PHENOTYPIC PLASTICITY, CELLULAR-DYNAMICS, AND EPITHELIAL TURNOVER OF THE INTESTINE OF JAPANESE-QUAIL (COTURNIX-COTURNIX-JAPONICA)

This paper discusses phenotypic plasticity of the avian intestine and presents data about the dynamics and mechanisms accounting for size va riation of the avian intestine. Gut lengths of 56 bird species were co mpared for interspecific and intraspecific coefficients of variation. Intraspecific gut length variation relates to seasonal changes in qual ity and composition of food in some species. Such phenotypic plasticit y is thought to adjust gut structure and function to seasonal differen ces in nutrition and to maintain optimized gut function under differin g feeding regimes. Morphometry at five segments along the intestine pr ovided basic measurements of the quail intestine. Whereas the duodenum can be separated from the rest of the intestine in almost all paramet ers, the small intestine, rectum, and caeca are rather uniform. Change s of circumference and length of the gut segments account for the majo r portion of size changes of the resorptive surface. BrdU/H-3-TdR doub le labelling experiments were performed to study the dynamics of cellu lar turnover of the intestine. The experiments revealed a constant S-p hase length of 6.5 hours along the intestine. The turnover time of the mucosa epithelium ranges between 9 and 17 days, depending on the circ umference of the gut segment. Such a turnover time permits reconstruct ion of the intestine in short periods and its adjustment to seasonal d ifferences in composition and quality of food. The study revealed sign ificant differences between cell proliferation activity at day and at night. Animals labelled at night had almost twice the labelling index of those labelled during the day. These results were consistent in oth er tissues (liver, muscle, connective tissue, glandular stomach). Beca use high night-time proliferation activity coincides with low antigen levels and high free radical scavenger concentration (e.g. melatonin), it is suggested that the circadian patterns in labelling index repres ent a fine tuning of DNA-replication activity to 'safer' periods of da y.