Biology of Reproduction, Vol 25, 699-707, Copyright © 1981 by Society for the Study of Reproduction

Characteristics of Luteal Function in the Superovulated, Pseudopregnant Hamster

¹ Department of Biology, University of Saskatchewan, Saskatoon, Saskatchewan, Canada S7N OWO
² Agriculture Canada Research Station, Brandon, Manitoba, Canada R7A 5Z7

Serum concentrations of progesterone, luteinizing hormone (LH), and prolaction (PRL), and luteal binding of ¹²⁵I-human chorionic gonadotropin (hCG) and ¹²⁵I-PRL were measured in superovulated hamsters rendered pseudopregnant (PSP) by mating with vasectomized males on Day 0. Animals were killed at 8 h intervals (4-6 per interval) beginning at 1600 h on Day 1 through 0800 h of Day 8, and ovaries and trunk blood collected. Mean serum progesterone was maximal at 0800 h on Day 3 of PSP and, for the most part, remained elevated through PSP until the decline associated with luteolysis occurred between 2400 h of Day 7 and 0800 h of Day 8. Progesterone was positively correlated with the number of corpora lutea (CL) and CL weight (P<0.01). Serum LH fluctuated about an overall mean of 4.6 ± 0.4 ng/ml throughout PSP, and was not correlated with any of the other parameters tested. Serum PRL displayed an initial peak at 0800 h of Day 2, after which levels declined through Day 3. Beginning on Day 4 of PSP, PRL was elevated in 2400 h samples for the next 4 days, suggesting a single nocturnal secretory peak of PRL in the hamster. Serum PRL was correlated with binding of ¹²⁵I-hCG to CL tissue suggesting that PRL may induce LH receptor. Binding of ¹²⁵I-hCG to luteal tissue was initially low through Day 3, but became elevated by 1600 h of Day 4 and remained thus until luteolysis ensued between 2400 h of Day 7 and 0800 h of Day 8. The binding of ¹²⁵I-PRL to luteal membranes was initially high, and fell on Days 2 and 3. Subsequent levels remained low throughout PSP with no apparent change during luteolysis. ¹²⁵I-PRL binding was not correlated with any other parameter studied, and did not decline with luteolysis.

Note:
ACKNOWLEDGMENTS We thank Shirley Shepstone for technical assistance, Bryon Buick for animal care; the NIH, NIAMDD for the provision of PRL, hCG, and rat kits for measurement of hamster LH and PRL; and Dr. H. Dobson for progesterone antiserum. This study was supported by grant #MA 6359 from the Medical Research Council of Canada to B. D. Murphy.

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