Failure of glucagon release in infants of diabetic mothers

Calcium metabolism in pregnancy: a review

Calcium metabolism in pregnancy is a complex process involving calcium, phosphorus, vitamin D, parathyroid hormone (PTH), and calcitonin (CT). Calcium absorption is enhanced in pregnancy, and increased storage in the maternal skeleton probably occurs as well. Adequate amounts are provided by the current Recommended Dietary Allowance of 1,200 mg. daily which can be met readily by natural foods, specifically milk. If supplemental calcium is given, a nonphosphate salt is probably advisable, since some evidence suggests that excessive phosphate intake may be related to leg cramps in pregnancy. Vitamin D is necessary for optimal calcium utilization in pregnancy, although the possibility of fetal toxicity with overdosage has been suggested. From a review of available information with respect to maternal-perinatal calcium interrelationships, I propose the following hypothesis: While total maternal serum calcium declines during pregnancy because of the physiologic hypoalbuminemia, the level of ionic calcium remains constant, in part, at least, because of increasing maternal PTH output. The placenta plays a primary role in fetal calcium metabolism by transporting calcium ions from the mother to the fetus against a concentration gradient. Relatively high fetal ionic calcium levels cause suppression of PTH and stimulation of CT in the fetus, facilitating growth of the fetal skeleton. With sudden loss of the placental source of calcium at birth, the newborn infant becomes functionally hypoparathyroid and/or hypercalcitonemic, and the serum calcium level declines until 3 to 4 days of life when PTH rises and CT falls with a resultant slight rise in calcium.

Spontaneous and amino acid-stimulated glucagon secretion in the immediate postnatal period. Relation to glucose and insulin

The extent and significance of spontaneous glucagon secretion in the immediate postnatal period were investigated in groups of normal infants studied cross-sectionally and longitudinally. Arginine-and alanine-stimulated glucagon secretion was also studied. Plasma glucagon concentrations were correlated with prevailing glucose and insulin concentrations. The characteristic fall in blood glucose, reaching a nadir within hours of birth, was associated with a significant increase in glucagon concentration. Despite persistence of relative glucopenia, glucagon did not change appreciably between 2 and 24 h of life. A further significant elevation in glucagon concentration occurred from day 1 to day 3 of life associated with a return of glucose to euglycemic levels. In contrast to the sluggishness of pancreatic glucagon release, glucagon-like immunoreactivity rose markedly to mean levels of approximately 2,000 pg/ml after introduction of formula feeding. No significant changes in insulin levels were observed in these studies. Arginine infusion via an umbilical vein catheter into six infants within 6 h of birth elicited a brisk, almost threefold increment in glucagon concentration (from 339+/-85 to 940+/-254 pg/ml) in blood obtained from, or close to, the portal circulation. Bolus injection of alanine (1 mmol/kg) into a peripheral vein to six infants resulted in significant increments in glucagon (mean maximal, 128 pg/ml) as well as glucose and insulin. The observations suggest that spontaneous glucagon secretion may be an important factor in neonatal glucose homeostasis. Secretion seems more brisk in response to amino acid stimulation than to a falling glucose concentration.

Fuels, hormones, and liver metabolism at term and during the early postnatal period in the rat

The metabolic response to the first fast experienced by all mammals has been studied in the newborn rat. Levels of fuels and hormones have been compared in the fetal and maternal circulations at term. Then, after cesarean section just before the normal time of birth, sequential changes in the same parameters were quantified during the first 16 h of the neonatal period. No caloric intake was permitted, and the newborns were maintained at 37 degrees C. Activities of three key hepatic enzymes involved in glucose production were estimated. Marked differences in maternal and fetal hormones and fuels were observed. Lower levels of glucose, free fatty acids, and glycerol but higher levels of lactate, alpha-amino nitrogen, alanine, and glutamine were present in the fetus. Pyruvate, glutamate, and ketone bodies were not significantly different. The combination of a strikingly higher fetal immunoreactive insulin and a slightly lower immunoreactive glucagon (pancreatic) resulted in a profound elevation in the insulin-to-glucagon ratio, a finding consistent with an organism in an anabolic state. The rat at birth presents a body composition with respect to fuels available for mobilization and conversion which is dominated by carbohydrate and protein, since little fat is present. However, at birth a transient period of hypoglycemia occurred, associated with a rapid fall in insulin and rise in glucagon, causing reversal of the insulin-to-glucagon relationship toward ratios such as were observed in the mother. After a lag period, hepatic activities of phosphorylase, glucose-6-phosphatase, and phosphoenolpyruvate carboxykinase increased. Concurrent with these enzyme changes, the blood glucose returned to levels at or above those of the fetus. Interestingly, the fall observed in levels of the gluconeogenic precursors, lactate and amino acids, preceded the rise in enzyme activities and restoration of blood glucose. After 4 h, however, hypoglycemia recurred, during a period of decreasing hepatic glycogen content and blood lactate, pyruvate, and glycerol levels but of stable or increasing amino acid concentrations. Hepatic gluconeogenesis in this phase of depleted glycogen stores was insufficient to maintain euglycemia. Substrates derived from fat showed early changes of smaller magnitude. The rise in free fatty acids which occurred was less than twofold the value at birth, though this rise persisted up to 6 h. Whereas glycerol rose transiently, acetoacetate did not change and beta-hydroxybutyrate concentration fell. Both ketone bodies showed a marked rise at 16 h. at a time of diminished free fatty acid levels. Plasma growth hormone, though higher in the fetal than the maternal circulation, showed no consistent change during the period of observation. The changes in levels of the endocrine pancreatic hormones at birth were appropriate in time, magnitude, and direction to be implicated as prime regulators of the metabolic response during the neonatal period in the rat.

Plasma glucagon levels in the term human infant and effect of hypoxia

The mean plasma pancreatic glucagon level at birth in 44 normal infants delivered vaginally was 140 pg/ml. The simultaneous maternal level was 122 pg/ml which was not quite significantly different at the P [unk]0.05 level. 2 hours after birth 30 of these infants had a mean rise in plasma glucagon of 51 pg/ml (P [unk] 0.01), and their mothers had a fall of 38 pg/ml (P [unk] 0.05). The mean plasma pancreatic glucagon level at birth in 12 normal infants delivered by caesarean section was 130 pg/ml which did not differ significantly from the group delivered vaginally. The glucagon level at birth in 20 infants with fetal distress (fetal scalp pH [unk] 7.2 or umbilical artery pH [unk] 7.15) was 244 pg/ml, and this was significantly higher than for normal infants at birth (P [unk] 0.01). Whereas the rise in neonatal glucagon 2 hours after birth might have been caused by a mean fall in blood glucose of 23 mg/100 ml, the infants with fetal distress had normal glucose levels, so that another mechanism must be responsible for their raised glucagon.