THE EFFECT OF LACTATION ON OUABAIN-SENSITIVE RESPIRATION OF THE DUODENAL MUCOSA OF COWS

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Abstract
Total O2 consumption, ouabain-sensitive and ouabain-insensitive respiration rates were measured for the duodenal mucosa of non-lactating and lactating cows. Support of Na+, K+-ATPase activity, as measured by ouabain-sensitive respiration, accounted for 55% of total mucosal respiration of the cows at peak lactation. In mid-lactation and during the non-lactating period the proportion of O2 uptake inhibited by ouabain declined to 34–35%; the amount of ouabain-sensitive O2 uptake declined from 3.6–4.0 to 2.5–2.8 μL O2/mg tissue per hour. The magnitude of ouabain-insensitive respiration was highest during late lactation and the non-lactating period. It was concluded that Na+, K+-ATPase accounted for a major proportion of the duodenal mucosa maintenance energy expenditure. The magnitude of this expenditure is not constant throughout lactation. Key words: Na+, K+-ATPase, duodenal mucosa, O2 consumption, cows