The effect of truncal vagotomy on the response of the canine lower esophageal sphincter to varying doses of pancreatic polypeptide.

Lower esophageal sphincter pressure (LESP) and plasma pancreatic polypeptide (PP) levels increase after ingestion of a protein meal. This study was done to determine whether an increase in LESP would occur during intravenous administration of exogenous PP at physiologic and pharmacologic doses and whether the integrity of vagal innervation would alter the response. Manometric observations were made, in each of five dogs, of the LESP before and during intravenous infusion of bovine PP at doses ranging from 0.05 to 10 micrograms/kg/hour. Blood samples were obtained simultaneously with LESP measurements for radioimmunoassay determinations of PP. The lowest dose of PP (0.05 microgram/kg/hour) did not produce an increase in either LES pressure or circulating levels of immunoreactive PP. At all other doses, a significant increase occurred in the LESPs and in plasma PP levels. Infusion of PP at 1.0 microgram/kg/hour produced levels of PP similar to those seen postprandially (300 to 400 pg/ml). After vagotomy, studies were repeated at doses ranging from 1.0 to 5.0 micrograms/kg/hour. Infusion of PP at 1.0 microgram/kg/hour produced PP levels similar to those seen in the prevagotomy period; however, there was no change in LES pressures from the fasting postvagotomy values. Administration of PP at 1.5, 2.0, and 5.0 micrograms/kg/hour did produce slight increases in LESP values, which were significantly less than those observed prevagotomy. These higher doses of PP postvagotomy also produced pharmacologic levels of plasma PP. These results demonstrate that an increase in LESP occurs when exogenous PP is administered at doses that produce physiologic levels of PP in dogs with intact vagi; vagotomy results in a marked attenuation of this response.