The role of the gut in albumin catabolism. I. Studies in the jejunoileectomized rabbit

Human gut endogenous proteins as a potential source of angiotensin-I-converting enzyme (ACE-I)-, renin inhibitory and antioxidant peptides

It is well known that endogenous bioactive proteins and peptides play a substantial role in the body's first line of immunological defence, immune-regulation and normal body functioning. Further, the peptides derived from the luminal digestion of proteins are also important for body function. For example, within the peptide database BIOPEP (http://www.uwm.edu.pl/biochemia/index.php/en/biopep) 12 endogenous antimicrobial and 64 angiotensin-I-converting enzyme (ACE-I) inhibitory peptides derived from human milk and plasma proteins are listed. The antimicrobial peptide database (http://aps.unmc.edu/AP/main.php) lists over 111 human host-defence peptides. Several endogenous proteins are secreted in the gut and are subject to the same gastrointestinal digestion processes as food proteins derived from the diet. The human gut endogenous proteins (GEP) include mucins, serum albumin, digestive enzymes, hormones, and proteins from sloughed off epithelial cells and gut microbiota, and numerous other secreted proteins. To date, much work has been carried out regarding the health altering effects of food-derived bioactive peptides but little attention has been paid to the possibility that GEP may also be a source of bioactive peptides. In this review, we discuss the potential of GEP to constitute a gut cryptome from which bioactive peptides such as ACE-I inhibitory, renin inhibitory and antioxidant peptides may be derived.

Gastrointestinal Function

This chapter describes the normal biochemical processes of intestinal secretion, digestion, and absorption. The digestive system is composed of the gastrointestinal (GI) tract, or the alimentary canal, salivary glands, the liver, and the exocrine pancreas. The principal functions of the gastrointestinal tract are to digest and absorb ingested nutrients, and to excrete waste products of digestion. Most nutrients are ingested in a form that is either too complex for absorption or insoluble, and therefore, indigestible or incapable of being digested. Within the GI tract, much of these substances are solubilized and further degraded enzymatically to simple molecules, sufficiently small in size, and in a form that permits absorption across the mucosal epithelium. This chapter explains in detail the mechanisms of salivary secretions, compositions of saliva, and the functions of saliva. The chapter also elaborates properties of bile as well as the synthesis of bile acids. The chapter explores the pathogenesis of the important gastrointestinal diseases of domestic animals, and the biochemical basis for their diagnosis and treatment. The chapter concludes with a discussion on disturbances of gastrointestinal function such as vomition, acute diarrheas, malabsorption, bacterial overgrowth, and ulcerative colitis.

The role of the gut in albumin catabolism. II. Studies in enterectomized rabbits

Using I¹³¹-albumin tracer methods, albumin breakdown rates were estimated in 7 rabbits following extensive gastrointestinal resection, including 5 with nearly complete enterectomy, 1 with total gastroenterectomy, and 1 with gastrectomy only, and in 4 sham operated rabbits. Breakdown rates in the resected animals varied from 48 to 187 per cent of the corresponding controls, with an average of 96 per cent. It is concluded that no more than one-half, and probably much less, of albumin breakdown occurs in the gastrointestinal tract.

Calculation of the albumin catabolic rate in the non-steady state

Methods which are in current use for the calculation of the albumin breakdown rate apply only to the steady state animal. In this paper a simple but more general method based on analyses of I(131)-albumin tracer data is presented. It utilizes easily measured plasma specific activity and excretory data and is equally applicable to the steady and non-steady states.

THE CATABOLISM OF PROTEIN ANTIGENS IN THE NEWBORN AND MATURING RABBIT

The rate of degradation, organ deposition, and blood clearance of SBSA, SRSA, and IRSA has been measured in the newborn, 6-, and 30-day-old rabbits. When the animals were injected with a weight-graded dose of the 3 proteins, differences in their catabolism in the newborns were demonstrable as compared to the 6-, and 30-day-old animals. The capacity to degrade the azo compounds was shown to be incompletely developed at birth. At 6 days of age, however, the rabbits catabolized these proteins much at the same rate as the 30-day-old animals. Addition of the benzenesulfonate moiety determined the rate of degradation organ deposition and excretion rather than the carrier protein when the azo compounds were injected. The biosynthetically labeled S(25) rabbit serum albumin (IRSA) was catabolized at a slower rate than the azoproteins in all age groups. Very little difference in the metabolism and organ deposition of the IRSA was shown to exist between the newborn and maturing animals. A dosage schedule, therefore, designed to test the immunological capacity of developing animals may not be valid when calculated upon body weight. The low level of activity of enzyme systems present at birth which degrade anti-genic material may serve as an explanation as to why this period of development is so vulnerable to the induction of tolerance rather than immunity when compared to the adult.

Gastrointestinal Function

This chapter discusses the functions of gastrointestinal tract. The principal functions of the gastrointestinal tract are assimilation of nutrients and excretion of the waste products of digestion. Within the gastrointestinal tract, these substances are solubilized and degraded enzymatically to simple molecules, sufficiently small in size and in a form that permits absorption across the mucosal epithelium. The distribution of the different types of secretory cells in the salivary glands varies among species. The mandibular and sublingual glands are mixed salivary glands containing both mucous and serous types of cells, and produce a viscous secretion that contains large amounts of mucus. The cytoplasm of the secretory cells contains numerous zymogen granules that vary in size and number depending on the activity of the gland. These granules contain the precursors of the hydrolytic enzymes responsible for digestion of the major dietary components. The cells of the terminal ducts probably secrete the bicarbonate ion responsible for neutralizing hydrochloric acid that enters the duodenum from the stomach.