Expression of the human beta(3)-adrenergic receptor gene in SK-N-MC cells is under the control of a distal enhancer.

Mechanisms of transcriptional regulation of the human beta(3)-adrenergic receptor were studied using SK-N-MC cells, a human neuroblastoma cell line that expresses beta(3)- and beta(1)-adrenergic receptors endogenously. Deletions spanning different portions of a 7-kb 5'-flanking region of the human beta(3)-adrenergic receptor gene were linked to a luciferase reporter and transfected in SK-N-MC, CV-1, and HeLa cells. Maximal luciferase activity was observed when a 200-bp region located between -6.5 and -6.3 kb from the translation start site was present. This region functioned only in SK-N-MC cells. Electrophoretic mobility shift assays of nuclear extracts from SK-N-MC, CV-1, and HeLa cells using double stranded oligonucleotides spanning different portions of the 200-bp region as probes and transient transfection studies revealed the existence of three cis-acting regulatory elements: A) -6.468 kb-AGGTGGACT--6.458 kb, B) -6.448 kb-GCCTCTCTGGGGAGCAGCTTCTCC-6.428 kb, and C) -6.405 kb-20 repeats of CCTT-6.385 kb. These elements act together to achieve full transcriptional activity. Mutational analysis, antibody supershift, and electrophoretic mobility shift assay competition experiments indicated that element A binds the transcription factor Sp1, element B binds protein(s) present only in nuclear extracts from SK-N-MC cells and brown adipose tissue, and element C binds protein(s) present in both SK-N-MC and HeLa cells. In addition, element C exhibits characteristics of an S1 nuclease-hypersensitive site. These data indicate that cell-specific positive cis-regulatory elements located 6.5 kb upstream from the translation start site may play an important role in transcriptional regulation of the human beta(3)-adrenergic receptor. These data also suggest that brown adipose tissue-specific transcription factor(s) may be involved in the tissue-specific expression of the beta(3)-adrenergic receptor gene.

LONG-TONGUED FLY POLLINATION AND EVOLUTION OF FLORAL SPUR LENGTH IN THE DISA DRACONIS COMPLEX (ORCHIDACEAE).

Field studies in South Africa showed that floral spur length in the Disa draconis complex (Orchidaceae) varies enormously between populations in the southern mountains (means = 32-38 mm), lowland sandplain (mean = 48 mm), and northern mountains (means = 57-72 mm). We tested the hypothesis that divergence in spur length has resulted from selection exerted through pollinator proboscis length. Short-spurred plants in several southern mountain populations, as well as long-spurred plants in one northern mountain population, were pollinated by a horsefly, Philoliche rostrata (Tabanidae), with a proboscis length that varied from 22 to 35 mm among sites. Long-spurred plants on the sandplain were pollinated by the tanglewing fly, Moegistorynchus longirostris (Nemestrinidae), which has a very long proboscis (mean = 57 mm). Selection apparently favors long spurs in sandplain plants, as artificial shortening of spurs resulted in a significant decline in pollen receipt and fruit set, although pollinaria removal was not significantly affected. Fruit set in the study populations was limited by pollen availability, which further suggests that selection on spur length occurs mainly through the female component of reproductive success.

New potent antihyperglycemic agents in db/db mice: synthesis and structure-activity relationship studies of (4-substituted benzyl) (trifluoromethyl)pyrazoles and -pyrazolones.

The synthesis, structure-activity relationship (SAR) studies, and antidiabetic characterization of 1,2-dihydro-4-[[4-(methylthio)phenyl]methyl]-5-(trifluoromethyl)-3H- pyrazol-3-one (as the hydroxy tautomer; WAY-123783, 4) are described. Substitution of 4-methylthio, methylsulfinyl, or ethyl to a benzyl group at C4, in combination with trifluoromethyl at C5 of pyrazol-3-one, generated potent antihyperglycemic agents in obese, diabetic db/db mice (16-30% reduction in plasma glucose at 2 mg/kg). The antihyperglycemic effect was associated with a robust glucosuria (> 8 g/dL) observed in nondiabetic mice. Chemical trapping of four of the seven possible tautomeric forms of the heterocycle by mono- and dialkylation at the acidic hydrogens provided several additional potent analogs (39-43% reduction at 5 mg/kg) of the lead 4 as well as a dialkylated pair of regioisomers that showed separation of the associated glucosuric effect produced by all of the active analogs in normal mice. Further pharmacological characterization of the lead WAY-123783 (ED50 = 9.85 mg/kg, po in db/db mice), in oral and subcutaneous glucose tolerance tests, indicated that unlike the renal and intestinal glucose absorption inhibitor phlorizin, pyrazolone 4 does not effectively block intestinal glucose absorption. SAR and additional pharmacological data reported herein suggest that WAY-123783 represents a new class of potent antihyperglycemic agents which correct hyperglycemia by selective inhibition of renal tubular glucose reabsorption.

Studies on new acidic azoles as glucose-lowering agents in obese, diabetic db/db mice.

Bioisosteric substitution was used as a tool to generate several new structural alternatives to the thiazolidine-2,4-dione and tetrazole heterocycles as potential antidiabetic agents. Among the initial leads that emerged from this strategy, a family of acidic azoles, isoxazol-3- and -5-ones and a pyrazol-3-one, showed significant plasma glucose-lowering activity (17-42% reduction) in genetically obese, diabetic db/db mice at a dose of 100 mg/kg/day x4. Structure-activity relationship studies determined that 5-alkyl-4-(arylmethyl)pyrazol-3-ones, which exist in solution as aromatic enol/iminol tautomers, were the most promising new class of potential antidiabetic agent (32-45% reduction at 20 mg/kg/d x4). Included in this work are convenient syntheses for several types of acidic azoles that may find use as new acidic bioisosteres in medicinal chemistry such as the antidiabetic lead 5-(trifluoromethyl)pyrazol-3-one (hydroxy tautomer) and aza homologs of the pyrazolones, 1,2,3-triazol-5-ones (hydroxy tautomer) and 1,2,3,4-tetrazol-5-one heterocycles. log P and pKa data for 15 potential acidic bioisosteres, all appended to a 2-naphthalenylmethyl residue so as to maintain a similar distance between the acidic hydrogen and arene nucleus, are presented. This new data set allows comparison of a wide variety of potential acid mimetics (pKa 3.78-10.66; log P -0.21 to 2.76) for future drug design.

Oral hypoglycemic agents. Pyrimido[1,2-a]indoles and related compounds.

A series of pyrimido[1,2-a]indoles were synthesized and studied for their hypoglycemic activity following oral administration at a standard dose of 100 mg/kg to fed rats. The effect of 10-alkoxyalkyl, 10-alkyl, 10-aryl, and 3,3-dialkyl substitution on the activity of 10-hydroxypyrimido[1,2-a]indoles was investigated. Relative potencies of a number of the most active compounds were defined by three-point dose-response studies. The most potent compounds were those with either 3,3-dimethyl substituents, compounds 21, 22, and 38, or 3,3-spirocyclohexane substituents, compounds 39 and 49. 10-Aminopyrimido[1,2-a]indoles were in general less active than the 10-hydroxy analogues, and potency was further decreased by derivatizing the 10-amino group. The most potent 10-amino derivatives were 57 and 58.

Perfluorocarbon-based antidiabetic agents.

In a preliminary communication (J. Med. Chem. 1989, 32, 11-13) a series of perfluoro-N-[4-(1H-tetrazol-5ylmethyl)phenyl]alkana mides (perfluoro anilides I), designed as novel analogues of ciglitazone, were reported to possess oral antidiabetic activity in two genetic animal models of non-insulin-dependent diabetes mellitus (NIDDM): obese (ob/ob) and diabetic (db/db) mice. In this report, the results from a structure-activity relationship (SAR) study of the series I are described. Comprehensive statistical analysis among the 86 analogues screened for blood glucose lowering in ob/ob mice was achieved by a new application of a general statistical procedure which made it possible to make meaningful comparisons between more than 140 separate experiments (N = 2966). Perfluoro anilides I lowered plasma glucose in the hyperglycemic ob/ob and db/db mice but not in euglycemic normal rats. In the hyperinsulinemic ob/ob mouse, decreases in plasma insulin levels paralleled the decline in plasma glucose. Potency and efficacy in the series was shown to be dependent on the length of the perfluorocarbon chain (RF) of I. Optimal activity occurred with the C7 and C8 RF chains. The more extensive SAR studies reported here, indicated that the lipophilic RF chain is the most important structural element of I since neither the phenyl nor tetrazole rings present in anilides I were necessary for antihyperglycemic activity while medium length (C7-C8) RF chains, especially the C7F15 chain, were shown to confer antihyperglycemic activity in ob/ob mice to a wide variety of structures.

Regulation of glucose metabolism by norepinephrine in conscious dogs.

The effects of norepinephrine (NE) at levels present in the circulation and synaptic cleft during stress on glucose metabolism were examined in overnight-fasted conscious dogs with fixed basal levels of insulin and glucagon. Plasma NE rose from 132 +/- 14 to 442 +/- 85 pg/ml and 100 +/- 20 to 3,244 +/- 807 pg/ml during 3 h of low (n = 6) and high (n = 5) NE infusion, respectively. Plasma glucose and glucose production rose only with high NE infusion (from 108 +/- 4 to 159 +/- 15 mg/dl and 2.78 +/- 0.24 to 3.41 +/- 0.38 mg.kg-1.min-1, respectively). NE infusion caused dose-dependent net hepatic lactate consumption, but net hepatic alanine uptake fell only with high NE infusion (31%). Alanine conversion to glucose rose by 67 +/- 13, 136 +/- 20, and 412 +/- 104%, and intrahepatic gluconeogenic efficiency rose by 42 +/- 27, 299 +/- 144, and 212 +/- 21% with saline and with low and high NE infusion, respectively. In conclusion, NE enhances gluconeogenesis by stimulating peripheral precursor release, by increasing substrate movement into the hepatocyte, and by increasing intrahepatic gluconeogenic efficiency. However, only the higher NE levels affected glucose metabolism profoundly enough to stimulate glucose production and to elevate the glucose level.

The effects of epinephrine on ketogenesis in the dog after a prolonged fast.

The effects of a selective increase in epinephrine on ketogenesis and lipolysis were determined in the conscious dog following a prolonged fast (7 days). Plasma insulin and glucagon were fixed at basal levels by infusion of somatostatin (0.8 micrograms/kg/min) and basal intraportal replacement amounts of insulin (210 +/- 20 microU/kg/min) and glucagon (0.65 ng/kg/min). Following a 40-minute control period, saline or epinephrine (0.04 microgram/kg/min) was infused for 3 hours. Plasma insulin, glucagon, and norepinephrine levels did not change during saline (6 +/- 1 microU/mL, 83 +/- 17 pg/mL, and 137 +/- 38 pg/mL, respectively) or epinephrine (10 +/- 1 microU/mL, 73 +/- 18 pg/ml, 98 +/- 13 pg/mL, respectively) infusion. Plasma epinephrine levels increased from 80 +/- 26 to 440 +/- 47 pg/mL in response to infusion of the catecholamine, but remained unchanged during saline infusion. Glycerol levels (93 +/- 10 mumol/L) remained unchanged during saline infusion, but increased in response to epinephrine (108 +/- 9 to 170 +/- 18 mumol/L by 30 minutes). The glycerol level had returned to baseline and to the value apparent in saline controls by 60 minutes. The nonesterified fatty acid (NEFA) level declined slowly during the 3-hour saline infusion, but was elevated in response to epinephrine infusion (1.27 +/- 0.16 to 1.97 +/- 0.25 mmol/L at 30 minutes). After the initial epinephrine-induced increase, the NEFA level declined so that by 3 hours it was not significantly different from the basal or saline values.(ABSTRACT TRUNCATED AT 250 WORDS)

Regulation of lipolysis and ketogenesis by norepinephrine in conscious dogs.

The lipolytic and ketogenic effects of norepinephrine (NE) at levels present in the circulation or the synaptic cleft during stress were examined in the overnight-fasted conscious dog. Insulin and glucagon were maintained at basal levels while NE, at a rate of either 0.04 (n = 6) or 0.32 micrograms.kg-1.min-1 (n = 5), or saline (n = 6) was infused for 3 h. NE rose from 129 +/- 17 to 442 +/- 85 pg/ml (P less than 0.05) and 100 +/- 24 to 3,244 +/- 807 pg/ml (P less than 0.05) with the low and high infusion rates, respectively (unchanged with saline infusion). There were no significant changes in lipolysis or ketogenesis with saline infusion. Both low and high NE infusion produced sustained increases in glycerol (from 72 +/- 20 to 119 +/- 24 microM and 59 +/- 19 to 248 +/- 32 microM, respectively, both P less than 0.05), while nonesterified fatty acids (NEFA) rose from 609 +/- 85 to 952 +/- 100 and 767 +/- 140 to 2,054 +/- 199 microM (both P less than 0.05). Ketone levels and net hepatic production rose significantly only with the high NE infusion (from 88 +/- 10 to 266 +/- 46 microM and 1.30 +/- 0.26 to 7.62 +/- 1.48 mumol.kg-1.min-1, respectively, both P less than 0.05). The ratio of net hepatic ketone production to NEFA uptake rose 54% with high NE infusion. In conclusion, at circulating levels seen during stress, NE stimulates lipolysis but does not directly influence ketogenesis. At circulating levels projected to exist in the synaptic cleft during stress, NE has a potent lipolytic effect and stimulates ketogenesis.

Dose-related effects of epinephrine on glucose production in conscious dogs.

The effects of increases in plasma epinephrine from 78 +/- 32 to 447 +/- 75, 1,812 +/- 97, or 2,495 +/- 427 pg/ml on glucose production, including gluconeogenesis, were determined in the conscious, overnight-fasted dog, using a combination of tracer [( 3-3H]glucose and [U-14C]alanine) and arteriovenous difference techniques. Insulin and glucagon were fixed at basal levels using a pancreatic clamp. Plasma glucose levels rose during the 180-min epinephrine infusion by 47 +/- 7, 42 +/- 22, and 74 +/- 25 mg/dl, respectively, in association with increases in hepatic glucose output of 1.04 +/- 0.22, 1.87 +/- 0.23, and 3.70 +/- 0.83 mg.kg-1.min-1 (at 15 min). Blood lactate levels rose by 1.52 +/- 0.24, 4.29 +/- 0.49, and 4.60 +/- 0.45 mmol/l, respectively, by 180 min, despite increases in hepatic uptake of lactate of 3.47 +/- 5.73, 12.83 +/- 3.46, and 37.00 +/- 4.20 mumol.kg-1.min-1. The intrahepatic gluconeogenic efficiency with which the liver converted the incoming alanine to glucose had risen by 84 +/- 40, 77 +/- 24, and 136 +/- 34% at 180 min, respectively. The latter effect plus the effect on net hepatic lactate uptake point to an intrahepatic action of high levels of the hormone in vivo. In conclusion, epinephrine produces dose-dependent increments in overall glucose production, which involve a progressive stimulation of both glycogenolysis (as assessed by glucose production at 15 min) and gluconeogenesis (assessed in the last 30 min of the study). The latter involves a peripheral action of the catecholamine to increase gluconeogenic substrate supply to the liver and may also involve a hepatic effect when high epinephrine levels are present.

Effects of insulin on glucagon-stimulated glucose production in the conscious dog.

The relative importance of insulin and glucagon as primary regulators of glucose metabolism in vivo was assessed in 18-hour fasted conscious dogs. Glucose turnover was determined using [3-3H]glucose and gluconeogenesis was assessed using tracer ([14C]alanine) and A-V difference techniques during a 40-minute control period and a 3-hour period during which various hormonal perturbations were brought about. During the infusion of somatostatin and basal intraportal replacement amounts of insulin and glucagon for the entire study, the plasma glucose concentration (109 +/- 5 mg/dL), glucose production (3.24 +/- 0.30 mg/kg/min), and glucose utilization (3.17 +/- 0.32 mg/kg/min) remained unchanged. When the glucagon infusion rate was increased fourfold at the end of the control period, the plasma glucose level increased from 107 +/- 4 to 225 +/- 23 mg/dL by 1 hour and remained elevated. Glucose production increased from 3.14 +/- 0.29 to 7.66 +/- 0.51 mg/kg/min by 15 minutes and decreased to 4.23 +/- 0.35 mg/kg/min by 3 hours. Glucose utilization rose from a basal value of 3.20 +/- 0.26 to 5.46 +/- 0.27 mg/kg/min by 3 hours. When a fourfold increase in the insulin infusion rate was brought about at the end of the control period, glucose production decreased from 2.83 +/- 0.20 to 1.16 +/- 0.57 mg/kg/min by 1 hour, after which it increased slightly (1.62 +/- 0.81 mg/kg/min). Glucose utilization increased from 2.92 +/- 0.30 to 8.12 +/- 1.12 mg/kg/min by 3 hours. Euglycemia was maintained by glucose infusion.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of alanine concentration independent of changes in insulin and glucagon on alanine and glucose homeostasis in the conscious dog.

The effect of an alanine load per se on hepatic alanine balance and hepatic glucose production is unclear. To examine this question, alanine was infused into six postabsorptive dogs at a rate of 6 mumol/kg-min, while maintaining insulin and glucagon levels using the pancreatic clamp technique. The arterial alanine concentration rose from a basal level of 227 +/- 16 mumol/L to 497 +/- 40 mumol/L during alanine infusion (P less than .01). The net hepatic fractional extraction of alanine remained unchanged, while hepatic alanine uptake increased from 3.0 +/- 0.3 to 6.0 +/- 0.4 mumol/kg-min (P less than .01). Conversion of alanine into glucose increased 87% to 2.7 +/- 0.3 mumol/kg-min during alanine infusion (P less than .01) while gluconeogenic efficiency remained essentially unchanged. Despite the increased gluconeogenic rate, the total rate of glucose production was unchanged. These data suggest that an increase in the alanine load to the liver causes a proportional increase in net hepatic alanine uptake and the gluconeogenic rate, but that in an overnight fasted animal this increase is insufficient to significantly increase glucose production.

Effect of somatostatin on glucose homeostasis in conscious long-fasted dogs.

The effects of somatostatin plus intraportal insulin and glucagon replacement (pancreatic clamp) on carbohydrate metabolism were studied in conscious dogs fasted for 7 days so that gluconeogenesis was a major contributor to total glucose production. By use of [3-3H]glucose, glucose production (Ra) and utilization (Rd) and glucose clearance were assessed before and after implementation of the pancreatic clamp. After an initial control period, somatostatin (0.8 microgram . kg-1 . min-1) was infused with intraportal replacement amounts of glucagon (0.42 ng . kg-1 . min-1) and insulin. The insulin infusion rate was varied to maintain euglycemia and then kept constant (68 +/- 16 microU . kg-1 . min-1) for 250 min. Plasma glucagon was similar (84 +/- 14 and 89 +/- 19 pg/ml) before and during somatostatin infusion, while plasma insulin was lower (9.3 +/- 0.9 and 6.6 +/- 0.5 microU/ml, P less than 0.05). Plasma glucose levels remained similar (89 +/- 2 and 96 +/- 9 mg/dl), while Ra and Rd and the ratio of glucose clearance to plasma insulin were significantly (P less than 0.05) increased (from 2.18 +/- 0.12 to 3.21 +/- 0.35 and 2.30 +/- 0.09 to 3.26 +/- 0.38 mg . kg-1 . min-1, and 0.30 +/- 0.03 to 0.59 +/- 0.11, respectively). Net hepatic lactate uptake and [14C]alanine plus [14C]lactate conversion to [14C]glucose increased (P greater than 0.05) (from 9.32 +/- 0.47 to 16.54 +/- 2.97 mumol . kg-1 . min-1 and 100 to 263 +/- 37%, respectively). In conclusion, somatostatin alters glucose clearance in 7-day fasted dogs, resulting in changes in several indices of carbohydrate metabolism.

Lack of effect of somatostatin on epinephrine-stimulated glucose production in the dog.

The effects of somatostatin on epinephrine-stimulated hepatic glucose production were assessed in the conscious overnight fasted dog. Glucose production was measured using a primed constant infusion of 3-3H-glucose. Two experiments were performed on each of four animals, each experiment consisting of a tracer equilibration period (80 minutes), a control period (40 minutes), and a test period (180 minutes). In the first experiment, epinephrine was infused at 0.08 microgram/kg/min during the test period so that the plasma concentration rose from 138 +/- 4 to 727 +/- 109 pg/mL. In the second experiment two weeks later, epinephrine was again infused (112 +/- 17 to 727 +/- 148 pg/mL) but with somatostatin (0.8 microgram/kg/min) and intraportal replacement amounts of insulin and glucagon. The pancreatic hormones were administered in such a way as to mimic the insulin and glucagon levels observed during epinephrine infusion in the first experiment. In the first experiment, epinephrine caused changes in insulin and glucagon levels at five minutes of plus 9 +/- 1 microU/mL and minus 1 +/- 3 pg/mL, respectively, and averaged plus 6 +/- 2 microU/mL and minus 9 +/- 5 pg/mL over the first hour. Glucose production peaked at 15 minutes (increment of 0.83 +/- 0.24 mg/kg/min) and increased by an average of 0.38 +/- 0.12 mg/kg/min in the first hour. In the second experiment, intraportal replacement of insulin and glucagon during epinephrine infusion resulted in changes in insulin and glucagon levels at five minutes of plus 8 +/- 3 microU/mL and plus 2 +/- 2 pg/mL, respectively, and averaged plus 4 +/- 2 microU/mL and minus 7 +/- 6 pg/mL over the first hour.(ABSTRACT TRUNCATED AT 250 WORDS)

Similar dose responsiveness of hepatic glycogenolysis and gluconeogenesis to glucagon in vivo.

This study was undertaken to determine whether the dose-dependent effect of glucagon on gluconeogenesis parallels its effect on hepatic glycogenolysis in conscious overnight-fasted dogs. Endogenous insulin and glucagon secretion were inhibited by somatostatin (0.8 micrograms X kg-1 X min-1), and intraportal replacement infusions of insulin (213 +/- 28 microU X kg-1 X min-1) and glucagon (0.65 ng X kg-1 X min-1) were given to maintain basal hormone concentrations for 2 h (12 +/- 2 microU/ml and 108 +/- 23 pg/ml, respectively). The glucagon infusion was then increased 2-, 4-, 8-, or 12-fold for 3 h, whereas the rate of insulin infusion was left unchanged. Glucose production (GP) was determined with 3-[3H]glucose, and gluconeogenesis (GNG) was assessed with tracer (U-[14C]alanine conversion to [14C]glucose) and arteriovenous difference (hepatic fractional extraction of alanine, FEA) techniques. Increases in plasma glucagon of 53 +/- 8, 199 +/- 48, 402 +/- 28, and 697 +/- 149 pg/ml resulted in initial (15-30 min) increases in GP of 1.1 +/- 0.4 (N = 4), 4.9 +/- 0.5 (N = 4), 6.5 +/- 0.6 (N = 6), and 7.7 +/- 1.4 (N = 4) mg X kg-1 X min-1, respectively; increases in GNG (approximately 3 h) of 48 +/- 19, 151 +/- 50, 161 +/- 25, and 157 +/- 7%, respectively; and increases in FEA (3 h) of 0.14 +/- 0.07, 0.37 +/- 0.05, 0.42 +/- 0.04, and 0.40 +/- 0.17, respectively. In conclusion, GNG and glycogenolysis were similarly sensitive to stimulation by glucagon in vivo, and the dose-response curves were markedly parallel.