Tamsulosin: the United States trials

Overall, tamsulosin has several advantages. Its long-acting action allows for once-daily dosing. The therapeutic effect, as indicated by > 30% increase in peak urinary flow rate, is realized in more than 50% of the patients receiving the therapy. The beneficial effect from treatment is seen as early as 2 to 3 weeks after the maximum dose is reached. In addition, the dose may be adjusted from 0.4 mg daily to 0.8 mg daily to obtain the desired decrease in urinary tract obstructive symptoms, although the vast majority of patients are effectively treated with 0.4 mg daily. Also, there is no known effect of alpha 1-adrenergic antagonists on the serum PSA concentration. The incidence of untoward cardiovascular system effects is less important because of tamsulosin's uroselective action. As with any other medical therapy for BPH, tamsulosin must be taken indefinitely to maintain the therapeutic effect.

Influence of risk factors on peripheral and cerebrovascular disease in men with coronary artery disease, low high-density lipoprotein cholesterol levels, and desirable low-density lipoprotein cholesterol levels. HIT Investigators. Department of Veterans Affairs HDL Intervention Trial

BACKGROUND

The Veterans Administration-HDL Intervention Trial is an ongoing, 20-center, randomized, double-blind, placebo-controlled study aiming to assess the effect of gemfibrozil-improved low high-density lipoprotein cholesterol levels on cardiovascular morbidity and mortality rates.

METHODS AND RESULTS

Eligible patients were men with low high-density lipoprotein cholesterol levels and demonstrable coronary heart disease. A total of 2531 patients (average age 63.5 years) were randomly assigned in this study, with a mean high-density lipoprotein cholesterol level of 0.83 mmol/L (32 mg/dL) and low-density lipoprotein cholesterol level of 2.87 mmol/L (111 mg/dL). Baseline data provided the opportunity to assess the interaction of several coronary heart disease risk factors and comorbid vascular diseases. Of these patients, 206 had diabetes mellitus (DM) alone, 1021 had hypertension (HTN) alone, 421 had both DM and HTN, and 883 had neither ("others"). Considering the influence of these risk factors on comorbidities independent of smoking status, patients with DM alone had a 2-fold increase in the prevalence of peripheral vascular disease and a 1.5-fold increase in congestive heart failure. Patients with HTN had a significant increase in the prevalence of cerebrovascular disease, stroke, and congestive heart failure. Patients with HTN and DM had a significant increase in all comorbidities. Smoking resulted in substantial increase of both peripheral vascular disease and cerebrovascular disease. Compared with nonsmoking patients with no DM or HTN, patients with DM and HTN and smoking had a 3-fold increase in the prevalence of peripheral vascular disease and a 3.5-fold increase in cerebrovascular disease (P < .001).

CONCLUSIONS

We conclude that DM is a strong correlate of peripheral vascular disease, hypertension of cerebrovascular disease, and that there is a strong additive effect between DM, HTN, and smoking on both.

Surface retention of an inactivating lutropin receptor mutant in exoloop 3

The heptahelical lutropin receptor (LHR) signals primarily via the Gs-adenylyl cyclase pathway and undergoes ligand-mediated receptor desensitization and internalization. A loss-of-function rat LHR mutant was recently described in which a single amino acid residue replacement in exoloop 3, K583E, had no effect on human choriogonadotropin (hCG) binding but essentially abolished signaling. This LHR mutant is a prime candidate for which to study hCG-mediated receptor internalization since it is highly unlikely that an amino acid residue in exoloop 3 , i.e. an extracellular portion of LHR connecting transmembrane helices 6 and 7, could have any direct interaction with Galpha(s), which is located on the cytoplasmic face of the plasma membrane. A method to study endocytosis was adapted that involves concanavalin A binding to the glycoproteins on the cell surface, thus facilitating separation of the plasma membrane fraction from other cellular membrane fractions by sucrose gradient centrifugation. Conditions were used such that a single round of endocytosis could be determined with [125I]hCG. Endocytic rate constants of 0.03 and O min(-1) were obtained for LHR and the mutant, respectively, in transfected human embryonic kidney 293 cells; moreover, internalization of the mutant could not be restored by the addition of 8-Br-cAMP. Thus, the presence of the second messenger cAMP is not sufficient for internalization of ligand-occupied LHR. Rather, it appears that ligand-mediated activation and subsequent internalization of LHR results from an altered conformational state or a conformation-dependent post-ligand binding modification such as phosphorylation.

Systematic biopsy-based staging of prostate cancer: scientific background, individual variables, combination of parameters, and current integrative models

Staging of the prostate cancer remains the mainstay of treatment decisions and prognostication. Multiple staging tests, which are currently available, fail to provide optimal staging accuracy in the management of prostate cancer. Systemic biopsy can provide useful data regarding bilaterality, Gleason grade, cancer map, perineural infiltration, tumor volume, percentage cancer and microvessel density. We have reviewed existing literature on systematic biopsy in this review. We have further discussed the role of neural network technology in integrating this information.

Novel staging tool for localized prostate cancer: a pilot study using genetic adaptive neural networks

PURPOSE

An estimated $1.5 billion is spent annually for direct medical expenses and an additional $2.5 billion for indirect costs for the management of prostate cancer. Today there are several procedures for staging prostate cancer, including lymph node dissection. Despite these procedures, the accuracy of predicting extracapsular disease remains low (range 37 to 63, mean 45%). Use of multiple staging procedures adds significantly to the costs of managing prostate cancer. Recently artificial intelligence based neural networks have become available for medical applications. Unlike traditional statistical methods, these networks do not assume linearity or homogeneity of variance and, thus, they are more accurate for clinical data. We applied this concept to staging localized prostate cancer and devised an algorithm that can be used for prostate cancer staging.

MATERIALS AND METHODS

Our study comprised 1,200 men with clinically organ confined prostate cancer who underwent preoperative staging using serum prostate specific antigen, systematic biopsy and Gleason scoring before radical prostatectomy and lymphadenectomy. The performance of the neural network was validated for a subset of patients and network predictions were compared with actual pathological stage. Mean patient age was 62.9 years, mean serum prostate specific antigen 8.1 ng./ml. and mean biopsy Gleason 6. Of the patients 55% had organ confined disease, 27% positive margins, 8% seminal vesicle involvement and 7% lymph node disease. Of margin positive patients 30% also had seminal vesicle involvement, while of seminal vesicle positive patients 50% also had positive margins.

RESULTS

The sensitivity of the network was 81 to 100%, and specificity was 72 to 75% for various predictions of margin, seminal vesicle and lymph node involvement. The negative predictive values tended to be relatively high for all 3 features (range 92 to 100%). The neural network missed only 8% of patients with margin positive disease, and 2% with lymph node and 0% with seminal vesicle involvement.

CONCLUSIONS

Our study suggests that neural networks may be useful as an initial staging tool for detection of extracapsular extension in patients with clinically organ confined prostate cancer. These networks preclude unnecessary staging tests for 63% of patients with clinically organ confined prostate cancer.

Prostatectomy tissue for research: balancing patient care and discovery

The application of modern technology in basic research often requires fresh tissue from human organs. The acquisition of this tissue challenges the anatomic pathologist to balance the needs of the basic scientist with the requirements of quality patient care. Our experience indicates that fresh tissue adequate for research can be obtained from neoplastic prostate glands without compromising patient care. The process requires dedicated, knowledgeable individuals and extensive documentation. Potential problems include low yield for research studies, loss of all residual carcinoma, compromise of the specimen margin, and unforeseen costs. Best collaborations occur in situations in which basic scientists and anatomic pathologists establish a working relationship and develop a mutually supportive means of funding.

The endothelin subtype A receptor undergoes agonist- and antagonist-mediated internalization in the absence of signaling

The potent vasoconstrictor and mitogen to smooth muscle cells, endothelin-1 (ET-1), acts via two distinct G protein-coupled receptors, subtype A (ETAR) and subtype B, that are coupled primarily to the Gq-phospholipase C signaling pathway. It is known that ET-1 binding to ETAR promotes internalization, with subsequent degradation of at least a portion of the bound ligand. To investigate whether signaling is required for endocytosis, we developed stably transfected lines of human embryonic kidney 293 cells expressing wild-type ETAR and a receptor chimera (ETARC) in which the C-terminal cytoplasmic tail to ETAR was replaced with that of the lutropin receptor, another G protein-coupled receptor, but one which signals through the Gs-adenylyl cyclase pathway. ETARC binds ET-1 like ETAR, but is deficient in signaling. Using a combined concanavalin A/sucrose gradient centrifugation technique to separate plasma membranes from other cellular membranes, we found that [125I]ET-1 is rapidly internalized into ETAR-expressing cells at 37 C (t1/2 for internalization = 5 min; endocytic rate constant = 0.1 min(-1); ETARC-expressing cells also internalize [125I]ET-1, albeit at a somewhat slower rate than wild-type receptor (t1/2 for internalization = 15 min; endocytic rate constant = 0.03 min(-1). Using immunofluorescence confocal microscopy and an antibody developed to the N-terminal region of ETAR, qualitatively similar results were obtained. In addition, it was found using confocal microscopy that the ETAR-selective antagonist, BQ123, also promoted rapid internalization in cells expressing ETAR. These results establish that inositol 1,4,5-trisphosphate signaling is not required for ligand-mediated internalization of ETAR and suggest that a receptor conformational change is necessary. Moreover, the finding that BQ123 promotes ETAR internalization is novel and has potentially important implications in its clinical use.

Adenosine A1 receptor stimulation antagonizes the negative inotropic effects of the PKC activator dioctanoylglycerol

It has been suggested that adenosine cardioprotection occurs via adenosine A1 receptor-mediated activation of protein kinase C (PKC). However, adenosine has well-known vasodilatory effects in the myocardium, whereas PKC is a vasoconstrictor. This study examined whether adenosine A1 receptor activation alters the effects of the PKC activator. 1,2-dioctanoyl-s,n-glycerol (DOG) in isolated perfused rat hearts (left-ventricular developed pressure) and rat ventricular myocytes ([Ca2+]i and cell shortening). Exposure to DOG decreased left-ventricular developed pressure by 30%, an effect that was completely reversible. Pretreatment of isolated hearts with either the PKC inhibitor chelerythrine or the adenosine A1 agonist 2-chloro-N6-cyclo-cyclo-isolated pentlyadenosine (CCPA) attenuated the negative inotropic effects of DOG. In the isolated myocytes, DOG decreased [Ca2+]i and cell shortening by 25 and 28%, respectively, effects that were attenuated by both chelerythrine and CCPA. The CCPA attenuation of the DOG-induced decrease in [Ca2+]i and cell shortening was blocked by pretreating the myocytes with the adenosine A1 antagonist, 8-cyclopentyl-1,3-dipropylxanthine (DPCPX). These results indicate that in rat ventricular myocardium, adenosine A1 receptor activation attenuates the apparent PKC-dependent negative inotropic effects of DOG via preservation of [Ca2+]i levels.

Overview of alpha-blocker therapy for benign prostatic hyperplasia

Management of benign prostatic hyperplasia (BPH) is rapidly changing. Established surgical procedures are being replaced by minimally invasive modalities such as electrovaporization and transurethral needle ablation. Improved understanding of pathophysiology and developments in molecular biology has provided drugs for alleviating the symptoms of prostatic enlargement. Currently, medical therapy is the first-line treatment modality in the management of BPH. There are two types of medical treatment available: alpha-adrenoceptor-blockers and 5-alpha-reductase inhibitors. Alpha-blockers relieve the dynamic component of obstruction whereas 5-alpha-reductase inhibitors relieve the mechanical component of obstruction. At present, alpha-blockers are used most frequently. However, they do have significant cardiovascular side effects. More uroselective alpha-blockers have recently become available and may reduce the risk of cardiovascular side effects. This review summarizes relevant literature on the use of alpha-blockers in the treatment of BPH.

Effects of moderate intensity exercise on serum lipids in African-American men with severe systemic hypertension

The prevalence of systemic hypertension and its cardiovascular consequences is higher in African-Americans than in whites. Low to moderate intensity aerobic exercise lowers blood pressure (BP) in African-American patients with severe hypertension. It is not known whether such exercise can improve lipid metabolism in these patients. Thirty-six African-American men with established essential hypertension, aged 35 to 76 years, were randomly assigned to an exercise (n = 17) or no exercise (n = 19) group. The exercise group exercised for 16 weeks, 3 times/week, at 60% to 80% of maximum heart rate. After 16 weeks, peak oxygen uptake in the exercise group improved (21+/-4 vs 23+/-3 ml/kg/min; p <0.001). Body weight did not change. Exercise intensity correlated with high-density lipoprotein (HDL) cholesterol changes from baseline to 16 weeks (r = 0.65; p <0.01) and was the strongest predictor of these changes (R2 = 0.4; p = 0.009). Lipoprotein-lipid changes in the 2 randomized groups did not differ significantly. A 10% increase in HDL cholesterol--42+/-19 versus 46+/-19 mg/dl; p = 0.003--noted in 10 patients who exercised > or = 75% of maximal heart rate suggested the existence of an exercise intensity threshold. Thus low to moderate intensity aerobic exercise may not be adequate to modify lipid profiles favorably in patients with severe hypertension. However, substantial changes in HDL cholesterol were noted in patients exercising at intensities > or = 75% of age-predicted maximum heart rate, suggesting an exercise-intensity threshold.

Transurethral needle ablation for benign prostatic hyperplasia: 12-month results of a prospective, multicenter U.S. study

OBJECTIVES

To report the safety and efficacy of the transurethral needle ablation (TUNA) procedure for the treatment of clinical benign prostatic hyperplasia (BPH).

METHODS

One hundred thirty patients with BPH were enrolled in two identical protocols and treated by the TUNA procedure. Entry criteria included an American Urological Association symptom index (AUA SI) of 13 points or higher and a peak flow rate of 12 mL/s or less. Patients were followed up for 12 months. Efficacy parameters included the AUA SI, AUA problem index, BPH impact index (BPH II), quality of life (QOL) score, and peak flow rate. At each visit, side effects were elicited. Follow-up data are available for 93 patients at 12 months. All patients were given intraurethral lidocaine augmented by oral and/or parenteral sedation. No patient received spinal or general anesthesia.

RESULTS

All patients tolerated the procedure well, and there were no deaths. Forty-one percent of patients (n = 53) had a catheter placed immediately after the procedure. At 12 months, the AUA SI had decreased from 23.7 to 11.9 (P < 0.0001) and the BPH II from 7.5 to 2.5 (P < 0.0001), whereas the peak flow rate had increased from 8.7 to 14.6 mL/s (P < 0.0001). Irritative voiding symptoms were noted in 20 patients (16%) at some point during follow-up. Two patients reported erectile dysfunction, and 1 reported retrograde ejaculation.

CONCLUSIONS

In this prospective study of 130 patients with clinical BPH and lower urinary tract symptoms, TUNA provided substantive and lasting improvement according to AUA SI, BPH II, and QOL scores as well as peak flow rate over 1 year. The TUNA procedure was well tolerated, with few major side effects and complications noted. Longer follow-up is needed to document the maintenance of clinical benefit beyond 12 months.

31P-NMR analysis of congestive heart failure in the SHHF/Mcc-facp rat heart

31P-NMR was used to monitor myocardial bioenergetics in compensated and failing SHHF/MCC-fa(cp) (SHF) rat hearts. The SHHF/Mcc-fa(cp) (spontaneous hypertension and heart failure) rat is a relatively new genetic model in which all individuals spontaneously develop congestive heart failure, most during the second year of life. Failing SHF rat hearts displayed a pronounced decrease in resting PCr:ATP ratios (P<0.001), which was explained by a significant (P<0. 0001) drop in total creatine (47.2+/-3.1 nmol/mg protein) v age matched controls (106+/-3 nmol/mg protein). In end stage failure, NMR determined PCr was 2.9+/-0.1 micro mol/g wet weight under basal conditions. In contrast, 6- and 20-month-old controls and compensated SHFs had PCr values of 5.3+/-0.1, and 5.1+/-0.5 and 5. 1+/-0.2 micro mol/g wet weight. Both compensated and failing SHF hearts were metabolically compromised when the rate pressure product (RPP) was increased, as evidenced by an increase in Pi and a drop in PCr. Compensated SHF hearts, however, were able to increase rate pressure products (RRP, mmHg X beats/min) from 44.5+/-1.4 to 66.6+/-3. 4 K with dobutamine infusion, whereas hearts in end-stage failure were able to increase their RPP from baseline values of 27+/-4 K to only 37+/-7 K. The data indicate that a pronounced decline in PCr and total creatine signals the transition from compensatory hypertrophy to decompensation and failure in the SHF rat model of hypertensive cardiomyopathy.

Minimally invasive therapies for the treatment of symptomatic benign prostatic hyperplasia: the University of Florida experience

OBJECTIVE

To describe the University of Florida experience with minimally invasive therapies in the surgical treatment of benign prostatic hyperplasia (BPH).

BACKGROUND DATA

Typically, the standard surgical treatment for symptomatic benign prostatic hyperplasia (BPH) has been transurethral resection of the prostate (TURP). Due to the morbidity associated with TURP, several minimally invasive therapies, such as laser, microwaves, high intensity focused ultrasound, and radiofrequency needle ablation, have been utilized to treat BPH.

METHODS

The authors review their experience, along with that of others, with various forms of heat therapy in the treatment of BPH.

RESULTS AND CONCLUSIONS

Although high intensity focused ultrasound (HIFU), interstitial laser, and microwaves procedures have been shown to be effective in the treatment of BPH, our experience has been with laser, VaporTrode, and TUNA. We found that VaporTrode and TUNA currently offer several advantages over many of the other modalities.

Identification of endothelin receptor subtypes in sheep choroid plexus

Endothelin (ET) and its G-protein-coupled receptors are distributed in a wide variety of tissues, including the brain. In this study, we have identified and characterized the endothelin receptor subtypes in sheep choroid plexus. Competitive binding experiments using [125I]ET-1 and the receptor subtype-selective ligands, ET-1, ET-3, BQ-123, Sarafotoxin 6c, and [Ala1,3,11,15] ET-1 demonstrated the presence of both ETA and ETB receptor subtypes in the ratio of 30:70. In addition, a small fraction of the total binding sites exhibited affinities for ET-1 in the subpicomolar range. Chemical crosslinking of [125I]ET-1 with bis(sulfosuccinimidyl)-suberate (BS3) to choroid plexus membranes revealed the presence of two bands, with apparent molecular masses of 89 and 45 kDa, corresponding to the ETA receptor, and three bands, with apparent molecular masses of 75, 58, and 33 kDa, corresponding to the ETB receptor. Of considerable interest was the finding that dimers of the [125I]ET-1-occupied ETA receptor could be identified by crosslinking, as could apparent dimers and tetramers of [125I]ET-1, but only when bound to receptor. In addition to mapping the distribution of ET receptors in sheep choroid plexus, our results strongly suggest that ET-1 binding to the ETA receptor leads to dimer formation.

Hydrochlorothiazide is superior to isradipine for reduction of left ventricular mass: results of a multicenter trial. The Isradipine Study Group

OBJECTIVES

We sought to determine the efficacy of isradipine in reducing left ventricular (LV) mass and wall thickness in hypertensive patients.

BACKGROUND

LV hypertrophy on the echocardiogram is a strong predictor of cardiovascular events. Reduction of LV mass may be a desirable goal of drug therapy for hypertension. However, although thiazide diuretic drugs have been advocated as first-line therapy for hypertension, their efficacy in reducing LV mass has been questioned.

METHODS

Patients with mild to moderate diastolic hypertension and LV mass in excess of 1 SD of normal values were randomized to isradipine (n = 89) or hydrochlorothiazide therapy (n = 45). Evaluations were obtained at baseline, after 3 and 6 months of treatment and 2 weeks after treatment was stopped.

RESULTS

At 6 months, LV mass decreased by 43 +/- 45 g (mean +/- SD) with hydrochlorothiazide (p < 0.001) but only by 11 +/- 48 g with isradipine (p = NS; between-group comparison, p < 0.001). Two weeks after drug therapy was stopped, LV mass remained 24 +/- 41 g lower than that at baseline in the hydrochlorothiazide group (p = 0.003) but only 7 +/- 50 g lower in the isradipine group (p = NS). Septal and posterior wall thicknesses were significantly and equally reduced with both isradipine and hydrochlorothiazide. Greater LV mass reduction with hydrochlorothiazide was related to a 2.8 +/- 3.3-mm reduction of LV cavity size with hydrochlorothiazide but no reduction with isradipine. At 6 months of treatment, diastolic blood pressure (BP) by design was equally reduced in both treatment groups. At 3 months, systolic BP was reduced by 17 +/- 15 mm Hg with isradipine and by 26 +/- 15 and 25 +/- 17 mm Hg at 3 and 6 months, respectively, with hydrochlorothiazide (p = 0.003, between-group comparison). However, on stepwise multivariable regression analysis, treatment selection (partial r2 = 0.082, p = 0.001), change in average 24-h systolic BP (partial r2 = 0.032, p = 0.029) and change in average sitting systolic BP (partial r2 = 0.017, p = 0.096) were predictive of LV mass reduction.

CONCLUSIONS

Despite an equivalent reduction of diastolic BP, 6 months of therapy with hydrochlorothiazide is associated with a substantial reduction of LV mass, greater than that with isradipine. The superior efficacy of hydrochlorothiazide for LV mass reduction is associated with a greater reduction of systolic BP as well as drug selection itself. These data may have important therapeutic implications.

Effect of retinoic acid on prostatic development

BACKGROUND AND METHODS

To assess the effect of retinoids on prostatic ductal branching morphogenesis, anterior prostates from newborn rats were cultured under serum-free conditions for 6 days in the presence of testosterone (10(-8) mM) plus 13-cis-retinoic acid (13-cis-RA), all-trans-retinoic acid (at-RA), or N-4-hydroxyphenyl-retinamide (4-HPR). Measures of morphologic complexity were computed and compared between specimens of different treatment groups.

RESULTS

Prostatic ductal growth and branching were inhibited in a dose-dependent fashion by both 13-cis-RA and at-RA, but not by 4-HPR. This inhibitory effect of 13-cis-RA was reversible, as the prostatic ducts resumed branching and growth after removal of retinoic acid from the culture medium. Using reverse transcription polymerase chain reaction, we then investigated the expression of nuclear receptor genes for retinoic acid.

CONCLUSIONS

This showed the presence of RAR-beta and RAR-gamma in the 0-day prostate, suggesting that the effects of these retinoids on ductal morphogenesis may be via these receptors.

Effects of aerobic training on exaggerated blood pressure response to exercise in African-Americans with severe systemic hypertension treated with indapamide +/- verapamil +/- enalapril

Hypertensive patients are likely to have an exaggerated blood pressure (BP) response during physical exertion. When moderate aerobic exercise was added to medical antihypertensive therapy in patients with severe hypertension, excessive elevations in BP during physical exertion were attenuated even with a modest reduction in BP at rest.

Transurethral evaporation of the prostate for treatment of benign prostatic hyperplasia: results in 168 patients with up to 12 months of followup

PURPOSE

We assessed the safety and efficacy of transurethral evaporation of the prostate for the treatment of symptomatic benign prostatic hyperplasia (BPH).

MATERIALS AND METHODS

A total of 168 patients with symptomatic BPH underwent transurethral evaporation of the prostate. Peak flow rate, American Urological Association symptom index and post-void residual were assessed at baseline, and at 3, 6 and 12 months of followup.

RESULTS

We found a statistically significant decrease in mean American Urological Association symptom index from 20.6 at baseline to 7.2 at 12 months (mean difference 13.4, 65% reduction, p < 0.0001). We also found a statistically significant improvement in mean peak flow rate from 8.2 to 18.2 cc per second, respectively (mean difference 10, 122% increase, p < 0.0001). The most frequent complications were irritative voiding symptoms in 22.6% of patients and urinary tract infections in 4.8%. There were no additional major complications.

CONCLUSIONS

From these results transurethral evaporation of the prostate appears to be safe and effective for treatment of BPH at 12 months of followup.

hCG-receptor binding and transmembrane signaling

The technique of site-directed mutagenesis has proven to be quite powerful in elucidating contact sites involved in the interaction of the heterodimeric glycoprotein hormones and their respective seven transmembrane (TM) G protein-coupled receptors. Our laboratory has focused on identification of the minimum core sequences of the alpha and beta subunits required for bioactivity, the minimum length of a conjoined (yoked) single-chain hCG, the amino acid residues on hCG and the LH/CG-receptor (LH/CG-R) responsible for high-affinity binding, and the regions of the receptor that are involved in TM signaling. A number of amino acid residues have been mapped on the alpha and beta subunits of hCG that appear important in receptor binding. When projected onto the crystal structure of HF-treated hCG, these residues, by and large, cluster on one side of the molecule and cover a sizeable surface area, indicating that the hormone-receptor binding interface is rather extensive. Based on mutagenesis studies of several conserved ionizable amino acid residues in the extracellular domain (ECD) of LH/CG-R and a model that we, in collaboration with Drs Lapthorn and Isaacs, have developed for this region based on the crystal structure of porcine ribonuclease inhibitor, a charged region that appears to play an important role in hormone-receptor recognition has been identified. We have also delineated several regions of LH/CG-R that do not appear to participate in hCG binding but are involved in hCG-mediated signaling. These regions are located in the ECD and extracellular loop III just prior to entry into the membrane via TM helices I and VII, respectively, and in TM helices VI and VII. Similarly, a homologous region in the ECD of the FSH receptor, located with ten residues of TM helix I, is important in signaling but not hormone binding. These results suggest that ligand binding and ligand-mediated receptor activation are quasi-distinct, albeit sequential phenomena. Collectively, our mutagenesis and modeling studies, coupled with results from other laboratories, argue for a ligand-induced conformational change of the receptor that may involve a relative reorientation of the TM helices.