Immunology

Expression and Regulation of Functional Oxytocin Receptors in Bovine T Lymphocytes

Abstract
The corpus luteum (CL) produces oxytocin (OXT) which has been proposed to regulate the pulsatile release of prostaglandin F2 alpha during luteolysis in ruminants. This action of oxytocin is mediated via oxytocin receptors (OXTR) present on uterine epithelial cells. It is hypothesized that luteal oxytocin acts as a paracrine regulator of resident immune cells. In the present study, OXTR mRNA expression in bovine lymphocytes was analyzed as well as its regulation during the estrous cycle. OXTR transcripts were observed in freshly purified bovine peripheral blood mononuclear cells (PBMC) and T lymphocytes. OXTR mRNA in bovine lymphocytes was numerically greater but not significantly different on day 3 than on day 19 of the estrous cycle (P = 0.091). In cultured T cells, estradiol (E₂) treatment significantly increased the steady-state concentrations of OXTR mRNA, but the stimulatory effect of E₂ was inhibited by the addition of progesterone (P₄). Each of the major T cell subsets (CD4⁺, CD8⁺, and gamma delta⁺) expressed OXTR mRNA with no significant difference in expression among them. Western blot analyses demonstrated the presence of the bovine OXTR protein at about 45 kDa in lymphocytes, as well as expression of the 14 kDa precursor of oxytocin. When lymphocytes were treated with OXT, intracellular concentrations of calcium ([Ca²⁺]i) were rapidly and dramatically increased. This study demonstrated that bovine lymphocytes express OXT receptors and that this expression can be regulated in a steroid-dependent manner. Furthermore, OXT elicited a functional [Ca²⁺]i response in T lymphocytes supporting the possibility that OXT within the CL could act as a paracrine or autocrine regulator of resident T lymphocytes.

Key words: Corpus luteum • Oxytocin • bovine • lymphocytes • oxytocin receptor