Muscle metabolism during 30, 60 and 90 s of maximal cycling on an air-braked ergometer.

This study examined the anaerobic and aerobic contributions to muscle metabolism during high intensity short duration exercise. Six males [mean (SD): age 25.0 (6.0) years, height 179.0 (8.2) cm, mass 70.01 (7.42) kg, VO2max 4.63 (0.53) l.min-1, body fat 12.7 (2.3)%] performed three counterbalanced treatments of 30, 60 and 90 s of maximal cycling on an air-braked ergometer. All treatments were also performed on days when biopsies were not taken from the vastus lateralis muscle and cannulae not inserted into a forearm vein to ascertain whether these procedures adversely affected performance. The mean results can be summarised as follows: (Table: see text). The muscle lactate and O2 deficit data suggested that 60 and 90 s were more appropriate durations than 30 s for assessing the anaerobic capacity on an air-braked cycle ergometer. The mean power outputs also indicated that the invasive procedures did not adversely affect performance [corrected].     

Assay of radiation effects in mouse skin as expressed in wound healing

The effect of 150 kVp X irradiation on the healing of full depth surgical wounds in the lower dorsal skin of the mouse was assayed by measuring the wound strength of seven 2-mm-wide segments along each wound. The strength of unirradiated wounds increased with time in two phases: during the first 2 weeks it reached nearly half of the values recorded from unwounded skin, after which the rate of increase slowed for at least 2 weeks before beginning a second increase. By 150 days, the breaking strength of the wound was about 80% of that of unwounded skin. A single dose of 18 Gy prior to wounding reduced the strength of the wounds to about one-third to one-half that of an unirradiated wounds within the 3 months of follow-up. The effect of irradiation on wound strength did not change as the interval between exposure and wounding was increased to 2 months but decreased slightly when this interval was extended to 3 months. When the healing wound was irradiated within 5 days of surgery, the effect on healing was about the same as with preirradiation; if irradiation was delayed for 12 days after wounding the second phase of healing was only postponed and the wound strength ultimately approached the values recorded from unirradiated wounds. The wound strength of skin preirradiated by X rays and assayed 14 days after wounding showed a clear sigmoid dose response with a threshold between 8 and 10 Gy and a plateau at the maximum effect above 20 Gy. The persistence for at least 3 months of the effect of radiation on wound healing suggests that the tissues involved in the healing process are normally proliferating slowly. The accelerated expression of radiation injury through surgical wounding permits the early quantification of the radiation response of tissues that would normally be delayed in their expression of radiation damage.     

The hemodynamic consequences of hemorrhage and hypernatremia in two amphibians

1. Graded hypovolemia was induced by hemorrhagic blood loss and graded hypernatremia by salt load in the toad, Bufo marinus, and the bullfrog, Rana catesbeiana. Maximal blood flow rates in the systemic arches and arterial and venous pressures were measured during activity after each stress. 2. Maximal blood flow rates in the B. marinus did not decline until blood loss exceeded 5% of initial body mass. In R. catesbeiana, losses of 2% initial body mass caused a decline (Fig. 1). 3. Maximal heart rates did not change with hemorrhage (Fig. 2). The decline in blood flow rates with hemorrhage was due to declining pulse volumes in both species (Fig. 3). 4. Arteriovenous pressure difference declined with hemorrhage in both species (Fig. 4). Peripheral resistance increased with hemorrhage in parallel with compromised blood flow rates (Fig. 5). 5. Plasma sodium concentration slightly increased with hemorrhage, while plasma protein concentration and hematocrit declined. Lymphatic compensation for hemorrhagic loss is indicated in both species (Fig. 6). 6. Induced hypernatremia compromised blood flow rates in both species at plasma sodium concentrations above 175 mM. The decline in flow rates was principally a result of a decrease in pulse volume, though maximal heart rates also declined (Figs. 2, 3, 7). 7. Induced hypernatremia had no effect on the arteriovenous pressure difference in B. marinus but caused it to decline in R. catesbeiana. Peripheral resistance increased in only B. marinus but not R. catesbeiana (Figs. 4, 5). Hematocrit did not change with salt load, indicative of a constant vascular volume.     

Stability of recombinant protein production by Penicillium chrysogenum in prolonged chemostat culture

Abstract A strain (WKW2) of Penicillium chrysogenum transformed with heterologous fungal acetamidase ( amd S) and bacterial β-galactosidase ( lac Z) was grown at a dilution rate of 0.17 h⁻¹ (doubling time of approx. 4.1 h) for 1600 h in a glucose-limited culture. By the end of the experiment the original strain had been almost completely replaced by spontaneous, morphological mutants, but the acetamidase and β-galactosidase activities of the culture were essentially unaltered. Furthermore, when WKW2 and the non-transformed parental strain (NRRL1951) were grown together in glucose- or NH₄⁺-limited chemostat cultures, neither strain had a selective advantage over the other. Thus, heterologous gene expression does not result in NRRL1951 having a selective advantage over WKW2. These results suggest that continuous flow culture systems could be used for efficient (and cost effective) production of recombinant proteins.