Serum luteinizing hormone, prolactin, and thyrotropin and their pituitary subunit mRNA levels during proestrus in the Syrian hamster.

ABSTRACT

mRNA levels for alpha, luteinizing hormone beta (LH beta), 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 TSH beta 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 alpha, LH beta, 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 TSH beta exhibited an earlier, broader peak on proestrus. Periodic regression indicated a significant 24-hour rhythm for alpha mRNA in data pooled from non-proestrous days (acrophase 05.00 h) and for TSH beta mRNA on proestrus (acrophase 04.54 h).(ABSTRACT TRUNCATED AT 250 WORDS)