Stimulation of hypertrophy of cultured neonatal rat heart cells through an alpha 1-adrenergic receptor and induction of beating through an alpha 1- and beta 1-adrenergic receptor interaction. Evidence for independent regulation of growth and beating

Catecholamines may be one of the molecular signals linking increased circulatory demand to myocardial hypertrophy, and I have found previously that norepinephrine stimulates hypertrophy of cultured neonatal rat heart muscle cells through an alpha 1-adrenergic receptor. Since catecholamine stimulation of contractility is believed to be under beta-adrenergic control, I asked whether these cultured heart cells had dual pathways regulating growth and contractility through alpha- and beta-adrenergic receptors, respectively. I examined the effect of adrenergic agents on hypertrophy and beating of myocytes in serum-free cultures. Hypertrophy was defined as an increase in myocyte surface area and in cell protein content, measured by a radioisotopic method, and chronotropic activity was examined visually. Norepinephrine and epinephrine were equipotent stimulants of hypertrophy and beating, increasing cell protein and area 1.5- to 2-fold, and the proportion of beating cells from 5% or less to 95%. Response maxima occurred 24-48 hours after exposure, and EC50 were 20-200 nM. Studies with other agonists (phenylephrine, methoxamine, clonidine, isoproterenol, dopamine) and antagonists (prazosin, terazosin, yohimbine, propranolol, betaxolol, ICI 118,551) indicated that hypertrophy was mediated through an alpha 1-adrenergic receptor, whereas the induction of beating required both alpha 1- and beta 1-receptor activation. Hypertrophied cells with minimal beating were produced by alpha-stimulation, alone. In contrast, alpha-plus beta-stimulation in the presence of cycloheximide to inhibit protein synthesis resulted in maximum beating but no hypertrophy. These findings imply that growth and beating can be regulated independently through separate cellular pathways.     

Mixed-lineage kinase 3 regulates B-Raf through maintenance of the B-Raf/Raf-1 complex and inhibition by the NF2 tumor suppressor protein

The Ras --> Raf --> MEK1/2 --> extracellular signal-regulated kinase (ERK) mitogen-activated protein kinase (MAPK) pathway couples mitogenic signals to cell proliferation. B-Raf and Raf-1 function within an oligomer wherein they are regulated in part by mutual transactivation. The MAPK kinase kinase (MAP3K) mixed-lineage kinase 3 (MLK3) is required for mitogen activation of B-Raf and cell proliferation. Here we show that the kinase activity of MLK3 is not required for support of B-Raf activation. Instead, MLK3 is a component of the B-Raf/Raf-1 complex and is required for maintenance of the integrity of this complex. We show that the activation of ERK and the proliferation of human schwannoma cells bearing a loss-of-function mutation in the neurofibromatosis 2 (NF2) gene require MLK3. We find that merlin, the product of NF2, blunts the activation of both ERK and c-Jun N-terminal kinase (JNK). Finally, we demonstrate that merlin and MLK3 can interact in situ and that merlin can disrupt the interactions between B-Raf and Raf-1 or those between MLK3 and either B-Raf or Raf-1. Thus, MLK3 is part of a multiprotein complex and is required for ERK activation. The levels of this complex may be negatively regulated by merlin.     

Acetylcholine release from rat atria can be regulated through an alpha 1-adrenergic receptor

Isolated superfused rat atria release [3H]acetylcholine when depolarized with 57 mM potassium. The depolarization-induced overflow of [3H]acetylcholine is markedly inhibited by micromolar concentrations of epinephrine and norepinephrine. The alpha 1-selective adrenergic agonist methoxamine also inhibits tritium overflow, but the alpha 2-selective adrenergic agonist clonidine and the beta-adrenergic agonist isoproterenol do not. Prazosin, an selective alpha 1-adrenergic antagonist, blocks adrenergic inhibition of [3H]acetylcholine overflow with a Ki of approximately 0.4 nM. Yohimbine has approximately one-hundredth the potency of prazosin for blocking adrenergic inhibition of [3H]acetylcholine overflow. [3H]Norepinephrine overflow from isolated rat atria is also inhibited by norepinephrine, but this effect is antagonized by yohimbine and not by prazosin. We suggest that the release of acetylcholine from cardiac parasympathetic neurons can be regulated through an alpha 1-adrenergic receptor, and that this mechanism may underly, at least in part, the relative lack of effects of prazosin on heart rate.     

Inhibitory action of the alpha 1-adrenergic receptor on growth hormone secretion in the dog

Intravenous administration of methoxamine ( METHOX , 5 mg, iv), a specific alpha 1-adrenergic agonist, reduced baseline GH levels of four unanesthetized beagle dogs 45 and 60 min post-injection and completely abolished the GH-releasing effect of the alpha 2-adrenergic agonist clonidine ( CLON , 4/ micrograms/kg, iv). Prazosin (PRA, 0.1 mg/kg, iv), an alpha 1-adrenergic antagonist, administered before METHOX re-instituted the GH-releasing effect of CLON . METHOX administered at the starting of an arginine infusion (ARG, 10% solution, 3.3 ml/min X 30 min) reduced consistently the GH releasing effect of the latter while, conversely, pretreatment with PRA, strikingly potentiated the GH-releasing effect of the amino acid (2 dogs). METHOX did not alter the GH-releasing effect of human pancreatic GH-releasing factor (hpGRF-40, 1/microgram/kg, iv), though it consistently delayed the occurrence of the GH secretory peak following hpGRF-40. These data indicate that alpha 1-adrenergic receptors located in the central nervous system, inhibit in the dog tonic and stimulated GH secretion.     

Hypocaloric diet reduces exercise-induced alpha 2-adrenergic antilipolytic effect and alpha 2-adrenergic receptor mRNA levels in adipose tissue of obese women

Previous investigations have shown that alpha 2-adrenoceptor (alpha 2-AR) stimulation blunts lipid mobilization during physiological activation of the sympathetic nervous system promoted by exercise in sc abdominal adipose tissue (SCAAT) in obese men. To investigate the effect of a low calorie diet (LCD) on the alpha 2-adrenergic responsiveness and on the expression of alpha 2-AR and beta 2-adrenoceptor (beta 2-AR) in SCAAT, 11 obese women (weight: 99.1 +/- 4.6 kg; body mass index: 34.3 +/- 1.1 kg/m(2)) received a 12-wk diet providing 500 kcal/d less than their usual diet. The exercise-induced alpha 2-adrenergic antilipolytic effect was investigated in SCAAT before and at the end of LCD. Changes in extracellular glycerol concentration and local blood flow were measured in SCAAT during a 45-min exercise bout (50% of heart rate reserve) using a control microdialysis probe and a probe supplemented with the alpha2-AR antagonist phentolamine. SCAAT biopsies were performed for determination of mRNA levels using RT-competitive PCR. Plasma catecholamine responses to exercise bout were not different before and at the end of LCD. Before LCD, the exercise-induced increase in extracellular glycerol concentration was potentiated by phentolamine supplementation, while this potentiating effect of the alpha-antagonist was not observed at the end of LCD. No changes were observed for beta 2-AR and hormone-sensitive lipase mRNA levels, while alpha 2-AR mRNA level was significantly decreased in adipose tissue during LCD. These findings show that alpha 2-AR-mediated antilipolytic action is reduced by a moderate hypocaloric diet and that down-regulation of alpha 2-AR mRNA levels may participate in the decrease of the alpha 2-adrenergic effect revealed by microdialysis.     

Selectivity of alpha 2-adrenergic agonists for the imidazoline-guanidine and alpha 2-adrenergic receptors

Imidazolines have been proposed as highly selective drugs for alpha 2-adrenergic receptors. However, we have recently showed that the imidazoline ligand 3H-RX 781094 (idazoxan) binds to both alpha 2-receptors and imidazoline guanidinium receptive substance (IGRS) in rabbit renal proximal tubule. Binding of 3H-RX 781094 to the purified basolateral membranes (15-fold enriched in Na-KATPase activity) was rapid (t 1/2 = 5 mn.) reversible (t 1/2) = 4 mn.), saturable and of high affinity. Scatchard analysis of equilibrium binding data showed that 3H-RX 781094 labels 566 +/- 118 fmol/mg of proteins of binding sites with an apparent dissociation constant (Kd) of 1.45 +/- 0.14 nM. On the other hand, the non imidazoline ligand 3H-rauwolscine binds only to the alpha 2-adrenergic receptors with a maximal density of 155 +/- 28 fmol/mg of protein and a Kd of 11.5 +/- 1.5 nM. In order to define the relative affinity of the alpha-2-agonists, clonidine, rilmenidine and guanfacine for the two classes of receptors, we performed competition studies of the alpha 2-antagonists 3H-RX 781094 (imidazoline) and 3H-rauwolscine (non imidazoline) binding to basolateral membranes from rabbit proximal tubule. The order of potency for inhibition of the two radioligand binding was rilmenidine greater than clonidine greater than guanfacine for 3H-RX 781094 and clonidine greater than guanfacine greater than rilmenidine for 3H-rauwolscine. Therefore, rilmenidine displayed a higher affinity for IGRS than for alpha 2 adrenergic receptors; on the other hand, clonidine and guanfacine preferentially interact with alpha 2 receptors.(ABSTRACT TRUNCATED AT 250 WORDS)     

Platelet-derived growth factor inhibits basic fibroblast growth factor angiogenic properties in vitro and in vivo through its alpha receptor

Basic fibroblast growth factor (bFGF) and platelet-derived growth factor-BB (PDGF-BB) modulate vascular wall cell function in vitro and angiogenesis in vivo. The aim of the current study was to determine how bovine aorta endothelial cells (BAECs) respond to the simultaneous exposure to PDGF-BB and bFGF. It was found that bFGF-dependent BAEC migration, proliferation, and differentiation into tubelike structures on reconstituted extracellular matrix (Matrigel) were inhibited by PDGF-BB. The role played by PDGF receptor alpha (PDGF-Ralpha) was investigated by selective stimulation with PDGF-AA, by blocking PDGF-BB-binding to PDGF-Ralpha with neomycin, or by transfecting cells with dominant-negative forms of the receptors to selectively impair either PDGF-Ralpha or PDGF-Rbeta function. In all cases, PDGF-Ralpha impairment abolished the inhibitory effect of PDGF-BB on bFGF-directed BAEC migration. In addition, PDGF-Ralpha phosphorylation was increased in the presence of bFGF and PDGF, as compared to PDGF alone, whereas mitogen-activated protein kinase phosphorylation was decreased in the presence of PDGF-BB and bFGF compared with bFGF alone. In vivo experiments showed that PDGF-BB and PDGF-AA inhibited bFGF-induced angiogenesis in vivo in the chick embryo chorioallantoic membrane assay and that PDGF-BB inhibited bFGF-induced angiogenesis in Matrigel plugs injected subcutaneously in CD1 mice. Taken together these results show that PDGF inhibits the angiogenic properties of bFGF in vitro and in vivo, likely through PDGF-Ralpha stimulation.     

Heterodimerization of beta1- and beta2-adrenergic receptor subtypes optimizes beta-adrenergic modulation of cardiac contractility

Intermolecular interactions between members of both similar and divergent G protein-coupled receptor subfamilies have been shown in various experimental systems. Here, we demonstrate heterodimerization of predominant beta-adrenergic receptor (betaAR) subtypes expressed in the heart, beta1AR, and beta2AR, and its physiological relevance. In intact adult-mouse cardiac myocytes lacking native beta1AR and beta2AR, coexpression of both betaAR subtypes led to receptor heterodimerization, as evidenced by their coimmunoprecipitation, colocalization at optical resolution, and markedly increased binding affinity for subtype-selective ligands. As a result, the dose-response curve of myocyte contraction to betaAR agonist stimulation with isoproterenol (ISO) was shifted leftward by approximately 1.5 orders of magnitude, and the response of cellular cAMP formation to ISO was enhanced concomitantly, indicating that intermolecular interactions of betaAR subtypes resulted in sensitization of these receptors in response to agonist stimulation. In contrast, the presence of beta1AR greatly suppressed ligand-independent spontaneous activity of coexisting beta2ARs. Thus, heterodimerization of beta1AR and beta2AR in intact cardiac myocytes creates a novel population of betaARs with distinct functional and pharmacological properties, resulting in enhanced signaling efficiency in response to agonist stimulation while silencing ligand-independent receptor activation, thereby optimizing beta-adrenergic modulation of cardiac contractility.     

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.     

Expansion of the alpha 2-adrenergic receptor family: cloning and characterization of a human alpha 2-adrenergic receptor subtype, the gene for which is located on chromosome 2

Pharmacologic, biochemical, and genetic analyses have demonstrated the existence of multiple alpha 2-adrenergic receptor (alpha 2AR) subtypes. We have cloned a human alpha 2AR by using the polymerase chain reaction with oligonucleotide primers homologous to conserved regions of the previously cloned alpha 2ARs, the genes for which are located on human chromosomes 4 (C4) and 10 (C10). The deduced amino acid sequence encodes a protein of 450 amino acids whose putative topology is similar to that of the family of guanine nucleotide-binding protein-coupled receptors, but whose structure most closely resembles that of the alpha 2ARs. Competition curve analysis of the binding properties of the receptor expressed in COS-7 cells with a variety of adrenergic ligands demonstrates a unique alpha 2AR pharmacology. Hybridization with somatic cell hybrids shows that the gene for this receptor is located on chromosome 2. Northern blot analysis of various rat tissues shows expression in liver and kidney. The unique pharmacology and tissue localization of this receptor suggest that this is an alpha 2AR subtype not previously identified by classical pharmacological or ligand binding approaches.     

Gastrin inhibits cholangiocarcinoma growth through increased apoptosis by activation of Ca2+-dependent protein kinase C-alpha

BACKGROUND/AIMS: We determined the role of gastrin in the regulation of cholangiocarcinoma growth. METHODS: We evaluated for the functional presence of cholecystokinin (CCK)-B/gastrin receptors in the cholangiocarcinoma cell lines, Mz-ChA-1, HuH-28 and TFK-1. We determined the effect of gastrin on the growth of Mz-ChA-1, HuH-28 and TFK-1 cells. We evaluated the effect of gastrin on growth and apoptosis of Mz-ChA-1 in the absence or presence of inhibitors for CCK-A (L-364, 718) and CCK-B/gastrin (L-365, 260) receptors, the intracellular Ca2+ chelator (BAPTA/AM), and the protein kinase C (PKC)-alpha inhibitor, H7. We evaluated if gastrin effects on Mz-ChA-1 growth and apoptosis are associated with membrane translocation of PKC-alpha. RESULTS: Gastrin inhibited DNA synthesis of Mz-ChA-1, HuH-28 and TFK-1 cells in a dose- and time-dependent fashion. The antiproliferative effect of gastrin on Mz-ChA-1 cells was inhibited by L-365, 260, H7 and BAPTA/AM but not L-364, 718. Gastrin induced membrane translocation of PKC-alpha. The inhibition of growth of Mz-ChA-1 cells by gastrin was associated with increased apoptosis through a PKC-dependent mechanism. CONCLUSIONS: Gastrin inhibits the growth of Mz-ChA-1, HuH-28 and TFK-1 cells. Gastrin inhibits growth and induces apoptosis in Mz-ChA-1 cells through the Ca2+-dependent PKC-alpha. The data suggest a therapeutic role for gastrin in the modulation of cholangiocarcinoma growth.     

A single amino acid change in Raf-1 inhibits Ras binding and alters Raf-1 function.

Ras and Raf-1 are key proteins involved in the transmission of developmental and proliferative signals generated by receptor and nonreceptor tyrosine kinases. Genetic and biochemical studies demonstrate that Raf-1 functions downstream of Ras in many signaling pathways. Although Raf-1 directly associates with GTP-bound Ras, an effect of this interaction on Raf-1 activity in vivo has not been established. To examine the biological consequence of the Ras/Raf-1 interaction in vivo, we set out to identify key residues of Raf-1 required for Ras binding. In this report, we show that a single amino acid mutation in Raf-1 (Arg89 to Leu) disrupted the interaction with Ras in vitro and in the yeast two-hybrid system. This mutation prevented Ras-mediated but not tyrosine kinase-mediated enzymatic activation of Raf-1 in the baculovirus/Sf9 expression system. Furthermore, kinase-defective Raf-1 proteins containing the Arg89-->Leu mutation were no longer dominant-inhibitory or capable of blocking Ras-mediated signal transduction in Xenopus laevis oocytes. These results demonstrate that the association of Raf-1 and Ras modulates both the kinase activity and the biological function of Raf-1 and identify Arg89 as a critical residue involved in this interaction. In addition, the finding that tyrosine kinases can stimulate the enzymatic activity of Raf-1 proteins containing a mutation at the Ras-interaction site suggests that Raf-1 can be activated by Ras-independent pathways.     

Autoantibodies against AT1-receptor and alpha1-adrenergic receptor in patients with hypertension.

This study will explore the autoantibodies against AT1-receptor and alpha1-adrenergic receptor in patients with hypertension. Forty normotensives and 194 patients with hypertension were recruited for participation in this study. All patients accepted systemic combination drug treatment for antihypertension. According to the treatment results and the definition of refractory hypertension, the patients were divided into two groups: a refractory hypertension group and a non-refractory hypertension group. The epitope of the 2nd extracellular loop of type 1 angiotensin (AT1) receptor and alpha1-adrenergic receptor were synthesized and used as antigens to screen the autoantibodies against AT1-receptor and alpha1-adrenergic receptor by ELISA. The plasma renin activity and concentration of angiotensin II and catecholamine were also examined. The positive rates of the autoantibodies against AT1-receptor and alpha1-adrenergic receptor in patients with hypertension, 26.8% (52/194) and 25.3% (49/194), respectively, were higher than those in normotensives (7.5% and 5%)(p < 0.01). Further investigation showed that the frequencies of the autoantibodies against AT1-receptor and alpha1-adrenergic receptor in patients with refractory hypertension, 42.9% (42/98) and 36.7% (36/98), respectively, were higher than those in patients with non-refractory hypertension under systematic treatment (10.4% and 13.5%)(p < 0.01). The levels of circulating angiotensin II, catecholamine, proteinuria and serum creatine were also higher in the refractory hypertension group than in the non-refractory hypertension group. The findings showed that the frequencies of autoantibodies against AT1-receptor and alpha1-adrenergic receptor were higher in patients with hypertension, particularly in those with refractory hypertension, and that these autoantibodies might play a role in the pathogenesis of hypertension.     

Phorbol esters promote alpha 1-adrenergic receptor phosphorylation and receptor uncoupling from inositol phospholipid metabolism.

DDT1 MF-2 cells, which are derived from hamster vas deferens smooth muscle, contain alpha 1-adrenergic receptors (54,800 +/- 2700 sites per cell) that are coupled to stimulation of inositol phospholipid metabolism. Incubation of these cells with tumor-promoting phorbol esters, which stimulate calcium- and phospholipid-dependent protein kinase, leads to a marked attenuation of the ability of alpha 1-receptor agonists such as norepinephrine to stimulate the turnover of inositol phospholipids. This turnover was measured by determining the 32P content of phosphatidylinositol and phosphatidic acid after prelabeling of the cellular ATP pool with 32Pi. These phorbol ester-treated cells also displayed a decrease in binding affinity of cellular alpha 1 receptors for agonists with no change in antagonist affinity. By using affinity chromatography on the affinity resin Affi-Gel-A55414, the alpha 1 receptors were purified approximately equal to 300-fold from control and phorbol ester-treated 32Pi-prelabeled cells. As assessed by NaDodSO4/polyacrylamide gel electrophoresis, the Mr 80,000 alpha 1-receptor ligand-binding subunit is a phosphopeptide containing 1.2 mol of phosphate per mol of alpha 1 receptor. After phorbol ester treatment this increased to 3.6 mol of phosphate per mol of alpha 1 receptor. The effect of phorbol esters on norepinephrine-stimulated inositol phospholipid turnover and alpha 1-receptor phosphorylation showed the same rapid time course with a t1/2 less than 2 min. These results indicate that calcium- and phospholipid-dependent protein kinase may play an important role in regulating the function of receptors that are coupled to the inositol phospholipid cycle by phosphorylating and deactivating them.     

Quinidine is a competitive antagonist at alpha 1- and alpha 2-adrenergic receptors

Although quinidine is known to have antiadrenergic effects in the cardiovascular system, the precise mechanism by which it exerts these effects is not well defined. We asked whether quinidine binds directly to adrenergic receptors. Radioligand-binding assays were used to identify alpha 1-adrenergic receptors [( 3H]prazosin-binding sites) on membranes prepared from rat heart and kidney, alpha 2-adrenergic receptor [( 3H]yohimbine-binding sites) on human platelets and rat kidney membranes, and beta-adrenergic receptors [( 125I]iodocyanopindolol-binding sites) on rat heart and kidney membranes. Although it did not effectively compete for binding to beta-adrenergic receptors, quinidine competed for binding to alpha 1- and alpha 2-adrenergic receptors and yielded equilibrium dissociation constants of 0.3-3 microM. Two other antiarrhythmic agents, lidocaine and procainamide, did not compete for binding to alpha-adrenergic receptors. Further experiments demonstrated that the interactions of quinidine with the cardiac alpha 1- and platelet alpha 2-adrenergic receptors were competitive and reversible. We conclude that that antiadrenergic actions of quinidine can be explained by occupancy and competitive blockade of alpha 1- and alpha 2-adrenergic receptors.     

Role of alpha 1- and alpha 2-adrenergic receptors in the growth hormone and prolactin response to insulin-induced hypoglycemia in man

The effects of intravenous infusion of the nonselective alpha-adrenergic antagonist phentolamine or of the selective alpha 2-adrenergic antagonist yohimbine on growth hormone (GH), prolactin (PRL) and cortisol secretion during insulin-induced hypoglycemia were studied in 11 healthy young men. The GH response was blunted following each antagonist used, PRL secretion was higher after yohimbine and diminished after phentolamine when compared to controls. The plasma cortisol response was not influenced by either compound. In another series of experiments no effect of an oral administration of prazosin, a selective alpha 1-adrenergic antagonist, on the secretion of GH, PRL and cortisol was found in any of 7 subjects. Prazosin inhibited blood pressure increase during hypoglycemia and induced slight drowsiness and fatigue in the subjects. It is concluded that in man alpha-adrenergic stimulation of GH secretion during hypoglycemia is transmitted via alpha 2-receptors, PRL secretion is mediated via alpha 1-receptors, whereas inhibition of PRL release is mediated via alpha 2-receptors. In this experiment no effect of alpha 1- or alpha 2-blockade on cortisol response to hypoglycemia was seen.     

Hepatic alpha 1-adrenergic receptor alteration in a rat model of chronic sepsis

Catecholamine therapy is often ineffective in reversing the peripheral vasodilatation and hypotension of septic shock. This suggests that catecholamines might not be able to activate alpha 1-adrenergic receptors to cause vasoconstriction. Despite elevations in endogenous catecholamines, hypoglycemia is also a complication of human sepsis, suggesting that among many other causes, hepatic alpha 1-receptors might be altered. To better understand the pathophysiologic basis for this pharmacologic dilemma, we studied the effect of experimental sepsis on alpha 1-adrenergic receptors in hepatic tissue, a rich source of alpha 1-receptors, from septic and control Sprague-Dawley rats. alpha 1-adrenergic receptors were measured with [3H]-prazosin and data analyzed by a computerized nonlinear least-square regression algorithm. Twenty-four hours following cecal ligation with puncture, a decreased number of alpha 1-adrenergic receptors was noted in crude and purified plasma membrane fractions (23 and 40% reductions respectively) from septic animals. No changes in either agonist or antagonist affinity for receptors from septic animals were noted. These data indicate that the catecholamine refractoriness seen in septic shock may be a result of alterations in alpha 1-adrenergic receptor number or receptor-effector coupling.