The effects of hypoglycaemia on cerebral blood flow and metabolism in the new‐born calf.

Abstract

SUMMARY1. The effects of insulin hypoglycaemia on cerebral blood flow and metabolism have been examined in unanaesthetized, unrestrained calves between 1 and 26 days after birth.2. Cerebral blood flow was measured with an inert gas technique using molecular hydrogen, and cerebral metabolism was quantified by determination of arteriocerebral venous (A -V) concentration differences for oxygen, glucose, lactate, pyruvate, acetoacetate, f-D-hydroxybutyrate and ammonia.3. During normoglycaemia the mean (A -V) difference for glucose was close to one sixth that of oxygen, on a molar basis. A small net loss of pyruvate from the brain was found, but there was no significant (A -V) difference for lactate. Arterial concentrations of acetoacetate and fl-D-hydroxybutyrate were low, and no utilization of ketone bodies by the brain was demonstrated.4. Moderate hypoglycaemia (arterial plasma glucose concentration 1-2 m-mole/l.) had no measurable effect on either cerebral blood flow or metabolism.5. During profound hypoglyeaemia (arterial plasma glucose concentration < I 0 m-mole/l.) cerebral glucose uptake was sufficient to account for only 56 % of the cerebral oxygen consumption. Cerebral oxygen consumption fell in comatose animals, but increased during hypoglyeaemic convulsions, as did cerebral blood flow.6. In day-old calves hypoglycaemia was associated with a rise in blood lactate concentration and uptake of lactate by the brain. 7. A net loss of ammonia by the brain was observed during hypoglycaemia in calves at all ages examined. The loss was greater in convulsing than in comatose animals.

Substrate Utilization and Brain Development

“…CMR02 was rather higher than would be required for the complete oxidation of the glucose plus lac tate taken up, but ketone bodies remained at low concentrations and still made no contribution. Since blood flow and CMR02 were unchanged from nor moglycemic conditions, it would appear that lactate had become an acceptable oxidizable substrate for the brain, and its contribution in glucose equiva lents was half that of glucose itself (Gardiner, 1980a).…”

“…Cerebral oxidative metabolism in the newborn calf has been studied in association with the effects of hypoglycemia (Gardiner, 1980a) and hypoxia (Gardiner, 1980b).…”

“…When either newborn calves or puppies were made profoundly hypogly caemic with insulin (and although there was a sig nificant uptake of lactate by the brain), the animals were comatose; when arterial plasma concentra tions of glucose fell below 0.5 mM , the animals had spontaneous seizures (Gardiner, 1980a;Vannucci et al, 1981).…”

Regional Differences in Vascular Autoregulation in the Rat Brain in Severe Insulin-Induced Hypoglycemia

“…Previous measurements in patients (Kety et aI., 1948;Eisenberg and Seltzer, 1962;Della Porta et aI., 1964) and in some animal studies (Pappenheimer and Setchell, 1973;Gardiner, 1980;Ghajar et aI., 1981) et aI., 1982;Siesjo et aI., 1982).…”

Catheterization of the sagittal sinus in the neonatal pig

“…Previous reports of the techniques employed have been extremely brief, and in general have been developed to allow sampling from anaesthetized animals (Hernandez, Vanucci Salcedo & Brennan, 1980;Pappenheimer & Setchell, 1973), or for use in the large species (Gardiner, 1980). It has been shown that both anaesthesia and the stress caused by restraint for sample collection can result in changes in cerebral blood flow and metabolism (Shapiro, Greenberg, Reivich, Ashmead & Sokoloff 1978' Wootton Flecknell & John, 1982.…”