1. Butyrate absorption in the proximal colon of the anaesthetized rabbit was evaluated by measuring the variations in the concentration of butyrate in colonie loops and in arterial and venous plasmas; metabolic conversions were studied using (3,4-14C) butyrate.
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2. Interrelations between butyrate absorption and metabolism and the excretory cycle of the rabbit were examined, as well as the effects of exogenous aldosterone, the hormone generally implicated in the diurnal rhythm of the fecal excretion.
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3. The colonie tissue metabolized butyrate via 2 main pathways. They were of differing intensity according to the 2 phases of the excretory cycle.
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4. When the plasma level of aldosterone was high (during hard faeces production), the butyrate was mainly oxidized to CO2, yielding energy for metabolic processes.
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5. When the plasma level of aldosterone was lower (during soft production), butyrate was also oxidized to CO2 but it was a better source of free amino acids.
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6. Exogenous aldosterone (30 μg/kg) enhanced absorption and oxidative metabolism of the butyrate, which occurred normally when hard faeces were elaborated.