In natural conditions young rabbit nurses once a day and therefore ingests the whole of his daily caloric intake during a single meal. The present work investigates glucose homeostasis during perinatal period in young rabbit by assessing blood glucose and glycogen stores before and after one single meal. Ponderal data, glycogen and blood metabolites were determined in 1-4 day- and 17-21 day-old rabbits before suckling and at different times (1, 3, 6, 9, 24, 48, 72 h) after controlled suckling. In "young" and "old" rabbits hepatic glycogen stores were exhausted after 48 and 72 h of fast. Within the first hours following milk ingestion, muscle and carcass glycogen did not vary until 9 h in the "young" and until 24 h in the "old" without notable variation of glycemia. From 24 to 72 h young rabbits were in a fasting period with low hepatic glycogen and a decrease of muscle and carcass glycogen, but glycaemia decreased only slightly at 48 and 72 h in "young" and at 72 h in "old" As blood alanine was decreased, it appears that gluconeogenesis was effective and that alanine-glucose and Cori cycles were operating in these conditions.
The stress of anaesthesia and of sampling on the concentrations of blood metabolites and tissue glycogen content was studied in awake, anaesthetized and decapitated young rabbits 1-2 days old ("young") and 17-18 days old ("old"), 24 h after the last controlled suckling. Stress of sampling and anaesthesia was particularly evidenced by high blood lactate observed for the three protocols in young rabbits and to a lesser extent in old animals. Decapitation appeared as the less aggressive procedure for blood lactate assessment in "young" and "old" rabbits. In "young" rabbits, blood glucose was not significantly modified by the mode of blood sampling while in "old" rabbits blood glucose was significantly lower in awake than in anaesthetized animals. Muscle and liver glycogen content data were not significantly different between the three protocols in old and young rabbits. From a comparison of these results with those found in adult animals in various species, it appears that blood puncture in awake "young" and "old" rabbits is a suitable procedure for determining the majority of blood metabolites except lactate in "young" animals.
In the young rabbit, immunoreactive serum insulin (IRI) significantly rises during the first 5 min after suckling and then 20–60 min later, at which time the maximum level is reached. Blood glucose levels remain stable, blood ketone bodies increase 2.7 times and the liver glycogen levels decrease. Replacement of maternal milk by an equal volume of 0.9% NaCl, 2% lactose or 3.5 % glycerol does not induce any change in IRI. IRI significantly rises if solutions of bovine milk proteins or skimmed rabbit’s milk are administered. This effect is quickened and strengthened by the addition of coconut oil or lipids of rabbit’s milk whereas sunflower oil is ineffective. It is suggested that medium-chain fatty acids, major components of rabbit’s milk lipids, play an important role in the regulation of insulin secretion in the young rabbit.
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