Effect of bromocriptine on neurophysin secretion in pregnant women in labour.

In order to determine whether dopamine plays a role in the control of neuropituitary function in pregnant women during labour, blood levels of nicotine (NSN)- and estrogen (ESN)-stimulated neurophysins were measured in 119 women treated orally with placebo (n = 59, control group) or 5 mg bromocriptine, a potent dopaminergic receptor agonist (n = 60, experimental group). Serum samples were taken before drug ingestion (basal sample) and at delivery. The serum basal concentrations of NSN and ESN were similar in both groups of pregnant women in labour. At delivery, serum ESN levels were similar in all women regardless of the treatment, whereas NSN concentrations were significantly lower in the bromocriptine-treated women than in those who were given placebo. In additional experiments the effect of 5 mg bromocriptine on the serum concentrations of NSN and ESN was tested for 6 hours after drug ingestion in 10 healthy, non-pregnant women and in 8 women in the 3rd trimester of pregnancy. Bromocriptine did not modify the circulating levels of NSN and ESN in either of these 2 groups of women. Since NSN and ESN are thought to be associated with vasopressin and oxytocin, respectively, these results indicate that in non-pregnant women and in pregnant women during late pregnancy dopaminergic stimulation with a dopaminergic receptor agonist does not inhibit the release of either vasopressin or oxytocin during rest. In contrast, dopaminergic receptor stimulation appears to play an inhibitory role in the regulation of vasopressin, but not oxytocin secretion in pregnant women in labour.