Cloning of porcine prepro-orexin cDNA and effects of an intramuscular injection of synthetic porcine orexin-B on feed intake in young pigs

Early growth is an important determinant of gain and efficiency in growing pigs. A major limiting factor of piglet growth is feed intake. Orexins, new ly discovered neuropeptides, may be important regulators of appetite. The o rexin gene, which encodes orexin-A and -B, was recently identified in roden ts 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 weanli ng pigs. Oligonucleotide primers were designed for reverse transcription po lymerase chain reaction production of porcine orexin cDNA. The polymerase-c hain-reaction products were cloned, sequenced, and found to be 88.5% homolo gous to the human orexin sequence. Predicted translation of porcine orexin cDNA revealed orexin-A and -B amino acid sequences that were 100% and 96% h omologous to the known human peptides, respectively. Porcine orexin-B was s ynthesized according to the predicted sequence. Twenty-six cross-bred pigle ts were utilized in three replicates (n = 8-10/replicate). Piglets were wea ned 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 inges ted 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 less than or equal to 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, particularl y following weaning, could result in significant improvements in swine-prod uction efficiency. (C) Elsevier Science Inc. 1999.