Factors Which Alter Drinking Responses of Dogs to Intravenous Injections of Hypertonic Sodium Chloride Solutions

Abstract

Using a long indwelling venous (polyethylene) catheter, hypertonic solutions were injected and the effect on the drinking response observed when: (1) the concentration (concn.) of the injected solution was altered, (2) water was injected intravenously (i. v.) before the salt injection, (3) procaine HC1 or Pitressin was injected i.v. prior to salt injection, (4) there was surgical interference with the autonomic nervous system. When the volume of the injected salt solution is combined with the volume ingested by the animal to give a total input, this value is directly proportional to the number of milliequivalents of NaCl administered regardless of the concn. of the injected solution. However, there is a threshold for concn. which varies with the individual dog and is from 1.25% to 2.25%. When the NaCl solution is 5% or less, there is a significant increase in the latent period of the response. It is possible to completely inhibit the drinking response by preceding the salt injection with the intravenous injection of water in volumes slightly in excess of the volumes normally ingested after such a dose of hypertonic salt solution. When the salt injection is preceded by an intravenous injection of 2 cc of 2% procaine HC1, the latent period is significantly prolonged in those dogs which are immediate drinkers. Pitressin, i.v., does not affect the latent period. Complete sympathectomy or bilateral section of the vagosympathetic trunk does not alter the magnitude or latency of the drinking response.