Dimethylnitrosamine adducts excreted in rat urine

Rats were injected with [¹⁴C] dimethylnitrosamine and urine was collected up to 5 days after the injection. Urine samples were concentrated and subjected to Sephadex G-10 chromatography. Three peaks of radioactivity (I–III, in the order of elution) were observed for all injection times. The peaks were analysed further by cation exchange and thin-layer chromatography and by phase-separation (pH-determination). The pK-determinations and the chromatographic properties suggested that Sephadex fraction I composed of methylated amino acids, such as N-acetyl-S-methylcysteine, 1-methylhistamine and S-methylcysteine, in addition to radioactive methionine. Sephadex fraction II was suggested to compose of allantoin and of a metabolite of thiazolidine-4-carboxylic acid. The latter compound was a reaction product of formaldehyde and cysteine, indicating activity of the formaldehyde moiety released from dimethylnitrosamine. By gel filtration properties Sephadex fraction III indicated identity as 7-methylguanine. Altogether the urinary radioactivity accounted for about 9% of the applied dose.     

Cerebrospinal fluid acid-base balance during muscular exercise

Ventilation, metabolism, arterial blood gases, and blood and cerebrospinal fluid (CSF) acid-base status were measured in exercise studies on seven ponies during mild, moderate, and near-maximal treadmill exercise. CSF and arterial blood were sampled via indwelling catheters. Generally measurements were made during the 3rd, 6th, and 9th minute of steady-state exercise, with CSF sampled only during the 9th minute. Alveolar ventilation (VA) and metabolic rate (VO2) increased proportionately during exercise below the anaerobic threshold, but above this threshold, VA increased at a faster rate than VO2. The similarity of these response to those observed in man suggests the pony is a suitable animal model for study of exercise hyperpnea. No change in CSF acid-base balance occurred with light-to-moderate work; however, with near-maximal work a fall in CSF carbon dioxide partial pressure due to hyperventilation caused CSF to become alkaline (pH = 7.380) relative to rest (pH = 7.330). CSF lactate increased slightly with exercise but had no effect on CSF [HCO3-], which remained constant from rest to severe exercise. We conclude that it is unlikely the hyperpnea at any intensity of exercise results from an increased H+ stimulation at the medullary chemoreceptor.     

A model of sweating during muscular exercise]

From a practical viewpoint, thermal sweating during exercise can be described by an exponential equation. The errors from this mathematical model are of few importance. Nevertheless, metrologic and physiological factors can complicate theoretically the model.     

Energy sources mobilization during muscular exercise in pregnant rats

The experiments were carried out on three groups of female Wistar rats: nonpregnant rats (NP), rats pregnant for 10 days (P-10) and rats pregnant for 19 days (P-19). The rats were exercised on a treadmill set at 10 degrees incline at a running speed of 1200 m/h. Measurements were made at rest, after 30 min exercise, and after exercise till exhaustion. It was shown that in P-10 group the ability for the exhaustive exercise and metabolism of energy substrates during exercise were similar to those in NP group. The ability for exhaustive exercise of P-19 rats was reduced by 54.6% vs. NP rats. During exercise in P-19 group mobilization of glycogen in skeletal muscles was accelerated, mobilization of liver glycogen was impaired and hypoglycemia developed earlier than in NP group. Plasma FFA level in P-19 group reached a peak already after 30 min of exercise. Plasma triglyceride level was reduced during exercise in NP and P-10 groups but not in P-19 group. The level of triglycerides in skeletal muscle of each group was reduced during exercise but in P-19 group it returned to the resting level after the exhaustive exercise.