Enteral arginine partially ameliorates parenteral nutrition-induced small intestinal atrophy and stimulates hepatic protein synthesis in neonatal piglets.

BACKGROUND: Arginine is an indispensable amino acid in neonates; de novo synthesis of arginine occurs in the small intestine (SI) but is reduced during parenteral nutrition (PN), limiting the arginine available to the mucosa. We assessed the effects of route of intake and dietary concentration of arginine on protein synthesis, superior mesenteric artery (SMA) blood flow, and SI morphology. METHODS: Piglets (n = 18, 14-17 days old) were given complete PN for 3 days to induce SI atrophy, then switched to 1 of 3 treatments: arginine-free PN plus an intragastric (IG) infusion of high arginine (1.6 g · kg(-1)· d(-1), IG-H Arg) or low arginine (0.6 g · kg(-1)· d(-1), IG-L Arg) or complete high-arginine PN (1.6 g · kg(-1)· d(-1), IV-H Arg). RESULTS: Enteral arginine, irrespective of amount provided, stimulated hepatic protein synthesis compared with intravenous delivery of arginine (P = .01). SMA blood flow declined for all groups following the initiation of PN. After 48 hours on the test diets, all groups reached low constant levels, but the IV-H group was significantly higher than both IG groups (P < .05). Despite greater blood flow, the SI morphological characteristics in IV-H Arg pigs were not significantly improved over the other groups. IV-H Arg pigs had higher plasma concentrations of indispensable amino acids (tyrosine, isoleucine, and valine) compared with IG-H Arg, despite identical amino acid intakes. CONCLUSIONS: Intravenous delivery of arginine sustained the best SMA blood flow, whereas even a moderate amount of enteral arginine stimulated liver protein synthesis and maintained SI growth, independent of blood flow.

Proline supplementation to parenteral nutrition results in greater rates of protein synthesis in the muscle, skin, and small intestine in neonatal Yucatan miniature piglets.

Proline and arginine are each indispensable during parenteral feeding due to limited interconversion by an atrophied gut. Commercial amino acid parenteral products designed for neonates contain proline concentrations that differ by almost 4-fold. To assess the adequacy of the lowest concentration of proline provided in commercial total parenteral nutrition (TPN) products, we compared rates of tissue-specific protein synthesis and nitrogen balance in neonatal piglets provided TPN at 2 different proline concentrations. Yucatan miniature piglets (9-11 d old, n = 12) were randomized to complete isonitrogenous TPN diets with low proline (LP; L-proline as 3% of amino acids) or proline supplemented (PS; 9%). After 7 d of receiving TPN, rates of protein synthesis in liver, gastrocnemius muscle, jejunal mucosa, and skin were determined by the flooding dose technique and tissue free amino acids were measured. Nitrogen balance was assessed during the last 3 d. The LP TPN resulted in lower free proline concentrations in plasma, muscle, and skin (P < 0.05) and lower rates of protein synthesis in the jejunum (by 25%; P = 0.02), muscle (by 45%; P = 0.015), and skin (by 60%; P = 0.01); there was no difference in liver. Nitrogen retention was 20% lower in the LP group (P = 0.01). In conclusion, muscle and skin protein synthesis was profoundly sensitive to parenteral proline supply and the reduced protein synthesis in the intestine could affect intestinal integrity. Low-proline TPN solutions that are currently in wide use in neonatal care may result in impaired tissue growth.

Stratospheric memory and skill of extended-range weather forecasts.

We use an empirical statistical model to demonstrate significant skill in making extended-range forecasts of the monthly-mean Arctic Oscillation (AO). Forecast skill derives from persistent circulation anomalies in the lowermost stratosphere and is greatest during boreal winter. A comparison to the Southern Hemisphere provides evidence that both the time scale and predictability of the AO depend on the presence of persistent circulation anomalies just above the tropopause. These circulation anomalies most likely affect the troposphere through changes to waves in the upper troposphere, which induce surface pressure changes that correspond to the AO.