title: Pulsatile secretion of oxytocin during parturition in the pig: temporal relationship with fetal expulsion.
abstract: 1. To assess changes in oxytocin release as they occur in relation to the rapid progress of events at fetal expulsion, continuous automated blood withdrawals (3 ml min-1) from an indwelling jugular catheter and intramammary pressure recordings were obtained from nine primiparous pigs (190-220 kg). Data were acquired over 16 h of normal parturition, during which thirty-five piglets were born. 2. Oxytocin secretion during parturition, when measured by radioimmunoassay (RIA) in blood collected and pooled every minute, showed a baseline secretion (19.8-88.37 pg ml-1) that was raised relative to preterm values. Analysis of individual secretion profiles revealed significant fluctuations or peaks of concentration superimposed on this baseline, with a slow periodicity of 4-12 min. These substantial peaks in secretion were not temporally related to fetal expulsion or visible abdominal contractions. 3. A small (13%) but significant increase in plasma oxytocin was also seen when assay data from the minutes coinciding with a birth were meaned and compared with the following minutes. This rise did not persist into further minutes. 4. Intramammary pressure recordings revealed a highly repeatable and characteristic phenomenon in that fetal expulsion was followed after 33.74 +/- 1.31 s (mean +/- S.E.M. time from emergence of fetus to peak pressure rise) in thirty-three of thirty-five instances by a distinctive and rapid bolus release of oxytocin. These 'postpartum oxytocin pulses' could be closely mimicked by injections of exogenous oxytocin (0.03-1.0 ng kg-1; lag time from jugular injection to peak pressure rise, 20.44 +/- 0.99 s). The timing of this event coincided with the small postpartum pulse measurable by radioimmunoassay.(ABSTRACT TRUNCATED AT 250 WORDS)
authors.affiliation: Department of Neurobiology, AFRC Babraham Institute, Cambridge.
authors.forename: C L
authors.initials: CL
authors.lastname: Gilbert
authors.forename: J A
authors.initials: JA
authors.lastname: Goode
authors.forename: T J
authors.initials: TJ
authors.lastname: McGrath
mesh_terms: D000818:Animals; D005260:Female; D005333:Fetus / Q000502:physiology; D007743:Labor, Obstetric / Q000502:physiology*; D007774:Lactation / Q000502:physiology; D008321:Mammary Glands, Animal / Q000502:physiology; D010121:Oxytocin / Q000032:analysis / Q000097:blood / Q000378:metabolism*; D011247:Pregnancy; D011863:Radioimmunoassay; D013552:Swine
chemical_list: D010121:Oxytocin