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A Given

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PubMed1991

Preincubation of human granulosa cells with gonadotrophin prevents the cloprostenol-induced inhibition of progesterone production.

Human granulosa cells, from women undergoing ovum collection for in-vitro fertilization (IVF), will luteinize in vitro and provide a model for investigating the antigonadotrophic action of a prostaglandin F2 alpha (PGF2 alpha) analogue, cloprostenol, on granulosa-derived luteal cells. The granulosa cells were cultured in a defined medium and exposed to treatments during a preincubation period of 0 to 3 days and a final incubation with low density lipoprotein (LDL) from days 3 to 4. In the absence of human chorionic gonadotrophin (HCG), progesterone production was low, whereas exposure to HCG in the final incubation resulted in a 10-fold increase in progesterone concentrations. The inclusion of cloprostenol with HCG in the final incubation significantly (P less than 0.05) inhibited HCG-stimulated progesterone production. Exposure to HCG during the preincubation prevented the antigonadotrophic action of cloprostenol in the final incubation. The antigonadotrophic action of cloprostenol was retained when the granulosa cells were exposed to cloprostenol during the preincubation. Omission of LDL from the final incubation lowered the production of progesterone but the pattern of responses to HCG and cloprostenol were similar. Prevention of the antigonadotrophic action of cloprostenol after exposure to HCG may be a mechanism through which chorionic gonadotrophin can prevent regression of the corpus luteum in early pregnancy. Cloprostenol does not appear to inhibit LDL-stimulated steroidogenesis in human granulosa cells.

Cells, Cultured↗

PubMed1991

Comparison of the luteolytic action of gonadotrophin-releasing hormone antagonist and cloprostenol, and the ability of human chorionic gonadotrophin and melatonin to override their luteolytic effects in the marmoset monkey.

The effects of the luteolytic and luteotrophic agents cloprostenol, human chorionic gonadotrophin (hCG) and melatonin on the corpus luteum have been investigated in marmoset monkeys treated with an LHRH antagonist to reduce endogenous LH secretion. This has allowed the effects of these agents to be investigated in the absence of the principal endogenous luteotrophin. Administration of the LHRH antagonist ([N-acetyl-D beta Nal1-D-pCl-Phe2-D-Phe3-D-Arg6-Phe7-Arg8-D-Ala10]NH2-LHRH) or cloprostenol between days 7 and 11 after ovulation (preimplantation) resulted in luteolysis. A significant (P less than 0.05) decrease in progesterone concentrations had occurred by 4 h after administration of the LHRH antagonist and was indeed preceded by a fall in LH concentrations. Coadministration of hCG with the LHRH antagonist prevented the fall in progesterone. In contrast, administration of cloprostenol resulted in an immediate fall in progesterone concentrations, to less than half the initial level within 1 h, and co-administration with hCG did not prevent the fall. Administration of hCG stimulated progesterone production when given 8 h after the LHRH antagonist but not after 24 h. Cloprostenol prevented the stimulation by hCG. Co-administration of melatonin with the LHRH antagonist did not prevent the decrease in progesterone concentrations. Melatonin was also not effective in preventing the fall in progesterone induced by cloprostenol. However, co-administration of melatonin and cloprostenol between days 17 and 21 after ovulation (post-implantation) significantly (P less than 0.05) delayed the fall in progesterone seen with cloprostenol alone. These results suggest that while the LHRH antagonist and cloprostenol have different sites of action their effect is similar at the corpus luteum, that is in depriving the corpus luteum of luteotrophic support. The results also suggest that melatonin may be able to influence the luteolytic action of cloprostenol but that its effect varies with the stage of the cycle. The physiological role for such an action, if any, remains unknown.

Animals↗

PubMed1991

Increased concentrations of immunoreactive inhibin during conception cycles in the marmoset monkey: suppression with an LHRH antagonist and cloprostenol.

Peripheral concentrations of immunoreactive (ir) inhibin have been measured during the ovarian cycle and early pregnancy in the marmoset monkey. Blood samples were taken (three per week) during conception (n = 6) and non-conception (n = 5) cycles. Ir-inhibin was measured by radioimmunoassay using an antiserum raised against a synthetic peptide fragment of the alpha subunit of human inhibin. Monomeric bovine alpha subunit and 32 kDa bovine inhibin were used as tracer and standard respectively. In all animals low concentrations of ir-inhibin were recorded during the follicular phase (40-60 micrograms/l) of the cycle. After ovulation, ir-inhibin concentrations increased but the peak concentrations attained differed between conception and non-conception cycles. In non-pregnant animals ir-inhibin concentrations reached a maximum of 242 +/- 16 micrograms/l on days 12/13 after ovulation. In pregnant animals ir-inhibin concentrations were significantly (P less than 0.05) higher (1.8-fold) than in non-pregnant animals on days 8/9 after ovulation, and reached a maximum value of 636 +/- 141 micrograms/l on days 20/21 after ovulation. Administration of an LHRH antagonist during the luteal phase on days 6-8 after ovulation resulted in a significant (P less than 0.05) decrease in progesterone and ir-inhibin concentrations within 4 and 8 h respectively. This was prevented by co-administration with human chorionic gonadotrophin. Administration of cloprostenol to pregnant animals between days 17 and 20 after ovulation halved the initial concentrations of both inhibin and progesterone within 1.5 h.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1989

Changing responsiveness of luteal cells of the marmoset monkey (Callithrix jacchus) to luteotrophic and luteolytic agents during normal and conception cycles.

Dispersed marmoset luteal cells were incubated for 2 h and progesterone production measured after exposure to hCG, cloprostenol, dibutyryl cAMP, PGF-2 alpha, PGF-2, adrenaline or melatonin. The cells were studied on Days 6, 14 and 20 after ovulation in conception and non-conception cycles. Luteal cells from Day 14 non-pregnant marmosets were compared with human luteal cells taken in the mid-luteal phase. All the treatments stimulated progesterone production including cloprostenol, which is luteolytic when administered to the marmoset in vivo, but the degree of response varied with the stage of the cycle or pregnancy and between marmoset and human luteal cells. In the marmoset, overall analysis of the effect of the treatments showed that, on Day 6 after ovulation, there was no significant effect of any of the treatments in cells from pregnant or non-pregnant animals. In contrast, luteal cells from non-pregnant animals on Day 14 showed a significant response to the treatments (F (8,41) = 2.79, P less than 0.0145) whereas cells from pregnant Day-14 animals were responsive; in cells from pregnant animals, the control production of progesterone was high and already equivalent to the levels stimulated by the treatments. By Day 20, cells from pregnant animals produced lower control concentrations of progesterone than did those on Day 14 and there was a significant overall effect of the treatments (F (8,33) = 3.78, P less than 0.003). These results show that the marmoset CL gains responsiveness to treatment between Days 6 and 14 after ovulation in the non-pregnant cycle. In pregnancy, on Day 14, 2 days after attachment of the embryo, the high control concentrations of progesterone and absence of response to treatment suggest that an embryo message may have affected the CL, providing an endogenous stimulus.

Animals↗

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