in the denervated rats were observed. Chronic infusion of dopamine was performed using an osmotic minipump, resulting in a decrease in the number of rat kidney dopamine receptors. These results suggest that the dopamine receptor subtype in the renal cortex was mainly DA1, and that the major source of dopamine which affected the dopamine receptors in the rat kidney was not the nerve ending, but rather the circulation.     

Renal alpha-1-adrenoreceptors in rats with obstructive jaundice

Alpha 1-Adrenoreceptor affinity constants (KD) and receptor numbers (Bmax) were determined in the kidneys of 3-day-old bile-duct-ligated (BDL) jaundiced rats using 3H-prazosin. The results were compared to 3-day-old pair-fed and nonpair-fed sham-operated rats as well as nonoperated rats as controls. Abdominal surgery (sham and BDL) resulted in a tendency towards a decrease in KD in all three groups of rats compared to nonoperated controls. The Bmax was also increased in the sham-operated groups compared to the nonoperated controls. In contrast, the tendency for a rise in the Bmax in the BDL group was significantly smaller than the rise seen in the two sham-operated groups. In summary, obstructive jaundice suppresses the normal renal alpha 1-adrenoreceptor response to abdominal surgery in the rat.     

Identification and characterization of parathyroid hormone receptors in rat renal cortical plasma membranes using radioligand binding

Parathyroid hormone (PTH) receptors have been described in renal tissue from several species, but not in the rat. In this study, radioligand binding techniques were used to identify and characterize PTH receptors in rat kidney cortical membranes. The sulfur-free PTH analog [Nle8,18Tyr34]bovine PTH-(1-34)amide was iodinated using the iodogen method. This ligand was suitable for use in identifying PTH receptors in canine renal membranes, but not rat renal membranes. Synthetic, unsubstituted rat PTH-(1-34) was iodinated using the milder, lactoperoxidase technique and was purified by HPLC on a C8 column. [125I]rat PTH-(1-34) bound rapidly to both rat and dog renal membranes. At 22 degrees C reaction reached steady state within 20 minutes, and this level was maintained for at least 3 h. Specific binding was routinely greater than 90% for rat kidney and greater than 95% for dog kidney. Similar results were obtained at 4 degrees C with a longer time required to attain steady state (approximately 45 minutes). Binding was reversible as demonstrated by dissociation of bound ligand after either infinite dilution or displacement with excess nonradioactive PTH. Binding was saturable and of high affinity (rat kidney: Bmax = 2.3 pmol/mg protein, Kd = 3.1 nM, dog kidney: Bmax = 2.1 pmol/mg protein, Kd = 3.7 nM). Rat renal cortical adenylate cyclase activity was stimulated by rat PTH in a dose-dependent manner with an EC50 of 4 nM, a value in good agreement with the binding data. This study demonstrates the feasibility of identifying and characterizing parathyroid hormone receptors in rat renal cortical plasma membranes using radioligand binding techniques.     

Epidermal growth factor receptors in parathyroid tumors

Hyperparathyroidism is caused by parathyroid adenomas, hyperplastic parathyroid glands, or rarely parathyroid carcinoma. Membrane receptors to epidermal growth factor (EGF), a growth-stimulating polypeptide, have been shown in other endocrine tissues such as thyroid, breast, and ovary, but not in parathyroid glands. Therefore we studied abnormal parathyroid glands from fourteen patients for the presence of EGF receptors. The binding of radioiodine-labeled EGF to the crude membrane fractions was studied using competitive inhibition with unlabeled EGF. In ten patients with solitary parathyroid adenomas, seven adenomas had no EGF binding, three had low affinity EGF binding with dissociation constants (Kd) of 28 to 148 nM and maximal specific binding (Bmax) of 285 to 1944 fmole/mg protein. In two patients with multiple adenomas, a high affinity EGF binding with Kd of 0.28 to 2.8 nM and Bmax of 6.7 to 43 fmole/mg protein was found. In one patient with hyperplastic parathyroid glands secondary to renal failure, a high affinity EGF binding with Kd of 1.7 nM and Bmax of 18 fmole/mg protein was found. In one patient with persistent hyperparathyroidism following a successful renal transplant (tertiary hyperparathyroidism), a low affinity EGF binding with Kd of 25 nM and Bmax of 219 fmole/mg protein was found. The binding of EGF did not correlate with the preoperative serum calcium or PTH levels. Thus, hyperplastic parathyroid glands (either primary or secondary) have high affinity EGF receptors whereas solitary parathyroid adenomas do not.     

3H]bunazosin, a novel selective radioligand of alpha 1 adrenoceptors in human prostates.

The binding properties of a new radioligand, [3H]bunazosin, were studied in membranes of human prostates with benign prostatic hypertrophy (BPH). Specific binding of [3H]bunazosin was saturable, reversible, and of high affinity (Kd = 0.55 +/- 0.04 nM). The density of [3H]bunazosin binding sites (Bmax) was 676 +/- 33 fmol/mg. protein. [3H]Bunazosin rapidly associated with its binding sites in membranes of human prostates and reached steady state by 20 min. at 25C. The rate constants for association and dissociation of [3H]bunazosin binding were calculated to be 0.11 +/- 0.01/nM/min. and 0.05 +/- 0.02/min. (n = 4), respectively. Seven alpha 1 adrenoceptor antagonists competed with [3H]bunazosin for the binding sites in the rank order: R-(-)-YM-12617 greater than prazosin greater than SGB-1534 greater than bunazosin greater than terazosin greater than naftopidil greater than urapidil. In parallel studies with [3H]bunazosin, the Kd and Bmax values for [3H]prazosin binding in human prostates were slightly lower. There was a similarity in the potency and rank order of seven alpha 1, adrenoceptor antagonists for the inhibition of [3H] bunazosin and [3H]prazosin binding in human prostates. The new [3H]bunazosin binding assay in human prostates is remarkable for its low degree of nonspecific binding as compared to [3H]prazosin, especially at high ligand concentrations. Thus, [3H]bunazosin may become a useful radioligand for the further analysis of the alph 1 adrenoceptor binding sites in human prostates.     

Alpha 2 adrenergic receptors in hyperplastic human prostate: identification and characterization using [3H] rauwolscine

[3H]Rauwolscine ([3H]Ra), a selective ligand for the alpha 2 adrenergic receptor, was used to identify and characterize alpha 2 adrenergic receptors in prostate glands of men with benign prostatic hyperplasia. Specific binding of [3H]Ra to prostatic tissue homogenates was rapid and readily reversible by addition of excess unlabelled phentolamine. Scatchard analysis of saturation experiments demonstrates a single, saturable class of high affinity binding sites (Bmax = 0.31 +/- 0.04 fmol./microgram. DNA, Kd = 0.9 +/- 0.11 nM.). The relative potency of alpha adrenergic drugs (clonidine, alpha-methylnorepinephrine and prazosin) in competing for [3H]Ra binding sites was consistent with the order predicted for an alpha 2 subtype. The role of alpha 2 adrenergic receptors in normal prostatic function and in men with bladder outlet obstruction secondary to BPH requires further investigation.     

In vitro preparation of nonenzymatically glucosylated human transferrin, alpha 2-macroglobulin, and fibrinogen with preservation of function

Human transferrin, alpha 2-macroglobulin, and fibrinogen were incubated with [3H]-glucose. After a 7-day, 37 degrees C incubation at 20 mM glucose, transferrin incorporated 1.1 mol of glucose/mol protein; alpha 2-macroglobulin, 10 mol of glucose/mol; and fibrinogen, 3.8 of glucose/mol, or approximately 14 mumol of glucose/g for each protein. These results were the same for glucose labeled in the 1 or 6 position. No radiolabel was incorporated into the proteins during incubations with glucose labeled in the 2 position. The rate and extent of iron binding were identical for both glucosylated and nonglucosylated transferrin. Glucosylated transferrin bound to Wil-2 human lymphoblast cells with a Kd = 33 nM and receptor number of 3.4 X 10(5) receptors/cell; nonglucosylated transferrin with a Kd = 31 nM and receptor number of 3.9 X 10(5) receptors/cell. Glucosylated and nonglucosylated alpha 2-macroglobulin showed the same conformational change as determined on native PAGE after reaction with trypsin, plasmin, or methylamine and had the same activity in the Ganrot assay after reaction with trypsin or plasmin. The clearance of 125I-labeled, methylamine-treated alpha 2-macroglobulin from the mouse circulation was identical for both glucosylated and nonglucosylated alpha 2-macroglobulin, t1/2 = 3 min. alpha 2-Macroglobulin that was first glucosylated then reacted with methylamine bound to mouse peritoneal macrophages with a Kd of 2.5 nM and receptor activity of 370 fmol/mg cell protein. alpha 2-Macroglobulin that was first reacted with methylamine and then glucosylated bound with a Kd of 3 nM and receptor activity of 320 fmol/mg cell protein. Glucosylated fibrinogen had the same clotting time as control fibrinogen.(ABSTRACT TRUNCATED AT 250 WORDS)     

Changes in the biochemical profiles of mid-cervically located adenosine A1 receptors after repeated theophylline administration in adult rats

BACKGROUND/OBJECTIVE: Adenosine A1 receptors localized in the phrenic motoneurons (PMNs), where the axons of the descending bulbospinal respiratory make synaptic contacts, may be involved in theophylline-induced respiratory-related activity in rats. The objective of this study was to characterize the biochemical profiles of adenosine A1 receptors in 2 groups of rats: (a) na?ve and (b) theophylline-treated (3-day oral administration). METHODS: Biochemical binding characteristics of adenosine A1 receptors in the C3 to C5 (PMN) of adult rats were assessed in na?ve (n = 6) and theophylline-treated animals (n = 6) using [3H]-DPCPX (10 pmol/L to 30 nmol/L), the specific adenosine A1 receptor antagonist in saturation-binding assays. Competition assays used theophylline as the competing ligand (20 mmol/L to 20 pmol/L), and protein concentration was determined with the Bradford assay using a range of standards (0.016-1.0 mg/mL). RESULTS: In saturation-binding assays in na?ve animals, the A1 receptor was characterized by a single binding site with Bmax and Kd values of 256.00 +/- 32.13 fmol/mg protein and 2.89 +/- 0.45 nmol/L, respectively. Analysis of the isotherm in theophylline-treated animals showed 1 site with Bmax and Kd values of 219.00 +/- 26.3 fmol/mg protein and 0.60 +/- 0.21 nmol/L, respectively, and a second site characterized by Bmax and Kd values of 492.6 +/- 3.15 fmol/mg protein and 14.09 +/- 2.06 nmol/L, respectively. CONCLUSIONS: Theophylline administration revealed 2 binding sites on receptors (characterized by the specific adenosine A1 antagonist, [3H]-DPCPX) located in the vicinity of phrenic motoneurons (C3-C5). Alteration of the receptor profiles after theophylline may underlie the respiratory-related actions of the drug.     

Density and localization of alpha 1-adrenoceptors in hypertrophied prostate.

Alpha-adrenoceptors have been considered to play an important role in the regulation of the voiding force. In order to determine the density and localization of the alpha-adrenoceptors in the prostate, binding assays for alpha-adrenoceptors were performed with [3H]prazosin and [3H] yohimbine in membrane preparations from enucleated hyperplastic prostate tissues. Furthermore, autoradiographic analysis of alpha-adrenoceptors in the sliced tissue specimens from benign prostatic hypertrophy was performed. Specific binding of both ligands were saturable and of high affinity in membrane preparations, and Scatchard analyses indicated Bmax = 104 fmole/mg. protein, Kd = 0.488 nM for [3H]prazosin, and Bmax = 41 fmole/mg, protein, Kd = 1.83 nM for [3H] yohimbine. Bmax and Kd for [3H]prazosin were greater in the adenoma than in the submucosal tissue of the prostatic urethra. No relationship was noted between the size of enucleated prostate and the density of alpha-adrenoceptors. Image analysis of autoradiograms using [3H]prazosin showed specific binding sites could not be clearly demonstrated, but only [125I]HEAT slightly exposed specific binding sites in the prostate.     

Autoradiographic localization of α1-adrenoceptors in the dog prostate and urethra with 3H-prazosin

The regional distribution of α₁-adrenoceptors in the dog urethra has been studied by quantitative autoradiography using the specific α₁-antagonist ³H-prazosin as a ligand. The binding of ³H-prazosin to urethral tissue sections was saturable, reversible, and of high affinity (Kd = 0.7 nM); it occurred at a single population of sites and possessed the pharmacological features of the α₁-adrenoceptor. The binding parameters of ³H-prazosin on urethral tissue sections were found similar to those obtained on urethral membranes. Autoradiographic results revealed that the α₁-adrenoceptors are heterogeneously distributed along the dog urethral axis. The highest densities of ³H-prazosin binding sites were found in the preprostatic urethra. Comparison between autoradiographic and histological slides revealed that the ³H-prazosin binding sites were only localized on the smooth muscle fibres of the dog urethra.     

Brain D1 dopamine receptor in alloxan-induced diabetes.

Specific binding of [3H]SCH 23390 to dopamine D1 receptors in the striatum and olfactory tubercle in 14-day alloxan-induced diabetic rats was investigated. The Scatchard analysis revealed decreased D1 receptor density in the striatum (Bmax values were 548 +/- 23 fmol/mg protein for the control and 466 +/- 33 fmol/mg for the diabetic rats). No change was observed in the olfactory tubercle (Bmax; 299 +/- 27 fmol/mg for the control and 317 +/- 32 fmol/mg for the diabetic rats). Thus, specific binding of [3H]SCH 23390 to striatal and olfactory tubercle membranes showed region-specific changes of brain dopamine D1 receptors in alloxan diabetic rats.     

Angiotensin II receptor-mediated proliferation of cultured human fetal mesangial cells.

Accumulating evidence suggests that angiotensin II (Ang II) may play an important role in renal growth and glomerular development. During nephrogenesis, a complex relationship between the capillary and renal mesangium develops. Since the mesangial cell is a centrally-located pericyte with contractile, endocrine, and immune modulating functions, it may play a unique role in maintaining normal glomerular function. Therefore, we examined whether Ang II affects proliferation of human fetal mesangial cells in vitro and compared these findings to mesangial cells isolated from adult kidney. In these primary isolates, we studied the relationship between Ang II receptors and the mitogenic activity of angiotensin. Scatchard analysis of the binding of 125I[Sar1,Ile8]Ang II to subconfluent cultured human fetal mesangial cells revealed the presence of one class of binding sites with a Kd of 1.25 nM and a Bmax of 70 fmol/1 x 10(5) cells. Ang II receptors on adult mesangial cells had similar binding kinetics with a Kd of 1.6 nM and Bmax of 65 fmol/10(5) cells in subconfluent culture. In subconfluent culture of fetal mesangial cells, Ang II increased [3H]thymidine incorporation by 130% (P less than 0.005). In subconfluent culture of adult mesangial cells, Ang II increased [3H]thymidine incorporation by only 35% (P less than 0.05). In confluent culture of fetal mesangial cells, Ang II receptor number and mitogenic response were reduced. The Ang II antagonist [Sar1,Ile8]Ang II (1 microM) inhibited the mitogenic response of fetal mesangial cells to Ang II. Ang II increased fetal mesangial cell number by 25% (after 4 days) in serum-free medium supplemented with insulin or supplemented with insulin and 1% Nutridoma (P less than 0.005).(ABSTRACT TRUNCATED AT 250 WORDS)     

The alpha adrenergic binding properties of terazosin in the human prostate adenoma and canine brain

Clinical trials are currently underway to evaluate the efficacy of terazosin for the treatment of symptomatic benign prostatic hyperplasia (BPH). Terazosin is a potent and selective alpha 1 adrenergic blocking agent structurally similar to prazosin. The alpha adrenergic binding properties of terazosin were studied in human prostate adenomas and canine brains using radioligand receptor binding methods. Saturation analyses were performed at varying concentrations of [125I]-Heat and [3H]rauwolscine [( 3H]Ra) in human prostate adenomas and canine brains. The binding of [125I]-Heat and [3H]Ra in the human prostates and canine brains was consistently saturable and of high affinity. The equilibrium dissociation constant (Kd) for [125I]-Heat binding in the canine brains and human prostate adenomas was 84.4 +/- 4.3 pM and 65.4 +/- 19.2 pM, respectively (p greater than 0.05). The (Kd) for [3H]Ra binding in the human prostate adenomas and canine brains was 1.21 +/- 0.23 nM and 1.52 +/- 0.28 nM, respectively (p greater than 0.05). The density of alpha 1 (0.37 +/- 0.15 fmol/mg. wet wt.) and alpha 2 (0.29 +/- 0.09 fmol/mg. wet wt. adrenergic binding sites in the human adenomas were similar (p greater than 0.05). The IC50 corrected (IC50 corr) of terazosin for [125I]-Heat and [3H]Ra binding sites in the human prostate was 2.5 nM and 1.0 micron., respectively. The IC50 corr of terazosin for [125I]-Heat and [3H]Ra binding sites in the canine brain was 2.0 nM and 0.8 microM, respectively. The competitive binding assays indicate that terazosin binds selectively to alpha 1 adrenergic binding sites in the human prostate and canine brain.     

大鼠卵巢内皮素－1受体的动态变化

应用放射配基结合分析法（ＲＢＡ）检测了大鼠不同发育阶段卵巢内皮素－１（ＥＴ－１）受体的动态变化。结果表明：大鼠卵巢上存在有特异性ＥＴ－１受体，受体最大结合量（Ｂｍａｘ）于窦前期卵泡含量最高（３５８．２±７３．２ｆｍｏｌ／ｍｇ蛋白），随卵泡发育到排卵前卵泡时显著降低（１６２．７±１７．２ｆｍｏｌ／ｍｇ蛋白）（Ｐ＜０．０１），排卵后的早期黄体化卵巢降至最低值（３７．８±３．４ｆｍｏｌ／ｍｇ蛋白）（Ｐ＜０．０１），于晚期黄体化卵巢又再次升高（９５．３±４．９ｆｍｏｌ／ｍｇ蛋白）（Ｐ＜０．０１）。受体亲和力（Ｋｄ值）也随卵泡和黄体发育的不同阶段呈现动态变化，在排卵前卵泡卵巢ＥＴ受体对ＥＴ－１的亲和力最低，晚期黄体化卵巢最高。结果提示，ＥＴ－１可能通过与ＥＴ－１受体结合参与卵泡和黄体发育的调节。本结果为ＥＴ－１作为卵巢内局部调节肽提供实验依据。     

Muscarinic cholinergic receptors in human gastric mucosa

Muscarinic cholinergic receptor sites in human gastric mucosa were analyzed directly by using radioligand binding techniques with the specific muscarinic antagonist³H-quinuclidinyl benzilate (QNB) as ligand. Specific binding of³H-QNB to membrane preparations from human gastric mucosa was saturable, of high affinity (Kd=4.17±1.94 nM, Bmax=0.37±0.04 pmol/mg protein) and selectively inhibited by muscarinic antagonists (atropine, scopolamine) and agonists (acetylcholine, pilocarpine). These findings provide direct evidence for the existence of muscarinic cholinergic receptors in human gastric mucosa. The specific³H-QNB binding to its receptor was blocked by atropine but not by histamine, cimetidine, pentagastrin, or synthetic human gastrin. The muscarine and histamine H₂-receptor, or muscarine and gastrin receptor, probably do not share the same locus.     

Binding properties of a selective tritiated vasopressin V2 receptor antagonist, [H]-SR 121463

BACKGROUND: [3H]-SR 121463 is the first radiolabeled selective nonpeptide vasopressin V2 receptor antagonist ligand that has been reported to date. In the present work, we studied the binding properties of [3H]-SR 121463 for renal V2 receptors from animal and human origins. METHODS: Binding studies were performed with [3H]-SR 121463 in Chinese hamster ovary (CHO) cells transfected with the human V2 receptor and in various kidney preparations expressing the native V2 receptors (rat, rabbit, dog, pig, monkey, and human). Autoradiographies were performed in rat and human kidney sections. RESULTS: [3H]-SR 121463 binding to CHO cells stably transfected with the cloned human renal V2 receptor was specific, highly stable, time dependent, saturable, and reversible. A single population of high-affinity binding sites was identified (Kd = 0.94 +/- 0.34 nmol/L, Bmax = 9876 +/- 317 fmol/mg protein). Of note, [3H]-SR 121463 revealed a higher number (about 40%) of V2 sites than [3H]-AVP in the same preparation. Displacement of [3H]-SR 121463 binding by reference peptide and nonpeptide vasopressin/oxytocin compounds exhibited a typical AVP V2 profile. [3H]-SR 121463 also displayed a high affinity for native V2 receptors in several kidney preparations from rat, pig, dog, rabbit, bovine, monkey, and human. The autoradiographic experiments using rat and human kidney sections showed intense labeling in the medullopapillary region and lower intensity in the cortex, consistent with a main localization of V2 receptors on collecting tubules. CONCLUSION: [3H]-SR 121463 is a useful ligand for the specific labeling of animal and human V2 receptors and could be a suitable probe for the search and in situ localization of V2 sites.     

The function of autonomic receptors in canine ureteral smooth muscle]

I have investigated the effects of autonomic drugs and prostaglandins on in vitro smooth muscle spontaneous contractions and made the quantitative analysis of autonomic receptors in the canine ureter. Ureteral muscle strip cut helically usually generated spontaneous contractions whereas those cut circularly or longitudinally did not generate spontaneous contractions. These results suggest the importance of knowing which direction to cut the ureteral smooth muscle in order to generate spontaneous contractions. Norepinephrine (alpha), phenylephrine (alpha 1), carbachol (muscarinic) and PGF2 alpha caused significant increase in contractile force. Terbutaline (beta 2) and PGE2 caused significant decreases in contractile force, while dobutamine (beta 1) and clonidine (alpha) caused no effect. Autonomic receptor densities were determined using radiology and binding techniques. The number of maximum binding sites (Bmax) of 3H-prazosin (PZ), 3H-yohimbine (YOH), 3H-dihydroaloprenolol (DHA) and 3H-quinuclidinylbenzilate (QNB) were 53.8, 16.9, 11.2 and 5.28 fmol/ml protein, respectively. These data suggest that the contractile responses to adrenergic and cholinergic agonists in the canine ureter are mediated through functional adrenergic (alpha 1, beta 2) and muscarinic cholinergic receptors and that the prostaglandins have a role in the contraction of the canine ureter.     

Autoradiographic localization of prazosin and rauwolscine binding sites in the human kidney

In the human kidney, binding sites for the alpha₁-adrenoceptor antagonist³H-prazosin and the alpha₂-adrenoceptor antagonist³H-rauwolscine were localized and quantified byin vitro autoradiography.³H-prazosin binding was found predominantly in the renal cortex. In the medulla, tubular structures were also specifically labelled. No binding sites, however, were detected in association with glomeruli or large blood vessels.³H-rauwolscine labelled the medullary vascular bundles intensively, but no binding sites were associated with glomeruli or other cortical structures. Thus, the binding pattern for³H-prazosin is quite similar in both human and rat renal cortex. There are, however, distinct differences between human and rat kidneys in the distribution of the alpha₂-adrenergic binding sites visualized with the antagonist³H-rauwolscine.