Prolactin Response to Secretin during the Spontaneous Menstrual Cycle in Women

The effect of an intravenous infusion of secretin (2.0 CU/kg/h) on serum prolactin (PRL) and estradiol levels and plasma levels of vasoactive intestinal polypeptide and somatostatin (SRIH) was studied in 8 healthy and normally cycling women during the midfollicular phase (cycle day 7), at midcycle (day 14), and during the midluteal phase (day 21) of the menstrual cycle. When compared to basal preinfusion levels, a significant decrease in serum PRL levels was observed at steady state concentrations of plasma secretion (+30 to +60 min) both during the follicular (p less than 0.03) and the luteal (p less than 0.0001) phases. At midcycle a nonsignificant decrease was observed. A significant and negative correlation existed between serum PRL and plasma secretin levels in the follicular phase (r = -0.33; p less than 0.05) and in the luteal phase (r = 0.73; p less than 0.0001). The plasma concentrations of SRIH increased significantly at steady state conditions of secretin at midcycle (p less than 0.02) and in the luteal phase (p less than 0.04), while no effect was found during the follicular phase. A significant and positive correlation between plasma levels of SRIH and secretin was observed at midcycle (r = 0.63; p less than 0.002) and in the luteal phase (r = 0.46; p less than 0.02). No effect of secretin on plasma vasoactive intestinal polypeptide and serum estradiol concentrations was demonstrated. These results suggest that the suppression of PRL in the follicular phase of the spontaneous menstrual cycle can be ascribed to an effect of secretin alone.(ABSTRACT TRUNCATED AT 250 WORDS)