Blood plasma levels of progesterone and oestradiol in the dog during the oestrous cycle and pregnancy.

Plasma oestradiol and progesterone levels were studied in German Shepherd and Greyhound bitches during the normal oestrous cycle, pregnancy and at parturition. The mean oestradiol level increased from approximately 7 to 13 pg/ml during the fifth week before onset of oestrus. Oestradiol stayed at this level until pro oestrus which was characterized by a steady increase to a mean peak level of about 30 pg/ml 5-6 days before oestrus. At the start of oestrus the level was approximately 12 pg/ml. A level between 10-15 pg/ml was kept during the following 10 weeks whether or not the bitch was pregnant and no change occurred at parturition. The mean progesterone level was found to be very low, around or under 1 ng/ml, until 1-4 days after the oestradiol peak after which the level gradually increased to around 10 ng/ml at the start of oestrus. During oestrus and metoestrus or pregnancy the pattern was inconsistent. In some bitches the level gradually increased during 3-4 weeks and reached a peak value of 30-50 ng/ml. The level then gradually decreased during 5-6 weeks. During the first 5 weeks of the same period progesterone in other bitches fluctuated between similar maximum levels and extremely low levels. After the fifth week the pattern was the same for all bitches. In the pregnant bitches there was a significant drop of the progesterone level at parturition. The data suggest that the dog is not an ideal test animal for steroids synthetized for use in man.