BLOOD LEVELS OF PROGESTERONE AND 15-KETO-13,14-DIHYDRO-PROSTAGLANDIN F2 DURING THE NORMAL OESTROUS CYCLE AND EARLY PREGNANCY IN HEIFERS

Abstract

Peripheral plasma levels of progesterone and 15-keto-13,14-dihydroprostaglandin [PG] F2.alpha. were measured during the normal estrous cycle in 3 heifers. Before the experiment the animals received an infusion each of different amounts of PGF2.alpha. to estimate the conversion of this compound into the main plasma metabolite, 15-keto 13,14-dihydro-PGF2.alpha.. The experimental period was initiated by heat synchronization with 25 mg PGF2.alpha. given i.m. Daily blood samples were collected from the jugular vein until day 14 of the estrous cycle and subsequently every 3rd h until heat occurred. During this heat the 3 heifers were mated, and blood samples were collected in the same way during the following cycle and over the next expected heat. Pregnancy occurred in 1 of the animals. High levels of 15-keto-13,14-dihydro-PGF2.alpha. were recorded as pulses during the last days of the normal estrous cycle. These pulses coincided with decrease in progesterone levels. In the pregnant hiefer neither decrease in progesterone nor increase in the PG metabolite level was seen.