Levels of Luteinizing Hormone,Estradiol and Progesterone in Serum During the Estrous Cycle and Pregnancy in the Beagle Bitch 1

Summary

Levels of luteinizing hormone (LH), estradiol-17/3 and progesterone were determined by specific radioimmunoassays in sera obtained from Beagle bitches during proestrus, estrus and diestrus. Concentrations of LH (expressed as NIH-LH-S1 equivalents) were: 2.8 ± 0.1 ng/ml in proestrus, 35.5 ± 10.0 ng/ml during early estrus and 2.2 ±0.1 ng/ml in early diestrus. Peak levels of estradiol-17/3 (68.9 ±11.0 ng/ml) were detected 24 hr prior to the LH peak, declined rapidly and reached basal levels (17.8 ± 6.3 ng/ml) by five days following the LH peak. Levels of progesterone were 1.7 ± 0.3 ng/ml during proestrus, 3.5 ± 0.3 ng/ml during early estrus and 23.3 ±2.8 ng/ml on day 5 after the LH peak. Progesterone levels remained elevated through day 28 of diestrus and pregnancy. A significant decrease (P < 0.05) in levels of progesterone occurred between day 28 of pregnancy and one day prior to whelping (3.3 ± 1.2 ng/ml), with a further decrease on the day of whelping (1.1 ± 0.2 ng/ml). Levels of estradiol-17β and LH did not change significantly (P > 0.05) during diestrus or pregnancy.