Biological Rhythms of Pancreatic Secretion in Young Pigs with empahasis to the time around weaning

Abstract: When the time structure (chronome) of pancreatic secretion was studied after weaning in 5-week-old pigs, the zero-amplitude (no-rhythm) assumption was rejected for the about-weekly (circaseptan, CS) and about-half-weekly (circasemiseptan, CSS) chronome components. When the data were assessed individually on a day-to-day basis, a 24-hour component was suggested (P<.10) for the variables measured in the pancreatic secretion. The circadian pattern showed a gradually increasing range of oscillation. Group results by population-mean cosinor analysis failed to demonstrate a statistically significant circadian and ultradian variation, mostly because of large inter-individual differences.No statistically significant circadian variation could be demonstrated either for plasma concentrations of insulin, glucose, glucagon or Immunoreactive Cationic Trypsin (IRCT). In 7-week-old pigs fed three times a day and kept in dim, white light, the pancreatic secretion exhibited a pattern characterised by distinct meal-related secretions, and by non-food-stimulated secretions. In animals that were later transferred to a regimen of 12 hours of light alternating with 12 hours of darkness (LD12:12), there was no distinct response of the pancreatic secretion to the meal given during the dark span. Apart from the anticipated circadian rhythm demonstrable by single cosinor analysis on a group basis, prominent 8-hour and an about 3.43-hour components were statistically significant. These data indicate that the circadian variation of exocrine and endocrine pancreatic secretion, glucose and IRCT immediately after weaning, at five weeks of age is still developing and is not yet synchronized among the different piglets fed ad libitum. Pancreatic secretions become circadian periodic by the 7th (but not by the 5th) week of age when their response to a standard meal also becomes circadian-stage dependent.