Insulin resistance and hypertension.

While clinicians have long recognized the apparent increased prevalence of hypertension among diabetics, sophisticated epidemiological analyses begun in the early 1970s have established that hypertensive individuals are more prone to hyperinsulinemia and glucose intolerance than normotensive individuals. Subsequently, the several hypertensinogenic effects of insulin were carefully studied in a number of laboratories. Most recently, the association of these two relatively common cardiovascular risk factors, hypertension and insulin resistance, was broadened to include lipid abnormalities, namely, increased concentrations of very low density lipoprotein triglycerides and decreased concentrations of high density lipoprotein cholesterol. These abnormalities, all of which appear in association more commonly than would be expected by chance, clearly predispose affected individuals to increased cardiovascular risk. This review summarizes our current understanding of the mechanisms underlying the relations between insulin resistance and hypertension and focuses discussion on the role of insulin as a common link between them. It concludes with recommendations, based on today's knowledge, for behavioral and therapeutic interventions aimed at the prevention of increased cardiovascular risk.

The function but not the expression of rat liver inhibitory guanine nucleotide binding protein is altered in streptozotocin-induced diabetes.

Adenylate cyclase activity was examined as a measure of inhibitory guanine nucleotide binding protein (Gi) function in liver plasma membranes from rats made chemically diabetic by streptozotocin (STZ) treatment. Clonidine activation of the alpha 2 adrenergic receptor, which activates Gi, inhibited forskolin--stimulated adenylate cyclase activity in control membranes. However, there was no effect on adenylate cyclase activity in membranes from STZ diabetic animals. Also, a polyclonal antipeptide antibody was raised to a highly conserved segment of the Gi alpha 2 subunit. This antibody specifically recognizes a 41 kilodalton protein, is blocked by an excess of peptide, does not recognize the alpha-subunit of transducin, and immunoprecipitates a 41 kilodalton protein which was ADP-ribosylated by pertussis toxin. Immunoblots using this antibody detect no difference between normal and STZ diabetic animals in the level of liver plasma membrane Gi expression. Therefore, STZ-induced diabetes altered the function of Gi but had no effect on Gi expression.

Effect of castration, DES, flutamide, and the 5 alpha-reductase inhibitor, MK-906, on the growth of the Dunning rat prostatic carcinoma, R-3327.

Male rats bearing implants of the Dunning rat prostatic carcinoma, R-3327, were used in a 42-day study to determine the effect of castration or orally administered flutamide (FL), DES (diethylstilbestrol) or the 5 alpha-reductase inhibitor, MK-906, on the growth of this androgen-responsive cancer. The rate of growth and final weights of the tumor and the ventral prostate (VP) were all reduced (P less than 0.05) by castration. Flutamide (25 mg/kg/day) significantly decreased tumor and VP weights in intact rats and castrates given 100 micrograms/day (SC) of testosterone propionate (TP) or dihydrotestosterone propionate (DHTP). It also significantly retarded tumor growth rate in TP- or DHTP-treated castrates and was marginally effective in intact animals. DES (100 micrograms/kg/day) reduced (P less than 0.05) tumor and VP weights of intact rats but did not significantly affect tumor growth rate or weight in castrates given TP or DHTP. These results indicated that the effect of DES on tumor growth is caused by its inhibition of the secretion or release of the gonadotropins necessary for testicular androgen production. MK-906 (25 mg/kg/day) affected neither the gross nor the histomorphology of the tumor in intact rats or castrates given TP or DHTP. Further, it caused no histological changes in the testes of intact rats. It did, however, significantly reduce VP weight in intact animals and TP-treated castrates but not in those given DHTP. This illustrates that the anti-androgenicity of MK-906 stems from its inhibition of DHT formation. The failure of MK-906 to influence tumor growth in the TP-treated castrates strongly suggests that the R-3327 tumor can respond to testosterone directly. If that is true, then its growth is unlikely to be affected by a pure 5 alpha-reductase inhibitor such as MK-906. In ancillary experiments, tumors from MK-906-treated animals were found to have reduced levels of DHT and, when assayed in vitro, to have a reduced capacity to convert [3H]-T to [3H]-DHT.

Effects of an alpha 2-adrenoceptor antagonist on glucose tolerance in the genetically obese mouse (C57BL/6J ob/ob).

This study examines the effects of a relatively selective alpha 2-adrenoceptor antagonist, 8-(L-piperazinyl)imado-[1,2-alpha] pyrazine (compound A), and the preferential alpha 2-agonist clonidine on blood glucose, glucose tolerance, and plasma insulin levels in the C57BL/6J ob/ob mouse and its lean littermate. While clonidine raised blood glucose levels and impaired glucose tolerance, oral administration of compound A resulted in decreased blood glucose levels, as well as improved glucose tolerance in ob/ob mice. Insulin levels in ob/ob mice treated with clonidine were significantly reduced, while compound A raised insulin levels threefold and blocked the effects of clonidine when co-administered to the same animals. Clonidine-induced hyperglycemia in lean littermates was not accompanied by a decrease in insulin levels, while a small but significant increase in insulin levels was observed by compound A administration. Glycogen synthesis in diaphragm of ob/ob mice was enhanced after oral administration of compound A and was accompanied by an increase in plasma insulin levels. Concomitant treatment with a potent somatostatin analog to inhibit insulin release blocked the effects of the alpha 2-adrenoceptor antagonist, compound A. These observations suggest that the alpha 2-antagonist studied, increased plasma insulin levels with an accompanying reduction in blood glucose and an improvement in glucose tolerance in a genetic model of insulin resistance. Differential sensitivity to alpha 2-agonist in these genetically obese mice, ob/ob, was demonstrated by decreased insulin levels due to clonidine administration.

Effect of insulin pump therapy on blood pressure and the renin-angiotensin system of diabetic rats.

Insulin therapy, administered by continuous subcutaneous infusion with osmotic pumps over a 28 day period at doses of 2.5 and 5.0 units/day, resulted in a statistically significant increase in body weight of diabetic rats. The concentration of blood glucose was reduced by 68% to 109 mg/dl blood sugar by the higher dose of insulin and only partial control of diabetes was achieved by the lower dose (185 mg/dl blood sugar, -39%). Blood pressure was normalized by both doses of insulin. Elevated serum angiotensin converting enzyme activity and plasma renin activity, expressed as generated angiotensin I, were unaffected by the lower dose of insulin, but were reduced by 26% and 40%, respectively at the higher dose. These data suggest that elevated serum ACE and plasma renin activity, commonly found in the streptozotocin-diabetic rat, may not be primarily responsible for hypertension in this model.

The effect of ponalrestat on sorbitol levels in the lens of obese and diabetic mice.

Sorbitol levels were determined in lens of genetically obese (ob/ob) and diabetic (db/db) mice, as well as in lean mice (+/db, +/ob) made diabetic by administration of streptozotocin (STZ). Treatment of lean mice with STZ resulted in hypoinsulinemia, whereas the ob/ob and db/db mice were hyperinsulinemic. Hyperglycemia was present in STZ-treated +/db and +/ob mice and in db/db mice, whereas relative euglycemia was observed in ob/ob mice and untreated +/db and +/ob mice. Sorbitol levels were elevated in lens tissue of db/db mice and STZ-treated +/db. In contrast, no changes in sorbitol content were observed in ob/ob mice and +/ob mice treated with STZ, suggesting that aldose reductase activity in lens of this animal model is considerably less than that present in db/db mice. Oral treatment of db/db mice and STZ-treated +/db mice with Ponalrestat reduced hyperglycemia-induced sorbitol accumulation significantly in lens, indicating that aldose reductase inhibitors may ameliorate long-term complications associated with sorbitol accumulation in diabetes.

Impaired insulin-like growth factor I-mediated stimulation of glucose incorporation into glycogen in vivo in the ob/ob mouse.

The ability of insulin to modulate glucose metabolism is impaired in insulin resistant ob/ob mice. It has been shown that insulin-like growth factor I stimulates the uptake and metabolism of glucose in muscle through the insulin-like growth factor receptor not the insulin receptor. Thus, we have compared the abilities of insulin-like growth factor I and insulin to stimulate the in vivo incorporation of [14C]-glucose into glycogen in the diaphragm of ob/ob mice and their lean littermates. The animals used in these studies were 12-14 weeks old and the serum insulin levels of the ob/ob mice were 16-fold higher than in their lean littermates. There were no differences in the serum levels of glucose or insulin-like growth factor I. Both insulin and insulin-like growth factor I stimulate the incorporation of [14C]-glucose into glycogen in lean mice. Significant stimulation occurs at doses as low as 1 micrograms/kg of either peptide. The effective doses of insulin and insulin-like growth factor I are quite similar, which indicates that the effect of insulin-like growth factor I is mediated by the insulin-like growth factor receptor and not the insulin receptor. In contrast, greater than 100 micrograms/kg of insulin-like growth factor I is required to stimulate [14C]-glucose incorporation into glycogen in the diaphragm of ob/ob mice. Thus, ob/ob mice are resistant to the action of both insulin and insulin-like growth factor I.(ABSTRACT TRUNCATED AT 250 WORDS)

Design of a selective insulin receptor tyrosine kinase inhibitor and its effect on glucose uptake and metabolism in intact cells.

An inhibitor of the insulin receptor tyrosine kinase (IRTK), (hydroxy-2-naphthalenyl-methyl) phosphonic acid, was designed and synthesized and was shown to be an inhibitor of the biological effects of insulin in vitro. With a wheat germ purified human placental insulin receptor preparation, this compound inhibited the insulin-stimulated autophosphorylation of the 95-kDa beta-subunit of the insulin receptor (IC50 = 200 microM). The ability of the kinase to phosphorylate an exogenous peptide substrate, angiotensin II, was also inhibited. Half-maximal inhibition of basal and insulin-stimulated human placental IRTK activity was found at concentrations of 150 and 100 microM, respectively, with 2 mM angiotensin II as the peptide substrate. The inhibitor was found to be specific for tyrosine kinases over serine kinases and noncompetitive with ATP. The inhibitor was converted into various (acyloxy)methyl prodrugs in order to achieve permeability through cell membranes. These prodrugs inhibited insulin-stimulated autophosphorylation of the insulin receptor 95-kDa beta-subunit in intact CHO cells transfected with human insulin receptor. Inhibition of insulin-stimulated glucose oxidation in isolated rat adipocytes and 2-deoxyglucose uptake into CHO cells was observed with these prodrugs. Our data provide additional evidence for the involvement of the insulin receptor tyrosine kinase in the regulation of glucose uptake and metabolism. These results and additional data reported herein suggest that this class of prodrugs and inhibitors will be useful for modulating the activity of a variety of tyrosine kinases.

The insulin-mimetic effect of vanadate is not correlated with insulin receptor tyrosine kinase activity nor phosphorylation in mouse diaphragm in vivo.

The in vivo administration of sodium orthovanadate stimulated the incorporation of [14C]glucose into [14C] glycogen, in a dose- and time-dependent manner, in mouse diaphragm. Activation of diaphragm insulin receptor was measured by exogenous tyrosine kinase activity and an antibody that recognizes a conformational change in the receptor beta-subunit upon autophosphorylation. Neither method detected insulin receptor activation by in vivo vanadate administration, suggesting that vanadate's insulin-mimetic effect on mouse diaphragm glycogenesis occurs at a site distal to the insulin receptor.

Clinical profile of angioedema associated with angiotensin converting-enzyme inhibition.

Based on data from three studies with complete recording of adverse events in about 12,000 patients each, we determined that angioedema in association with the angiotensin converting-enzyme inhibitor enalapril maleate occurred during the first week of therapy at the rate of one case per 3000 patients per week. Thereafter, the incidence was 14-fold lower, without evidence of a temporal trend in incidence beyond the first week of therapy. The cumulative incidence was one case per 1000 patients treated (0.1%). An additional 138 case reports consistent with the diagnosis of angioedema were obtained from our overall controlled and marketed experience using enalapril in more than 1.2 million patients. These reports were examined to further characterize the reaction. The cases generally were mild, and they resolved on discontinuation of drug therapy. Seven patients experienced angioedema or urticaria in association with both enalapril and captopril, a structurally different angiotensin converting-enzyme inhibitor. This further suggested that the side effect is mechanism based. If angioedema is suspected, therapy with any angiotensin converting-enzyme inhibitor should be interrupted promptly, respiratory distress should be treated appropriately, and subsequent therapy should be initiated with an agent from an alternative class of medication.

Effects of the angiotensin converting enzyme inhibitor, lisinopril, on normal and diabetic rats.

The comparative effects of lisinopril, a third generation angiotensin converting enzyme (ACE) inhibitor, on components of the renin-angiotensin system were assessed in normal and in an animal model of diabetes-related hypertension, the streptozotocin-diabetic rat. Two weeks after injection of streptozotocin the mean systolic blood pressure of diabetic rats was elevated 11% above that of normal rats. This effect was prevented by daily injection of insulin. The mean serum ACE activity was elevated 71% above that of normal rats. Lisinopril reduced systolic blood pressure and inhibited serum ACE activity in both normal and diabetic rats in a dose-response fashion. In normal rats maximum inhibition of blood pressure occurred at a mean dose of 1.0 mg/kg and in the diabetic rat at a mean dose of 5.0 mg/kg. At a mean dose of 5 mg/kg, ACE was inhibited by 100 and 92% in normal and diabetic rats, respectively. Plasma renin activity (PRA) increased sharply in both groups of rats treated with the lower doses of lisinopril, only to decrease at the 5 mg/kg level. At 20 mg/kg, PRA continued to decline in normal animals, but not in diabetic rats. Formation of angiotensin II (Ang II) in both normal and diabetic rats was maximally inhibited at doses of 1.0 and 0.1 mg/kg of lisinopril, respectively without a significantly greater effect at the higher doses of the drug. In separate experiments the effects of chronic treatment with lisinopril at two dosage levels on various physiological parameters of streptozotocin-diabetic rats were compared with the effects of another hypotensive agent, hydralazine, an arteriolar vasodilator.(ABSTRACT TRUNCATED AT 250 WORDS)

Inability of a mouse cell line transformed to produce biologically active recombinant human insulin-like growth factor I (IGF-I) to respond to exogenously added IGF-I.

A plasmid expression vector encoding human insulin-like growth factor I (hIGF-I) in the form of a 97-amino acid precursor protein containing the first 27 amino acids of prebovine GH and the 70 amino acids of hIGF-I has been used to transform mouse L cells. A stably transformed mouse L cell clone has been isolated which expresses and secretes hIGF-I. The secreted peptide comprises 3% of the protein in conditioned medium. IGF-I can be purified to homogeneity in 2 chromatographic steps. One liter of conditioned medium yields approximately 200 micrograms purified peptide. Amino-terminal sequence analysis confirms that the signal peptide has been proteolytically hydrolyzed from the precursor protein before secretion to form [Ala0]hIGF-I. The recombinant peptide and serum-derived hIGF-I are equipotent as inhibitors of the binding of [125I]IGF-I to the type 1 receptor of human placenta and to a crude preparation of acid-stable human serum binding proteins. The peptides are equipotent in 2 in vitro assays, the stimulation of the rate of 2-[1,2-N-3H]deoxyglucose transport in BC3H1 cells and the stimulation of [methyl-3-3H]thymidine incorporation into DNA in A10 cells. In contrast to a control mouse L cell line, DNA synthesis in the [Ala0]IGF-I-secreting line is completely unresponsive to [Thr59]IGF-I, while it responds normally to calf serum (10%). Thus, the [Ala0]IGF-I-secreting line is selectively desensitized to IGF-I. The binding of [125I]IGF-I to both lines is identical, indicating that the loss of responsiveness to IGF-I is not due to a loss of cell surface receptor. The ability to render mouse L cells unresponsive to IGF-I is transferred in the conditioned medium of the [Ala0]IGF-I-secreting cell line. In addition, pretreatment of control cells with [Thr59]IGF-I (10 nM) results in attenuation of the response to a subsequent dose of IGF-I. These data indicate that prolonged exposure to high levels of IGF-I may cause a postreceptor-mediated desensitization to IGF-I. Alternatively, IGF-I may promote secretion of an inhibitor of IGF-mediated DNA synthesis.

A protein phosphotyrosine phosphatase distinct from alkaline phosphatase with activity against the insulin receptor.

Rat liver plasma membranes were found to have a relatively high ratio of acid to alkaline phosphatase activity when compared to rabbit liver and human placental membranes, respectively. The rat liver plasma membranes contained PPTl phosphatase activity against the soluble autophosphorylated insulin receptor beta-subunit. The PPT phosphatase activity of the membranes, using 32P-histone 2b as a substrate, was inhibited by 100 microM Zn+2, insensitive to 10 mM EDTA, and displayed maximal activity at neutral pH. Dephosphorylation of the insulin receptor beta-subunit by rat liver membranes was inhibited by Zn+2, and stimulated by EDTA. These results prove that the plasma membrane of a physiologically relevant insulin target tissue contains a PPT phosphatase, distinct from alkaline phosphatase, which catalyzes the dephosphorylation of the insulin receptor beta-subunit.

Mechanism of action and biological profile of HMG CoA reductase inhibitors. A new therapeutic alternative.

Lovastatin (MK-803, mevinolin) and simvastatin (MK-733, synvinolin), 2 highly potent 3-hydroxy-3-methylglutaryl coenzyme A (HMG CoA) reductase inhibitors, have been heralded as breakthrough therapy for the treatment of atherosclerotic disease. This paper discusses the biochemical attributes of these HMG CoA reductase inhibitors, their structures and inhibitory properties in a variety of biological systems and presents the rationale for their therapeutic use. Not only do lovastatin and simvastatin potently inhibit cholesterol biosynthesis; they also can result in the induction of hepatic low density lipoprotein (LDL) receptors, thus increasing the catabolism of LDL-cholesterol. Lovastatin and simvastatin are the first HMG CoA reductase inhibitors to receive regulatory agency approval for marketed use. Their safety profiles are reviewed and 2 aspects of this evaluation are stressed. First, the objective in the clinical use of these inhibitors is to normalise plasma cholesterol levels in hypercholesterolaemic individuals. This contrasts with the profound reductions in cholesterol obtained when normocholesterolaemic animals are treated by the high doses of these drugs required for toxicological assessment. Second, both lovastatin and simvastatin are administered as prodrugs in their lactone forms. As lactones, they readily undergo first-pass metabolism, hepatic sequestration and hydrolysis to the active form. Consequently, lovastatin and simvastatin achieve lower plasma drug levels than do other HMG CoA reductase inhibitors in clinical development. Low plasma levels have been established as an important determinant of safety in the use of HMG CoA reductase inhibitors in both animal and human studies.

Insulin receptor tyrosine kinase activity is unaltered in ob/ob and db/db mouse skeletal muscle membranes.

Insulin binding and insulin receptor tyrosine kinase activity were examined in two rodent models with genetic insulin resistance using partially-purified skeletal muscle membrane preparations. Insulin binding activity was decreased about 50% in both 12-week (219 +/- 184 vs 1255 +/- 158 fmoles/mg, p less than 0.01) and 24-week old (2120 +/- 60 vs 1081 +/- 60 fmoles/mg, p less than 0.01) ob/ob mice. In contrast, insulin binding to membrane derived from 24-week old db/db mice was not significantly different from lean controls (1371 +/- 212 vs 1253 +/- 247 fmoles/mg). Insulin-associated tyrosine kinase activity of membranes from ob/ob skeletal muscle was decreased, compared to its normal lean littermate, when compared on a per mg of protein basis in both 12-week (37 +/- 3 vs 21 +/- 3 pmoles/min/mg, p less than 0.05) and 24-week old (71 +/- 5 vs 37 +/- 6 pmoles/min/mg, p less than 0.01) mice. However, no significant differences in kinase activities were observed when the data were normalized and compared on a per fmole of insulin-binding activity basis for the 12-week (12 +/- 1 vs 11 +/- 2) and 24-week (27 +/- 2 vs 20 +/- 3) age groups. Insulin receptor tyrosine kinase activity of db/db skeletal muscle membranes was not different than its normal lean littermate whether expressed on a protein (34 +/- 7 vs 30 +/- 3) or fmole of insulin-binding activity (21 +/- 4 vs 18 +/- 4) basis. These data suggest that insulin receptor tyrosine kinase is not associated with the insulin resistance observed in ob/ob and db/db mice and demonstrate differences in receptor regulation between both animal models.

Synthetic segments of the mammalian beta AR are preferentially recognized by cAMP-dependent protein kinase and protein kinase C.

Desensitization of the beta-adrenergic receptor has been correlated in some cell systems with receptor phosphorylation. Various kinases have been implicated in these phosphorylation processes, including both cAMP-dependent protein kinase and protein kinase C. In the present study, we have utilized the protein sequence information obtained from the cloning of the mammalian beta-adrenergic receptor to prepare synthetic peptides corresponding to regions of the receptor which would be predicted to act as possible substrates for these kinases in vivo. Two of these receptor-derived peptides were found to serve as substrates for these protein kinases. A peptide corresponding to amino acids 257-264 of the beta-receptor is the preferred substrate for the cAMP-dependent protein kinase, while protein kinase C showed a marked preference for phosphorylation of a peptide corresponding to residues 341-351 of the beta-adrenergic receptor.

Insulin receptor desensitization correlates with attenuation of tyrosine kinase activity, but not of receptor endocytosis.

A model of insulin-receptor down-regulation and desensitization has been developed and described. In this model, both insulin-receptor down-regulation and functional desensitization are induced in the human HepG2 cell line by a 16 h exposure of the cells to 0.1 microM-insulin. Insulin-receptor affinity is unchanged, but receptor number is decreased by 50%, as determined both by 125I-insulin binding and by protein immunoblotting with an antibody to the beta-subunit of the receptor. This down-regulation is accompanied by a disproportionate loss of insulin-stimulated glycogen synthesis, yielding a population of cell-surface insulin receptors which bind insulin normally but which are unable to mediate insulin-stimulated glycogen synthesis within the cell. Upon binding of insulin, the desensitized receptors are internalized rapidly, with characteristics indistinguishable from those of control cells. In contrast, this desensitization is accompanied by a loss of the insulin-sensitive tyrosine kinase activity of insulin receptors isolated from these cells. Receptors isolated from control cells show a 5-25-fold enhancement of autophosphorylation of the beta-subunit by insulin; this insulin-responsive autophosphorylation is severely attenuated after desensitization to a maximum of 0-2-fold stimulation by insulin. Likewise, the receptor-mediated phosphorylation of exogenous angiotensin II, which is stimulated 2-10-fold by insulin in receptors from control cells, is completely unresponsive to insulin in desensitized cells. These data provide evidence that the insulin-receptor tyrosine kinase activity correlates with insulin stimulation of an intracellular metabolic event. The data suggest that receptor endocytosis is not sufficient to mediate insulin's effects, and thereby argue for a role of the receptor tyrosine kinase activity in the mediation of insulin action.

Stimulation of DNA synthesis in rat A10 vascular smooth muscle cells by threonine-59 insulin-like growth factor I.

The clonal smooth muscle cell line A10, derived from fetal rat aorta, binds 125I-insulin-like growth factor I at a Type 1 insulin-like growth factor receptor. Threonine-59 insulin-like growth factor I, multiplication stimulating activity, and insulin inhibit the binding with IC50 = 10 nM, 84 nM, and 500 nM, respectively. Insulin in high concentrations (greater than 5 microM) completely inhibits 125I-insulin-like growth factor I binding to A10 cells. Threonine-59 insulin-like growth factor I and insulin stimulate [3H]thymidine incorporation into DNA in A10 cells that had been growth arrested by incubation in serum-free media (DMEM/0.1% BSA) for 24-36 hours. The stimulation produced by the peptides is 50-60% of the stimulation produced by 10% fetal calf serum. Low levels of serum (0.1 and 0.5%) also stimulate DNA synthesis, and the effects of Threonine-59 insulin-like growth factor I and low serum are additive. The ED50 for the effects of Threonine-59 insulin-like growth factor I, multiplication stimulating activity, and insulin are 6.8 +/- 0.3 nM, 36 +/- 2.5 nM, and 360 +/- 242 nM, respectively. Incubation of A10 cells for 24 hours with Threonine-59 insulin-like growth factor I or serum increases the protein content per culture dish by 85 +/- 21 and 183 +/- 26%, respectively (mean +/- SEM). Thus, both protein levels and DNA synthesis are increased by incubation with peptides. However, Threonine-59 insulin-like growth factor I does not increase the number of cells in serum starved cultures, although 10% fetal calf serum does.(ABSTRACT TRUNCATED AT 250 WORDS)

Cloning of the gene and cDNA for mammalian beta-adrenergic receptor and homology with rhodopsin.

The adenylate cyclase system, which consists of a catalytic moiety and regulatory guanine nucleotide-binding proteins, provides the effector mechanism for the intracellular actions of many hormones and drugs. The tissue specificity of the system is determined by the particular receptors that a cell expresses. Of the many receptors known to modulate adenylate cyclase activity, the best characterized and one of the most pharmacologically important is the beta-adrenergic receptor (beta AR). The pharmacologically distinguishable subtypes of the beta-adrenergic receptor, beta 1 and beta 2 receptors, stimulate adenylate cyclase on binding specific catecholamines. Recently, the avian erythrocyte beta 1, the amphibian erythrocyte beta 2 and the mammalian lung beta 2 receptors have been purified to homogeneity and demonstrated to retain binding activity in detergent-solubilized form. Moreover, the beta-adrenergic receptor has been reconstituted with the other components of the adenylate cyclase system in vitro, thus making this hormone receptor particularly attractive for studies of the mechanism of receptor action. This situation is in contrast to that for the receptors for growth factors and insulin, where the primary biochemical effectors of receptor action are unknown. Here, we report the cloning of the gene and cDNA for the mammalian beta 2AR. Analysis of the amino-acid sequence predicted for the beta AR indicates significant amino-acid homology with bovine rhodopsin and suggests that, like rhodopsin, beta AR possesses multiple membrane-spanning regions.