Prolactin is associated with the development of photorefractoriness in intact, castrated, and testosterone-implanted starlings.
Using radioimmunoassays, prolactin, luteinizing hormone (LH), and follicle-stimulating hormone (FSH) were measured in the plasma of intact, castrated, and testosterone-implanted male starlings. Two groups of birds (intact and castrated males) were transferred when photosensitive from short (8-hr) to long (16-hr) day lengths; in both cases plasma prolactin levels increased steadily reaching a peak after 5 weeks of photostimulation, at the time of the onset of photorefractoriness . Three groups ( intacts , castrates, and castrates implanted with Silastic capsules containing testosterone) were exposed to day lengths increasing by 30 min per week from 8 to 16 hr. Again, prolactin levels increased in a similar fashion in all three groups at the time of refractoriness, which occurred when the day length reached 15-16 hr. Thus the timing of photorefractoriness and the associated rise in prolactin secretion which occur in response to photostimulation do not depend upon the presence of the gonads and are not affected when testosterone is maintained at a constant high level. Nor is the increase in prolactin altered when the cycle of gonadotrophin secretion which normally precedes it is completely suppressed by the implantation of a testosterone capsule. It would seem that prolactin secretion in the starling is stimulated by transfer from short to long day lengths, but not as a consequence of high gonadotrophin or androgen secretion rates.
D000818:Animals; D001717:Birds / Q000502:physiology*; D002369:Castration; D005640:Follicle Stimulating Hormone / Q000097:blood; D008027:Light; D007986:Luteinizing Hormone / Q000097:blood; D008297:Male; D010507:Periodicity; D011388:Prolactin / Q000097:blood*; D012098:Reproduction / Q000187:drug effects / Q000528:radiation effects; D013739:Testosterone / Q000494:pharmacology*
D013739:Testosterone; D011388:Prolactin; D007986:Luteinizing Hormone; D005640:Follicle Stimulating Hormone