Breathing at a rate of 5.5 breaths per minute with equal inhalation-to-exhalation ratio increases heart rate variability.

OBJECTIVES: Prior studies have found that a breathing pattern of 6 or 5.5 breaths per minute (bpm) was associated with greater heart rate variability (HRV) than that of spontaneous breathing rate. However, the effects of combining the breathing rate with the inhalation-to-exhalation ratio (I:E ratio) on HRV indices are inconsistent. This study aimed to examine the differences in HRV indices and subjective feelings of anxiety and relaxation among four different breathing patterns. METHODS: Forty-seven healthy college students were recruited for the study, and a Latin square experimental design with a counterbalance in random sequences was applied. Participants were instructed to breathe at two different breathing rates (6 and 5.5 breaths) and two different I:E ratios (5:5 and 4:6). The HRV indices as well as anxiety and relaxation levels were measured at baseline (spontaneous breathing) and for the four different breathing patterns. RESULTS: The results revealed that a pattern of 5.5 bpm with an I:E ratio of 5:5 produced a higher NN interval standard deviation and higher low frequency power than the other breathing patterns. Moreover, the four different breathing patterns were associated with significantly increased feeling of relaxation compared with baseline. CONCLUSION: The study confirmed that a breathing pattern of 5.5 bpm with an I:E ratio of 5:5 achieved greater HRV than the other breathing patterns. This finding can be applied to HRV biofeedback or breathing training in the future.

Mutational analysis of the cytoplasmic tail of the human transferrin receptor. Identification of a sub-domain that is required for rapid endocytosis.

It has been reported that the sequence Tyr20-X-Arg-Phe23 present within the cytoplasmic tail of the transferrin receptor may represent a tyrosine internalization signal (Collawn, J.F., Stangel, M., Kuhn, L.A., Esekogwu, V., Jing, S., Trowbridge, I.S., and Tainer, J. A. (1990) Cell 63, 1061-1072). However, as Tyr20 is not conserved between species (Alvarez, E., Gironès, N., and Davis, R. J. (1990) Biochem. J. 267, 31-35), the functional role of the putative tyrosine internalization signal is not clear. To address this question, we constructed a series of 32 deletions and point mutations within the cytoplasmic tail of the human transferrin receptor. The effect of these mutations on the apparent first order rate constant for receptor endocytosis was examined. It was found that the region of the cytoplasmic tail that is proximal to the transmembrane domain (residues 28-58) is dispensable for rapid endocytosis. In contrast, the distal region of the cytoplasmic tail (residues 1-27) was found to be both necessary and sufficient for the rapid internalization of the transferrin receptor. The region identified includes Tyr20-X-Arg-Phe23, but is significantly larger than this tetrapeptide. It is therefore likely that structural information in addition to the proposed tyrosine internalization signal is required for endocytosis. To test this hypothesis, we investigated whether a heterologous tyrosine internalization signal (from the low density lipoprotein receptor) could function to cause the rapid endocytosis of the transferrin receptor. It was observed that this heterologous tyrosine internalization signal did not allow rapid endocytosis. We conclude that the putative tyrosine internalization signal (Tyr20-Thr-Arg-Phe23) is not sufficient to determine rapid endocytosis of the transferrin receptor. The data reported here indicate that the transferrin receptor internalization signal is formed by a larger cytoplasmic tail structure located at the amino terminus of the receptor.

Cholesterol kinetic analyses in copper-deficient rats.

Ninety weanling male Sprague-Dawley rats were randomly allotted into two treatment groups (copper-deficient and adequate; less than 2 mg and 8 mg Cu/kg of diet. Feed and distilled water were provided ad libitum for 16 weeks. After 5 weeks of treatment, the rats were injected intraperitoneally with 6.35 microCI [4-14C]cholesterol/kg body weight. A disappearance curve of the serum cholesterol specific activity (SA) was obtained for each treatment group by killing one animal at 1, 2, 7, 14, 28, 42, 56, 70 and 77 days after the tracer injection. Disappearance curves of serum cholesterol SA were constructed for the rats fed the copper-adequate and copper-deficient diets. Each disappearance curve of cholesterol SA in the serum was subjected to a kinetic two-pool analysis. The size of the fast turning over cholesterol pool (pool A) and the half-life of pool A were significantly greater in rats fed the copper-deficient diet than the controls. In addition, copper deficiency decreased the rate of removal of cholesterol from pool A (KAA), decreased the irreversible removal of cholesterol from pool A (KA) and reduced the rate of transport of cholesterol (KAB) from pool A to the slowly exchangeable pool (pool B). However, copper deficiency did not alter the production rate of cholesterol (PRA) in pool A. Thus, the reduction in the rate of removal of cholesterol from pool A might have been responsible for the hypercholesterolemia observed previously in rats fed copper-deficient diets.

Studies on duck nutrition. II. Calcium and phosphorus requirements of mule ducklings.

Experiments were conducted to determine calcium and phosphorus requirements of mule ducklings. Two-day-old, straight-run mule ducklings were fed diets containing graded levels of calcium or phosphorus for three weeks. Weight gain, feed consumption, tibia ash content, and levels of serum calcium and phosphorus were used as criteria for the determination of the optimum dietary calcium and phosphorus levels required by the ducklings. The minimum calcium requirements were .48% and .58%, respectively, for maximum growth and optimum tibia ash content as determined by regression analysis of body weight gain and tibia ash content against calcium level in the diet. The minimum available phosphorus requirements were .26% and .34%, respectively, for maximum body weight gain and optimum tibia ash content as determined by the same method.