LH, progesterone and oestrogens in blood of cows after GnRH- or HCG-application

The synthetic GnRH analog Buserelin (20 μg) was given i.m. to pregnant cows 10, 6, 2 and 1 week before term (group A - D; n=8/group). Two days later HCG (2.400 IU) was injected in all animals. Additionally 8 cows which were pregnant between 28 - 32 weeks served as controls. In other 4 cows oesterone (10 mg i.m. daily) was given for a period of 6 days. Blood samples were calculated at -60, -30, 30, 60, 90, 120, 240 and 360 minutes after GnRH- or HCG-injections from the jugular vein. The concentrations of LH, progesterone, unconjugated and conjugated oestrogens were measured by radioimmunoassay. In the control group maximal LH-values occured 120 to 240 min after GnRH-injection (20.3 ± 4.7 ng/ml). Progesterone values increased to 8.4 ± 1.2 ng/ml at the same time. At later stages of pregnancy the LH-maxima decreased (group A - D: 11.1 ± 5.6; 9.0 ± 7.7; 4.6 ± 1.9 and 2.8 ± 0.6 ng/ml). Progesterone maxima showed a decrease from 8.2 ± 1.2 (controls) to 4.4 ± 1.8 ng/ml (group B). Progesterone values were not different between groups A and B whereas significant differences were found in LH and progesterone values compared to the control group. HCG-injections had similar effects as GnRH on progesterone concentrations, whereas LH-values were not altered. Oestrogen concentrations increased with ongoing pregnancy and showed no alterations by GnRH/HCG-application. The GnRH/HCG-injections did not prolong pregnancy. The injection of oestrone did not decrease the progesterone concentration after GnRH or HCG application, respectively. (author)