Roles of growth hormone and insulin-like growth factor 1 in mouse postnatal growth.

Osmotic regulation in crustaceans

The role that mechanical factors deriving from blood flow play in the growth of blood vessels was most probably mentioned for the first time by John Hunter in his “Treatise on the Blood Flow, Inflammation and Gunshot Wounds,” published in 1794. Hunter was an anatomist who kept a deer herd in Richmond Park. He described enlargement of the carotid arteries in deer, coincident with the development of new antlers, which is known to involve intensive vascular growth. Almost a century later, Thoma (1) demonstrated that ontogenetic growth of vessels is caused by a combination of hemodynamic forces — increased blood flow, blood pressure, and wall tension — and mechanical stretch of vessels owing to the growth of the surrounding tissue. The importance of flow for capillary development was later shown in tadpole tails by Clark (2), who exposed to observation under the microscope the same site over many days, and in wound healing in the rabbit ear chamber (3). Today, the roles in angiogenesis of mechanical factors such as shear stress, circumferential stress, stretch, or physical forces owing to modification of the extracellular matrix are widely studied in tissue culture.

Angiogenesis in skeletal and cardiac muscle

Carbonic anhydrase (CA) is a central enzyme to both transport and metabolic processes at the cellular level. In metabolically active tissue such as muscle, CA in the cytoplasm and on the sarcolemma appears to be important in facilitating CO2 transport out of the cell. Membrane-associated CA, with an extracellular orientation, also appears to be important in acidifying the outer boundary layer through the catalyzed hydration of excreted CO2. This facilitates cellular ammonia transport by providing H+ ions for the protonation of NH3, thus maintaining the trans-membrane NH3 gradient. Mitochondrial CA is known to supply HCO3- for the initial reactions of gluconeogenesis and ureagenesis in mammalian tissues, but systematic comparative studies of CA as a metabolic enzyme are lacking. CA probably evolved as an enzyme of trans-membrane facilitated CO2 transport and took on a secondary metabolic role later in metazoan evolution.

Multiple Roles of Carbonic Anhydrase in Cellular Transport and Metabolism

The energetics of four fossorial mammals, Spalacopus cyanus, Cannomys radius, Aplodontia rufa, and Scalopus aquaticus, are examined and compared to data available in the liter- ature. Basal rates of metabolism are lower than expected from mass if fossorial mammals weigh >80 g, but they are higher than expected if they weigh 100 g. Small burrowers may have low basal rates unrelated to burrowing habits. Minimal thermal conductances in fossorial and burrowing mammals are usually near the expected values at masses 1 kg have high minimal conductances. The temperature differential maintained at the lower limit of thermoneutrality and at temperatures above thermoneutrality is proportional to the ratio of basal rate to minimal conductance. Adaptations to a burrowing habit include (1) maintaining a small temperature differential independent of mass, which is accomplished by matching the mass sensitivity of the basal rate to that of the minimal conductance, (2) reducing basal rate, (3) increasing minimal conductance, and (4) reducing mass. The limits that exist to a reduction in mass and a reduction in basal rate of metabolism and to an increase in minimal conductance result in geographical limits to the distribution of fossorial mammals, but not necessarily to the distribution of other burrowing mammals.

H. Bartels

Papers

Biophysics and Physiology of Carbon Dioxide

Blood oxygen transport and organ weights of small bats and small non-flying mammals.

Oxygen affinity of chicken blood before and after hatching.

Factors governing the oxygen affinity of human adult and foetal blood.

Comparative studies of the respiratory function of mammalian blood. V. Insectivora: Shrew, mole and nonhibernating and hibernating hedgehog