Effect of PGF 2α analogue on ovarian oxytocin and progesterone release in heifers: catecholamines are not involved in this process

Abstract

The assumption that catecholamines are involved in the stimulation of ovarian oxytocin release by PGF 2α is examined in this study. On Day 10 of the oestrus cycle, heifers ( n = 18) were allotted to one of three groups: I, injected with PGF 2α; II, for 15 min before and after injection of PGF 2α, propranolol at a dose of 1.2 μg kg −1 min −1 was infused into the aorta abdominalis ahead of the origin of the ovarian artery, III, for 15 min before and after injection of PGF 2α, heifers were infused with phentolamine (2.5 μg kg −1 body weight min −1). Blood samples were collected frequently from the vena jugularis for 1 h before PGF 2α analogue injection and for 3 h thereafter. The pattern of oxytocin and progesterone release was similar in heifers of all three groups soon after PGF 2α analogue injection; oxytocin piasma concentration rose abruptly from 4 min ( P < 0.01), reached the highest concentration in 6–10 min and thereafter decreased rapidly. Progesterone concentration was elevated concomitantly with oxytocin in Groups I and II ( r = 0.37, P < 0.008 and r = 0.32, P < 0.03, respectively) or followed its surge. We propose that PGF 2α causes the release of oxytocin and temporary elevation of progesterone independently of catecholamines.