| Abstrakt: |
Functional corpora lutea were induced in 28 day old, female rats with 4 iu of pregnant mare's serum, followed 72 h later with cervical stimulation. PGF2α(3 mg/kg) and ergocryptine (2 mg/kg) were administered (sc) 7 days following cervical stimulation. Prolactin (NIH-S11; 2 iu) was administered on the same day 4 h before, and 3 and 15 h after drug treatment. Animals were sacrificed at either 2, 8 or 24 h following treatment with PGF2αor ergocryptine. Serum progesterone was significantly depressed (P<0.05) at 2, 8 and 24 h (12.1 ± 0.6, 14.9 ± 1.4 and 10.5± 0.5 ng/ml, respectively) after PGF2αtreatment from the 0 h concentration of 40.5 ± 12.4 ng/ml. Serum 20α-ol was unchanged at 2 h (11.2 ± 5.6 ng/ml), but was significantly elevated (P<0.01) at 8 (37.8 ± 4.7 ng/ml; P<0.01) and 24 h (52.6 ± 8.5) after PGF2αtreatment. The LH receptor was decreased 16, 30 and 72 percent at each respective time period but the change was not significant 2 h after PGF2αtreatment. Simultaneous treatment of the animals with prolactin blocked the effect of PGF2αon serum progesterone and the LH receptor when animals were sacrificed 24 h after PGF2αtreatment.Ergocryptine caused a significant drop (P<0.05) in serum progesterone 2 h after treatment (30.4 ± 6.2 ng/ml) which became more pronounced at 8 (12.7 ± 6.3 ng/ml) and 24 h (10.4 ± 3.5 ng/ml) from the 0 h control level of 68.5 ± 17.4 ng/ml. Ergocryptine had no effect on gonadotropin binding capacity at 2 or 8 h, but 24 h after treatment the corpus luteum LU receptor was decreased 70 percent (P<0.005). Simultaneous treatment of animals with prolactin produced a complete block of the ergocryptine effect on serum progesterone and the corpus luteum LH receptor. These data were interpreted as evidence for a direct role of prolactin in regulation of the corpus luteum LH receptor in the rat and may be the mechanism of the cooperativity known to exist between these gonadotropins. The early depression of serum progesterone by PGF2αappears not to be due to a loss of LH receptor. Loss of the LH receptor was directly correlated with the first appearance of functional luteolysis (elevated 20α-ol) which indicates this is a possible mechanism to ensure that luteolysis continues once initiated and would explain the continued progression of luteolysis hours after PGF2αtreatment. |
