Inverse changes in plasma prolactin and LH concentrations in female canaries after disruption and reinitiation of incubation.

Prolactin and LH concentrations were measured in the plasma of female canaries sampled during the breeding cycle and after disruption and reinitiation of incubation behaviour. The late incubation period was characterized by low LH and high prolactin concentrations, and canaries separated from their nests at this stage showed an increased in LH and a decline in prolactin within 3 h. In one experiment mean (+/- S.E.M.) concentrations before and 24 h after nest deprivation were: prolactin 397 +/- 86 and 18 +/- 5 micrograms/l; LH 1.04 +/- 0.21 and 2.03 +/- 0.17 micrograms/l. Female canaries which abandoned their nests after the eggs had been removed also showed an increase in LH together with a fall in prolactin 24 h after egg removal. When nest-deprived canaries were allowed to resume incubation, plasma prolactin increased again within 5 h and after 2 days had reached levels normal for incubating birds (398 +/- 46 micrograms/l). Concentrations of LH changes more gradually but had decreased 2 days after the resumption of incubation. Thus prolactin and LH show inverse changes after the disruption and reinitiation of incubation behaviour; it is not clear, however, if the change in one is dependent on the other or if both hormones are responding to the same external stimulus.