PULSATILE SECRETION OF PROLACTIN IN LAYING AND INCUBATING TURKEY HENS

Incubation behavior in the turkey hen is associated with a large incre ase in prolactin secretion. Previous research using hourly sampling of incubating hens has shown that prolactin levels fluctuate widely thro ughout a 24-hr period, suggestive of pulsatile secretion. This study c ompared the prolactin secretory patterns of laying and incubating turk eys to determine if prolactin is secreted episodically and if the high prolactin levels characteristic of the incubating hen may result, at least in part, from a change in the amplitude or frequency of secretor y pulses. Blood samples were collected from cannulated, unrestrained l aying and incubating hens at 10-min intervals for up to 24 hr. Data we re analyzed with the PULSAR program to determine baseline prolactin le vels and to establish the magnitude, frequency, and duration of episod ic secretory peaks. The results revealed that prolactin is secreted in a pulsatile pattern in both laying and incubating turkey hens. Incuba ting hens had ninefold higher mean and baseline plasma prolactin level s than laying hens. The prolactin pulses were of approximately 12-fold greater amplitude in incubating hens than in laying hens, but the dur ation and frequency of pulses were the same in both groups. Therefore, the high prolactin levels required for incubation do not appear to re sult from an increase in the frequency of lactotroph stimulation, but rather from an increase in the prolactin secretion rate.