The effect of arginine vasotocin on the isolated amniotic membrane of the guinea pig

Abstract

Amniotic membranes from fetal guinea pigs at 0.46 of term were maintained in vitro by means of salines which reproduced the electrolytes of the natural fluids, and. which maintained small osmotic and hydrostatic gradients from the fetal to the maternal solutions. Water passed slowly from the fetal to the maternal side (average rate = 3.93 mg/cm2 per minute). Synthetic arginine vasotocin (AVT) at 8–100 vasopressor mU/ml of amniotic saline slowed the fetal–maternal flow, or reversed it to give a net uptake of water into the amniotic saline (maximum reversed flow = 10.4 mg/cm2 per minute). Despite individual variability between membranes, there was a linear relationship between the change in the rate of flow, and the log of the dose of AVT (AVT threshold indicated = 6.4 mU/ml). Synthetic arginine vasopressin (AVP) and fetal pituitary extracts produced similar responses (AVP threshold = about 1.0 mU/ml). Synthetic oxytocin was without effect in doses up to 100 oxytocic mU/ml. Although the doses tested appeared to be pharmacological, evidence is reviewed for a possible physiological significance. It is suggested that amounts of AVT, or more probably AVP, are liberated from the fetal pituitary by osmotic or other stimuli, and pass in the fetal urine into the amniotic cavity; there they act on the amnion to stimulate it to conserve or augment amniotic fluid by transporting water inwards from the maternal environment.