Altered Na + /K + -ATPase expression plays a role in rumen epithelium adaptation in sheep fed hay ad libitum or a mixed hay/concentrate diet

In this study we investigated rumen papillae morphology and the localization and expression of the Na + /K + -ATPase in eight sheep fed hay ad libitum (h) or hay ad libitum plus additional concentrate (h/c). Four sheep were provided with the ad libitum h-diet for the complete three-week experimental period. The second group of four sheep received the h-diet for only one week and was fed the mixed hay/concentrate (h/c) diet for another two weeks. The amount of concentrate supplement was stepwise increased from 150 to 1000 g/day and given in two meals. Following slaughter rumen papillae from the atrium ruminis (AR), the rumen ventralis (RV) and the ventral blind sac (BSV) were fixed and examined for morphological changes and Na + /K + -ATPase localization by morphometric methods and immunohistochemistry. Ruminal epithelial cells (REC) originating from the strata basale to granu- losum were also isolated. Cellular Na + /K + -ATPase expression (mRNA and protein) and differentiation state were determined by RT-PCR, Western blot, and flow cytometry. Compared with data from h-fed sheep, morphometric analysis revealed an increased length and width of rumen papillae in h/c-fed sheep, resulting in a marked 41% and 62% increase in rumen papillae surface in AR and RV, respectively. The rumen mucosa of h/c-fed sheep was char - acterized by a predominant stratum corneum (42 ± 0.7 µm vs. 28 ± 0.5 µm), but the thickness of the metabolically active cell layers remained unchanged. REC suspensions from sheep fed the h/c diet generally contained more cells (7.30 ± 0.83 vs. 3.49 ± 0.52 × 10 7 /ml; P < 0.001) and an increased proportion of REC positive for basal cytokeratin and for the differentiation marker cytokeratin 10 (P < 0.05). Cellular (cell membrane) and epithelial (stratum basale