To determine whether membrane-related events may be involved in
attenuated luteal function after gonadotropin-releasing hormone (GnRH)
administration, corpora lutea (CL) were removed from 10 beef heifers on day 7
of the estrous cycle after i.v. injection of GnRH or saline on day 2 of the cycle.
Luteal slices were incubated with saline (control), luteinizing hormone (LH) or
8-bromo-cAMP for 2 h. In vivo administration of GnRH reduced LH and cAMP-stimulated
progesterone production by tissue (p<0.01), but basal progesterone
production was not affected (p>0.05). Luteal adenylyl cyclase activity did not
differ between saline and GnRH-treated animals (p>0.05). Results of this
experiment suggested that GnRH-induced alteration of bovine luteal function
may be due to an effect distal to the point of cAMP accumulation.
To explore further the effect of GnRH on luteal cell function, 10 heifers
were injected with saline or GnRH and CL removed as above. Dissociated
(mixed) and small luteal cells (SC) were cultured overnight, then incubated for 2
h with medium alone (control), LH or cAMP. In vitro treatment with LH and
cAMP increased progesterone in the medium relative to controls (p<0.01),
however, there was no effect of GnRH injection on progesterone production
(p>0.05) nor in the percentage of large cells (LC) present in the mixed cell
cultures (p=0.95). It has been previously found that the ratio of LC to SC
increases in GnRH-treated animals. Many LC can be ruptured during
dissociation of the CL, and it is possible that this procedure altered the number
of LC, such that any differences that may have existed between the saline and
GnRH-exposed CL were minimized. These data suggest that differences in the
LC to SC ratio may indeed account for attenuated luteal function after exposure
to GnRH.
To examine if early administration of GnRH alters response of the CL to
prostaglandin (PG) Fav beef heifers were injected with saline or GnRH on day 2
of the cycle (n=4/group), then injected with PGF[subscript 2��], on day 8 and the CL
removed 60 min later. Blood samples were collected for oxytocin (OT) analysis
at frequent intervals after PGF[subscript 2��], injection and for progesterone at 0 and 60 min.
Induction of the early response gene c-jun or release of OT by PGF[subscript 2��], was not
altered by GnRH injection (p>0.05). Injection of PGF[subscript 2��], decreased serum
progesterone by 60 min post-injection (p<0.05), but was also unaffected by
GnRH (p>0.05). These data support the hypotheses that c-jun expression and OT
release are involved in PGF[subscript 2��]-induced luteolysis, but early administration of
GnRH did not affect these processes. / Graduation date: 1996
| Identifer | oai:union.ndltd.org:ORGSU/oai:ir.library.oregonstate.edu:1957/34487 |
| Date | 28 August 1995 |
| Creators | Bertrand, Jennifer Elaine |
| Contributors | Stormshak, Fredrick |
| Source Sets | Oregon State University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
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