Abstract

The current study examined the localization and the effect of circulating peptides on the expression of aminopeptidase N (APN; EC 3.4.11.2) in caprine mammary gland. Four lactating goats in mid to late lactation were used in cross-over design and were subjected to two dietary treatments. Abomasal infusion technique of casein hydrolysate was used to increase the concentration of peptide-bound amino acid (PBAA) in the circulation. Samples of mammary gland tissue from each goat were taken by biopsy procedure at the end of each treatment period in order to measure gene and protein expression of APN in the tissue. There were no measurable effects on feed intake and milk production for any of the treatments. Abomasal casein-hydrolysate infusion caused a marked change in the profile of arterial blood of free AA and PBAA smaller than 1500 Da. Abundance of APN mRNA and protein increased (P< 0.05) by 51% and 58%, respectively in casein-hydrolysate infused goats compared with the control treatment.