Prematurity in the rat. I. Fuels and gluconeogenic enzymes

Changes in liver glycogen, plasma glucose, lactate, alanine and glycerol concentrations during the first 2 h after delivery by cesarean section in term and preterm rats were studied. Liver glycogenolysis initiated in both groups just after delivery, the rates of glycogenolysis being about 50 mumol/h/g wet weight. Glycogen breakdown came along with very low plasma glucose concentrations suggesting that glycogenolysis could be promoted by neonatal hypoglycemia. Plasma alanine concentrations decreased in both groups at similar rates suggesting that alanine utilization was enhanced during the first 2 h of extrauterine life. The plasma glycerol concentration increased in preterm rats but no changes were observed in term rats. The plasma lactate concentration progressively decreased during the first 2 h in term rats. However, preterm rats showed no changes in plasma lactate concentrations during the first hour, then decreased during the second hour at similar rates to those observed in term rats. These results suggest that preterm rats showed a transient resistence to lactate utilization at delivery which was overcome during the first hour of extrauterine life.

Prematurity in the rat. II. Effect of hypothermia

The time-courses of liver glycogen, plasma glucose, lactate, alanine and glycerol concentrations in term and preterm rats undergoing hypothermia (30 degrees C) during the first 2 h after delivery have been studied. Hypothermia prevented liver glycogenolysis and the neonatal decrease of plasma glucose concentration in term and preterm rats during the first 2 h after delivery. Hypothermia decreased plasma glucose, lactate and alanine utilization but increased plasma glycerol concentration. These results suggest that hypothermia blunts the utilization of the main metabolic substrates but increases brown adipose tissue lipolysis for thermogenesis.

Cytogenetic and endocrine studies in a 45,X female subject with spontaneous sexual development

Cytogenetic and endocrine evaluation of a postpubertal 45,X female subject with Turner's stigmas and spontaneous sexual development was performed. A 45,X chromosomal complement was found in the peripheral blood lymphocytes, bone marrow, and fibroblasts derived from skin and ovaries. Menarche, pubarche, and thelarche occurred at age 12; at age 16 she developed menstrual irregularities, with endometrial bleeding occurring every 60 to 90 days. The ovaries were normal in size, and histologic examination revealed a marked paucity of primordial follicles, increased collagenization, and absence of corpora albicans. Anovulatory cycles with moderately elevated levels of luteinizing hormone (LH) and low follicle-stimulating hormone (FSH) levels were observed. LH-releasing hormone pituitary stimulation induced a normal LH release with a very slight FSH increase. Administration of clomiphene citrate successfully induced a normal-length ovulatory cycle. Similarities in the hormonal situation of this patient and that seen in the Stein-Leventhal syndrome are pointed out.

Changes in the liver lactate dehydrogenase isozyme profile after induced glycogenolysis

Treatment with cystamine, phlorrhizin or nicotinic acid, which induced liver glycogenolysis, resulted in the increase of liver lactate dehydrogenase activity. This increase was counteracted by the administration of cycloheximide or actinomycin D and coincided with the increase os isozymes 4 and 3 and the decrease of isozyme 5. The enhancement of liver lactate dehydrogenase activity and the changes observed in the isozyme profile were similar to those observed after starvation. These results suggest that the changes in the lactate dehydrogenase isozyme profile found after cystamine, phlorrhizin or nicotinic acid administration may be related to the glycogenolytic effect of these compounds. These result in an adaptation of the liver lactate dehydrogenase to gluconeogenesis.

Stimulation of ketogénesis after glycogen depletion by nicotinic acid in perfused rat liver

Treatment with nicotinic acid produced an enhancement of ketone bodies production from endogenous, substrates, either oleate or octanotate. The enhancement was accounted for by an increase of acetoacetate synthesis. These results suggest that the increase of acetoacetate production may be due to the enhancement of extramitochondrial ketogenesis as a consequence of the inhibition of lipogenesis.

Pyruvate kinase activity and gluconeogenesis in rat liver after glycogen depletion with nicotinic acid

Nicotinic acid administration, which depletes liver glycogen, leads to an increase of both pyruvate kinase L and phosphoenolypyruvate carboxykinase in liver by a factor of nearly two. The former is not prevented by either cycloheximide or actinomycin D. L-Cysteine, an allosteric inhibitor of pyruvate kinase L, favors gluconeogenesis from lactate in both nicotinic acid treated and starved animals.

Stimulation of phosphoenolpyruvate carboxykinase (guanosine triphosphate) activity by low concentrations of circulating glucose in perfused rat liver

1. After nicotinic acid treatment, rat liver glycogen is depleted and phosphoenolpyruvate carboxykinase activity increased, to about twice the initial value. 2. The increase in phosphoenolpyruvate carboxykinase activity promoted by nicotinic acid is prevented by cycloheximide or actinomycin D, suggesting that this effect is produced by synthesis of the enzyme de novo. 3. Despite the enhancement of phosphoenolpyruvate carboxykinase activity and glycogen depletion, which occurs 5h after the injection of nicotinic acid, the gluconeogenic capacity of liver is low and considerably less than the values found in rats starved for 48h. 4. When the livers of well-fed rats are perfused in the presence of low concentrations of glucose, the activity of phosphoenolpyruvate carboxykinase significantly increases compared with the control. 5. This increase is not related to the glycogen content, but seems to be also the result of synthesis of the enzyme de novo, since this effect is counteracted by previous treatment with cycloheximide or actinomycin D. 6. Phosphoenolpyruvate carboxykinase activity is not increased in the presence of low concentrations of circulating glucose when 40 mM-imidazole (an activator of phosphodiesterase) is added to the perfusion medium. 7. Addition of dibutyryl cyclic AMP to the perfusion medium results in an increase in phosphoenolpyruvate carboxykinase activity, in spite of the presence of normal concentrations of circulating glucose. On the other hand, the concentration of cyclic AMP in the liver increases when that of glucose in the medium is low. 8. These results suggest that, in the absence of hormonal factors, the regulation of phosphoenolpyruvate carboxykinase can be accomplished by glucose itself, inadequate concentrations of it resulting in the induction of the enzyme. The mediator in this regulation, as in hormonal regulation, seems to be cyclic AMP.