Alpha adrenergic receptors in renal pelvis and calyces: can rat models be used?

We aimed, in this study, to determine the distribution of α-1 AR subtypes in rat and human pelvis and calyces, and to evaluate, by comparing these two species, the possibility of rats to be used as models for humans. Twenty patients with renal carcinoma were included into the study. The patients underwent radical nephrectomy for renal cell carcinoma (RCC). After nephrectomy, specimens were evaluated and excisional biopsies from healthy pelvis and calyces tissues were performed. When pathology confirmed the non-invasion of RCC, specimen was included into the study. A total of 7 adult Wistar Albino (250-300 g) female rats were used in this study. Specimens included renal pelvis and calyces. All specimens were evaluated under light microscope histopathologically. The concentrations of the receptor densities did not differ between the two groups. With the demonstration of the α receptors in rat kidneys and calyces, many receptor-based studies concerning both humans and rats can take place. Novel medication targeting these subtypes -in this matter α1A and α1D for renal pelvis and calyces- may be helpful for expulsive therapy and/or pain relief. With the demonstration of similar receptor densities between human and rat tissues, rat model may be useful for α-receptor trials for renal pelvis and calyces.

Direct relationship between mononuclear leukocyte and lung beta-adrenergic receptors and apparent reciprocal regulation of extravascular, but not intravascular, alpha- and beta-adrenergic receptors by the sympathochromaffin system in humans.

To examine putative relationships between adrenergic receptors on accessible circulating cells and relatively inaccessible extravascular catecholamine target tissues, we measured mononuclear leukocyte (MNL) and lung beta-adrenergic receptors and platelet and lung alpha-adrenergic receptors in tissues obtained from 15 patients undergoing pulmonary resection. Plasma catecholamine concentrations were measured concurrently to explore potential regulatory relationships between the activity of the sympathochromaffin system and both intravascular and extravascular adrenergic receptors. MNL and lung membrane beta-adrenergic receptor densities were correlated highly (r = 0.845, P less than 0.001). Platelet alpha 2-adrenergic receptor and lung alpha 1-adrenergic receptor densities were not. Lung alpha 1-adrenergic receptor densities were positively related to plasma norepinephrine (r = 0.840, P less than 0.01) and epinephrine (r = 0.860, P less than 0.01) concentrations; in contrast, lung beta-adrenergic receptor densities were not positively related to plasma catecholamine concentrations (they tended to be inversely related to plasma norepinephrine and epinephrine [r = -0.698, P less than 0.05] levels). This apparent reciprocal regulation of alpha- and beta-adrenergic receptors by the sympathochromaffin system was only demonstrable with adrenergic receptor measurements in the extravascular catecholamine target tissue. Neither MNL beta-adrenergic receptor nor platelet alpha-adrenergic receptor densities were correlated with plasma catecholamine levels. Thus, although measurements of beta-adrenergic receptors on circulating mononuclear leukocytes can be used as indices of extravascular target tissue beta-adrenergic receptor densities (at least in lung and heart), it would appear that extravascular tissues should be used to study adrenergic receptor regulation by endogenous catecholamines in humans. These data provide further support for the concept of up regulation, as well as down regulation, of some adrenergic receptor populations during short-term activation of the sympathochromaffin system in humans.

Acute reduction in human platelet alpha 2-adrenoreceptor affinity for agonist by endogenous and exogenous catecholamines.

The binding characteristics of l-epinephrine to intact human platelets were assessed under conditions of physiological and pharmacological variations in plasma catecholamine concentration. In competition with the alpha 2-adrenoreceptor antagonist yohimbine, mean platelet receptor affinity for l-epinephrine was decreased 3.4-fold after 2 h of upright posture and exercise. This change in agonist affinity correlated significantly with the increases in plasma epinephrine and norepinephrine that were stimulated by upright posture and exercise. Supine subjects infused with l-norepinephrine or l-epinephrine for 2 h also averaged a 3.3- and 2.7-fold decrease in platelet alpha 2-adrenoreceptor affinity for agonist with no change in receptor number or antagonist affinity. The alpha 2-adrenoreceptor agonist affinity changes were specific for alpha-agonists since they were blocked by phentolamine, and incubation with 10(-5) M isoproterenol produced no change in alpha 2-adrenoreceptor affinity for l-epinephrine. In vitro exposure of intact human platelets to 10(-6) to 10(-10) M l-epinephrine for 2 h produced a concentration-related decrease in alpha 2-adrenoreceptor affinity for agonist. In all three paradigms, average slope factors approached 1.0 as affinity decreased, which is consistent with a heterogeneous receptor population that becomes more homogeneous after agonist exposure. Incubation of platelet-rich plasma with 10(-6) to 10(-8) M l-epinephrine resulted in a dose- and time-related loss of aggregatory response to l-epinephrine; this demonstrates that agonist affinity changes are correlated with changes in receptor sensitivity. These observations demonstrate that physiological variations in plasma catecholamines acutely modulate the intact human platelet alpha 2-adrenoreceptor's affinity for agonist, and can thereby alter the sensitivity of platelets to alpha 2-adrenergic agonist.

Beta-adrenergic neuroeffector abnormalities in the failing human heart are produced by local rather than systemic mechanisms.

In order to investigate the general cause of beta-adrenergic receptor neuroeffector abnormalities in the failing human heart, we measured ventricular myocardial adrenergic receptors, adrenergic neurotransmitters, and beta-adrenergic receptor-effector responses in nonfailing and failing hearts taken from nonfailing organ donors, subjects with endstage biventricular failure due to idiopathic dilated cardiomyopathy (IDC), and subjects with primary pulmonary hypertension (PPH) who exhibited isolated right ventricular failure. Relative to nonfailing PPH left ventricles, failing PPH right ventricles exhibited (a) markedly decreased beta 1-adrenergic receptor density, (b) marked depletion of tissue norepinephrine and neuropeptide Y, (c) decreased adenylate cyclase stimulation in response to the beta agonists isoproterenol and zinterol, and (d) decreased adenylate cyclase stimulation in response to Gpp(NH)p and forskolin. These abnormalities were directionally similar to, but generally more pronounced than, corresponding findings in failing IDC right ventricles, whereas values for these parameters in nonfailing left ventricles of PPH subjects were similar to values in the nonfailing left ventricles of organ donors. Additionally, relative to paired nonfailing PPH left ventricles and nonfailing right ventricles from organ donors, failing right ventricles from PPH subjects exhibited decreased adenylate cyclase stimulation by MnCl2. These data indicate that: (a) Adrenergic neuroeffector abnormalities present in the failing human heart are due to local mechanisms; systemic processes do not produce beta-adrenergic neuroeffector abnormalities. (b) Pressure-overloaded failing right ventricles of PPH subjects exhibit decreased activity of the catalytic subunit of adenylate cyclase, an abnormality not previously described in the failing human heart.

Plasma catecholamine modulation of alpha 2 adrenoreceptor agonist affinity and sensitivity in normotensive and hypertensive human platelets.

We measured alpha 2-adrenoreceptor density as well as affinity for and sensitivity to agonist on intact platelets of normotensive and hypertensive subjects before and after physiological increases in plasma catecholamines. In normotensives, posture-induced rises in plasma catecholamines correlated with reduced alpha 2-adrenoreceptor agonist affinity and fewer high affinity state receptors. Platelet aggregation and inhibition of adenylate cyclase by L-epinephrine also was reduced. Hypertensive subjects had similar rises in plasma catecholamines with upright posture, but showed no change in receptor affinity or sensitivity. No change in platelet alpha 2-adrenoreceptor number occurred in these studies. In vitro incubation with L-epinephrine revealed that platelets from hypertensives had slower desensitization than those from normotensives. Binding studies at different temperatures and with varying sodium concentrations found no thermodynamic or sodium-dependent differences between normotensive and hypertensive groups. These studies demonstrate that platelets from hypertensive subjects exhibit a defect in the ability of physiological concentrations of agonist to desensitize the alpha 2-adrenoreceptor.

Glucagon-stimulable adenylyl cyclase in rat liver. The impact of streptozotocin-induced diabetes mellitus.

Glucagon receptor levels, glucagon-stimulated and other forms of adenylyl cyclase activity, and regulatory component activity of adenylyl cyclase were determined in hepatic plasma membranes of rats administered streptozotocin without and with insulin to produce varying degrees of hyperglycemia. Receptor levels were assayed by direct binding of the specific probe [125I-Tyr10]-iodoglucagon; regulatory component activity was assayed by the capacity to reconstitute stimulatory regulation in deficient membranes from cyc- S49 murine lymphoma cells. In rats given 150 mg streptozotocin, glucagon stimulation of adenylyl cyclase as well as basal, sodium fluoride, 5' guanylylimidodiphosphate [GMP-P(NH)P] and Mn-dependent activities were reduced 50%, glucagon receptor levels but not affinity were reduced 67%, and regulatory component activity was decreased 50%. In addition, alpha 1-adrenergic receptors and 5'-nucleotidase were similarly reduced in diabetes. However, specific ouabain-inhibitable Na+, K+, ATPase activity was not altered by streptozotocin treatment. The streptozotocin-induced changes were noted within 24 h and became maximal by 120 h after its administration. All of these decreases were partially reversed by in vivo insulin treatment. DNA, cytochrome c oxidase, glucose-6-phosphatase, and N-acetyl-beta-glucosaminidase content in hepatic plasma membrane preparations were not substantially different in diabetic as compared with control animals. The data demonstrate that glucagon-mediated regulation of cyclic AMP formation is deranged in insulin deficiency owing to a combined decrease in receptors, derangement of the coupling mechanism intervening between receptor and adenylyl cyclase, and possibly, an altered basal effector system. Some of these changes appear to reflect a "desensitization-like" phenomenon which may or may not be attributable to the hyperglucagonemia of diabetes mellitus. There also appears to be a concurrent generalized decrease in several but not all plasma membrane receptor and enzymatic proteins. This may be the result of a number of processes among which is the accelerated proteolysis of uncontrolled diabetes.

Characterization and distribution of alpha 2-adrenergic receptors in the human intestinal mucosa.

The subtype and the expression of the alpha 2-adrenergic receptor were investigated in the normal mucosa from human intestine by means of radioligand binding, RNase mapping, and measurement of adenylate cyclase activity. The study of the binding of the alpha 2-adrenergic antagonist, [3H]RX821002, to epithelial cell membranes indicated the existence of a single class of noninteracting sites displaying a high affinity for the radioligand (Kd = 1.1 +/- 0.5 nM). The rank order of potency of antagonists to inhibit [3H]RX821002 binding (RX821002 > yohimbine = rauwolscine > phentolamine approximately idazoxan >> chlorpromazine > prazosin) suggested that the receptor is of the alpha 2A subtype. A conclusion which is confirmed by the fact that only alpha 2C10 transcripts were found in the human intestine mucosa. Competition curves with (-)-norepinephrine demonstrated that 60% of the receptor population exhibited high affinity for agonists. This high-affinity state was abolished by the addition of GTP plus Na+ or by prior treatment of the membranes with pertussis toxin indicating it corresponded to G protein-coupled receptors. [32P]ADP-ribosylation and immunoblotting experiments identified two pertussis toxin-sensitive G proteins corresponding to Gi2 and Gi3. The study of the distribution of the receptor indicated that (a) the proximal colon is the intestine segment exhibiting the highest receptor density and (b) the receptor is predominantly expressed in crypts and is preferentially located in the basolateral membrane of the polarized cell. The distribution of the receptor along the crypt-surface axis of the colon mucosa can be correlated with a higher level of alpha 2C10-specific mRNA and a higher efficiency of UK14304 to inhibit adenylate cyclase in crypt cells.

Effects of verapamil on experimental cardiomyopathy in the Bio 14.6 Syrian hamster.

The Bio 14.6 Syrian hamster provides a good model for experimental study of cardiomyopathy. Cardiac receptor binding sites (alpha-1-, beta- and calcium antagonists) were studied in early (21 days old) and late (70 days old) stages of cardiomyopathy. The effects of verapamil on histologic features and free radicals in the heart were studied. The number of alpha-1- and beta-cardiac receptor binding sites was significantly greater in the late stage of cardiomyopathy when compared with findings in normal golden hamsters used as controls. The calcium antagonist receptors were significantly increased in the early stage but alpha-1- and beta-receptors were not. Verapamil-treated hamsters received intraperitoneal injections of verapamil at a dose of 5 mg/kg per day for 70 days from age 20 days. The percent areas of fibrosis and calcification in the verapamil-treated group were significantly smaller than those in the control group. The concentrations of lipid peroxides in the whole heart and free radicals in the heart mitochondria were significantly higher in the cardiomyopathic hamsters, and verapamil inhibited the increase in free radical concentration in the hearts of these hamsters. This study confirms that the number of calcium channels is increased early in the course of cardiomyopathy in the Bio 14.6 Syrian hamster. A larger number of free radicals may participate in the accumulation of calcium and cell injury in the myocytes of these hamsters. Verapamil protects against myocardial damage and may do so by inhibiting voltage-dependent calcium uptake and by preventing cell injury from free radicals.

alpha-Adrenergic receptor function in schizophrenia. Receptor number, cyclic adenosine monophosphate production, adenylate cyclase activity, and effect of drugs.

alpha-Adrenergic receptor function was assessed in platelets from drug-free schizophrenic patients and control subjects. The number of alpha-receptors was similar in platelet membranes from schizophrenic patients and control subjects. In intact platelets from schizophrenic male, but not female, patients, prostaglandin E1 (PGE1)-stimulated cyclic adenosine monophosphate (cAMP) level was less than in control subjects. This defect may be due, at least in part, to decreased adenylate cyclase activity. In platelet lysates from schizophrenic patients, but not from normal control subjects, adenylate cyclase activity was diminished and PGE1-stimulated adenylate cyclase activity could be restored partially by the addition of guanosine triphosphate. Treatment with neuroleptic drugs or lithium carbonate did not change alpha-receptor number or cAMP production in platelets from schizophrenic patients, but high doses of propranolol hydrochloride increased cAMP production without affecting the number of alpha-receptors. If the production of cAMP in neurons is similar to that in platelets, diminished cAMP production may be associated with a vulnerability to schizophrenia.

Alpha-1 adrenergic receptor number and receptor density in isolated hepatocytes from foetal, juvenile and adult rats.

Alpha-1 adrenergic receptor number was defined by [3H]-prazosin binding in crude membrane preparations of hepatocytes and in intact hepatocytes isolated from foetal (day 22 of gestation), juvenile (12 days old), adult female and adult male (90-150 days old) rats and compared with the alpha-1 adrenergic response (measured by epinephrine stimulated glucose liberation in presence of the beta-antagonist propranolol). The alpha-1 receptor number (expressed as fmol bound [3H]-prazosin/mg membrane protein or as receptor number/cell) increases in an age-dependent fashion reaching the highest values in hepatocytes of adult female and male rats. Statistically significant differences could be found between foetal, juvenile and adult rat hepatocytes. No differences in [3H]-prazosin binding were observed between hepatocytes of adult female and adult male rats. The receptor density (expressed as receptor number/microns 2 cell surface), however, was found to be equal in juvenile and adult rats. There are no differences of alpha-1 adrenergic response in juvenile, adult female and adult male rat hepatocytes, whereas the values in foetal hepatocytes were significantly lower. So the biological response is closely correlated with the receptor density and not with the receptor number per cell.

Decreased numbers of platelet alpha-adrenergic binding sites in diabetes mellitus.

Eleven men with diabetes mellitus were compared with 45 male controls for platelet alpha-adrenergic binding sites by using [3H]dihydroergocryptine (DHE) as the radioligand antagonist. There was no difference between the two for binding affinity, but the number of sites was 430 +/- 30 (means +/- SEM) for diabetic subjects and 574 +/- 29 for controls (P = .005). Decreased sites were related to increased glycosylated hemoglobin levels (P = .002). There was no relationship between the decreased sites and catecholamine levels, duration of disease, body weight, or fasting blood sugar. Hence, binding sites were inversely related to control, but further studies are needed to define the pathophysiologic significance of this.

Dissociation between reperfusion induced arrhythmias and increases in ventricular alpha 1 receptor density in the anaesthetised rat.

Using anaesthetised rats we have assessed (1) whether the density of alpha 1 adrenergic receptors increases during coronary artery occlusion, (2) whether any change in density can be associated with the onset of reperfusion induced ventricular fibrillation, and (3) whether alpha 1 blockade with prazosin modifies the incidence of reperfusion induced ventricular fibrillation. The incidence of fibrillation upon reperfusion after 3, 5, 10, 20 and 30 min occlusion was 20, 75, 50, 16 and 10% (n = 10-12 in each group) respectively. alpha 1 Receptor density was measured using [3H]-prazosin in non-ischaemic and ischaemic tissue obtained after 0, 5 and 30 min ischaemia. Receptor density was not significantly altered at the time of maximum incidence of reperfusion induced ventricular fibrillation (5 min occlusion) but did significantly increase in both non-ischaemic and ischaemic tissue after 30 min occlusion, when the incidence of fibrillation upon reperfusion was very low (8%). At this time the values were 17.0(SEM 2.3) and 18.4(0.6)fmol.mg-1 protein in non-ischaemic and ischaemic zones as compared to 10.7(0.6) and 12.8(1.0)fmol.mg-1 protein in sham operated control animals (p less than 0.05 in both cases). Prazosin (0.1 or 1.0 mg.kg-1 body wt intravenously, 5 min prior to coronary occlusion) did not alter the incidence of ventricular fibrillation, ventricular tachycardia or total number of premature ventricular complexes upon reperfusion. We conclude that ischaemia induced changes in alpha 1 receptor density do not parallel changes in vulnerability to reperfusion induced arrhythmias.(ABSTRACT TRUNCATED AT 250 WORDS)

Cardiac alpha 1 and beta adrenoceptors in rabbits: effects of dietary sodium and cholesterol.

To investigate the effects of dietary sodium and cholesterol on alpha 1 and beta adrenoceptors in hearts, male Japanese white rabbits were treated with either deoxycorticosterone acetate (DOCA) (50 mg/week sc) plus 1% saline in drinking water, frusemide (10 mg/2 days im), or cholesterol enriched diet (2%, w/w) for eight weeks. Using myocardial membrane preparations, characteristics of alpha 1 and beta adrenoceptors were assessed by a radioligand binding assay using 3H-prazosin and 125I-iodocyanopindolol (125I-CYP) as radioactive ligands respectively. Although the treatment with DOCA and salt induced a small but significant increase in the mean arterial blood pressure, other treatments did not affect blood pressure. None of these interventions affected body weight, ventricular weight, ratio of ventricular weight to body weight, or protein yield of membrane preparations. Neither the number nor the affinity of cardiac alpha 1 adrenoceptors (Bmax 15.1(1.7) fmol X mg protein-1, KD 0.63(0.13) nmol X litre-1 for controls) was affected by any of the treatments given. In contrast to alpha 1 adrenoceptors, the number of beta adrenoceptors (Bmax) decreased significantly from 109.9(9.6) fmol X mg protein-1 for controls to 54.8(5.2) and 52.7(6.9) for rabbits treated with DOCA salt and cholesterol respectively. KD values of beta adrenoceptors for 125I-CYP decreased significantly with cholesterol treatment from 22.5(2.5) to 13.6(2.7) pmol X litre-1. Salt depletion produced by frusemide administration did not affect either the number or the affinity of beta adrenoceptors. These results suggest that changes in the sensitivity of tissues to catecholamines induced by the administration of DOCA salt and cholesterol enriched diet are due to alterations in beta adrenoceptors in the heart.

Role of alpha 1-adrenoceptor activity in progression of cardiac hypertrophy in guinea pig hearts with pressure overload.

To elucidate the role of alpha 1- and beta-adrenergic activities in pressure overload hypertrophy, changes of alpha 1- and beta-adrenoceptors were measured by radioligand binding assay, and the preventive effects of alpha 1- and beta-adrenoceptor blockade on cardiac hypertrophy were assessed in guinea pigs after aortic banding. Five days after banding, dry weight of left ventricle had not increased, though wet weight increased due to marked intercellular oedema. In this period, the maximum binding capacity of [3H] prazosin increased to 31.1 (SEM 2.2) fmol.mg-1 from (sham operation) 17.0(2.1) fmol.mg protein-1, p less than 0.01, whereas the maximum binding capacity of [3H]dihydroalprenolol did not increase: 143(16) fmol.mg-1 (banded) v 153(13) fmol.mg-1 (sham). Three weeks after aortic banding, the maximum binding capacity of both ligands increased to 45.6(5.5) fmol.mg-1 and 232(21) fmol.mg-1, respectively, accompanied by a significant increase in left ventricular dry weight, from 0.46(0.02) mg.g-1 (sham) to 0.62(0.08) mg.g-1 (banded), p less than 0.01. Continuous subcutaneous administration of the alpha 1-blocker bunazosin (0.1 mg.kg-1.d-1) significantly attenuated the increase in left ventricular dry weight whereas the beta-blocker propranolol (5 mg.kg-1.d-1) did not: 0.55(0.03) v 0.66(0.04) mg.g-1 respectively, after 3 weeks. These results show that pressure overload elicited an increase in myocardial alpha 1-adrenoceptors before the onset of cardiac hypertrophy, and that an alpha 1-blocker could prevent the development of hypertrophy in the pressure overloaded heart.

Ovine pineal alpha 1-adrenoceptors: characterization and evidence for a functional role in the regulation of serum melatonin.

Plasma melatonin in sheep increases to nocturnal levels rapidly (10-20 min) after dark onset. This increase is blocked by iv prazosin (1 mg), but not propranolol (6 mg). Prazosin also blocks the elevation in pineal melatonin content after dark onset, but does not significantly alter the rise in N-acetyltransferase activity or the elevation in pineal N-acetylserotonin content. Since the nocturnal elevation in N-acetyltransferase, a neurally regulated event, was unaltered, this suggests that prazosin does not significantly impair the transmission of neural signals from the eye to the gland, but does act on pineal alpha 1-adrenoceptors to block melatonin production. This is supported by binding studies in ovine pineal membranes using [125I] iodo-2-[beta-(4-hydroxyphenyl)ethylaminomethyl]tetralone, which revealed that binding is rapid, reversible, saturable, and stereo-specific. Saturation studies indicated the presence of a single class of binding sites, with an equilibrium binding constant (Kd) of 32 +/- 6 pM and a maximum binding of 139 +/- 19 fmol/mg protein. The relative potencies of several adrenergic agonists and antagonists in competition studies indicated that the receptor belongs to the alpha 1-subclass of adrenoceptors. Together, these data suggest that melatonin synthesis in the sheep pineal gland is controlled in part by an alpha 1-adrenoceptor mechanism at a step beyond N-acetylation.

Androgenic regulation of adipocyte alpha 2-adrenoceptor expression in male and female Syrian hamsters: proposed transcriptional mechanism.

Adaptation of male hamsters to short daily (SD) photoperiod induced a reduction of the adipocyte alpha 2-adrenoceptor (alpha 2-AR) expression which was related to a sexual involution and could be reversed by testosterone administration. In the present paper, the possible mechanisms of such a physiological regulation are explored. The effect of testosterone on the adipocyte alpha 2-AR was rapid, dose-dependent, occurred at the physiological plasma concentrations of androgen, and was mimicked by dihydrotestosterone, but not by 17 beta-estradiol, progesterone, hydrocortisol, insulin, or T3. Adaptation of female hamsters to SD photoperiod also induced a sexual involution, but no modification of the adipocyte alpha 2-AR number was observed. Administration of testosterone induced a large up-regulation of the adipocyte alpha 2-AR. Testosterone was also able to up-regulate the adipocyte alpha 2-AR in male hamsters adapted to long day photoperiod whatever their age (6-, 12-, and 25-week old). Adaptation to SD photoperiod did not modify the adipocyte adenylyl cyclase activity (basal, forskolin-stimulated, GppNHp-inhibited). Conversely, UK14304-mediated inhibition of the adenylyl cyclase was suppressed in SD photoperiod and recovered after testosterone treatment. Administration of testosterone in young male hamsters adapted to long day photoperiod induced an increase in the amount of the alpha 2-AR messenger RNA, which coincided with the increase in the alpha 2-AR maximal number. The existence of a specific regulation of the adipocyte alpha 2-AR by the androgens, probably via a transcriptional mechanism, can be hypothesized. This regulation, which occurs in both male and female hamsters, appears to be physiologically relevant.

Drop in the "atypical" beta-adrenergic response and modification of the beta/alpha 2-adrenoceptor balance in fat cells from aging rabbits.

Previous studies have shown a strong reduction of catecholamine-induced lipolysis in perirenal white fat cells in aging rabbits. The molecular basis of this observation was explored on scapular and perirenal adipocytes from 45 and 300- to 500-day-old rabbits. ACTH and forskolin were used to define the maximal lipolytic potencies of the adipocytes. beta-Adrenergic responsiveness was explored with isoproterenol and specific agonists of the "atypical" beta-adrenoceptor (beta-AR) (BRL37344 and (+/-)CGP12177); beta 1/beta 2-ARs were identified with [125I]cyanopindolol. alpha 2-adrenergic responses were evaluated with the full alpha 2-agonist, UK14304. The alpha 2 AR number was determined with the alpha 2-antagonist radioligand [3H]RX821002. Whatever the fat deposit, the relative order of lipolytic potency of the beta-agonists was: isoproterenol greater than BRL37344 greater than (+/-)CGP12177. As previously reported for catecholamines, the maximal lipolytic response initiated by isoproternol decreased with aging; the stronger reduction was observed in perirenal adipocytes compared to subscapular adipocytes. The most striking observation concerns the parallel and complete disappearance of the lipolytic responses induced by the atypical beta-agonists (BRL37344 and (+/-)CGP12177) and the preservation of a residual action of isoproterenol (30% of that described in young animals) which was attributed to the stimulation of beta 1/beta 2-ARs. The number of beta 1/beta 2-AR binding sites was practically equivalent whatever the fat deposite and the age of the animals. alpha 2-Adrenergic responsiveness and alpha 2-adrenergic receptor number were increased with aging in the various deposits but the stronger changes were observed in the perirenal adipocytes where epineprine initiated a biphasic effect on lipolysis (antilipolytic and then lipolytic). To conclude, the reduction of catecholamine-induced lipolysis observed in the rabbit fat cells with aging can be explained by changes in the atypical beta-AR/alpha 2-AR balance. First, a loss of responsiveness to the atypical beta-adrenergic agents was observed (it is impossible for the moment to distinguish between the loss of atypical beta-AR binding sites and their putative uncoupling from the adenylate cyclase system) whereas beta 1/beta 2-AR-mediated responses were maintained. Second, an increment of alpha 2-adrenergic responsiveness and of the alpha 2-AR binding sites accompanied aging and fattening. In the absence of, or after a strong reduction of the atypical beta-AR component of the lipolytic response in fat cells of aged rabbits, epinephrine exerts a biphasic effect on lipolysis, demonstrating the changes occurring in the atypical beta-AR/alpha 2-AR balance.(ABSTRACT TRUNCATED AT 400 WORDS)

On the role of renal alpha-adrenergic receptors in spontaneously hypertensive rats.

We tested the hypothesis that a genetically determined increase in renal alpha-adrenergic receptor density might be a pathophysiologically important factor in the spontaneously hypertensive rat model of genetic hypertension. In a first study, we compared renal alpha 1 and alpha 2-adrenergic receptor density with systolic blood pressure in 45 rats of an F2 generation of Wistar-Kyoto x spontaneously hypertensive rat hybrids but were unable to detect significant cosegregation between either receptor density or blood pressure. In a second study, we determined renal alpha 1- and alpha 2-adrenergic receptor density in Wistar-Kyoto and spontaneously hypertensive rat kidneys that were transplanted into an F1 generation of Wistar-Kyoto x spontaneously hypertensive rat hybrids. Although Wistar-Kyoto kidneys lowered blood pressure in these animals and spontaneously hypertensive rat kidneys increased blood pressure, renal alpha-adrenergic receptor densities were similar in membranes from both types of kidneys. Since rat kidney coexpresses alpha 1A- and alpha 1B-adrenergic receptors, we also investigated whether differential regulation of these two subtypes might conceal ongoing alterations. The alpha 1A/alpha 1B-adrenergic receptor ratio, however, was similar in Wistar-Kyoto rats, spontaneously hypertensive rats, and F1 rats transplanted with a kidney from either strain. Taken together these data do not support the hypothesis that genetically determined alterations of renal alpha-adrenergic receptor numbers play an important role in the development of elevated blood pressure in the spontaneously hypertensive rat.

Renal nerve contribution to NaCl-exacerbated hypertension in spontaneously hypertensive rats.

Previous studies demonstrate that bilateral renal denervation enhances urinary sodium excretion and delays the onset of hypertension in young (7-week-old) spontaneously hypertensive rats (SHR) maintained on ordinary laboratory chow. We interpret these data as suggesting that increased renal nerve activity in this model contributes to hypertension by causing excess sodium retention. More recent studies show that dietary NaCl supplementation increases blood pressure and peripheral sympathetic nervous system activity in NaCl-sensitive SHR (SHR-S). The present study tests the hypothesis that the renal nerves contribute to the rise in arterial pressure caused by dietary NaCl supplementation in this model. SHR-S were fed a high (8%) or basal (1%) NaCl diet beginning at age 7 weeks. Bilateral renal denervation was carried out 2 weeks after the initiation of the diets, at which time systolic blood pressure was significantly higher in the high (compared with the basal) NaCl group. Systolic blood pressure was reduced slightly less in denervated SHR-S on the high (compared with basal) NaCl diet during the following 5 weeks. Renal denervation performed 1 week before initiation of the diets attenuated the subsequent development of hypertension equally in both groups. Both renal denervation and the high NaCl diet increased alpha 2-adrenergic receptor numbers in the kidney; renal denervation caused an approximately equal increase in alpha 2-adrenergic receptor binding in SHR-S on high and basal NaCl diets. The high NaCl diet increased plasma noradrenaline concentration, and renal denervation lowered mean arterial pressure but did not decrease circulating catecholamines in either diet group.(ABSTRACT TRUNCATED AT 250 WORDS)

Vascular angiotensin II receptors in SHR.

We investigated the density (Bmax) of angiotensin II (ANG II) receptors in the mesenteric vascular bed of spontaneously hypertensive rats (SHR) and age-matched Wistar-Kyoto (WKY) control rats. In 12-week-old SHR, the Bmax and the dissociation constant (Kd) of ANG II binding sites were not different from those of WKY rats in the sodium replete state or after sodium depletion. In prehypertensive (4- and 6-week-old) SHR, the Bmax of the vascular ANG II receptors was significantly higher (p less than 0.05) than in age-matched WKY rats. This result could not be attributed entirely to differences in the circulating renin-angiotensin-aldosterone system in 4-week-old-rats. In 6-week-old WKY rats, the plasma renin activity was significantly higher (p less than 0.05), which may account in part for the higher density of ANG II binding sites in SHR. There was an age-related decrease in the number of ANG II receptors in SHR. The increased density of vascular ANG II receptors in young SHR may play a role in the development of high blood pressure in this model of spontaneous hypertension. The higher number of ANG II binding sites in young SHR is not selective for ANG II receptors, since an increased density of alpha 1-adrenergic receptors was also found in the mesenteric arteries of 4-week-old SHR.