Concentrations of catecholamines, ascorbic acid, progesterone and oxytocinin the corpora lutea of cyclic and pregnant cattle

To determine if there are inter-relationships between progesterone, oxytoci n (OT), dopamine (DA), noradrenaline (NA) and ascorbic acid, these compound s were measured in the corpus luteum (CL) from cattle at different stages o f the oestrous cycle (n = 42) and from 1-5 months of pregnancy (n = 27). Th ey were measured by radioimmunoassay (RIA), high performance liquid chromat ography (HPLC) and colorimetric methods. Corpora lutea were collected from heifers and cows within 30 min of slaughter on days 1-5, 6-10, 11-16 and 17 -21 of the oestrous cycle. The stage of pregnancy was determined on the bas is of foetal size and development. Each CL was divided into four parts and stored in liquid nitrogen. For hormone estimation, the tissue was homogenis ed/powdered and suspended in phosphate buffer (for OT and progesterone), 0. 1 M trichloracetic acid (TCA; for catecholamines) or in ice-cold metaphosph oric acid (for ascorbic acid). There were no significant differences in the measured parameters between cows and heifers, and so the data were combine d. The concentration of DA was correlated with NA (r = 0.66; P < 0.001) dur ing the oestrous cycle and was highest in newly formed CL (P < 0.01) as com pared with early CL, regressed CL and CL of pregnant females. NA was negati vely correlated (P < 0.01) with progesterone (r = -0.53) and OT (r = -0.41) . In contrast, progesterone and OT were positively correlated with each oth er (r = 0.81; P < 0.01) during all stages of the oestrous cycle, but not du ring pregnancy. The lowest concentrations of ascorbic acid were observed in regressed CL. Ascorbic acid concentrations were correlated (P < 0.01) with those of progesterone (r = 0.68), OT (r = 0.42) and DA (r = -0.37). Luteal concentrations of ascorbic acid, progesterone and OT followed a pattern co nsistent with the development and regression of the CL. Luteal concentratio ns of catecholamines were not consistent with this pattern. (C) Inra/Elsevi er, Paris.