Serum luteinizing hormone, prolactin, and thyrotropin and their pituitary subunit mrna levels during proestrus in the syrian hamster

mRNA levels for α, luteinizing hormone β (LHβ), and prolactin (Prl) were examined during the hamster estrous cycle, with sampling most frequent (1-hour intervals) on the afternoon of proestrus. These transcripts encode the peptide subunits for the pituitary hormones LH and Prl which are necessary for reproductive function. Serum hormone levels of LH and Prl, analyzed by 24-hour periodic regression, exhibited a 24-hour periodicity on proestrus characterized by a large surge peaking at about 18.00 h. Combining the data for non-proestrous days of the cycle disclosed a rhythm with similar timing for LH and Prl. Thyroid-stimulating hormone (TSH) and TSHβ RNA profiles during hamster proestrus are reported for the first time. Serum TSH exhibited a pronounced peak coincident with that of the other hormones on proestrus. Because of variations at other times on the day of proestrus, however, a 24-hour periodicity was not manifested by regressional analysis. Combined non-proestrous serum TSH data also revealed no consistently timed regressional 24-hour periodicity. During proestrus, pituitary mRNA values for α, LHβ, and Prl simultaneously exhibited a rise from the lowest to the highest of all proestrous values in the 3-5 h prior to the time of the pre-ovulatory peak of circulating hormone concentrations. RNA for TSHβ exhibited an earlier, broader peak on proestrus. Periodic regression indicated a significant 24-hour rhythm for α mRNA in data pooled from non-proestrous days (acrophase 05.00 h) and for TSHβ mRNA on proestrus (acrophase 04.54 h). The necessity to pool the pituitary tissue from animals at particular time points limits the opportunity for statistical analysis of the mRNA levels. However, it is interesting that, on the afternoon of proestrus. the fluctuations of mRNAs for α subunit, LHβ, and prolactin were the widest for that day, were simultaneous, and preceded the hormone peak by 3-5 h; also, that the earlier rise of TSHß mRNA on proestrus was detectable as a 24-hour rhythm. It is thus possible to hypothesize that a fluctuation in respective mRNA related to LH, Prl and TSH may occur in the hours preceding the proestrous surge of these hormones in the circulation, and may thus play a role in the hormonal surge.