Frederick K. Hilton

Taurine concentrations in hearts of big brown bats (Eptesicus fuscus) during hibernation, arousal and normothermic behavior

Abstract 1. 1. Hearts from bats (a) hibernating in a cave at 0°C, (b) after additional weeks in a hibernaculum at 2°C, (c) removed from the hibernaculum and exposed to room temperature for periods ranging from 8 to 120min, and (d) emerging from a summer roost, were rapidly removed, dissected and frozen. 2. 2. Mean concentrations of taurine in ventricles of hearts of bats from these five groups did not differ significantly. 3. 3. Plasma from a small subset of animals from the hibernaculum, sampled 0–120 min after transfer to room temperature, contained 324–1269 μM taurine. There was no apparent relationship between plasma taurine concentration and time at 23°C.

Use of the soluble peptide γ-L-glutamyl-L-tyrosine to provide tyrosine in total parenteral nutrition in rats

Limited solubility restricts amounts of tyrosine (Tyr) in amino acid solutions used in total parenteral nutrition (TPN). Excess phenylalanine (Phe) is included in TPN for conversion to Tyr by liver Phe hydroxylase. However, this conversion is limited, especially in infants. We have confirmed that infants receiving TPN have low Tyr concentrations and high Phe/Tyr ratios in plasma compared with published values for enterally fed neonates. Tyr is important in the synthesis of proteins and other biomolecules, including catecholamines in the brain. We tested the soluble peptide gamma-glutamyl-tyrosine (Glu(Tyr)) as a possible precursor of Tyr in TPN. Groups of five rats were given infusions of TPN containing an amino acid mixture simulating a commercial formulation (group A), TPN in which Glu(Tyr) was substituted for half the Phe in the group A solution) (group B), or saline (group C). Control animals (group C) were fed rodent chow. Blood was sampled at 0 time and daily for 4 days. Brains were collected at 96 hours, and aromatic amino acids in plasma and brains were measured by high-performance liquid chromatography. Throughout the experiment, plasma of animals in group A had significantly elevated Phe and reduced Tyr concentrations compared with control values; plasma concentrations in groups B and C were similar. In groups A and B, brain Tyr levels were 31% and 63% of control values, respectively. In group B, Glu(Tyr) was not detected in brains. These data suggest that supplementing current TPN mixtures with Glu(Tyr), which is stable in solution, can produce normal plasma Tyr concentrations and Phe/Tyr ratios and improve the supply of Tyr to the brain.

Use of the stable peptide, γ-l-glutamyl-l-tyrosine, as an intravenous source of tyrosine in mice

The relative insolubility of tyrosine (Tyr) at neutral pH limits amounts of this amino acid in solutions used for total parenteral nutrition (TPN). We have tested the potential of the natural peptide, gamma-L-glutamyl-L-tyrosine (Glu(Tyr], to release Tyr in vivo by making 20-microL injections, containing 2.9 mumol Glu(Tyr) (approximately 80 mumol/kg body weight), into the external jugular veins of mice. Mean concentrations of Glu(Tyr) in plasma were 138.5 and 11.4 mumol/L after 10 and 60 minutes, respectively; plasma Tyr was significantly elevated at 10 minutes, but returned to control levels at 60 minutes. When 5.8 mumol of Glu(Tyr) was injected, levels of Glu(Tyr) and of Tyr were significantly higher at both 10 and minutes than when 2.9 mumol of peptide was injected. Animals showed no evidence of toxicity. Two percent or less of the peptide could be detected in the urine, even in mice injected with 5.8 mumol Glu(Tyr). Pretreatment of mice with acivicin, a potent inhibitor of gamma-glutamyl transpeptidase (GGTase), prevented the increase in plasma Tyr seen after injection of 2.9 mumol Glu(Tyr) and led to higher levels of Glu(Tyr) in the plasma both at 10 and at 60 minutes than seen in mice given the same amount of Glu(Tyr) but no acivicin. The presence of the inhibitor also led to loss of as much as 48% of the administered peptide in the urine in 60 minutes. These data suggest that GGTase catalyzes hydrolysis of intravenous (IV) Glu(Tyr) to release Tyr in vivo. Glu(Tyr) in the blood is not partitioned into red blood cells; it remains in the plasma, available to GGTase, which functions at the external surface of cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Biochemical and physiological changes in the blood of dominant and subordinate CF-1 male mice, Mus musculus

Abstract 1. 1. When two previously isolated male CF-1 mice are placed together, they will fight to establish a dominant-subordinate relationship. 2. 2. In response to this behaviorly stressful situation, various physiological and biochemical parameters in the mice are altered. 3. 3. When compared to dominants and controls, subordinates showed decreased hemoglobin concentration and bicarbonate levels, with a concomitant increase in hydrogen ion concentration, negative base excess and blood lactate levels. PCO 2 and PO 2 remained unchanged. 4. 4. No significant differences were observed in levels of 2,3-diphosphoglyceric acid in dominants, subordinates or controls. 5. 5. Subordinate individuals were anemic with persistent lactic acidemia reflecting the inability of the liver to catabolize excess lactate.

Genetically determined differences in the amylase activity of mouse submandibular glands.

Summary Examination of 10 different inbred strains and 2 hybrids of mice indicated that the normal levels of amylase activity vary from one strain to another. Further, the activity of the enzyme in the salivary gland tissue is markedly altered by gonadectomy. The effect of such endocrinological imbalancing varies with each strain. In some strains enzyme activity remains unchanged. In some, activity increases while in others it decreases. The pattern of change was not always the same for females as for males of the same strain. In other words, we are dealing with an enzyme system which is related to the genotype, but which may be influenced in an undetermined fashion by endocrine manipulation.

Intravenous γ-glutamyl-tyrosine elevates brain tyrosine but not catecholamine concentrations in normal rats☆

A number of clinical situations may benefit from intravenous supplements of tyrosine (Tyr). In total parenteral nutrition (TPN), the supply of Tyr is limited by its poor solubility. In both rats and infants maintained on pediatric TPN, plasma Tyr levels are approximately 30% of normal, and in rat brains Tyr concentrations are similarly reduced. We reported previously that supplementing a TPN solution with the soluble peptide, gamma-glutamyl-Tyr [Glu(Tyr)], normalizes plasma Tyr and doubles brain Tyr in rats. To assess more fully the behavior of intravenous Glu(Tyr) in vivo, 20 mmol/L Glu(Tyr) was infused into the inferior vena cava of rats at rates increased every 2 hours over an 8-hour period (300 to 450 mumol Glu(Tyr)/kg body weight/h). The surgical procedure for catheterization is described. At the maximum rate of infusion, plasma Tyr and Glu(Tyr) concentrations reached mean plateau values of 326 and 252 mumol/L, respectively. Brain Tyr concentrations were 71 and 264 nmol/g wet weight in control rats infused with heparinized saline (SAL group) and rats infused with Glu(Tyr) (PEP group) respectively. No differences were found in concentrations of norepinephrine (NE), dopamine (DA), or homovanillic acid (HVA) in prefrontal cortex (PFC), striatum (STR), or remaining brain (RB) tissue in PEP and SAL rats. We did not detect undergraded Glu(Tyr) in the brain, and less than 0.5% of infused Glu(Tyr) appeared in the urine.

Relationships of testicular cholesterol to hormonal activity and behavior in the starling.

Summary Levels of cholesterol were determined in testes of starlings collected from all portions of the gonadal and behavioral cycle. The lowest concentration of cholesterol was observed during recrudescence of the testes and at the time of most active behavior. The highest concentration was observed during regression of the testes and at the period of lowest behavioral activity. Intermediate concentrations of cholesterol accompanied the moderate behavioral activity observed in fall and winter. An hypothesis relating cholesterol concentration, hormone production and behavioral activity is advanced.

The effects of temperature on isolated hearts from neonatal through post-weanling rats

1. 1. Isolated hearts from neonatal (<48hr) rats ceased contractility at 4.5 C while those from 21–30 days old stopped beating at 10 C. 2. 2. Heart rate-temperature data analyzed by Arrhenius plots and Q4 determinations demonstrated that hearts from neonates respond in a manner approaching that of hearts from hibernators, while the response from the 21–30 day olds was more typical of hearts from adult, non-hibernators.

The effects of temperature on the isolated heart of the European starling, Sturnus vulgaris

Abstract 1. 1. The heart rate from the European starling (Sturnus vulgaris) reacts to increasing hypothermia as a typical nonhibernator, stopping at 15°C. 2. 2. The heart rate-temperature graph was linear between the temperatures of 41 and 19°C. but became curvilinear between 19 and 15°C. 3. 3. The cooling and rewarming curves for the heart rate-temperature graph exhibited no hysteresis. 4. 4. Arrhenius graphs showed a change in energy of activation (Ea,) in the temperature range of 25–27°C. 5. 5. During cooling from 41 to 27°C, the hearts showed an Ea of 10.2 kcal/mole while from 27 to 15°C the Ea was 29.8 kcal/mole. During rewarming, the Ea between 15 and 25°C was 30.5 kcal/mole and between 25 and 41°C was 11.6 kcal/mole.

In vitro Cardiac Performance of the Big Brown Bat, Eptesicus fuscus, at Normothermic and Hibernating Temperatures

Heart rates recorded in vitro for the bat at normothermic and hibernating temperatures were 450 ± 26 and 34 ± 6 beats/min, respectively. These rates are very similar to in vivo rates previously reported. Glucose uptake and utilization (efficiency) were 384 ± 34 μmol glucose/g dry weight (C₆/gdw) per hour and 58 ± 6 beats/μmol C₆/gdw for hearts at normothermic temperatures and 90 ± 12 μmol C₆/gdw per hour and 43 ± 11 beats/μmol C₆/gdw for hibernating hearts. Although lactate production was much greater among normothermic hearts when compared with those at hibernating temperatures (159 ± 18 and 11 ± μmol C₃/gdw per hour), both groups beat a similar number of times during the production of 1 μmol lactic acid. Glycogenolysis was observed among normothermic hearts (40%) following 90 min of perfusion. Hearts from hibernating animals did not show any significant difference in glycogen content following perfusion.