CHARACTERIZATION OF CONTRACTILE AND NONCONTRACTILE PROTEIN-SYNTHESIS IN THE STOMACH, SMALL AND LARGE-INTESTINE AND CECUM OF THE RAT, AND RESPONSE TO ACUTE ETHANOL DOSAGE

An investigation was made into the relative composition and synthesis rates of smooth muscle contractile proteins in vivo in different regio ns of the rat gastrointestinal tract. There was considerable homogenei ty in the composition of sarcoplasmic proteins in the small bowel (i.e . 54-58 mg/g but considerable variability in the large bowel, i.e, hig hest in the caecum (97 mg/g) and lowest in the colon (21 mg/g). The my ofibrillary protein concentration was constant throughout the gastroin testinal tract, i.e. 20-34 mg/g. Stromal fractions varied from 6 to 39 mg/g and was highest in the cardiac region of the stomach and lowest in the duodenum. Fractional rates of protein synthesis were measured w ith a flooding dose of L-[4-H-3]phenylalanine. In control rats synthes is rates in sarcoplasmic protein fractions were relatively much higher (43-107%/day) than myofibrillar (27-52%/day) or stromal (6-26%day) pr oteins. Fractional rates of stromal protein synthesis showed the great est variability while myofibrillar synthesis rates the least, througho ut the alimentary tract. Jejunal seromuscular layer myofibrillar prote ins had the highest synthesis rates (49%/day). In response to acute et hanol injection, protein synthesis in all jejunal fractions fell by 20 -30%. Contractile and non-contractile proteins from the cardiac region of the stomach, duodenal seromuscular layer and large bowel seromuscu lar layer were insensitive to ethanol administration. Protein synthesi s of sarcoplasmic proteins from the antrum, ileum seromuscular layer a nd myofibrillar proteins from the ileum seromuscular layer and caecum were also significantly depressed as a result of ethanol treatment.