Low-dose dopamine infusions do not ablate luteinizing hormone pulses in women

The effect of dopamine on the secretion of luteinizing hormone in 15 euprolactinemic and 15 hyperprolactinemic women was investigated using infused doses of dopamine that achieved circulating levels from 2 to 100 times basal physiologic concentrations. The normal women were studied in the early follicular phase of the cycle. Different concentrations of dopamine were maintained at each dose level for 2 hours. Blood samples were obtained every 15 minutes and concentrations of dopamine, luteinizing hormone, follicle-stimulating hormone, and prolactin quantified. Mean basal concentrations of estradiol were 53 +/- 19 pg/ml in the euprolactinemic and 33 +/- 12 pg/ml in the hyperprolactinemic women; mean prolactin levels were 8.1 +/- 3.9 ng/ml in euprolactinemic and 183 +/- 174 ng/ml in hyperprolactinemic women; mean basal dopamine concentrations were 323 +/- 308 pg/ml in euprolactinemic and 337 +/- 232 pg/ml in hyperprolactinemic women. All doses of dopamine achieved some degree of prolactin suppression, but doses that achieved nanomolar circulating concentrations did not significantly affect luteinizing hormone secretion. Eight of the women in each group exhibited high-amplitude luteinizing hormone pulses, which persisted during the dopamine infusions. Neither the amplitude nor frequency of luteinizing hormone release correlated with basal estradiol, luteinizing hormone, or prolactin levels. We conclude that low doses of dopamine infused into the peripheral circulation do not achieve significant suppression of luteinizing hormone release. In some women during the early follicular phase of the menstrual cycle and in some amenorrheic hyperprolactinemic women, luteinizing hormone is secreted in a pulsatile manner characterized by high-amplitude low-frequency bursts. These bursts of luteinizing hormone were not influenced by elevations in circulating dopamine concentrations sufficient to suppress prolactin.