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Title: PULSATILE SECRETION OF PROLACTIN IN LAYING AND INCUBATING TURKEY HENS

Author
item Proudman, John
item WENTWORTH, B - UNIV OF WISCONSIN

Submitted to: Domestic Animal Endocrinology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/9/1995
Publication Date: N/A
Citation: N/A

Interpretive Summary: Prolactin (PRL), produced by the pituitary gland, causes incubation behavior and ovarian regression in turkey hens and decreases hatching-egg production. PRL secretion changes greatly during the reproductive cycle, such that plasma PRL concentrations vary up to 100-fold and are diagnostic of the reproductive state of the hen. In mammals, PRL is secreted in pulses and the primary difference between normal and hyperprolactinemic individuals is in the amplitude of these secretory pulses. Since the control of PRL secretion by the brain is opposite in birds to that found in mammals, this study was conducted to determine if pulsatile secretion of PRL occurs in birds, and if the hyperprolactinemia which is characteristic of incubation behavior results from a change in PRL pulse amplitude, frequency, or duration. Results showed that PRL is secreted in pulses in laying, incubating, and photorefractory turkey hens. It was determined that PRL pulse amplitude is nearly 12-fold greater in incubating hens than in laying hens, but that the duration and frequency of pulses does not change with reproductive state. Therefore, the high PRL levels which initiate incubation behavior do not appear to result from an increase in the frequency at which the brain stimulates pituitary cells to stimulate PRL, but rather result from an increase in the ability of the pituitary to secrete PRL. These findings suggest that the pituitary, rather than the brain, may regulate the primary hormone changes which initiate incubation behavior. This knowledge will be used by scientists to develop technology to reduce hatching-egg losses due to incubation behavior.

Technical Abstract: Incubation behavior in the turkey hen is associated with a large increase in prolactin secretion. Previous research using hourly sampling of incubating hens has shown that prolactin levels fluctuate widely throughout a 24-hr period, suggestive of pulsatile secretion. The present study compared the prolactin secretory patterns of laying and incubating turkeys 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 secretory pulses. Blood samples were collected from cannulated, unrestrained laying and incubating hens at 10 min intervals for up to 24 h. Data were analyzed using the PULSAR program to determine baseline prolactin levels and to establish the magnitude, frequency, and duration of episodic secretory peaks. The results revealed that prolactin is secreted in a pulsatile pattern in both laying and incubating turkey hens. Incubating hens had 9- fold higher mean and baseline plasma prolactin levels than laying hens. The prolactin pulses were of approximately 12-fold greater amplitude in incubating hens than in laying hens, but the duration and frequency of pulses were the same in both groups. Therefore, the high prolactin levels required for incubation do not appear to result from an increase in the frequency of lactotroph stimulation, but rather from an increase in the prolactin secretion rate.