title: Does prolactin modify testosterone feedback in the hamster? Suppression of plasma prolactin inhibits photoperiod-induced decreases in testosterone feedback sensitivity.
abstract: The hormonal changes during the photoperiodically driven annual reproductive cycle of the male golden hamster can be explained partially by a change in the sensitivity of the hypothalamo-pituitary axis to negative feedback by testosterone (T). The present studies test the hypothesis that the increases in plasma levels of LH and FSH that follow photo-stimulation are due to decreasing feedback sensitivity and examine if this change in sensitivity is dependent upon increasing PRL levels. Adult males were exposed to a lighting schedule of 5 h of light, 19 h of darkness (5:19) for 12 weeks to induce gonadal regression. The animals were castrated; treated with an inhibitor of PRL release, bromocriptine (CB-154), or oil; and received a Silastic capsule that was empty or filled with T. Subsequently, the animals were transferred to 14:10 and killed 9 or 31 days later. There were no significant changes in FSH and LH in animals receiving oil injections and empty implants between days 9 and 31, suggesting no steroid-independent changes in gonadotropin secretion during this time period. However, 4-mm T implants were more effective in suppressing LH and FSH levels on day 9 than on day 31. This suggests that there is a gradual decrease in feedback sensitivity to T following photostimulation. T was more effective in inhibiting LH and FSH levels in CB-154-treated than in oil-treated animals on both day 9 and day 31. Thus, increases in PRL release are instrumental in causing decreases in feedback sensitivity following photostimulation.
mesh_terms: D000818:Animals; D001971:Bromocriptine / Q000494:pharmacology; D002369:Castration; D006224:Cricetinae / Q000502:physiology*; D005246:Feedback; D005640:Follicle Stimulating Hormone / Q000097:blood; D008027:Light; D007986:Luteinizing Hormone / Q000097:blood; D008297:Male; D008647:Mesocricetus; D010507:Periodicity; D011388:Prolactin / Q000097:blood / Q000502:physiology*; D013739:Testosterone / Q000494:pharmacology / Q000502:physiology*; D013997:Time Factors
chemical_list: D001971:Bromocriptine; D013739:Testosterone; D011388:Prolactin; D007986:Luteinizing Hormone; D005640:Follicle Stimulating Hormone