Redistribution of amylase activity accompanying its secretion by the pancreas.

Abstract

Amylase activity in several tissue and body fluid compartments in the rat changed markedly when the secretion of digestive enzyme was augmented over a 3-hr period with a cholinergic agonist. As a result of stimulation, the pancreas was depleted of about one-third of its amylase activity and accounted for only 75% of the amount recovered from the animal, compared to 92% in the fasted state. Despite the continuous augmented secretion of the enzyme into the small intestine, no increase in amylase activity was detected there at the end of 3 hr. On the other hand, amylase activity in plasma and extracellular fluid increased by about an order of magnitude and accounted for 13% of the total pool, compared to approximately 1% in the fasted state. Amylase activity in several solid tissues also increased, including a 50-to 100-fold increase in parotid gland and an almost 10-fold increase in submandibular gland and kidney. The potential sources of the increased amylase activity in blood, the endocrine secretion of the enzyme by the pancreas, and its absorption from the intestine are considered. Changes in the amylase content of various tissues appear to reflect increased uptake due to increased plasma levels.In the classical description of digestion, the pancreas is an exocrine gland that secretes numerous digestive enzymes through its duct system into the intestine, where they digest food and are eventually digested themselves except for a small remnant that finds its way into feces. In recent years this view has been questioned in two ways. The first is that digestive enzymes can be reabsorbed intact although not necessarily in unaltered chemical form (1)(2)(3)(4)(5)(6) and that, at least after several hours of highly augmented secretion, enzyme appears to be conserved in this fashion (2). The second is that there is a substantial flux of at least some digestive enzymes from pancreas to blood-an endocrine secretion that can be greatly enhanced by natural secretagogues and that has been shown to be capable of rates as large as 10-20% of maximal duct-directed secretion (7-13).As an outgrowth of these observations, we have examined the distribution of the activity of one digestive enzyme, amylase, in a number of tissues in the unstimulated fasted rat and compared it to the distribution seen after pancreatic secretion of digestive enzymes was stimulated by a cholinergic drug for a 3-hr period. The treatment regimen used augments the secretion of digestive enzymes into the intestine by an order of magnitude or more above unstimulated rates for at least 4 hr (14).In the traditional view of the digestive process, under these circumstances the gland would become depleted of its amylase content, and amylase activity in the small bowel would simultaneously be increased. Conversely, removal of the secretory drive would lead to an increase in amylase activity in the pancreas and a decrease in the small intestine, because the rate of secretion would now be less than the rate of amylase synthesis in the gland and amylase degr...

Trypsin cycling in poultry is associated with metabolic regulation

“…For example, the rate of synthesis of digestive enzymes is compared with the rate at which they are excreted into the intestine (Rothman et al, 2002). Based on data obtained in anesthetized rats after overnight fasting, the amount of protein secreted by the pancreas is defined as The amount of protein secreted by the pancreas is 70-140 mg per 1 g of tissue daily (Miyasaka and Rothman, 1982;Ho and Rothman, 1983). In the absence of exogenous stimuli, the basal secretion rate is ~0.25-1.0 mg per 1 g of tissue per hour (Rothman, 1975), i.e., the pancreas can produce from 6 to 24 mg of protein per day per 1 g of tissue, which is 4%-35% of the protein secreted into the intestine (Rothman et al, 2002).…”