AJP - Gastrointestinal and Liver Physiology, Vol 250, Issue 4 484-G488, Copyright © 1986 by American Physiological Society
Seasonal fluctuations in pepsinogen secretion from frog esophageal peptic glands
T. Shirakawa and B. I. Hirschowitz
The seasonal activity of pepsinogen secretion in the Rana catesbeiana was
studied by use of peptic gland bearing esophageal mucosa mounted in a
perfused double chamber. The amount of the basal pepsinogen secretion
during hibernation (winter) and breeding (spring) periods was approximately
25 and 55% of basal secretion during the active (summer) period. The
circumannual variation of basal secretion was highly correlated (r = 0.88,
n = 37) with the pepsinogen content of the mucosa. The fractional rate of
basal secretion (approximately 2% of content per hour) remained essentially
constant, and pepsinogen as a fraction of total protein remained at between
20 and 25%. The results indicate that the decrease in absolute basal
secretion from frog peptic glands during winter is a consequence of
decreased content and hence synthesis of protein, including pepsinogen, by
the mucosa. In addition, stimulated secretory responses to both bethanechol
and bombesin, as a multiple of basal rate, were reduced during both
hibernation and breeding periods, whereas the response to isoproterenol was
entirely abolished during the hibernation period. By contrast, the
secretory response to isobutylmethylxanthine remained constant
(approximately 200% of basal) through all seasons, suggesting that
mechanisms responsible for enzyme translocation and secretion remained
intact. Reduced basal and secretagogue-stimulated secretion during
hibernation and breeding seasons is thus likely due to a combination of
reduced protein synthesis and decreased number or function of agonist
receptors in peptic cells of the frog.
