Kimberly W. Black

Effect of chain length on absorption of biologically active peptides from the gastrointestinal tract.

Objectives: Protein digestion generates many peptides in the gut lumen. Some of these peptides possess biological effects when tested using in vitro systems. It is clear that dipeptides and tripeptides can be absorbed intact from the gastrointestinal tract. However, the fate of larger peptides and small proteins remains unclear. Equally unclear are the biologic potencies of absorbed peptides and the quantity of peptide that must be administered into the gut to produce a biologic effect. Thus, the purpose of this study was to determine the effect of amino acid chain length on the ability of enterally administered peptides to produce biologic effects. Methods: Small bowel feeding tubes, jugular catheters, and arterial lines were placed into adult male Sprague-Dawley rats. Rats were administered intravenous (50 μg) and enteral (125 and 500 μg) thyrotropin-releasing hormone (TRH, a tripeptide), intravenous (100 μg) and enteral (100 and 500 μg) luteinizing hormone-releasing hormone (LHRH, a decapeptide), and intravenous (0.5 mg) and enteral (0.5 and 25 mg) insulin (a 51-amino acid polypeptide). The quantity of peptide administered represented less than 0.5% of a rat’s normal daily protein intake. The biologic effect of TRH, LHRH, and insulin were assessed using thyroid-stimulating hormone (TSH) response, follicle-stimulating hormone (FSH) response, and glucose. We also measured serum levels of insulin in the rats following enteral insulin administration. Results: The results indicate that enteral TRH (125 and 500 μg) produced the same TSH response as intravenous TRH. The response to 500 μg enteral LHRH was 50% of the response to intravenous LHRH and the response to 25 mg enteral insulin was 30% of the response to 0.5 mg intravenous insulin. Serum insulin levels increased significantly following both 0.5 and 25 mg enteral insulin. Conclusions: These results support the concept that small (di- and tripeptides) and large (10–51 amino acids) peptides generated in the diet can be absorbed intact through the intestines and produce biologic effects at the tissue level. The potency of the enterally administered peptides decreases as the chain length increases. We postulate that absorbed dietary peptides play a role in the modulation of organ function and disease progression.

Immediate postoperative enteral feeding decreases weight loss and improves wound healing after abdominal surgery in rats.

ObjectiveTo determine the effect of immediate vs. delayed (72 hrs) postoperative enteral feeding on weight loss and wound healing after experimental abdominal surgery. DesignProspective, randomized, controlled study. SettingLaboratory of a large university-affiliated medical school. SubjectsSeventeen male Sprague-Dawley rats, each weighing 350 to 400 g. InterventionsFour-centimeter longitudinal midabdominal incisions were made and gastroduodenal feeding tubes were inserted in the animals. The abdominal wound was closed in two layers. Immediately after closure, animals were randomized to receive immediate enteral feeding (early-fed group) with a peptide-based enteral formula or 5% dextrose in water at 4 mL/hr. Seventy-two hours after surgery, the 5% dextrose in water group was switched to the peptide formula (late-fed group). Animals were weighed daily. On postoperative day 5, the strength of the abdominal wound was deter-mined using a balloon-bursting pressure technique. Blood was also obtained for measurement of insulin growth factor 1 concentrations. Mucosal protein content of the small bowel was measured. ResultsTotal body weight loss was less in the early-fed group (26 ± 4 vs. 46 ± 5 g/5 days) and wound strength was increased in the early-fed group compared with the late-fed group (6 ± 0.4 vs. 2.9 ± 0.8 kPa; 45 ± 3 vs. 22 ± 6 mm Hg). There were no differences between groups for circulating insulin growth factor 1 concentrations or small intestinal mucosal protein concentrations. ConclusionsImmediate postoperative enteral feeding results in decreased weight loss and improved wound healing after abdominal surgery in rats. (Crit Care Med 1992; 20:115)

Enteral feeding minimizes liver injury during hemorrhagic shock.

Liver injury is common in patients following hemorrhage and sepsis. There are multiple etiologies for this liver injury which involve both decreased nutrient blood flow and direct cellular injury. Enteral nutrients vasodilate gut blood vessels and increase blood flow to the intestines and liver. Since enteral nutrients vasodilate gut blood vessels, we wondered whether luminal nutrition would prevent hepatic injury during shock states. We randomized Sprague-Dawley rats to saline or enteral nutrition via duodenal feeding tubes. Animals were then subjected to 60 min of hemorrhagic hypotension or intraperitoneal injection of lipopolysaccharide (LPS). Liver injury was assessed by measuring levels of aspartate aminotransferase (AST) and alanine aminotransferase (ALT) before and after hemorrhage or LPS. Enteral nutrients significantly decreased liver injury following hemorrhage. AST increased from 246 +/- 17 to 1605 +/- 593 U/L in saline animals and 283 +/- 39 to 551 +/- 94 U/L in enterally fed animals. ALT increased from 60 +/- 4 to 726 +/- 355 U/L in saline animals and 61 +/- 6 to 161 +/- 38 U/L in enterally fed animals. Enteral nutrients did not significantly alter the increase in AST/ALT following LPS. These results indicate that enteral nutrients can decrease liver injury following hemorrhagic hypotension.

Human sepsis increases lymphocyte intracellular calcium

ObjectiveTo determine whether free intracellular calcium is increased during human bacterial sepsis. DesignProspective controlled study of lymphocyte free intracellular calcium concentrations from patients with sepsis compared with critically ill nonseptic patients and healthy subjects. SettingA large multidisciplinary ICU of a university hospital. PatientsEleven patients with sepsis, six patients after cardiac surgery, six patients with head injury, and 22 healthy control subjects. InterventionsBlood samples obtained for lymphocyte isolation and measurement of free intracellular calcium concentrations. MeasurementsLymphocytes were isolated using Ficoll-paque centrifugation and free intracellular calcium concentrations were measured using the fluorescent dye fura-2. We also evaluated the effect of septic serum, endotoxin, tumor necrosis factor (TNF), and lysophosphati-dylcholine on lymphocyte free intracellular calcium concentrations. Main ResultsMean (± sem) lymphocyte free intracellular calcium concentrations were significantly (p < .05) higher in the septic patients (176 ± 12 nM) compared with cardiac surgical (112 ± 9 nM), head-injured (110 ± 11 nM), or healthy control patients (112 ± 5 nM). Endotoxin (0.1 and 1.0 mg/mL) and TNF (10 and 100 ng/mL) did not alter lymphocyte free intracellular calcium values. Lysophosphatidylcholine (100 and 200 uM) significantly increased lymphocyte free intracellular calcium in a dose-dependent manner. Septic serum had no effect on resting lymphocyte free intracellular calcium concentrations but potentiated the free intracellular calcium response to lysophosphatidylcholine. ConclusionsLymphocyte intracellular calcium homeostasis is altered during human sepsis. In addition, circulating factors present in septic serum are capable of altering cellular calcium handling. (Crit Care Med 1993; 21:196–202)

Dietary peptides improve wound healing following surgery

To determine if peptide-based enteral diets improve wound healing when compared to amino acid-based diets, a prospective randomized study was conducted using 38 male Sprague-Dawley rats. Following placement of a standardized abdominal wound, 20 animals were randomized to an isonitrogenous peptide-based (PEP) versus amino acid-based diet (AA) for 10 d. In addition, 18 animals were randomized to an amino acid-based diet supplemented with the peptide carnosine (CARN) or its constituent amino acids (Control). Diets were administered through small bowel feeding tubes. Wound bursting pressure was significantly higher in the PEP animals compared to the AA animals (179+/-9 versus 138+/-12 mmHg; P=0.02). In addition, wound bursting pressure was significantly greater in the CARN animals compared to the Control animals (143+/-10 versus 116+/-8 mmHg; P=0.005). Peptide-based enteral diets improve wound healing when compared to nonpeptide generating amino acid-based diets. We also conclude that the dietary peptide carnosine represents a dietary peptide that improves wound healing when administered as part of a complete enteral formula. This effect on wound healing may be clinically relevant because carnosine is not found in most enteral formulas.

Total parenteral nutrition increases mortality after hemorrhage

ObjectivesTo determine the effect of total parenteral nutrition (TPN) and different enteral feeding formulas on survival and liver function following hemorrhage in rats. DesignProspective randomized controlled study. SettingLaboratory of a large university-affiliated medical school. SubjectsSixty-seven male Sprague-Dawley rats weighing 350 to 450 g. InterventionsJugular and gastroduodenal feeding catheters were inserted in animals 1 day before hemorrhage, and animals were started on one of six different fluid or nutritional regimens: TPN, iv saline, an enteral amino acid-based formula (AA) (Vivonex-TEN), an enteral peptide-based formula (PEP) (Reabilan-HN), an enteral intact-protein based formula (PRO) (Osmolite-HN), or enteral saline. A catheter was inserted in the tail artery and animals were hemorrhaged 5 mL/kg at baseline and 1 hr later. Animals were returned to their cages and observed for survival. Liver function was determined by measuring circulating bile acid levels at baseline and 24 hr after hemorrhage. Measurements and Main ResultsMortality was significantly increased in animals receiving TPN (63%) and AA (24%). Mortality was 13% in animals receiving PRO and 0% in animals receiving PEP and saline. Liver function deteriorated in all animals after hemorrhage except the PEP group. ConclusionTPN and AA increased mortality in animals after hemorrhage. PEP was associated with zero mortality and protection of liver function after hemorrhage. (Crit Care Med 1990; 19:54)

Normal Parathyroid Hormone Responses to Hypocalcemia during Cardiopulmonary Bypass

To determine whether the calcium-magnesium-parathyroid hormone-calcitriol (vitamin D) axis responds appropriately to the hypocalcemia that routinely follows initiation of cardiopulmonary bypass (CPB), we measured blood ionized calcium (CaI), total calcium (CaT), total magnesium (MgT), ultrafilterable magnesium (MgI), total protein, intact parathyroid hormone (PTH), and calcitriol concentrations at eight defined time points in 28 patients undergoing elective cardiac surgery. With the onset of CPB, CaI decreased from 1.14 +/- 0.02 to 0.91 +/- 0.03 mM, P less than 0.05) (n = 17), and then gradually returned to a normal value by the time of separation from CPB (0.98 +/- 0.01 mM). CaT, MgI, MgT, and total protein concentrations declined significantly upon initiation of CPB and remained depressed thereafter. PTH initially decreased upon initiation of CPB (from 50 +/- 8 to 24 +/- 9 pg/ml, n = 9, P less than 0.05), remained inappropriately decreased during the early phases of CPB, and then gradually increased to maximal concentrations in response to hypocalcemia (103 +/- 15 pg/ml) before emergence. Calcitriol concentrations (n = 8) were unchanged during surgery. Based on these initial results, which suggested an association between hypomagnesemia and the slow PTH response to hypocalcemia, measurements were repeated in 10 additional patients, to whom magnesium (Mg) (1 g MgSO4 in two separate intravenous doses) was administered. Mg administration neither altered the PTH response to ionized hypocalcemia nor hastened the return of CaI to normal.(ABSTRACT TRUNCATED AT 250 WORDS)

Magnesium inhibits the hypertensive but not the cardiotonic actions of low-dose epinephrine

Intravenous magnesium supplementation is often used to control cardiac arrhythmias and coronary artery vasospasm resulting from disturbances of magnesium homeostasis after coronary artery bypass surgery. Many such patients also require inotropic drug support of depressed myocardial function. However, increased serum magnesium concentrations directly depress cardiac contractility in animals and may interfere with catecholamine actions. To determine whether small intravenous doses of magnesium sulfate (MgSO4) interfere with the cardiotonic actions of epinephrine, we examined the hemodynamic effects of MgSO4 and epinephrine infusion in 17 cardiac surgical patients on their 1st postoperative day in a prospective, controlled study. In 11 patients, infusion of MgSO4 (7-mg.kg-1 bolus followed by 10 mg.kg-1.h-1 as a continuous infusion) increased serum magnesium concentrations by 44% (mean +/- standard error of the mean [SEM] of 0.8 +/- 0.1 to 1.2 +/- 0.1 mM; P less than 0.01) but had no significant effect on heart rate; mean arterial, central venous, or pulmonary arterial occlusion pressures; or cardiac output. Epinephrine infusion (30 ng.kg-1.min-1) significantly increased cardiac index (2.7 +/- 0.1 to 3.1 +/- 0.21.min-1.m-2; P less than 0.05); this effect was not altered by MgSO4 administration (n = 11). However, MgSO4 significantly blunted epinephrines hypertensive action and prevented a significant increase in mean arterial pressure during concurrent MgSO4-epinephrine administration. Six placebo control patients were given two sequential infusions of epinephrine separated by a placebo infusion to rule out an effect of time on the hemodynamic response to epinephrine. Mean arterial pressure and cardiac index responses to epinephrine were identical before and after placebo infusion.(ABSTRACT TRUNCATED AT 250 WORDS)