Electrophysiological evidence that the twitch contraction of guinea-pig vas deferens is triggered by phasic activation of P2x-purinoceptors

The aim of this study was to investigate the extent of sympathetic nervous system activation during parturition in four unrestrained goats. Chronically implanted radiotelemetry devices registered heart rate and arterial blood pressure around the clock and blood was sampled for determination of plasma adrenaline and noradrenaline concentrations before, during and after labour. Two goats delivered two kids after moderately intensive abdominal contractions. A third goat had dystocia, and was treated with prostaglandin F_2α. One normal kid and one mummified foetus were delivered manually. After milking, a third kid was born spontaneously. The fourth goat experienced severe abdominal contractions and delivered one kid. Mean blood pressure was 69 ± 2 mmHg the day before parturition, increased gradually during the labour pains, and reached a maximal value of 120 ± 7 mmHg when the head of the first kid was visible (P ≤ 0.05). Heart rate was 134 ± 4 beats min^?1 the day before parturition and peaked when the first kid was born (159 ± 6 beats min^?1, P ≤ 0.05), as did plasma adrenaline concentration (from 0.4 ± 0.2 nmol L^?1 to 2.7 ± 1.2 nmol L^?1, P ≤ 0.05). The concentration of noradrenaline increased from 4.8 ± 2.3 nmol L^?1 to 12.2 ± 8.4 nmol L^?1 (P ≤ 0.05), when the head of the first kid was visible. Expulsion of the second and third kids caused relatively smaller increases in blood pressure, heart rate and catecholamines than those seen with the first born kid. It is concluded that changes in pressure, heart rate and catecholamines during parturition are related to the different phases of labour and not to its duration or severity.