Hypoxemia raises muscle sympathetic activity but not norepinephrine in resting humans

The experimental objective was to determine whether moderate to severe hypoxemia increases skeletal muscle sympathetic nervous activity (MSNA) in resting humans without increasing venous plasma concentrations of norepinephrine (NE) and epinephrine (E). In nine healthy subjects (20-34 yr), we measured MSNA (peroneal nerve), venous plasma levels of NE and E, arterial blood pressure, heart rate, and end-tidal O2 and CO2 before (control) and during breathing of 1) 12% O2 for 20 min, 2) 10% O2 for 20 min, and 3) 8% O2 for 10 min--in random order. MSNA increased above control in five, six, and all nine subjects during 12, 10, and 8% O2, respectively (P less than 0.01), but only after delays of 12 (12% O2) and 4 min (8 and 10% O2). MSNA (total activity) rose 83 +/- 20, 260 +/- 146, and 298 +/- 109% (SE) above control by the final minute of breathing 12, 10, and 8% O2, respectively. NE did not rise above control at any level of hypoxemia; E rose slightly (P less than 0.05) at one time only with both 10 and 8% O2. Individual changes in MSNA during hypoxemia were unrelated to elevations in heart rate or decrements in blood pressure and end-tidal CO2--neither of which always fell. We conclude that in contrast to some other sympathoexcitatory stimuli such as exercise or cold stress, moderate to severe hypoxemia increases leg MSNA without raising plasma NE in resting humans.

Determination of the primary charge separation rate in Photosystem II reaction centers at 15 K

We have measured the rate constant for the formation of the oxidized chlorophyll a electron donor (P680(+)) and the reduced electron acceptor pheophytin a (-) (Pheo a (-)) following excitation of isolated Photosystem II reaction centers (PS II RC) at 15 K. This PS II RC complex consists of D1, D2, and cytochrome b-559 proteins and was prepared by a procedure which stabilizes the protein complex. Transient absorption difference spectra were measured from 450-840 nm as a function of time with 500fs resolution following 610 nm laser excitation. The formation of P680(+)-Pheo a (-) is indicated by the appearance of a band due to P680(+) at 820 nm and corresponding absorbance changes at 490, 515 and 546 nm due to the formation of Pheo a (-). The appearance of the 490 nm and 820 nm bands is monoexponenital with τ=1.4±0.2 ps. Treatment of the PS II RC with sodium dithionite and methyl viologen followed by exposure to laser excitation results in accumulation of Pheo a (-). Laser excitation of these prereduced RCs at 15 K results in formation of a transient absorption spectrum assigned to (1*)P680. We observe wavelength-dependent kinetics for the recovery of the transient bleach of the Qy absorption bands of the pigments in both untreated and pre-reduced PS II RCs at 15K. This result is attributed to an energy transfer process within the PS II RC at low temperature that is not connected with charge separation.

Perifused precision-cut liver slice system for the study of hormone-regulated hepatic glucose metabolism

A nonrecirculatory perfusion system for precision-cut rat liver slices has been developed and utilized for investigating hormone-regulated hepatic glucose metabolism. In this system, slices are cultured in a highly controlled environment and exhibit excellent retention of viability as judged by their maintenance of intracellular potassium and glycogen contents. Using this system, the complex physiological phenomenon of hormone-regulated glycogenolysis was investigated at both extra- and intracellular sites. Specifically, the sensitive responses of intracellular cyclic AMP (cAMP) production, activation of cyclic AMP-dependent protein kinase, and production of glucose upon glucagon stimulation have been measured. The maximal responses observed for these parameters were either equal to or greater than those previously reported for either isolated hepatocytes or perfused livers, demonstrating the sensitivity of this technique. Upon dose-response examination of glucagon challenge, it was observed that high doses of glucagon (greater than 16 nM) stimulate glucose production by activating the cAMP-second messenger cascade. In contrast, low doses (less than 4 nM) stimulate this process without production of intracellular cAMP or activation of cAMP-dependent protein kinase, suggesting the operation of cAMP-independent messenger. Since this system permits measurements of parameters common to many cellular processes, this methodology is suitable for addressing both pharmacological and toxicological questions.

Inbreeding of and relationship among registered Holsteins

Holstein-Friesian Herdbooks (Holstein-Friesian Association of America, Brattleboro, VT) were used to draw random samples of 600 registered females born during each of the yr 1970, 1976, and 1982. A two-line pedigree, one random line of ancestry tracing from the sire and another tracing from the dam to the beginning of the Holstein-Friesian Herdbook, was tabulated for each of these 1800 females. These were used to estimate inbreeding and inter se relationship for the Holstein breed. Estimates of inbreeding were 4.7, 3.8, and 4.3% for 1970, 1976, and 1982. These estimates were not different from one another or from 1928 and 1931 estimates. Estimates of inter se relationship were 5.2, 7.3, and 9.8% for 1970, 1976, and 1982. These estimates were different from one another and from an estimate of 3.4% for 1931. The increase in inter se relationship without corresponding increase in inbreeding indicates that a change in mating strategies has evolved over time. The majority of breeders now apparently mate animals that are less related than if mating was random, whereas in the past there was more of a tendency to mate within the same line. Despite these attempts to avoid inbreeding, it may be only a matter of time until increasing inter se relationship causes an increase in inbreeding. Because of detrimental effects associated with inbreeding, it is important that the Holstein breed be monitored on a regular basis for these parameters. Ancestors that occurred most frequently in the 1982 sample were identified and their direct relationships to the breed tabulated for the years studied.

Comparison of sweet white lupin seeds with soybean meal as a protein supplement for lactating dairy cows

Data were from 45 Holstein cows (23 multiparous, 22 primiparous) assigned by calving date and parity within groups to one of two isonitrogenous (16% crude protein) diets. The diets were 50% forages (corn silage, alfalfa silage) and 50% concentrate, dry basis. In diet A, soybean meal supplied 34.2% of total crude protein; in diet B, ground sweet white lupin seeds provided 37.9% of total crude protein. Cows were fed once daily during the experimental period (d 4 to 116 postpartum). Cows fed lupins consumed significantly less dry matter, produced 1.8 kg/d less milk (but not significantly different), and had lower milk protein percent. Milk fat and total solids percents were similar. Reasons for reduced intake of cows fed lupins were not evident. Traces of alkaloids (.005% dry basis) were present in diet B. Combined results of in vitro continuous culture fermentation and in situ degradation measurements indicated that crude protein from lupins was more degradable than that of soybean meal. Poor performances of cows fed lupins could be partly due to a reduced true protein supply to the small intestine.

Synthesis of two glucagon antagonists: receptor binding, adenylate cyclase, and effects on blood plasma glucose levels

In diabetes mellitus, hyperglycemia is often associated with elevated levels of glucagon in the blood. This suggests that glucagon is a contributing factor in the metabolic abnormalities of diabetes mellitus. A glucagon-receptor antagonist would provide direct evidence for glucagon's role in diabetes mellitus. On the basis of careful consideration of conformational, amphiphilic, and structural factors, we have synthesized two new glucagon analogues with antagonist biological activities by using solid-phase methodology. These two new analogues, [Asp3,D-Phe4,Ser5,Lys17,18,Glu21]glucagon (2) and [D-Phe4,Tyr5,3,5-I2-Tyr10,Arg12,Lys17,18,G lu21]glucagon (3) had IC50 values 5.4% and 50% those of glucagon, respectively, and showed no measurable adenylate cyclase activity. When tested in normal rats, 2 lowered plasma glucose levels and suppressed glucagon-mediated hyperglycemia 105 +/- 8%, back to basal levels. Analogue 3, which lowered the basal adenylate cyclase activity in rat liver plasma membranes, increased plasma glucose levels at very high concentration in vivo and inhibited glucagon-mediated hyperglycemia in normal rats by 50%. However, neither of the new glucagon antagonists lowered the plasma glucose levels of diabetic animals. The data would suggest these new glucagon-receptor antagonists may have two actions: (a) in normal rats they can act as standard glucagon-receptor inhibitors of glucagon-mediated glycogenolysis; (b) in diabetic rats, however, because of the low levels of glycogen in the liver, the antagonists apparently have little or no antagonist effect or enhancement on glucagon-mediated glucose production.

Antihypertensive effects of parenteral nicardipine alone and in combination with captopril

We studied the safety and efficacy of intravenous nicardipine alone and in combination with oral captopril. Sixteen patients with essential hypertension received a single oral dose of captopril, 50 mg, to be certain that excessive hypotension would not occur. Nicardipine was given intravenously as a 2 mg bolus, followed by an infusion at a rate designed to lower the supine diastolic blood pressure at least 10 mm Hg; then oral captopril, 50 mg, or placebo was given. The next week, nicardipine was again infused, but the alternate oral treatment was given. Intravenous nicardipine reduced blood pressure from 156 +/- 15/101 +/- 5 mm Hg (mean arterial blood pressure 120 +/- 6 mm Hg) to 140 +/- 11/88 +/- 4 mm Hg (mean arterial blood pressure 105 +/- 5 mm Hg). When captopril was added to nicardipine, the mean arterial blood pressure fell an additional 8 mm Hg but the heart rate did not increase. The combination of angiotensin-converting enzyme inhibition and calcium channel blockage produces additive antihypertensive effects without additional reflex tachycardia.

Atrial natriuretic peptide levels during development of chronic heart failure after myocardial infarction in rats

Serum levels of atrial natriuretic peptide (ANP) are elevated in chronic heart failure presumably due to dilatation of the left atrium resulting from increases in intracardiac pressures. To define the time course of changes in serum ANP levels and to determine the relationship to left ventricular end-diastolic pressure, rats were subjected to coronary artery ligation to produce myocardial infarction and left ventricular failure. Atrial natriuretic peptide levels were measured weekly for four weeks thereafter. In rats with myocardial infarction and elevation of left ventricular end-diastolic pressure there was no change in ANP levels at 7 and 14 days. However, at day 21 and 28, ANP levels were elevated more than 3 fold. There was a correlation between ANP levels and left ventricular end-diastolic pressures. There was no correlation between ANP levels and right atrial pressures or serum sodium concentrations. We conclude that the chronic elevation of left ventricular end-diastolic pressure is required to produce an increase in ANP after myocardial infarction which results in chronic heart failure.

Design and synthesis of glucagon partial agonists and antagonists

The hyperglycemia and ketosis of diabetes mellitus are generally associated with elevated levels of glucagon in the blood. This suggests that glucagon is a contributing factor in the metabolic abnormalities of diabetes mellitus. A glucagon-receptor antagonist might provide important evidence for glucagons's role in this disease. In this work we describe how we combined structural modifications that led to glucagon analogues with partial agonist activity to give glucagon analogues that can act as competitive antagonists of glucagon-stimulated adenylate cyclase activity. Using solid-phase synthesis methodology and preparative reverse-phase high-performance liquid chromatography, we synthesized the following seven glucagon analogues and obtained them in high purity: [D-Phe4,Tyr5,Arg12]glucagon (2); [D-Phe4,Tyr5,Lys17,18]glucagon (3); [Phe1,Glu3,Lys17,18]glucagon (4); [Glu3,Val5,Lys17,18]glucagon (5); [Asp3,D-Phe4,Ser5,Lys17,18]glucagon (6); I4-[Asp3,D-Phe4,Ser5,Lys17,18]glucagon (7); [Pro3]glucagon (8). Purity was assessed by enzymatic total hydrolysis, by chymotryptic peptide mapping, and by reverse-phase high-performance liquid chromatography. The new analogues were tested for specific binding, for their effect on the adenylate cyclase activity in rat liver membranes, and for their effect on the blood glucose levels in normal rats relative to glucagon. Analogues showing no adenylate cyclase activity were examined for their ability to act as antagonists by displacing glucagon-stimulated adenylate cyclase dose-response curves to the right (higher concentrations). The binding potencies of the new analogues relative to glucagon (= 100) were respectively 1.0 (2), 1.3 (3), 3.8 (4), 0.4 (5), 1.3 (6), 5.3 (7), and 3 (8). Glucagon analogues 3-5 and 8 were all weak partial agonists with EC50 values of 500 (3), 250 (4), 1600 (5), and 395 nM (8), respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

United States citizens studying medicine abroad. Their backgrounds and test performance

To acquire information about the characteristics of U.S. citizens who had recently studied medicine abroad, the Educational Commission for Foreign Medical Graduates (ECFMG) and the Association of American Medical Colleges merged independently collected data on a study group of 10,460 U.S. citizens who attended 359 medical schools in 75 foreign countries and who took their first ECFMG examination between 1978 and 1982. The study group was markedly heterogeneous: 21 percent were not U.S. citizens at birth, 32 percent did not have English as a native language, and 12 percent had two or more years of undergraduate college education in Puerto Rico. Sixty-seven percent resided in New York, New Jersey, California, Florida, or Puerto Rico, and 74 percent studied medicine in Mexico or the Caribbean. Forty-six percent passed the ECFMG examination on their first attempt, and 22 percent passed a subsequent examination. Only 45 percent had applied to a U.S. medical school, and 65 percent had taken the Medical College Admission Test. The means of the college grade-point averages, known for 39 percent of the study group, and of the scores on the admission test, known for 65 percent, were lower than those of both accepted and unaccepted applicants to U.S. medical schools in the 1976 and 1978 entering classes. The finding that 55 percent of the study group did not apply to a U.S. medical school does not support the widely held belief that most, if not all, U.S. citizens who attend foreign medical schools do so only after several unsuccessful attempts to gain admission to a U.S. school.

Maintenance of adult rat liver slices in dynamic organ culture

Adult rat liver slices were maintained for 20 h in a novel organ culture system with minimal loss of viability and function. Potassium and adenosine triphosphate levels were maintained at in vivo levels, following an initial recovery period (2 to 4 h), for up to 20 h. Protein synthesis and secretion were linear for 20 and 16 h, respectively. In addition, the liver slices synthesized glycogen between 4 and 12 h in culture. Finally, the liver slices were hormonally responsive during the 20 h culture period as exemplified by glucagon-stimulated glucose production. This system provides a simple and effective method for the culture and biochemical maintenance of adult rat liver for 20 h with minimal loss of biochemical function.

Increased response to insulin of glucose metabolism in the 6-day unloaded rat soleus muscle

Hind leg muscles of female rats (85-99 g) were unloaded by tail cast suspension for 6 days. In the fresh-frozen unloaded soleus, the significantly greater concentration of glycogen correlated with a lower activity ratio of glycogen phosphorylase (p less than 0.02). The activity ratio of glycogen synthase also was lower (p less than 0.001), possibly due to the higher concentration of glycogen. In isolated unloaded soleus, insulin (0.1 milliunit/ml) increased the oxidation of D-[U-14C]glucose, release of lactate and pyruvate, incorporation of D-[U-14C]glucose into glycogen, and the concentration of glucose 6-phosphate more (p less than 0.05) than in the weight-bearing soleus. At physiological doses of insulin, the percent of maximal uptake of 2-deoxy-D-[1,2-3H]glucose/muscle also was greater in the unloaded soleus. Unloading of the soleus increased by 50% the concentration of insulin receptors, due to no decrease in total receptor number during muscle atrophy. This increase may account for the greater response of glucose metabolism to insulin in this muscle. The extensor digitorum longus, which generally shows little response to unloading, displayed no differential response of glucose metabolism to insulin.

Receptor binding and adenylate cyclase activities of glucagon analogues modified in the N-terminal region

In this study, we determined the ability of four N-terminally modified derivatives of glucagon, [3-Me-His1,Arg12]-, [Phe1,Arg12]-, [D-Ala4,Arg12]-, and [D-Phe4]glucagon, to compete with 125I-glucagon for binding sites specific for glucagon in hepatic plasma membranes and to activate the hepatic adenylate cyclase system, the second step involved in producing many of the physiological effects of glucagon. Relative to the native hormone, [3-Me-His1,Arg12]glucagon binds approximately twofold greater to hepatic plasma membranes but is fivefold less potent in the adenylate cyclase assay. [Phe1,Arg12]glucagon binds threefold weaker and is also approximately fivefold less potent in adenylate cyclase activity. In addition, both analogues are partial agonists with respect to adenylate cyclase. These results support the critical role of the N-terminal histidine residue in eliciting maximal transduction of the hormonal message. [D-Ala4,Arg12]glucagon and [D-Phe4]glucagon, analogues designed to examine the possible importance of a beta-bend conformation in the N-terminal region of glucagon for binding and biological activities, have binding potencies relative to glucagon of 31% and 69%, respectively. [D-Ala4,Arg12]glucagon is a partial agonist in the adenylate cyclase assay system having a fourfold reduction in potency, while the [D-Phe4] derivative is a full agonist essentially equipotent with the native hormone. These results do not necessarily support the role of an N-terminal beta-bend in glucagon receptor recognition. With respect to in vivo glycogenolysis activities, all of the analogues have previously been reported to be full agonists.(ABSTRACT TRUNCATED AT 250 WORDS)

Multiple intestinal atresia and amyoplasia congenita in four unrelated infants: a new association

Four unrelated infants with multiple segments of nonduodenal intestinal atresia and amyoplasia congenita are described. The extreme rarity of each of these conditions as a single entity indicates that their concurrent incidence in four separate unrelated patients is of significance with respect to pathogenesis. The nature of the relationship between the two conditions is unknown.

Bronchodilator activity of a nonxanthine phosphodiesterase inhibitor; 2,4-diamino-5-cyano-6-bromopyridine (compound I)

The ability of 2,4-diamino-5-cyano-6-bromopyridine (compound 1) to inhibit bronchiolar smooth muscle constriction was examined in isolated rings of rabbit primary bronchi and intrapulmonary bronchioles. After carbachol-induced constriction these tissue were significantly relaxed by either compound I or 1-methyl-3-isobutylxanthine (MIX) in a similar dose-dependent manner with 50 to 80% relaxation occurring at 100 microM of either compound. Compound I also attenuated the constrictor response of bronchial rings to histamine and significantly reduced the tension generated by horseradish peroxidase in sensitized tissues responding to this antigen. In addition, both compound I and MIX were found to inhibit the soluble cyclic AMP phosphodiesterase activity of rabbit bronchioles. Finally, both compound I and MIX caused a nearly 2-fold, time-dependent increase in cyclic AMP levels in isolated rabbit intrapulmonary bronchioles. The similarities of both the in vitro tissue responses to these compounds and the phosphodiesterase inhibitory properties suggest that the ability of compound I to reduce constrictor-induced tension generation in bronchial smooth muscle is related to the inhibition of cyclic nucleotide phosphodiesterases and the consequent elevation of cyclic AMP.

Value of tests for evaluation of gastroesophageal reflux in children

The accuracy of five tests for the diagnosis of gastroesophageal reflux in children was performed in 93 symptomatic children with gastroesophageal reflux and 16 nonreflux patients. These tests include the barium esophagram, the Tuttle test, extended esophageal pH monitoring, esophagoscopy, and esophageal biopsy. Esophagoscopy was less sensitive in detecting reflux in patients than any other test (P = less than 0.001), and biopsy was more likely to identify reflux patients than the barium swallow (P = less than 0.02), but there was no test superior to others. The severity of esophagitis noted at endoscopy or the presence of eosinophils or neutrophils in the mucosa was not associated with a decreased possibility that one other test would be normal or that surgical repair of the reflux would be performed. Patients with extended esophageal pH test scores markedly elevated were less likely to have another negative test (P = less than 0.01) and more likely to have surgical repair of gastroesophageal reflux (P = less than 0.001). Obtaining two tests of esophageal function that agree increases the certainty of diagnosis, and use of several tests are indicated if the results of a single test do not support the clinical impression.

Current thinking on the role of surgery in gastroesophageal reflux

Gastroesophageal reflux is common in infants and children. In most cases it causes little more than inconvenience and remits spontaneously with time and maturation. A small and select group of refluxing children, however, will develop complications of reflux severe enough to justify operative control when medical treatment fails. Recurrent pulmonary infections, obstructive apnea, nutritional wasting, and progressive inflammatory injury to the esophagus all qualify as surgical indications, provided a reasonable cause-effect relationship with reflux can be established. The procedure of choice depends very much upon the skill and experience of the surgeon. The complete fundoplication seems to offer more complete control of reflux, but it has the potential for more frequent and more complicated side-effects.

Intraoperative measurement of maxillary repositioning: an ancillary technique

A technique for measuring maxillary movement with the LeFort I osteotomy is described. Three-dimensional measurement of upper jaw position can be gauged to within 1 mm by means of a simple two-point measurement system. When used in combination with direct bone measurements and appropriate surgical sequencing, assessment of maxillary repositioning is possible at virtually any time during the surgical procedure.

Bronchoscopic removal of aspirated foreign bodies in children

Foreign body aspiration is the cause of death in over 500 children per year in the United States. Tracheobronchial inhalation of foreign bodies may result in acute respiratory distress, chronic pulmonary infections, atelectasis, or death. A review of 262 children ranging from 4 months to 13 years of age was undertaken to identify factors important in diagnosis to illustrate the effectiveness of newer endoscopic techniques and equipment, and to evaluate results and complications. Coughing, choking, and wheezing were the presenting symptoms seen in 91 percent of the patients. Inspiratory and expiratory chest radiographs were positive in 81 percent of the 224 children with foreign bodies removed. Fluoroscopy was positive in 41 patients, 88 percent of whom had foreign bodies removed. Bronchoscopy is required for treatment, and with experience, this procedure can be simple and safe. Ninety-nine percent of foreign bodies identified at bronchoscopy were removed successfully. Minor complications occurred in 8 percent of the patients, and there were no deaths.

Use of the orthognathic surgery simulating instrument in the presurgical evaluation of facial asymmetry

The use of Orthognathic Surgery Simulating Instrument (OSSI) is described. Two cases of facial asymmetry, one with hemifacial microsomia and one with unilateral condylar hyperplasia, are presented to demonstrate the diagnostic capabilities of the articulator. The OSSI has greatly improved our ability to plan the treatment of cases of gross facial asymmetry.

Hypoxemia increases plasma catecholamine concentrations in exercising humans

To determine whether plasma catecholamine concentrations (a measure of sympathetic nervous activity [SNA]) rise above normoxic levels during exercise with hypoxemia, we exercised seven men for 15 min at three loads that required from 40 to 88% of maximal O2 uptake (VO2max). Subjects breathed room air on one day and 11-12% O2 on another with relative work loads corrected for the 24% fall in VO2max during hypoxemia. Hypoxemia caused large increments in norepinephrine (NE) concentration (radioenzyme technique) to 1.21 +/- 0.20 ng/ml (mean +/- SE), 2.79 +/- 0.38, and up to 5.90 +/- 0.75 (hypoxemia) compared with 0.89 +/- 0.06, 1.66 +/- 0.16, and 3.95 +/- 0.39 in normoxia at the three loads, respectively (P less than 0.001). Epinephrine (E) concentration approximately doubled (P less than 0.001) in hypoxemia at each load when compared with normoxic levels (i.e., 0.10 +/- 0.01 ng/ml, 0.23 +/- 0.03, and 0.46 +/- 0.06 in normoxia). However, hypoxemia did not significantly alter linear relationships between log plasma NE concentration and either heart rate (HR) or percent VO2max utilized, or between HR and percent VO2max. Thus NE concentration, like HR, appeared to reflect relative severity of exercise and overall SNA in both hypoxemia and normoxia. Above 40% VO2max during hypoxemia, circulating NE and E far exceeded levels known to have direct vasoconstrictor and metabolic effects in normoxic humans, but hypoxemia may blunt vasoconstriction in some regions.