Two peaks of aromatase activities were detected in bovine cotyledons, 2.76 +/- 0.96 pmol min-1 mg-1 protein at month five of gestation and 3.62 +/- 0.78 pmol min-1 mg-1 protein immediately after parturition, but aromatase activity in caruncles was very low throughout gestation. Oestrone concentrations in the cotyledons and caruncles were 0.93 +/- 0.50 and 1.51 +/- 0.69 ng mg-1 protein at month five of gestation, but 4.31 +/- 1.66 and 3.36 +/- 0.98 ng mg-1 protein immediately after parturition, indicating a biphasic pattern. Our findings suggest that oestrogen synthesis in the bovine placenta increased to a maximum at least twice during the period from gestation to parturition; at month five of gestation and at parturition the changes in aromatase activity may only be partially explained by changes in oestrogen production.

3 beta-Hydroxysteroid dehydrogenase (3 beta-HSD) activity in bovine cotyledons was much higher than in caruncles throughout the gestation period. The activity of this enzyme in cotyledons increased greatly to 150.6 +/- 5.8 pmol min-1 mg-1 protein during the seventh month of gestation, reached a peak of 221.0 +/- 34.9 pmol min-1 mg-1 protein during the eighth month, and decreased at parturition. Progesterone and 20 alpha-hydroxyprogesterone concentrations in cotyledons also increased sharply to 2.69 +/- 0.30 and 2.15 +/- 0.42 ng mg-1 protein, respectively, during the seventh month of gestation, reaching peaks of 2.86 +/- 0.47 and 2.51 +/- 0.36 ng mg-1 protein, respectively, during the eighth month and decreasing at parturition, in a manner similar to the activity of 3 beta-hydroxysteroid dehydrogenase. The fluctuation of 17 alpha-hydroxyprogesterone concentration in cotyledons was different from that of progesterone and 20 alpha-hydroxyprogesterone. These findings indicate that the activity of 3 beta-hydroxysteroid dehydrogenase in the placenta is enhanced during the third trimester, and progesterone synthesized in the cotyledons is converted concurrently to 20 alpha-hydroxyprogesterone before progesterone is transferred to the fetal blood.

ABSTRACT. In the present study, the effect of 4-day fasting on steroid hormone metabolism in the liver and secretion of LH was examined in cows. Six non pregnant, dry Holstein cows were used. The estrous cycle was synchronized in all cows using CIDR-Ovsynch. Cows were allocated to a control group (n=3) and a fasting group (n=3). In the fasting group, cows were fasted for four days from day -4 to day -1 (day 0=day of 2nd GnRH injection) but otherwise were fed ad libitum. The experiment was repeated in a crossover design after an interval of about one month. The peripheral progesterone (P 4 ) concentration in the fasting group was significantly higher than in the control group on day -1 and 0. The peripheral estradiol-17 concentration in the fasting group was also significantly higher than in the control group on day -1 and 0. The portal vein P 4 concentration in the fasting group was significantly higher than in the control group. On day 0, there was no difference in LH secretion between groups. The mean percentages of lipid droplets in liver cells in the fasting group were significantly higher than in the control group on day 0. These results suggest that short-term fasting leads to reduced hepatic steroid hormone metabolism by accumulation of fat in the liver, which causes high peripheral steroid hormone concentrations. Gonadal steroid hormones, such as progesterone (P 4 ) and estradiol-17 (E 2 ), are metabolized primarily in the liver and partially in the kidney and intestine before being excreted into the urine and feces [4]. Peripheral concentrations of these hormones are therefore largely affected by their metabolic clearance rates in the liver, which increase with liver blood flow. In fact, the amount of P 4 flowing into the liver has been directly associated with the plasma P 4 level [12]. Feed intake is another factor that affects steroid metabolism because it is directly correlated with the portal blood flow rate in sheep [12]. Lactating cows, which are maintained with high dry matter intake, have increased hepatic blood flow resulting in 2.3 times higher metabolic clearance rates of E 2 and P 4 compared to non lactating cows [16]. This increased metabolism leads to decreased levels of peripheral E 2 and P 4 , which are associated with decreased reproductive efficiency, such as decreased conception rate, increased pregnancy loss, increased multiple ovulation rate and decreased estrous behavior [16]. Thus, feed intake can affect gonadal steroid hormone secretion by alterations in the liver blood flow. Feed intake is also considered to affect LH secretion from the pituitary gland via the feedback action of steroid hormones.Periparturient dairy cows are in a state of negative energy balance, which results in decreased liver function due to fatty liver. Fatty liver, too, is associated with poorer reproductive performance such as decreased conception rate and longer calving intervals [2]. In the present study, the effect of short-term fasting on steroid hormone metabolism in the liver was investigated by c...

In the present report, the incidence and prognosis of ovarian diseases were evaluated in correlation to the grades of the fatty livers (FL). 233 animals were diagnosed with a FL, based on fat deposition of >10% into the hepatic parenchyma obtained from liver biopsy, and were eventually cured of the FL. These 233 animals were classified into mild group (n=99: hepatic fat deposition rates ranging from 10 to <30%), moderate group (n=56: hepatic fat deposition rates ranging from 30 to <60%) and severe group (n=78: hepatic fat deposition rates of >60%). The incidence of ovarian diseases and the culling rate were, respectively, 40.0% and 10.0% in mild group, 58.3% and 37.5% in moderate group, and 84.9% and 69.7% in severe group. The incidence of ovarian diseases and the culling rates in severe group were significantly (P<0.05) higher than those in mild and moderate groups. It was, therefore, concluded that the elevated incidence of ovarian disease and culling rates tend to be dependent on the higher severity scores of the fat deposition rates in dairy cows with FL and that cases with severe FL, with a fat deposition rate of 60% or higher, were greatly associated with death and culling.

Uridine 5’-diphospho-glucuronosyltransferase (UGT) liver activity was measured using estradiol-17β as a substrate in dairy cows with follicular cysts. The activity was significantly lower than that in dairy cows with normal estrous cycles (P<0.01). Liver disorders, such as fatty liver and hepatitis, were observed in half cows with follicular cysts, and liver UGT activity was lower than that in cows with normal estrus cycles. In addition, the liver UGT activity was significantly lower in dairy cows with follicular cysts without liver disorders than in dairy cows with normal estrous cycles. Therefore, the cows were divided into those with low, middle and high liver UGT activities, and liver disorder complication rates were investigated. The complication rate was significantly higher in the low- (78.1%) than in the middle- (22.2%) and high-level (8.3%) groups, suggesting that liver disorders are closely associated with the development of follicular cysts in dairy cows and that steroid hormone metabolism is delayed because of reduced liver UGT activity, resulting in follicular cyst formation. We conclude that reduced estradiol-17β glucuronidation in the liver and liver disorders are associated with follicular cyst occurrence in dairy cows.