Cloning of Porcine Prepro-Orexin cDNA and Effects of an Intramuscular Injection of Synthetic Porcine Orexin-B on Feed Intake in Young Pigs

Abstract

Early growth is an important determinant of gain and efficiency in growing pigs. A major limiting factor of piglet growth is feed intake. Orexins, newly discovered neuropeptides, may be important regulators of appetite. The orexin gene, which encodes orexin-A and -B, was recently identified in rodents and man. The objectives of this study were to clone the cDNA for porcine orexin, utilize the cDNA sequence information to produce synthetic hormone, and evaluate the effect of orexin administration on feed intake in weanling pigs. Oligonucleotide primers were designed for reverse transcription polymerase chain reaction production of porcine orexin cDNA. The polymerase-chain-reaction products were cloned, sequenced, and found to be 88.5% homologous to the human orexin sequence. Predicted translation of porcine orexin cDNA revealed orexin-A and -B amino acid sequences that were 100% and 96% homologous to the known human peptides, respectively. Porcine orexin-B was synthesized according to the predicted sequence. Twenty-six cross-bred piglets were utilized in three replicates (n = 8–10/replicate). Piglets were weaned between 2–3 wk of age. One week after weaning, equal numbers of animals in each replicate received intramuscular (im) injections of orexin-B (3 mg/kg body weight) or vehicle (sterile water). Feed intake was monitored from −24 to 24 h relative to injection (time 0). The orexin-injected pigs ingested an additional meal at 12 h when compared with the control animals (P = 0.02). Cumulative feed intake was increased by orexin-B administration from 12 to 24 h postinjection (P ⩽ 0.05). Total feed intake at 24 h was improved by 18% in orexin-treated pigs (P = 0.05). The ability to stimulate appetite during critical periods of early growth, particularly following weaning, could result in significant improvements in swine-production efficiency.

Introduction

The importance of optimizing piglet growth is well recognized by the swine industry. Evidence exists to show that heavy weanling pigs can reach market weight as much as 2 wk earlier than lighter littermates (1). One of the greatest challenges in swine production is to decrease the postweaning growth lag by optimizing feed intake. Factors that contribute to the adverse effects of weaning include psychological adaptation to solid feed, movement to the nursery facility, and the capacity of the piglet’s gastrointestinal system to digest and absorb components of the solid diet. In order to develop strategies to improve postweaning feed intake and subsequent growth, our lab has focused on elucidating the biochemical methods by which an animal’s appetite is controlled.

Recently a novel family of neuropeptides—orexins (also called hypocretins)—were discovered in the rat 2, 3, 4, 5. The orexins increase feed intake in these animals when administered directly into the brain (2). After cloning porcine orexin-A and -B, we tested the ability of synthetic orexin-B to stimulate feed intake in weanling pigs when given in a single intramuscular (im) injection.