To investigate possible factors that limit fat utilization during exercise, arteriovenous differences of plasma nonesterified fatty acids (NEFA) and glycerol were measured across the subcutaneous adipose tissue of the anterior abdominal wall in nine subjects who exercised for 60 min at 50-70% of their maximal O2 consumption. The large gradient of NEFA concentration from adipose tissue venous to arterial plasma increased throughout the exercise period. Maximal plasma NEFA concentrations in adipose venous drainage were reached postexercise (median 3,800 mumol/l), with a median NEFA-to-albumin molar ratio of 5.7. Fractional reesterification of fatty acids within the tissue (assessed from the ratio of NEFA to glycerol release) was 20-30% in the basal state and declined during exercise. After exercise there was apparently negative reesterification, implying release of NEFA retained in adipose tissue during exercise. Although these findings challenge current views on the regulation of NEFA release, they are in agreement with the concept of supply of fatty acids from adipose tissue as the major factor limiting fat oxidation during sustained exercise.
Experiments are described which emphasize the importance of avoiding loss of carbon dioxide when estimating the pH or bicarbonate concentration of ruminal fluid. The high pCO2 of ruminal fluid is stressed; this may be 10 times or more as great as that of arterial blood. The relationship between pCO2, pH, and [HCO3-] was examined in terms of the Henderson-Hasselbalch equation over a wide range of pCO2. From this, the pK1' of the carbonic acid system in four ruminal fluids was determined as 6.21-6.28, mean 6.25. The higher pH of saliva-free samples of ruminal fluid withdrawn by suction through a tube passed down the oesophagus, as compared with that of the bulk fluid obtained through a ruminal fistula, is considered to be due to loss of carbon dioxide during collection. A better estimate of intraruminal pH is obtained, even when salivary contamination occurs, if such samples are equilibrated with a sample of the animal's ruminal gas; if this is not practicable, an arbitrary gas mixture of high pCO2, e.g. 50 per cent. carbon dioxide and nitrogen, may be used.
SUMMARY In the sheep the spleen has been shown to act as a dynamic reservoir of highly concentrated blood. As the number of red cells retained in the spleen is dependant upon the emotional state of the animal at the time, the values of the jugular haematocrit and of the F cells ratio are subject to wide variations. The extent to which such variations can affect the calculated values of blood volume (BV) and red cell volume (RCV) from plasma volume (PV) and jugular haematocrit has been demonstrated. Separate determination of RCV by labelled‐cell techniques, such as 51Cr‐labelling, may also be fallacious, because a considerable proportion of the total red cells (of the order of 10 p.c.) was found to be withheld from free “mixing” in some sheep; but this was readily overcome by the intravenous administration of adrenaline. Little error could result, and considerable saving of time could be made, by basing estimates of RCV and PV on a single sample taken 10 minutes after administration of labelled cells and T‐1824 together with adrenaline to contract the spleen and thereby promote rapid and complete “mixing”. More simply, after injection of only T‐1824 plus adrenaline, BVpl could be calculated from the formula PV/(100 – H × F cells) where H is the haematocrit determined after 2–3 minutes, PV is based on a single plasma sample at 10 minutes and F cells after adrenaline is taken to be 0·81. The mean PV of 21 determinations on 13 Merino sheep, as determined by the T‐1824 method, was 44·6 ml./kg. (S.D., 3·1 ml./kg.). The mean BV, RCV and PV of 5 sheep, as determined by 51Cr‐labelled cells and T‐1824, were 66·4, 19·7 and 46·7 ml./kg. respectively (S.D., 5·4, 2·8 and 3·6 ml./kg, respectively).
Acid-base titration curves of ovine ruminal fluid confirmed the findings of Clark and Lombard (1951) that ruminal fluid is relatively well buffered against addition of acid, but relatively poorly against additions of alkali. However, considerable differences were observed between samples from different sheep. These were associated with differences in the interval after feeding, the nature of the diet, and the consumption of drinking water; and were correlated with differences in total and relative concentrations of bicarbonate, phosphate, and volatile fatty acids (VFA). The relative importance of the main buffering components in particular fluids was studied by examining the effects of the following procedures upon titration curves: ( a ) varying bicarbonate concentration by varying pCO2; ( b ) removing, and restoring, bicarbonate, phosphate, and VFA; and ( c ) removing particulate material. Particulate material was relatively unimportant as a buffer. Within the usual pH range of the rumen, the important buffering components were bicarbonate and phosphate. In the fasting rumen, bicarbonate was more important than phosphate, and this was found to be also true in parotid saliva. As ruminal fermentation proceeded and as VFA accumulated, bicarbonate and pH decreased and the buffer value depended more and more upon phosphate. In actively fermenting rumens, in which VFA concentration was high and the pH less than 6, VFA contributed significantly to the buffer resistance against further additions of acid. It is pointed out that, because the acids and bases generated during ruminal fermentation are relatively weak, they alter ruminal pH less, mole for mole, than the strong titrants conventionally used in titrations.
SUMMARY.The influence of the intensity of centrifugational treatment upon tl-.o lnaHnitudu aiul precision of haematocrit values of sheep blood, nnd upon the proportion of trapped plasma, was investigated.Examination of the concept of Dole and Cotzias (1951), which implies that equivalent multiplication products of RCF and time (i.e., impulse) have the same centrifugational effects failed to support it insofar as sheep blood is concerned; for this the relationship between impulse and haematocrit is represented by a family of hyperboloid curves each corresponding to a particular value of RCF. In the determination of haematocrit values with sheep blood, more inttiise centrif\igatioiial treatment is desirable than has been found adequate for human blood.The recommended ceutrifugatioaal conditions when the radius of gyration measured to the bottom of the tube is 17 cm. are 5000 rpm. (=4756 g.) for 60 min. Under these conditions the \ariance is low, differences in haematocrits of 0-17-0-20 between the means of duplicates being significant (P = 0-05) in the range 20-40, and over the range 24-53 tlie trapped pLisina correction factor is approximate!>• 0-97, being related to haematocrit by the linear equation, y = 2*26 -I-0-03x, where y = p.c. trapped plasma and x = haematocrit value.
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