Oxytocin Receptors in Bovine Mammary Tissue

Abstract

Oxytocin receptors were identified and characterized in bovine mammary tissue. ³H]-oxytocin was specifically bound to the 105,000 × g particulate fractions from 5 lactating cows and 5 non-lactating cows. Binding reached equilibrium by 50 min at 20°C and by 8 hr at 4°C. The half-time of displacement at 20°C was approximately 1 hr. ACTH, TRH, angiotensin I, angiotensin II, pentagastrin, bradykinin, xenopsin and L-valyl-histidyl-L-leucyl-L-threonyl-L-prolyl-L-valyl-L-glutamyl-L-lysine were not competitive in the dose range tested at 20°C. The ability of other peptides to inhibit ³H-oxytocin binding was as follows: oxytocin > vasotocin > arginine - vasopressin >lysine - vaso-pressin > Pen¹ Phe² Thr⁴ - oxytocin. The Kd of the oxytocin receptor averaged 1.66 ± 1.19 nMol/L for lactating cows and 0.97± 0.49 nMol/L for non-lactating cows, respectively. The maximum number of binding sites was 0.14 ± 0.12 nM/mg protein and 0.15 ± 0.08 nM/mg protein for lactating cows and non-lactating cows, respectively. Identification and characterization of these receptors now makes it possible to study the dynamics of hormonal binding throughout various physiological states of the animal.