The American journal of physiology
-
The rapidity with which lung growth is initiated and completed after pneumonectomy was examined in young rats (4 wk of age; 82 g). After left pneumonectomy, the remaining lobes of the right lung grew to equal the weight of both lungs of control animals by day 7 and within 14 days increased from 366 to 968 mg. The tissue concentrations of RNA, DNA phosphate, collagen, and noncollagen proteins did not increase during the growth response. ⋯ Although cell size increased in control lungs during the experimental period, there was little evidence of additional cellular hypertrophy associated with compensatory lung growth. The character of the response to pneumonectomy in these rats was similar to that observed previously in older animals (320 g). Thus in spite of the higher basal rate of lung growth in the younger rats, the pattern and rapidity of compensation after pneumonectomy was similar in both age groups.
-
Recent studies have suggested that potassium, like urea, undergoes medullary recycling. The present cortical and papillary micropuncture studies were designed to confirm the existence of medullary potassium recycling and to determine whether acute infusions of aldosterone affected this phenomenon. ⋯ The clearance results demonstrated that aldosterone has an acute antinatriuretic and a kaliuretic effect, whereas the micropuncture studies demonstrated that 1) aldosterone increases potassium secretion between early and late distal tubule punctures; 2) aldosterone causes an increase in delivery of potassium to the papillary collecting duct; 3) aldosterone does not increase potassium secretion across the papillary collecting duct; and 4) aldosterone significantly increases medullary potassium recycling as evidenced by increased quantities of potassium present at the bend of the loop of Henle in response to aldosterone infusions. Thus, the studies confirm the existence of potassium recycling and suggest that this phenomenon is a feedback system that, in part, regulates urinary potassium excretion.
-
Comparative Study
Muscle metabolism and performance in perfused rat hindquarter during heavy exercise.
An isolated perfused rat hindquarter model was used to examine muscle metabolism and performance during heavy muscular contraction. A one-pass system was used to perfuse the hindquarter for 30 min at rest and 20 min while electrically stimulated at 0.5 Hz with tetanic stimuli (100 Hz). The isometric tension generated by the gastrocnemius-plantaris-soleus muscle group was recorded continuously, and muscle biopsies were taken pre- and postperfusion. ⋯ An additional 15 min of stimulation further decreased glycogen concentrations while lactate concentrations decreased in all muscles. Calculations based on the measured amounts of O2 and CP consumed and the amount of lactate produced revealed a heavy glycolytic contribution to energy production during the initial 5 min of stimulation (23%) and an aerobic domination during the final 15 min (90%). With this model heavy muscular contraction can be sustained to permit the measurement of uptake and release of substrates and products of the main energy-yielding pathways.
-
A theoretical model has been developed to simulate solute and water transport in the medullary microcirculation of the normal hydropenic rat. The model is formulated in terms of a countercurrent vascular unit consisting of one descending (DVR) and several ascending vasa recta (AVR) extending from the corticomedullary junction to the tip of the papilla. Steady-state mass balances relate gradients in NaCl, urea, and plasma protein concentrations and variations in the flow rates of plasma and red blood cells to permeability properties of the vasa recta and erythrocytes. ⋯ It is calculated that at a given blood flow rate, the lower the initial medullary hematocrit, the more effective the vascular unit is at removing water. Several unresolved issues are discussed, including the role of the capillary plexus that joins DVR with AVR. To the extent that the volume uptake observed in the exposed papilla in structures beyond the DVR occurs in the capillary plexus and not in the AVR, estimated values of AVR hydraulic permeability are reduced, as is predicted overall volume uptake by the vascular unit in the inner medulla.
-
A systems analysis of intrinsic regulation of intestinal blood flow and oxygenation is presented. The model is based on current concepts of metabolic control of tissue oxygen delivery and incorporates recent data from the literature regarding the influence of oxygen availability-to-demand ratio on intestinal vascular resistance and perfused capillary density. ⋯ However, the combination of capillary recruitment and blood flow autoregulation provides a large margin of safety against tissue hypoxia in the intestine. Simulation results also predict that oxygen extraction plays a greater role than blood flow in providing additional oxygen to the hypermetabolic intestine irrespective of which control system (resistance or exchange vessel) is operating.