Catabolic enzyme activities in relation to premigratory fattening and muscle hypertrophy in the gray catbird (Dumetella carolinensis)

Abstract

The flight muscles of the gray catbird (Dumetella carolinensis) were examined to determine if short term adjustments occur in the activity of key catabolic enzymes during preparation for long distance migration. The aerobic capacity of the pectoralis muscle as indicated by citrate synthase activity (CS) is among the highest reported for skeletal muscle (200 ~tmoles [rain. g fresh mass]-1 at 25 ~ The mass specific aerobic capacity as indicated by CS activity or cytochrome c concentration does not change during premigratory fattening (Fig. 2) or in relation to the muscle hypertrophy that occurs concomitantly. The maintenance of mass specific aerobic capacity indicates that the total aerobic capacity increases in proportion to the increase in muscle size. The augmented potential for total aerobic power output is considered an adaptation to meet the increased power requirements of flight due to the increased body mass. Additionally, the capacity to oxidize fatty acids, as indicated by fl-hydroxyacyl-CoA dehydrogenase activity, approximately doubles during premigratory fattening (from 35 to 70 gmoles [min.g fresh mass] 1 at 25 ~ Fig. 1 A). This adaptation should favor fatty acid oxidation, thereby sparing carbohydrate and prolonging endurance. The activity of phosphofructokinase, a key glycolytic enzyme, does not change before migration.

Seasonal Metabolic Acclimatization in Mountain Chickadees and Juniper Titmice

“…Increased pectoralis mass in winter may be more important for elevation of M sum than BMR. If massspecific aerobic capacity remains seasonally static in chickadees and titmice, as reported for some other passerines (Marsh 1981;Yacoe and Dawson 1983), then any winter increase in pectoralis mass represents an increase in overall aerobic capacity. Even in birds that have a significantly higher mass-specific aerobic capacity in winter, the increase is generally low (∼7%).…”

“…These conditions include low air temperatures and decreased foraging time due to shorter days, which can be further restricted by snow or ice cover. Small birds meet this energetic challenge primarily through metabolic adjustments (reviews: Dawson and Marsh 1989;Marsh andDawson 1989a, 1989b;Dawson and O'Connor 1996). These metabolic adjustments generally include tolerance of colder temperatures in winteracclimatized birds relative to summer birds (Hart 1962;Barnett 1970;Pohl and West 1973), increased thermogenic endurance in winter birds (Dawson and Carey 1976;Dawson et al 1983;Swanson 1990;O'Connor 1995), and increased summit metabolism (M sum ) in winter birds (Hart 1962;Dawson and Smith 1986;Swanson 1990;Cooper and Swanson 1994;O'Connor 1995;Liknes and Swanson 1996).…”

The Enzymatic Basis of High Metabolic Rates in Calling Frogs

“…Anurans with access to insect prey during the breeding season may rely less on stored lipids and possess a different complement of substrate-oxidizing enzymes in the trunk muscles. In contrast to CS and HOAD activities, PFK activity in trunk muscle is low relative to other vertebrate skeletal muscles (Crabtree and Newsholme Alp et al 1976Alp et al 1976Marsh 1981 NOTE.-CS activities of male spring peeper leg and trunk muscles were measured at 20 C. All other values were measured at 25 C. Except for temperature, the CS assay procedures used in the studies referenced in this table were identical. 1972).…”

“…Trunk muscle tissue and mixed leg muscle tissue were divided in half, with one-half used for the determination of PFK activity and the other half for measurement of CS and HOAD activity. Catalytic activities ofPFK, CS, and HOAD were measured in crude muscle homogenates at 20 C using spectrophotometric assays with saturating levels of substrates, as described in Marsh (1981). We used a Gilford model 260 UV /VIS spectrophotometer with a computerized data acquisition system (Apple 11+ computer with Interactive Microware, Inc., Adalab System) in these measurements.…”

“…Muscles were quickly dissected from pithed male and female frogs and weighed immediately on an electronic balance (±0.001 g) to determine fresh mass of the combined hind limb muscles and the trunk muscles. We assayed for three enzymes: (1) phosphofructokinase (PFK), an indicator of glycolytic capacity (Crabtree and Newsholme 1972); (2) citrate synthase (CS), an indicator of capacity for aerobic A TP production (Marsh 1981); and (3) [3-hydroxyacyl-CoA dehydrogenase (HOAD), an indicator of capacity for fatty acid oxidation (Marsh 1981). Trunk muscle tissue and mixed leg muscle tissue were divided in half, with one-half used for the determination of PFK activity and the other half for measurement of CS and HOAD activity.…”