Reversible and irreversible glucose disposal in dogs: influence of fasting and cold exposure.

Rates of total glucose entry rate, irreversible loss, and recycling were measured in unanesthetized dogs with indwelling arterial and venous catheters. Four experimental conditions were selected: 16 or 26 hr of fasting and neutral (+25 degrees C) or cold (-21 degrees C) ambient temperatures. A mixture of U 14C-glucose and 2-3H-glucose was used as a tracer, according to the primed infusion technique. No matter what the ambient temperature was, increase of fasting time from 16 to 26 hr induced a slight, but nonsignificant, decrease in both the total glucose entry rate and the irreversible loss. At neutral ambient temperature, the amount of glucose promptly recycled was less after 16 hr than after 26 hr of fasting, while an opposite pattern was observed during cold exposure. Thus, that part of hepatic glucose entry promptly recycled was significantly increased from 22% (16 hr of fasting) to 31% (26 hr of fasting) at neutral ambient temperature. It remained almost unchanged (20% and 18%) in cold. It was, therefore, suggested that this increase might be considered as an compensatory mechanism, exerting a sparing effect on glucose utilization. This mechanism does not occur in cold ambient temperature, thus, worsening a possible shortage in glucose supply.

Dietary protein and the control of fatty acid synthesis in rat adipose tissue.

Fatty acid synthesis in adipose tissue normally proceeds at a high rate when fasted animals are refed a diet containing carbohydrate, protein, and low levels of fat. This study investigated the effect of omitting protein from the refeeding diet. Rats were fasted for 48 hr and refed either a protein-free diet or a balanced diet, and the rate of fatty acid synthesis from glucose, pyruvate, lactate, and aspartate was measured. Refeeding the animals a diet devoid of protein resulted in a low rate of fatty acid synthesis from each of these substrates as well as a reduction in carbon flow over the citrate cleavage pathway. The activities of glucose-6-phosphate dehydrogenase, 6-phosphogluconate dehydrogenase, NADP-malate dehydrogenase, and ATP-citrate lyase were also reduced in epididymal fat pads from these rats. On the other hand, adipose tissue phosphoenolpyruvate carboxykinase activity was five times as great as that in tissue from animals refed a balanced diet. This difference could be eliminated if actinomycin D was injected coincident with refeeding. Refeeding rats diets high in carbohydrate is not, therefore, capable of inducing high rates of fatty acid synthesis in adipose tissue in the absence of dietary proteins. Thus, liver and adipose tissue respond differently to dietary protein.

Effect of epinephrine upon irreversible disposal and recycling of glucose in dogs.

Irreversible utilization and recycling of glucose during epinephrine-induced hyperglycemia were studied in adrenal-demedullated dogs exposed to neutral or cold ambient temperature. Whatever the ambient temperature, most of the extra glucose mobilized by epinephrine is recycled rather than irreversibly utilized by the peripheral tissue.

Combined effects of cold and somatostatin on glucose kinetics in dogs.

The role of the endocrine pancreas in glucose production (Ra), utilization (Rd), and metabolic clearance (R'd) was investigated during acute exposure to cold in normal normothermic dogs. Two ambient temperatures (TaN = +25 degrees C and TaC = -21 degrees C) were selected. At TaC, metabolic rate and glucose turnover of the shivering dogs were 4.3 and 2.4 times, respectively, higher than in dogs resting at TaN. As compared with the pre-experimental period, somatostatin infusion at TaN induced a 25% (arterial) and 34% (portal) glucagon deficiency, while insulin concentration dropped by 59% (arterial) and 74% (portal). Similar values were obtained at TaC for glucagon (39% arterial and 47% portal) and for insulin (52% arterial and 56% portal). At TaN, these simultaneous hormonal alterations provoked a slight reduction in plasma glucose concentration which levelled down to 4.4 mM. This reduction was due to a decrease in Ra, followed by a parallel decrease in Rd whereas R'd remained unchanged. At TaC, plasma glucose concentration dropped to the same level but quickly rose again during somatostatin infusion. This rise was due to a larger reduction in Rd than in Ra, accompanied by an abrupt fall in R'd. This reduction in R'd appears to be an important mechanism able to restore euglycemia during global pancreatic hormone deficiency in cold exposed dogs.

Independence of circulating insulin levels of the increased glucose turnover in shivering dogs.

In dogs, selective insulin deficiency induced by simultaneous somatostatin and glucagon infusion does not alter the high rate of glucose utilization provoked by acute cold exposure. However, both in resting and in shivering dogs, lowering of plasma insulin decreases plasma glucose metabolic clearance significantly.

[Benign pulsatile cranial bruit in children. Apropos of 6 cases]. / Souffle pulsatile crânien bénin chez l'enfant. A propos de 6 cas.

The authors report a series of 6 patients aged 8-25 months, without any intracranial vascular pathology, presenting with an objective intracranial bruit associated with visible veins in the naso-orbital region. These bruits, frequent in children between 4 months and 5 years, become rare when patients grow older and disappear in adulthood. Naso-orbital veins are frequently normally detected until the age of 3 years. An intracranial bruit and visible facial veins may be clinical signs indicative of an underlying intracranial vascular malformation (IVM). Enhanced CT scanning should be performed when these two symptoms are associated. If the scan is abnormal, a selective angiography should be performed.

Tolerance to cold and glucose homeostasis in adrenal demedullated dogs.

The rise in O2 consumption and in glucose turnover, induced by acute cold exposure is not suppressed by adrenal demedullation in dogs. However, both at neutral and cold ambient temperature, the mean plasma glucose concentrations are higher in normal (N) than in adrenal-demedullated dogs (ADMX). In the cold, the fall in rectal temperature is larger in ADMX than in N dogs.