THE EFFECT OF SERUM ON THE SECRETION OF RADIOLABELED MUCOUS MACROMOLECULES INTO THE LUMEN OF THE CAT TRACHEA

Abstract

The effect of placing serum within segment of trachea on secretion into its lumen in the cat was studied. A segment of cervical trachea was isolated from the rest of the airway in situ. Secretions were radiolabeled biosynthetically by the administration of 2 radiolabeled precursors: [35S]NaSO4 and [3H]glucose. Autologous serum placed in the segment at a dilution of 1 in 8 increased the output of radiolabeled macromolecules: [35S] by 80% and [3H] by 159% (P < 0.001). At a dilution of 1 in 24, serum still increased the output of both isotopes. At dilutions of 1 in 48 and 1 in 80 the increases were significant for [35S] but not for [3H]. Heating the serum to 90.degree. C diminished its effects. Fractionating the serum by dialysis and gel filtration showed that the components of MW < .apprx. 13,000 daltons had no effect on secretion; 3 higher MW fractions all increased secretion. Two alien proteins (horseradish peroxidase and bovine serum albumin) stimulated secretion but a large MW carbohydrate (carboxymethyl cellulose) did not. Atropine and propranolol, at doses that greatly reduced the effect of parasympathetic and sympathetic nerve activity, did not diminish the effects of serum, which appeared to be independent of nerve activity. Gel filtration of the secretions elicited by serum showed that the predominant component was excluded even by Sepharose CL-2B and had a high MW. There are several components of serum that promote the secretion of mucus glycoproteins into the cat trachea. The relevance of these findings to diseases of human airways is considered.