DIFFERENT RESPONSES IN LITTLE AND BIGBIG PROLACTIN TO METOCLOPRAMIDE IN SUBJECTS WITH HYPERPROLACTINEMIA DUE TO 150-170 KD (BIGBIG) PROLACTIN

We have studied in vivo induction of serum prolactin (PRL) levels in f our females and one male, and regulation of PRL in the menstrual cycle in three females all with hyperprolactinemia with large amounts (72-9 2%) of bigbig PRL (MW 150-170 kD). Metoclopramide (MTC) iv induced a 4 -29-fold increase in little PRL (2 5 kD PRL) at 30 min. while the incr ease in 150-170 kD PRL was 1.1-2,2-fold. The maximal response in 150-1 70 kD PRL was seen after 2-6 h, and the decrease after the maximal PRL values for 1 50-1 70 kD PRL was delayed compared to the decrease in 2 5 kD PRL. The different kinetics for 2 5 kD PRL and 150-170 kD PRL was responsible for the prolonged increase in total PRL seen in the subje cts with large amounts of 150-170 kD PRL compared to the controls. The percentage of 150-170 kD PRL decreased to 29-60% at 30 min and return ed to unstimulated values after 6-24 h. In contrast, prolonged stimula tion of PRL secretion, as in the luteal phase, did not change the perc entage of 150-170 kl) PRL. In a male subject secreting large amounts o f 150-170 kD PRL the increase in PRL after MTC was less, while the tem poral changes in the 25 kD PRL levels were almost the same as in the f emales.