Maternal plasma vasopressin, oxytocin and cortisol concentrations following foetal ejection in the pig

Experiments were performed to determine the effect of foetal ejection on the secretion of the neurohypophyseal hormones lysine vasopressin (LVP) and oxytocin (OT), and the adrenocortical hormone cortisol in the parturient pig. As these hormones are all believed to be influenced in some circumstances by stressful stimuli, subsequent studies were carried out in which animals gave birth in putative ideal or suboptimal environments and the consequences of this on hormone release at foetal ejection examined. In Experiment 1, six freely moving gilts gave birth in a strawed pen (1.2 × 1.5 m) during which time blood was withdrawn (3 ml min−1 for 2 h) from an intravenous catheter using an automatic apparatus, and plasma assayed for LVP, OT and cortisol using specific RIAs. Overall LVP and OT release was pulsatile throughout parturition and positively correlated between the birth of the first and last piglet (P < 0.05) but not correlated at other times. Both LVP and OT increased (by 38.8 and 13.5%, respectively; P < 0.05) immediately following each foetal ejection. There were no changes in plasma LVP or OT immediately pre-delivery. Cortisol secretion during parturition was very variable and was not influenced by foetal ejection. eriment 2, 33 sows 5 days prior to expected parturition were housed either in strawed pens (2.1 by 3.1 m: Group P; n = 16) or concrete-floored farrowing crates (2.0 by 0.54 m: Group C; n = 17) which prevented the animals from turning around. At birth, blood samples were taken every 15 min for 2 h following Piglet 1 plus an additional sample following each delivery, and assayed as above. Following delivery, plasma LVP in Group C increased from an overall mean of 3.08 to 5.06 pmol l−1 (64.3%) and in Group P from 2.48 to 3.54 pmol l−1 (42.8%). Post-delivery plasma OT in Group C increased from 39.6 to 79.3 (100.3%) and in Group P from 43.8 to 70.2 pmol l−1 (60.3%). These post-ejection increases in both hormones were significantly greater in Group C than Group P animals (P < 0.05). Plasma cortisol was unaffected by delivery in Group C but fell (P < 0.05) following delivery in Group P. results demonstrate that foetal expulsion results in rapid alterations in neurohypophyseal hormone secretion and that these phenomena are altered by the imposition of differing environments on the parturient pig.