Circulating Progesterone Levels in the Golden Hamster During the Estrous Cycle, Pregnancy, and Lactation1

Individual blood samples were collected from the vena cava of cycling, pregnant, and lactating hamsters under conditions of known ovarian Δ5-3β-hydroxysteroid dehydrogenase (3βHSD) activity. Progesterone was purified by two thin-layer chromatographic steps and measured by gas liquid chromatography. Progesterone levels (µg/100 ml blood) were corrected for procedural losses. During the estrous cycle, the progesterone concentration rose between early and late proestrus (0.23 to 1.10), peaked at preovulatory estrus (1.89), and appeared to increase again on the second postovulatory day (1.08). During pregnancy, progesterone levels increased between Days 1 and 2 postcoitum, rose gradually from Day 3 (0.75) to Day 14 (2.55), and dropped sharply between Day 15 (1.67) and Day 16 (0.20) before parturition. Progesterone levels were low during lactation. These results establish that circulating progesterone is elevated in the female hamster during behavioral estrus, implantation, and pregnancy when progesterone is known to be required. Follicular 3βHSD activity at behavioral estrus and luteal 3βHSD activity during pregnancy correlate closely with the observed changes in peripheral progesterone. The shape of the progesterone curve during the hamster estrous cycle and pregnancy is similar to that of the laboratory rat. In contrast to the rat, the hamster has a much lower progesterone level during pregnancy and a very low level during lactation.