University of Arkansas, Fayetteville Division of Agriculture


Vasotocin receptors are members of seven transmembrane spanning G-protein associated receptors. Several isoforms have been recognized in mammals and birds. It has been shown that VT-1 expression occurs primarily in the brain while VT-2 expression occurs mainly in the pituitary. There is no current evidence to support that both VTR-1 and -2 are found in a single tissue. Our goal in this experiment was to see if VT-1 and VT-2 receptor mRNA expression varied in known sites of expression over the period of the ovulatory cycle of broiler breeder hens. In order to study potential changes in VT-1 and VT-2 expression, birds were sacrificed at 3 hour intervals over a 24 hour period. Blood samples were drawn. After cervical dislocation, the brain, pituitary, shell gland, and kidney were removed. Plasma was stored at -20ºC prior to determination of corticosterone levels by radioimmuno assays. Isolated mRNA from the brains and the pituitaries was transferred to nylon membranes for northern slot blot analysis. cDNA for VT-1 and VT-2 was used to make random primed cDNA probes. Corticosterone levels significantly increased at 9 hours post oviposition relative to all other times. Neither VT-1 or VT- 2 expression showed any significant variation over the 24 hour cycle. Based on these results, we conclude that VT-1 and VT-2 steady state mRNA levels do not fluctuate dramatically over the ovulatory cycle of broiler breeder hens. Further work on membrane bound receptors and on circadian variations in membrane bound receptors in the brain and pituitary is currently underway of broiler breeder hens.