Reinitiation of ovulatory cycles in incubating female turkeys by an inhibitor of serotonin synthesis, P-chlorophenylalanine

Nest deprivation of incubating turkeys caused a decrease in serum prolactin (Prl) levels from 1184.5 +/- 116.4 ng/ml to 896.8 +/- 83.0 ng/ml 1 day after initiation of deprivation, with a further decline to 156.5 +/- 111.7 ng/ml at the end of the 22-day experimental period. Serum luteinizing hormone (LH), progesterone and estradiol levels following nest deprivation were similar to those in birds allowed to incubate (controls). Oral administration of p-chlorophenylalanine (PCPA, 50 mg/kg) to incubating turkeys for 3 consecutive days reduced nesting frequency (P less than 0.05) on the 4th day after initiation of treatment and the nesting virtually ceased by the 9th day. Pretreatment Prl was 1655 +/- 210 ng/ml and declined (P less than 0.05) after PCPA administration to a low of 28.6 +/- 2.8 ng/ml. In addition, PCPA caused a sustained rise in serum LH peaking (5.59 +/- 1.09 ng/ml) 3 days after treatment initiation. Contrary to nest deprivation, serum levels of progesterone and estradiol increased (P less than 0.05) as a consequence of PCPA treatment. Seven of 8 PCPA-treated birds later came into lay when their Prl levels and nesting frequency increased again. The results suggest a role for serotonin (5-HT) in incubation behavior, and Prl and LH secretion in turkeys.