Effects of aging and weaning on mRNA expression of leptin and CCK receptors in the calf rumen and abomasum

In order to know the effects of weaning and volatile fatty acid feeding on gastric leptin expression, we investigated the expression of leptin and CCK receptor mRNA in the bovine rumen, abomasum and duodenum using RT-PCR in 3-week-old pre-weaning, 13-week-old post-weaning and adult animals. Leptin mRNA was expressed in the rumen and abomasum of 3-week-old pre-weaning animals, but it was abolished in 13-week-old and adult animals. In the duodenum, leptin expression was observed in the 3-, 13-week-old and adult animals. In the rumen, CCK_A receptor mRNA was expressed in 3-week-old animals, but not in 13-week-old and adult animals. In the abomasum, CCK_B receptor expression gradually decreased from 3-week-old to adult animals. Expression of CCK_B receptor and of CCK_A receptor was slight in the rumen and abomasum, respectively. In the next study, we examined the effect of weaning of 6 weeks or non-weaning (fed on milk replacer alone (milk) or milk replacer with volatile fatty acids (milk + VFA) until 13 weeks old) on leptin mRNA expression in the rumen and abomasum. In 13-week-old calf rumen and abomasum, leptin mRNA expression was detected in non-weaning milk-fed animals at 13 weeks old, although it was not observed in weaning and non-weaned milk + VFA-fed animals. The change in CCK_A receptor expression in the rumen was similar to those of leptin mRNA expression. CCK_B receptor transcription in the abomasum of milk-fed animals was higher than that of the weaning and milk + VFA-fed animals. These results indicate that leptin expression is coincident with CCK receptor expression in calf stomachs, and that leptin and CCK receptor mRNA expression are affected by the change in the physiological status brought about by weaning and VFA feeding.