Human pituitary chronoendocrinology: repetitive stimulation with LRH/TRH at different times of the day.
To determine whether human pituitary is characterized by a circadian periodicity in response to repetitive injection of hypothalamic hormones, 8 healthy subjects were challenged iv with a triple stimulation with 50 micrograms of LRH and 100 micrograms of TRH in a single bolus at 0, 90 and 180 min, receiving the first pulse of hypothalamic hormones either at 02.00 h (02.00 h test) or at 09.00 h (09.00 h test). In addition, a placebo was injected instead of LRH/TRH to evaluate the spontaneous hormonal changes during the 02.00 h test. The LH, FSH, Prl and TSH basal levels were similar in the two phases studied. The mean LH, FSH and TSH peaks after each injection of LRH/TRH were similar among them. The mean Prl peak responses to the third pulse of LRH/TRH, in both the 02.00 h and the 09.00 h tests, were lower (P less than 0.05) than those after the first pulse of LRH/TRH. Placebo did not significantly change circulating LH, FSH, Prl or TSH during nocturnal sampling. The mean LH, FSH and Prl levels after LRH/TRH during the 02.00 h test were similar to those during the 09.00 h test. The mean TSH levels 15 min after the second and third pulses of LRH/TRH during the 02.00 h test were higher (P less than 0.05) than those of the 09.00 h test. Thus, thyrotropes responsiveness to pulsatile stimulation with LRH/TRH is greater during the night than in the morning, while LH, FSH and Prl responses remain constant at the two phases studied.
D000328:Adult; D002940:Circadian Rhythm / Q000187:drug effects*; D005640:Follicle Stimulating Hormone / Q000097:blood; D007987:Gonadotropin-Releasing Hormone / Q000494:pharmacology*; D006801:Humans; D007986:Luteinizing Hormone / Q000097:blood; D008297:Male; D010902:Pituitary Gland / Q000187:drug effects*; D011388:Prolactin / Q000097:blood; D013972:Thyrotropin / Q000097:blood; D013973:Thyrotropin-Releasing Hormone / Q000494:pharmacology*
D007987:Gonadotropin-Releasing Hormone; D013973:Thyrotropin-Releasing Hormone; D011388:Prolactin; D007986:Luteinizing Hormone; D005640:Follicle Stimulating Hormone; D013972:Thyrotropin