Effects of Presence of an Egg and Calcium Deposition in the Shell Gland on Levels of Messenger Ribonucleic Acid of CaBP-D_28K and of Vitamin D₃ Receptor in the Shell Gland of the Laying Hen

Levels of calbindin-D_28K (CaBP D_28K) mRNA and vitamin D₃, 1α, 25(OH)₂D₃, receptor (VDR) mRNA in the intestine and shell gland were measured in the laying hen during the ovulatory cycle by Northern and slot blot analyses. In addition, effects of presence of an egg and calcium deposition in the shell gland on the levels of both mRNAs were studied either by delay in oviposition (retaining the egg in the shell gland beyond the expected time of oviposition) or premature oviposition (emptying the shell gland and arrest of calcium deposition). During the ovulatory cycle mRNA levels of CaBP-D_28K and of VDR remained relatively constant in the intestine. In contrast, both mRNA levels of the shell gland were low when there was an egg in the infundibulum, magnum, and isthmus, but significantly increased when there was an egg in the shell gland during shell formation. The im injection of indomethacin 3 hr before expected ovulation delayed oviposition but increased neither shell thickness nor mRNA levels of CaBP-D_28K and of VDR. On the other hand, premature oviposition reduced mRNA levels of both CaBP-D_28K and VDR in the shell gland. These results suggest that the presence of an egg and calcium deposition in the shell gland may be a stimulatory factor for synthesis and accumulation of CaBP-D_28K mRNA and VDR mRNA in association with calcification.