Oxygen consumption in resting dog gracilis muscle perfused at varying oxygen delivery.

The different response of O2 uptake (VO2) of resting skeletal muscle to the changes in blood flow has been thought to reflect a species difference. To scrutinize this notion, we investigated the relation between O2 delivery (arterial O2 content multiplied by blood flow) and VO2 in isolated dog gracilis muscle perfused solely with normal hematocrit (Ht) blood (n = 9), or alternately with normal and low Ht blood (n = 6), or alternately with normal and high Ht blood (n = 3) at varying perfusion rates. Eleven out of the 18 preparations showed an autoregulation of blood flow, and the others did not. But, in all preparations, the VO2 was delivery-independent above a critical O2 delivery (0.45 ml/(min.100 g muscle)) and showed the constant VO2 of 0.30 ml/(min.100 g), while below the critical level it turned out to be delivery-dependent. The maximal extraction ratio was 0.67. The same relationship was found with the low and high Ht perfusion. The pattern observed in dog gracilis muscle was essentially the same as that in rat gracilis muscle (KOLAR and JANSKY, 1984).     

Assimilatory and excretory function of the isolated perfused dog liver

In experiments on dogs the assimilatory-excretory function of the liver was studied by means of the bromsulfthalein method in the intact animal and during perfusion of the isolated organ through the portal vein by means of an artificial circulation apparatus. Under perfusion conditions the rate of uptake of the dye was 50–60% of the value of this index in the intact animal. The rate of elimination of bromsulfthalein with the bile and the biliary plasma clearance in the intact animal were five to six times higher. The main cause of the reduction in the assimilatory-excretory function of the isolated liver is evidently hypoxia developing after denervation and removal of the organ from the body, and also during extracorporeal perfusion itself.Laboratory of Experimental Surgery, Medical Institute, Riga. (Presented by Academician of the Academy of Medical Sciences of the USSR N. N. Savitskii.) Translated from Byulleten' Éksperimental'noi Biologii i Meditsiny, Vol. 81, No. 4, pp. 405–407, April, 1976.     

Cerebral blood flow and oxygen consumption in the newborn dog

Cerebral blood flow (CBF), CBF responses to changes in arterial CO2 tension, and cerebral metabolic rate for oxygen (CMRO2) were measured in newborn dogs, by means of a modification of the Kety and Schmidt technique employing 133Xe. Mongrel dogs of 1-7 days of age were paralyzed and passively ventilated with 70% N2O and 30% O2. CBF was derived by analysis of paired serial 20-microliter samples of arterial and of cerebral venous blood from the superior sagittal sinus. At an arterial PCO2 of 36.9 +/- 3.7 Torr and a mean arterial blood pressure of 62 +/- 10 Torr, CBF was 23 +/- 8 ml/min per 100 g. The arteriovenous oxygen content difference averaged 5.6 vol%, and CMRO2 was 1.13 +/- 0.30 ml O2/min per 100 g. CBF increased or decreased by 0.58 ml/min/100 g per Torr change in PCO2. Our results suggest that in the newborn, basal CBF and CBF responses to CO2 are considerably lower than in the adult and parallel the lower metabolic needs of the newborn brain.     

Oxygen supply, oxygen consumption, and endocrine and exocrine secretions of the isolated, perfused, porcine pancreas

We studied the effect of varying oxygen supply on the endocrine and exocrine secretions of the isolated perfused porcine pancreas utilizing completely synthetic perfusion medium with and without the addition of erythrocytes. With synthetic medium oxygenated to a Po2 of 500 mmHg, oxygen consumption was constant for flow rates at or above 0.5 ml x min-1 x g-1 (wet weight). Addition of erythrocytes to the medium did not increase oxygen consumption at flow rates above this level. Furthermore, the secretion of fluid, bicarbonate and protein in response to secretin and acetylcholine was not influenced by addition of erythrocytes. Similarly, the secretion of insulin, glucagon, pancreatic polypeptide, and somatostatin in response to arginine and acetylcholine was unchanged; arginine stimulated the secretion of all four peptides, whereas acetylcholine stimulated the secretion of insulin and pancreatic polypeptide and inhibited glucagon and somatostatin secretion. The results indicate that the porcine pancreas is respiring adequately, when perfused with a completely synthetic perfusion medium at flows above about 0.5 ml x min-1 x g-1 and Po2 about 500 mmHg, and that addition of erythrocytes is not necessary for the study of its secretory functions.     

Optical measurement of perfused rat hindlimb muscle with relation of the oxygen metabolism.

Optical measurements of myoglobin (Mb) and cytochromes (Cyts) in the isolated rat hindlimb muscle perfused with cell-free medium were performed at 35 and 15 degrees C under various oxygen supply, in the relation to the oxygen metabolism. Molar ratio of Cyt a + a3, Cyt b, Cyt c + c1, and Mb, oxygen affinity of Mb (P50), and the thermodynamic parameter (delta H degree) of Mb oxygenation in cyanide-perfused muscle were similar to those reported. The "apparent P50" of Mb in cyanide-free muscle was almost two orders larger in magnitude than P50 in the presence of cyanide. O2 uptake by the perfused hindlimb muscle was constant above O2 supply of 0.73 mumol/(min.g muscle) (under a flow rate of 1.0 ml/(min.g muscle) at 35 degrees C). Below the value of O2 supply, the O2 uptake decreased and lactate/pyruvate ratio increased. The critical mean oxygen tension in tissue (estimated by Mb oxygenation) for O2 uptake at 35 degrees C was ca. 10 mmHg. It was found that oxidation level (%) of Cyt a + a3 was equivalent to oxygenation level (%) of Mb at 35 degrees C, while the oxidation level of Cyt a + a3 was higher than the oxygenation level of Mb at 15 degrees C. Based on the results, the uneven distribution of O2 in the muscle tissue and the intracellular O2 gradient were discussed.     

Vasoconstrictor and pilomotor fibres in skin nerves to the cat's tail

Summary Postganglionic neurones to the tail's skin of the cat were investigated with regard to their spontaneous activity, response characteristics to somatic stimuli and asphyxia, the conduction velocity of their axons, and the conduction velocity of the preganglionic axons converging on them. The cats were anaesthetized with chloralose, immobilized, and arteficially ventilated. With this regimen the postganglionic neurones were divided into two types: 1. Type 1 neurones are spontaneously active and exhibit reflexes upon somatic stimulation. During asphyxia they are mostly first depressed and then excited for about 2–3 min. Their axons conduct with 0.57±0.13 m/s (mean ± SD). The preganglionic axons converging on them conduct with 5.4±1.6 m/s. 2. Type 2 neurones are not spontaneously active and exhibit with few exceptions no reflexes on somatic stimuli. During asphyxia they are activated after 3–4 min, concomitantly with piloerection, when the activity in type 1 neurones is already decreasing. Their axons conduct with 0.84±0.14 m/s, the preganglionic axons converging on them conduct with 9.9±2.9 m/s. 3. From these characteristics it is concluded that type 1 neurones have vasomotor function and most type 2 neurones pilomotor function.