Source of dietary protein influences kinetics of plasma gut regulatory peptide concentration in response to feeding in preruminant calves

A Mechanistic Model of Intermittent Gastric Emptying and Glucose-Insulin Dynamics following a Meal Containing Milk Components

To support decision-making around diet selection choices to manage glycemia following a meal, a novel mechanistic model of intermittent gastric emptying and plasma glucose-insulin dynamics was developed. Model development was guided by postprandial timecourses of plasma glucose, insulin and the gastric emptying marker acetaminophen in infant calves fed meals of 2 or 4 L milk replacer. Assigning a fast, slow or zero first-order gastric emptying rate to each interval between plasma samples fit acetaminophen curves with prediction errors equal to 9% of the mean observed acetaminophen concentration. Those gastric emptying parameters were applied to glucose appearance in conjunction with minimal models of glucose disposal and insulin dynamics to describe postprandial glycemia and insulinemia. The final model contains 20 parameters, 8 of which can be obtained by direct measurement and 12 by fitting to observations. The minimal model of intestinal glucose delivery contains 2 gastric emptying parameters and a third parameter describing the time lag between emptying and appearance of glucose in plasma. Sensitivity analysis of the aggregate model revealed that gastric emptying rate influences area under the plasma insulin curve but has little effect on area under the plasma glucose curve. This result indicates that pancreatic responsiveness is influenced by gastric emptying rate as a consequence of the quasi-exponential relationship between plasma glucose concentration and pancreatic insulin release. The fitted aggregate model was able to reproduce the multiple postprandial rises and falls in plasma glucose concentration observed in calves consuming a normal-sized meal containing milk components.

Gastrin, cholecystokinin and gastrointestinal tract functions in mammals

The aim of the present review is to synthesise and summarise our recent knowledge on the involvement of cholecystokinin (CCK) and gastrin peptides and their receptors in the control of digestive functions and more generally their role in the field of nutrition in mammals. First, we examined the release of these peptides from the gut, focusing on their molecular forms, the factors regulating their release and the signalling pathways mediating their effects. Second, general physiological effects of CCK and gastrin peptides are described with regard to their specific receptors and the role of CCK on vagal mucosal afferent nerve activities. Local effects of CCK and gastrin in the gut are also reported, including gut development, gastrointestinal motility and control of pancreatic functions through vagal afferent pathways, including NO. Third, some examples of the intervention of the CCK and gastrin peptides are exposed in diseases, taking into account intervention of the classical receptor subtypes (CCK1 and CCK2 receptors) and their heterodimerisation as well as CCK-C receptor subtype. Finally, applications and future challenges are suggested in the nutritional field (performances) and in therapy with regards to the molecular forms or in relation with the type of receptor as well as new techniques to be utilised in detection or in therapy of disease. In conclusion, the present review underlines recent developments in this field: CCK and gastrin peptides and their receptors are the key factor of nutritional aspects; a better understanding of the mechanisms involved may increase the efficiency of the nutritional functions and the treatment of abnormalities under pathological conditions.

A new role of phosphopeptides as bioactive peptides released during milk casein digestion in the young mammal: regulation of gastric secretion

The aim of this work was to study in vivo the effect of ingestion of phosphopeptides (PP) alone or associated with caseinomacropeptide (CMP) on gastric secretion and to elucidate some possible mechanisms involved. Seven calves fitted with a gastric pouch received either a diet based on whey proteins without PP and CMP (C diet) or C diet in which PP or PP+CMP was introduced at concentrations similar to that of PP or PP+CMP in cow milk (PP diet and PP+CMP diet, respectively). Gastric juice secretion was measured during successive periods throughout the day. Twenty-four calves were fitted with a catheter introduced in one external jugular vein for blood sample collections. The daily secretion of electrolytes decreased with the presence of PP or PP+CMP in the diet. During the day, peptide supplementation in the diet resulted in (1) short term (1st-2nd postprandial h), a decrease of secreted quantities of gastric juice, enzymes and electrolytes, (2) long term (7-24h after the morning meal), a decrease of electrolyte secretions. Intervention of gastrin, CCK, somatostatin and BPP could be probable. Globally, inhibition of gastric secretions seemed more important when PP was given in association with CMP in the diet rather than alone. CMP and PP may have short and long term action respectively over the 24h day. To our knowledge, it is the first time that phosphopeptides coming from milk casein digestion are demonstrated to inhibit gastric secretion. Therapeutic uses are suggested.

Reviewing the low efficiency of protein utilization in heavy preruminant calves – a reductionist approach

The efficiency of protein utilization for growth in preruminant calves is decreasing with increasing body weight. In contrast to calves weighing less than 100 kg of body weight, heavy preruminant calves do not respond in protein retention to an increased intake of indispensable amino acids in dose-response studies. The marginal efficiency of protein utilization is low compared with pigs and milk-fed lambs at a similar stage of maturity. A reductionist approach was taken to perceive the potential mechanisms for the low protein utilization in preruminant calves. Neither an imbalance in the dietary protein to energy ratio nor a single limiting indispensable amino acid was responsible for the low efficiency. Also, amino acids were not specifically used to detoxify ammonia. Alternative hypotheses to explain the low efficiency are discussed and result in (i) a reduced post-absorptive supply of amino acids: e.g. by fermentation of milk in the (premature) rumen or preferential amino acid utilization by specific tissues; or (ii) a reduced post-absorptive amino acid utilization: e.g. by decreased insulin sensitivity, utilization of amino acids for gluconeogenesis or an asynchronous nutrient supply. In conclusion, several mechanisms for the low efficiency of protein utilization in heavy preruminant calves were excluded. Other physiological processes which are potentially involved remain to be studied, because the large potential for improving protein utilization in heavy preruminant calves asks for further exploration of their amino acid metabolism.