INTESTINAL-ABSORPTION UNDER THE INFLUENCE OF VASOPRESSIN - STUDIES IN UN-ANESTHETIZED RATS

Different intestinal segments of unanesthetized rats were studied to assess the effect of vasopressin [ADH] on intestinal absorptive processes. Within a physiological range of doses, ADH diminished the net Na absorption mainly by reducing the unidirectional Na influx, whereas the behavior of the efflux was not uniform. The unidirectional volume fluxes showed the same behavior as did the Na fluxes. ADH produced an oral-aboral gradient (jejunum > ileum > colon). ADH did not significantly change the transfer of actively transported sugars; it did influence passively transported substances. During the i.v. application of ADH, a substance was secreted into the perfusion solution which diminished the absorption of volume and electrolytes. Cyclic AMP acted on intestinal absorption in the same way as did ADH. Two mutually independent transport pathways for Na and water were proposed, one influenced by ADH or cAMP. Based on a 2-membrane model, an ADH mechanism was discussed. The permeability of the luminal membrane system was enhanced in the presence of vasopressin.