Regulation of pancreatic amylase and lipase gene expression by diet and insulin in diabetic rats

Although insulin has been proposed to mediate the dietary regulation of pancreatic amylase, its interaction with diet in the regulation of amylase and lipase is not well understood and was examined in diabetic rats fed diets high in carbohydrate (HC), protein (HP), or fat (HF) and treated with insulin. Diabetes, independent of diet, decreased amylase content (97%; P < 0.0001) and mRNA (90%; P < 0.0001), but insulin only restored amylase content and mRNA to respective dietary control values. Diabetes, independent of diet, also increased lipase mRNA 1.6-fold (P < 0.004) but interacted (P < 0.0003) with diet on lipase content, resulting in opposite effects in HC- (increased 202%) and HF-diabetic rats (decreased 40%). Insulin partially restored lipase content and mRNA to respective dietary control values. Diet, independent of diabetes, regulated amylase content (P < 0.0001) and mRNA (P < 0.0003), which were three- to fourfold greater in HC- than in HF-fed rats, and lipase content (P < 0.001) and mRNA [rat pancreatic lipase 1 (rPL-1), P < 0.04; rPL-3, P < 0.0001], which were 1.8-fold greater in HF- than in HC- or HP-fed rats. Insulin failed to stimulate maximal amylase gene expression in HP- or HF-fed diabetic rats, suggesting that it is necessary, but not sufficient, for this dietary regulation. Differential regulation of lipase activity and mRNA by diet and insulin raises the possibility that lipase gene expression is regulated by a complex interaction of diet and insulin.

Endurance exercise training is associated with elevated basal sympathetic nerve activity in healthy older humans

We tested the hypothesis that endurance training is associated with altered basal levels of muscle sympathetic nerve activity (MSNA) and responses to acute stress in healthy older adults. MSNA (peroneal microneurography) and plasma norepinephrine (NE) concentrations were measured during supine rest, a cold pressor test, and isometric handgrip (40% maximal voluntary force to exhaustion) in 16 older masters endurance athletes [10 men, 6 women; 66 +/- 1 (SE) yr] and 15 healthy normotensive untrained control subjects (9 men, 6 women; 65 +/- 1 yr). The athletes had higher levels of estimated daily energy expenditure and maximal oxygen uptake and lower levels of resting heart rate and body fat than the control subjects (all P < 0.05). MSNA during supine rest was elevated in the athletes whether expressed as burst frequency (43 +/- 2 vs. 32 +/- 3 bursts/min, respectively; P < 0.05) or burst incidence (75 +/- 4 vs. 52 +/- 5 bursts/100 heartbeats, respectively; P < 0.01). These whole group differences were due primarily to markedly higher levels of MSNA in the athletic vs. untrained women (48 +/- 4 vs. 25 +/- 3 bursts/min, 82 +/- 3 vs. 38 +/- 3 bursts/100 heartbeats, respectively, P < 0.001). In contrast, basal plasma NE concentrations were not significantly different in the athletes vs. control subjects. The MSNA and plasma NE responses to acute stress tended to be greater in the athletes. These findings indicate that vigorous regular aerobic exercise is associated with an elevated level of MSNA at rest and a tendency for an enhanced response to acute stress in healthy normotensive older humans.

Head and neck malformations of the pediatric airway

The authors describe the head and neck malformations that can affect the upper aerodigestive tract. The article is organized so that it begins with the nose and extends through the larynx. A diagnostic table for the localization for an airway lesion is given. Medical and surgical treatment regarding various malformations including choanal atresia, Pierre Robin sequence, laryngomalacia, laryngeal edema, and subglottic stenosis are discussed.

Autoregulatory control of E2F1 expression in response to positive and negative regulators of cell cycle progression

Both positive and negative signals govern the progression of cells from G1 into S phase, and a variety of data implicate the E2F transcription factor as a target for the action of one class of negative regulators, the Rb family of growth suppressors. We now find that the E2F1 gene, which encodes one of the components of E2F activity, is subject to autoregulatory control during progression from G0 to S phase and that this primarily reflects a negative control in G0 and early G1, a time when the majority of E2F activity exits as a complex with Rb family members. In addition, we find that deregulated expression of G1 cyclins in quiescent cells stimulates the E2F1 promoter and that this is augmented by coexpression of cyclin-dependent kinases in an E2F-dependent manner. We conclude that the E2F1 gene is a downstream target for G1 cyclin-dependent kinase activity, most likely as a consequence of phosphorylation of Rb family members, and that the autoregulation of E2F1 transcription may provide a sensitive switch for regulating the accumulation of E2F activity during the transition from G1 to S phase.

Sympathetic neural reactivity to stress does not increase with age in healthy humans

Sympathetic nervous system reactivity to stress is though to increase with age in humans. We tested this hypothesis by recording postganglionic sympathetic nerve activity to skeletal muscle (MSNA) (peroneal microneurography) and by measuring plasma norepinephrine concentrations (PNE), heart rate, and arterial pressure before (prestress control) and during cognitive challenge (mental arithmetic and colored word test), thermal stress (i.e., the cold pressor test), and exhaustive isometric handgrip exercise (40% of maximum voluntary force)/postexercise ischemia in 15 older (60-74 yr, mean +/- SE = 64 +/- 1) and 15 young (19-30 yr, mean +/- SE = 25 +/- 1) healthy men and women (8 males, 7 females each). The initial prestress control level of MSNA was higher in the older subjects (P < 0.01 vs. young), but there were no significant differences for PNE, heart rate, or arterial pressure. The MSNA and PNE responses to mental stress were small and not different in the two groups. MSNA and PNE increased markedly in response to the cold pressor test and isometric handgrip exercise/post exercise ischemia in both groups. The absolute unit increases in MSNA were similar in the two groups, but the relative (percentage) increases were actually smaller in the older subjects (P < 0.05 vs. young) due to their elevated baseline levels. The stress-evoked increases in arterial pressure were similar in the groups, but the older subjects tended to demonstrate smaller increases in heart rate. In general, no gender differences were noted in either age group. These findings fail to support the long-held concept that stress-induced sympathetic nervous system stimulation becomes exaggerated with age. Thus, sympathetic neural hyperreactivity does not appear to be a fundamental property of the aging process in humans.

Evaluation of calf starters containing different amounts of crude protein for growth of Holstein calves

Holstein calves (n = 110) were used to evaluate the effect of calf starters containing 15, 16.8, 19.6, or 22.4% CP, DM basis (diets A, B, C, and D, respectively), on calf performance from d 4 to 56 of life. Preweaning daily gain tended to increase linearly as protein content of diets increased, averaging .37, .39, .38, and .44 kg/d for diets A, B, C, and D, respectively. After weaning, calves fed diet C gained the most (.86 versus .71, .75, and .79 kg/d for A, B, and D, respectively). Overall BW gains from d 4 to 56 averaged .54, .56, .62, and .61 kg/d for A, B, C, and D, respectively. Throughout the experiment, starter consumption tended to increase as CP content of diet increased. Under these conditions, maximum growth was supported by diet C (19.6% CP); no advantage was gained from higher (22.4%) protein content. Calf growth was moderate when calf starters of lower protein contents (15 or 16.8%) were fed.

Bronchoscopic removal of aspirated foreign bodies in children

Foreign body aspiration is the cause of death for more than 300 children each year in the United States. Tracheobronchial inhalation of foreign bodies may result in acute respiratory distress, atelectasis, chronic pulmonary infections, or death. A review of the records of 548 children (aged 4 months to 18 years) was undertaken to identify factors important in diagnosis, to illustrate the effectiveness of current endoscopic techniques and equipment, and to evaluate the results and complications of management. Coughing, choking, and wheezing were the presenting symptoms seen for 95% of the patients. Results of inspiratory and expiratory chest radiographs were positive in 83% of the 440 children who had foreign bodies removed. Fluoroscopy findings were positive for 67 patients, 90% of whom had foreign bodies removed. Foreign bodies were successfully identified and removed in 440 patients (80%). A wide variety of objects was recovered, the most common being peanuts, organic material, other nuts, popcorn, seeds, plastic objects, and pins. The foreign bodies were in the right bronchus in 49%, the left in 44%, and the trachea and hypopharynx in 4%. Two thirds of the objects were lodged in the mainstem bronchi, on either side, and the remainder were in the distal bronchi. Bronchoscopy is required for treatment, and with experience this procedure can be simple and safe. Ninety-nine percent of the foreign bodies identified during bronchoscopy were removed successfully. Minor complications occurred in 5%, and there were no deaths.

Treatment of myopic astigmatism with the 193 nm excimer laser utilizing aperture elements

In this paper, we examine the 193 nm excimer laser's efficacy and safety in treating myopic astigmatism. The VISX Twenty/Twenty excimer laser uses aperture elements to effect astigmatic photorefractive keratectomy. In 70 patients with six months follow-up, the average postoperative sphere was -0.14 and the average postoperative cylinder was -0.54. Seventy-one percent of these patients had uncorrected visual acuity of 20/40 or better at six months. In 12 patients with one year follow-up, the average postoperative sphere was -0.05 and the average postoperative cylinder was -0.59. Eighty-three percent of these patients had uncorrected acuities of 20/40 or better; none had a clinically significant loss of best corrected acuity. This investigation demonstrates that the excimer laser can be used to treat myopic astigmatism successfully.

Characterizing nutrient intakes of adolescents by sociodemographic factors

PURPOSE

The purpose of this study was to provide a description of the current dietary intake of a large sample of U.S. adolescents and to identify sociodemographic risk factors for nutrient intakes that did not meet recommended levels.

METHODS

The 1987-88 USDA Nationwide Food Consumption Survey was used to assess the nutrient intake of 933 adolescents aged 11 to 18 years. Analysis of covariance was used to determine the effect of the following on the nutrient intakes of males and females: household income and size, race, geographic region, degree of urbanization, and head of household status. Subject age was entered as a control variable.

RESULTS

Vitamin A, vitamin E, calcium, magnesium, and zinc were the nutrients most often consumed below recommended levels. In addition the females consumed low levels of phosphorus and iron. Percent calories from total fat and saturated fat and mean sodium intakes were above recommended levels for the majority of the sample. Females were more likely to meet cholesterol recommendations than males. Race and region affected the most nutrient intake variables. For the females, living in the south was a significant predictor for low intakes of several essential vitamins and minerals.

CONCLUSIONS

On average, the adolescents consumed diets that were low in several essential vitamins and minerals and high in some nutrients related to increased incidence of chronic disease. There were groups of teens who had dietary patterns that placed them at especially high risk, in particular the black and Southern females.

Treatment of overt isolated testicular relapse in children on therapy for acute lymphoblastic leukemia. A report from the Childrens Cancer Group

BACKGROUND

Fifty-seven children with acute lymphoblastic leukemia (ALL) receiving therapy who experienced overt isolated testicular relapse while in bone marrow remission were entered into a study that featured an intensive retreatment regimen.

METHODS

The objective was to determine whether a change in chemotherapy and local irradiation would prevent subsequent marrow relapse and increase the survival rate. The regimens used (modified Berlin-Frankfurt-Munster or modified New York) delivered acceptable therapy based on analyses of toxicity data.

RESULTS

Overall survival at 5 years from the time of testicular relapse was 47%, with an event-free survival of 43%. Events have been documented in 28 of 55 evaluable children. Analysis of these patients revealed that 23 children had bone marrow relapse, 4 children had central nervous system relapse, and 1 child had testicular relapse. In addition, two patients were removed from the study for toxicity, one child for infection (mucormycosis), and five children had a bone marrow transplantation while in remission and became ineligible to continue in the study. Two children were removed at the request of their parents, and nine children were lost to follow-up.

CONCLUSION

Because of their high risk of developing systemic relapse, boys with ALL who experience isolated overt testicular relapse during active therapy should be retreated with intensive treatment.

Morphologic basis for loss of regulated insulin secretion by isolated rat pancreatic islets

Laboratories engaged in secretory studies of rat pancreatic islets often encounter high baseline insulin secretion with poor secretory response to secretagogues, such as glucose. The specific morphologic abnormalities that accompany this unregulated release have not been described. We isolated islets comparing two approaches. Both used stationary digestion with collagenase. In method I, we distended the biliary duct extracorporeally with collagenase and minced the pancreas after a 28 min digestion (37 degrees C). In method II, we distended the pancreas intracorporeally and digested for 40 min without mincing. Both methods utilized a similar collagenase concentration (2 micrograms/ml in Hank's balanced salt solution (HBSS). Both methods yielded over 300 islets/rat. Islets from both methods appeared intact, when viewed under the dissecting microscope. We found that adequate secretion from incubated islets was evoked with method I, i.e., low basal insulin levels at low glucose (3.3 mM), tripling at 11.0 mM glucose, and nearly quadrupling in response to higher glucose (16.7 mM). In contrast, method II was characterized by high basal levels without response to higher glucose. Ultramicroscopic examination of islet B cells in method I revealed normal cytological features, while B cells in method II showed marked degranulation, profiles of swollen endoplasmic reticulum, and swollen mitochondria. Morphometric analysis of B cells confirmed quantitatively a decrease in secretory granule density and mitochondrial enlargement in method II compared to method I. Anatomic changes, largely confined to the B cells of islets may account for functional alterations of responses. Defects cannot be predicted from gross appearance of islets.

cDNA cloning and expression of guinea pig neutrophil attractant protein-1 (NAP-1). NAP-1 is highly conserved in guinea pig

cDNA for neutrophil attractant protein-1 (NAP-1, also known as IL-8) was cloned from Con A-stimulated guinea pig spleen cells with human NAP-1 cDNA as a probe. Guinea pig NAP-1 cDNA is composed of 1433 bp with an open reading frame which encodes for a 101-amino-acid protein. Guinea pig NAP-1 had 70% amino acid sequence similarity to human NAP-1, which was much higher than a similarity between human and guinea pig monocyte chemoattractant protein-1 (MCP-1) (56%). Nucleotide sequence similarity within the coding region was 75%. To confirm its biological activity in guinea pig, recombinant guinea pig NAP-1 was expressed in COS-7 cells then purified. N-terminal sequence analysis gave two different N-termini at position 23 (Met) or 24 (Val). The two proteins showed their peak activity for guinea pig neutrophils at the concentration of 1 microgram/ml (10-7 M). Despite its high similarity to human NAP-1, the responsiveness of human neutrophils to guinea pig NAP-1 was minimum. Recombinant guinea pig NAP-1 caused strong neutrophil infiltration after intradermal injection into guinea pig skin. Since guinea pig is classified as a rodent, it was of interest to know whether human NAP-1 cDNA hybridizes to genomic DNA of other rodents such as mouse or rat, in which a NAP-1 homologue has not been found. Under low stringency conditions, human NAP-1 cDNA hybridized to human, rabbit, and guinea pig DNA, but not to mouse or rat DNA. Unlike NAP-1, human MCP-1 cDNA hybridized to genomic DNA of rabbit, guinea pig, mouse, and rat; MCP-1 cDNA have been cloned from these species. The apparent absence of a NAP-1 gene in mouse or rat makes this chemoattractant unique among the members of the protein family to which NAP-1 and MCP-1 belong.

cDNA cloning and expression of guinea pig neutrophil attractant protein-1 (NAP-1). NAP-1 is highly conserved in guinea pig

cDNA for neutrophil attractant protein-1 (NAP-1, also known as IL-8) was cloned from Con A-stimulated guinea pig spleen cells with human NAP-1 cDNA as a probe. Guinea pig NAP-1 cDNA is composed of 1433 bp with an open reading frame which encodes for a 101-amino-acid protein. Guinea pig NAP-1 had 70% amino acid sequence similarity to human NAP-1, which was much higher than a similarity between human and guinea pig monocyte chemoattractant protein-1 (MCP-1) (56%). Nucleotide sequence similarity within the coding region was 75%. To confirm its biological activity in guinea pig, recombinant guinea pig NAP-1 was expressed in COS-7 cells then purified. N-terminal sequence analysis gave two different N-termini at position 23 (Met) or 24 (Val). The two proteins showed their peak activity for guinea pig neutrophils at the concentration of 1 microgram/ml (10-7 M). Despite its high similarity to human NAP-1, the responsiveness of human neutrophils to guinea pig NAP-1 was minimum. Recombinant guinea pig NAP-1 caused strong neutrophil infiltration after intradermal injection into guinea pig skin. Since guinea pig is classified as a rodent, it was of interest to know whether human NAP-1 cDNA hybridizes to genomic DNA of other rodents such as mouse or rat, in which a NAP-1 homologue has not been found. Under low stringency conditions, human NAP-1 cDNA hybridized to human, rabbit, and guinea pig DNA, but not to mouse or rat DNA. Unlike NAP-1, human MCP-1 cDNA hybridized to genomic DNA of rabbit, guinea pig, mouse, and rat; MCP-1 cDNA have been cloned from these species. The apparent absence of a NAP-1 gene in mouse or rat makes this chemoattractant unique among the members of the protein family to which NAP-1 and MCP-1 belong.

Black medical pioneers: African-American 'firsts' in academic and organized medicine. Part three

Images

A genetic analysis of the E2F1 gene distinguishes regulation by Rb, p107, and adenovirus E4

The cellular transcription factor E2F appears to be a target for the regulatory action of the retinoblastoma tumor suppressor gene product. The recent isolation of the E2F1 cDNA clone, which encodes a polypeptide with properties characteristic of E2F, has now allowed a more detailed analysis of the regulation of E2F function by Rb as well as the Rb-related p107 protein and the adenovirus 19-kDa E4 gene product. Previous experiments have shown that each of these regulatory proteins can modulate the activity of cellular E2F. We find that each of these regulatory events can be mediated through the E2F1 product. Moreover, an examination of various E2F1 mutations reveals distinct specificities for these regulatory proteins. For instance, the ability of E4 to alter E2F1 function is dependent upon sequences within a putative leucine repeat of E2F1 as well as within the C-terminal acidic domain. In contrast, the leucine repeat element was not important for Rb- or p107-mediated inhibition of E2F1 activity. Although the C-terminal acidic domain of E2F1, previously shown to be important for Rb binding, appears to be a site for regulation of E2F1 by Rb and p107, point mutations within this region distinguish recognition by Rb and p107. These results underscore the complexity of E2F regulatory interactions and also demonstrate a qualitative distinction in the interactions of Rb and p107 with E2F1, perhaps reflective of functional differences.

Expression of transcription factor E2F1 induces quiescent cells to enter S phase

Several lines of evidence implicate the E2F transcription factor as an important component of cell proliferation control. First, E2F binding sites are found in the promoters of genes responsive to proliferation signals and the level of E2F binding activity increases at a time when many of these genes are activated. Second, the tumour suppressor protein Rb, as well as the related p107 protein, complexes with E2F, resulting in an inhibition of E2F transcriptional activity. Third, oncogenic products of the DNA tumour viruses can dissociate these E2F complexes. We provide here direct evidence that E2F is involved in cellular proliferation control. Specifically, we demonstrate that overexpression of the E2F1 complementary DNA can activate DNA synthesis in cells that would otherwise growth-arrest, with an efficiency that is similar to that achieved by the expression of the adenovirus E1A gene. Moreover, microinjection of the E2F1 cDNA into quiescent cells can induce S-phase entry, whereas two E2F1 mutants, which are unable to transactivate the DHFR and TK promoters, are unable to induce S phase. We conclude that the E2F transcription factor plays an important role in progression into S phase and that this probably coincides with its capacity to stimulate transcription.

Lupins (Lupinus albus) as a protein supplement for lactating Holstein dairy cows

Three experiments were conducted to determine optimal substitution of lupin for soybean meal in dairy cattle diets; the effects of whole versus ground lupins and the effects of whole lupins versus whole soybeans on milk production were examined. In the first experiment, 57 cows were assigned randomly to treatments in blocks of five by calving order within parity. Treatments began 22 d postpartum and continued through d 140. Diets were isonitrogenously balanced using soybean meal as control: lupins replaced 0, 25, 50, 75, and 100% of supplemental protein. Cows that consumed 75% of supplemental protein as lupins produced more 3.5% FCM and fat than cows that consumed the control diet. In a second experiment, 30 primiparous cows were assigned randomly by calving order to either ground or whole lupins (60% of supplemental protein). Treatments began 32 +/- 3 d after calving and lasted for 84 d. Cows that consumed ground lupins produced more milk and 3.5% FCM than cows that consumed whole lupins. In the third experiment of 84 d, 28 primiparous midlactation cows were assigned randomly to diets containing whole lupins or whole soybeans to supply 1 kg of supplemental protein. Cows fed whole lupins produced milk with higher fat content, more 3.5% FCM, and more fat than cows consuming whole soybeans. Lupins are an acceptable supplemental protein source for dairy cows.

Age and gender influence muscle sympathetic nerve activity at rest in healthy humans

Muscle sympathetic nerve activity at rest increases with age in humans. The respective influences of the aging process per se and gender on this increase and whether age and gender effects on muscle sympathetic nerve activity can be identified with plasma norepinephrine concentrations, however, have not been established. To examine these issues, nine young women (aged 24 +/- 1 years; mean +/- SEM), eight young men (aged 26 +/- 1 years), seven older women (aged 63 +/- 1 years), and eight older men (aged 66 +/- 1 years) were studied. All were healthy, normotensive (blood pressure < 140/90 mm Hg), nonobese (< 20% above ideal weight), unmedicated, nonsmokers engaged in minimal to recreational levels of chronic physical activity. Arterial blood pressure (manual sphygmomanometry, brachial artery), heart rate, muscle sympathetic nerve activity (peroneal microneurography), and antecubital venous plasma norepinephrine concentrations (radioenzymatic assay) were determined during quiet supine resting conditions. Body weight was higher in men, but there were no age-related differences, whereas estimated body fat (sum of skinfolds) was higher in women and in the older groups (p < 0.05). Estimated daily energy expenditure, arterial blood pressure, and heart rate were not different among the groups. Both muscle sympathetic nerve activity burst frequency and burst incidence at rest were progressively higher in the young women, young men, older women, and older men (10 +/- 1 versus 18 +/- 2 versus 25 +/- 3 versus 39 +/- 5 bursts/min and 16 +/- 1 versus 30 +/- 4 versus 40 +/- 3 versus 61 +/- 6 bursts/100 heartbeats, respectively; all p < 0.05 versus each other).(ABSTRACT TRUNCATED AT 250 WORDS)

Tissue-specific noradrenergic activity during acute heat stress in rats

The purpose of this study was to determine whether nonexertional heat stress alters the behavior of internal organ and skeletal muscle sympathetic nervous system (SNS) activity in unrestrained conscious rats. Norepinephrine (NE) synthesis was blocked with alpha-methyl-p-tyrosine, and the rate of decline in tissue NE concentration after synthesis blockade was used to estimate SNS activity in the left ventricle, kidney, liver, adrenal gland, and soleus and extensor digitorum longus muscles of the hindlimb. Male Sprague-Dawley rats (250-320 g) were maintained in thermoneutral control conditions (ambient temperature = 24 degrees C, n = 10) or exposed to an ambient temperature of 42 degrees C until a colonic temperature (Tc) of 39.5 or 41.0 degrees C (n = 10 each) was attained. During heating, as Tc rose from control levels (approximately 38 degrees C) to 41.0 degrees C, mean arterial pressure and heart rate increased from 120 +/- 3 to 141 +/- 3 mmHg and from 381 +/- 4 to 420 +/- 5 beats/min, respectively (P < 0.05). There was a strong trend for increased NE turnover rates in the left ventricle, liver, and adrenal gland in NE synthesis-blocked rats attaining a Tc of 39.5 degrees C compared with the normothermic values, whereas the turnover rate in the kidney was significantly elevated at this level of hyperthermia (126%) vs. the control condition. In animals heated to a Tc of 41.0 degrees C, the NE turnover rate was markedly increased in the left ventricle (590%), kidney (531%), liver (262%), and adrenal gland (602%) compared with normothermic control values.(ABSTRACT TRUNCATED AT 250 WORDS)

Crisis management: forewarned is forearmed

Big disasters remind executives that crisis communications is a critical part of strategic planning. But consciousness fades quickly, and with it, response time. Don't be caught unprepared.

New glucagon analogues with conformational restrictions and altered amphiphilicity: effects on binding, adenylate cyclase and glycogenolytic activities

In an effort to obtain highly potent glucagon antagonists, we have investigated glucagon (1) structure-function relationships utilizing the following design principles: (1) structural changes known to lead to partial agonist activities; (2) conformational restrictions; (3) changes in the conformational probabilities of the primary sequence; and (4) increased amphiphilicity. In this report we present the total synthesis, purification, receptor binding, adenylate cyclase activity, in vivo glycogenolytic activity and CD spectrum of the following four glucagon analogues: [Ahx17,18]glucagon (2), [D-Phe4,Tyr5, 3,5-diiodo-Tyr10,Arg12,Lys17,18,Glu21]glucagon (3), [Asp9,Lys12,Lys17,18,Glu21]glucagon 4, and [Glu15,Lys17,18]glucagon 5. Compound 2 binds exclusively to the high affinity receptor and compound 3 was a highly potent antagonist with respect to adenylate cyclase activity. Analog 4 showed distinct biphasic binding (IC50 5.6 nM and 630 nM), with only the low affinity binding leading to adenylate cyclase activity. Furthermore in analogue 5 receptor binding and adenylate cyclase activity were dissociated by a factor of 5. The results are consistent with a multistep binding mechanism in which glucagon interacts first nonspecifically with the anisotropic interphase of the cell membrane, followed by a conformational transition which occurs in the sequences 10-14 and 15-18 when the membrane bound peptide binds to its receptor.