Biomedical subjects

W Hansel

Publications and source records attributed to W Hansel.

At least 55 records · Page 3Linked to original sources

PubMed1990

Phorbol ester receptors in bovine luteal cells: relationship to protein kinase C.

We investigated the binding kinetics of the tumor-promoting phorbol ester, phorbol-12,13-dibutyrate (PBt2) to dispersed total bovine luteal cells, purified small luteal cells, and purified luteal protein kinase C (PKC). Saturation analysis and competitive displacement techniques were used. Binding of [3H]PBt2 to total luteal cell preparations resulted in two distinct affinities. The high affinity component was characterized by a Kd of 4.5 +/- 1.5 nM. Analysis of [3H]PBt2 binding to total cells using competitive displacement demonstrated that the low affinity binding was specific and displaceable but dependent on concentrations of [3H]PBt2 far above the Kd for the high affinity binding. In contrast to the total cell preparations, only high affinity binding was observed in intact purified small luteal cells (Kd = 0.96 +/- 0.04 nM). Partial purification of luteal cytosolic PKC by DEAE-Sephadex chromatography resulted in co-elution of PKC enzyme activity and the [3H]PBt2 binding activity. Under conditions of saturating calcium (0.1 mM) and phosphatidylserine (PS) (100 micrograms/tube) concentrations, binding to the partially purified PKC preparation was found to be of a single high affinity and exhibited a Kd (1.3 +/- 0.2 nM) similar to the high affinity binding observed in intact cells. These results suggest that the primary phorbol ester receptor in luteal cells is PKC. However, a low affinity, high capacity [3H]PBt2 binding site also exists within the corpus luteum, either in the large cells or in the accessory cell fraction which consists mainly of endothelial cells.

Animals↗

PubMed1990

Arachidonic acid and its metabolites increase cytosolic free calcium in bovine luteal cells.

We studied the effects of arachidonic acid and its metabolites on intracellular free calcium concentrations ([Ca2+]i) in highly purified bovine luteal cell preparations. Corpora lutea were collected from Holstein heifers between days 10 and 12 of the estrous cycle. The cells were dispersed and small and large cells were separated by unit gravity sedimentation and flow cytometry. The [Ca2+]i was determined by spectrofluorometry in luteal cells loaded with the fluorescent Ca2+ probe, Fura-2. Arachidonic acid elicited a dose-dependent increase in [Ca2+]i in both small and large luteal cells, having an effect at concentrations as low as 5 microM; and was maximally effective at 50 microM. Several other fatty acids failed to exert a similar response. Addition of nordihydroguaiaretic acid (NDGA) or indomethacin failed to suppress the effects of arachidonic acid. In fact, the presence of both inhibitors resulted in increases of [Ca2+]i, with NDGA exerting a greater stimulation of [Ca2+]i than indomethacin. Prostaglandin F2 alpha (PGF2 alpha) as well as prostaglandin E2 (PGE2) increased [Ca2+]i in the small luteal cells. These results support the idea that arachidonic acid exerts a direct action in mobilizing [Ca2+]i, in the luteal cells. Furthermore, they demonstrate that the cyclooxygenase (PGF2 alpha and PGE2) and lipoxygenase products of arachidonic acid metabolism also play a role in increasing [Ca2+]i in bovine luteal cells. Since the bovine corpus luteum contains large quantities of arachidonic acid, these findings suggest that this compound may regulate calcium-dependent functions of the corpus luteum, including steroid and peptide hormone production and secretion.

Animals↗

PubMed1990

Oxytocin-specific RNA, oxytocin and progesterone concentrations in corpora lutea of heifers treated with oxytocin.

Sixteen virgin Holstein heifers were used to study the role of oxytocin in luteal function. Oxytocin (100 i.u.) was administered on Days 2-5 (Exp. 1) or Days 2-6 (Exp. 2), and the corpora lutea were collected and weighed on Day 6 or Day 8, respectively. Plasma progesterone values and tissue concentrations of progesterone and oxytocin were determined by radioimmunoassay. In addition, the tissue level of the oxytocin-specific transcript was measured by dot-blot hybridization. Expression of the oxytocin-specific transcript was not affected by oxytocin treatment in either experiment. In contrast, plasma progesterone values and tissue progesterone and oxytocin concentrations were all decreased after 5 days of oxytocin treatment (Exp. 2), but not after 4 days (Exp. 1). Since oxytocin concentrations were reduced while the level of its transcript remained unaffected, oxytocin injections might be influencing either peptide processing or release.

Animals↗

PubMed1989

Second messenger systems and progesterone secretion in the small cells of the bovine corpus luteum: effects of gonadotropins and prostaglandin F2a.

The present studies were conducted to determine the effects of gonadotropins (LH and hCG) and prostaglandin F2a (PGF2a) on the production of "second messengers" and progesterone synthesis in purified preparations of bovine small luteal cells. Corpora lutea were removed from heifers during the luteal phase of the normal estrous cycle. Small luteal cells were isolated by unit-gravity sedimentation and were 95-99% pure. LH provoked rapid and sustained increases in the levels of [3H]inositol mono-, bis-, and trisphosphates (IP, IP2, IP3, respectively), cAMP and progesterone in small luteal cells. LiCl (10 mM) enhanced inositol phosphate accumulation in response to LH but had no effect on LH-stimulated cAMP or progesterone accumulation. Time course studies revealed that LH-induced increases in IP3 and cAMP occurred simultaneously and preceded the increases in progesterone secretion. Similar dose-response relationships were observed for inositol phosphate and cAMP accumulation with maximal increases observed with 1-10 micrograms/ml of LH. Progesterone accumulation was maximal at 1-10 ng/ml of LH. LH (1 microgram/ml) and hCG (20 IU/ml) provoked similar increases in inositol phosphate, cAMP and progesterone accumulation in small luteal cells. 8-Bromo-cAMP (2.5 mM) and forskolin (1 microM) increased progesterone synthesis but did not increase inositol phosphate accumulation in 30 min incubations. PGF2a (1 microM) was more effective than LH (1 microgram/ml) at stimulating increases in inositol phosphate accumulation (4.4-fold vs 2.2-fold increase for PGF2a and LH, respectively). The combined effects of LH and PGF2a on accumulation of inositol phosphates were slightly greater than the effects of PGF2a alone. In 30 min incubations, PGF2a had no effect on cAMP accumulation and provoked small increases in progesterone secretion. Additionally, PGF2a treatment had no significant effect on LH-induced cAMP or progesterone accumulation in 30 min incubations of small luteal cells. These findings provide the first evidence that gonadotropins stimulate the cAMP and IP3-diacylglycerol transmembrane signalling systems in bovine small luteal cells. PGF2a stimulated phospholipase C activity in small cells but did not reduce LH-stimulated cAMP or progesterone accumulation. These results also demonstrate that induction of functional luteolysis in vitro requires more than the activation of the phospholipase C-IP3/calcium and -diacylglycerol/protein kinase C transmembrane signalling system.

Animals↗

PubMed1989

The effects of platelet-activating factor and platelet-derived compounds on bovine luteal cell progesterone production.

This study was conducted to characterize bovine platelets with respect to serotonin (5-HT) concentration and platelet-activating factor (PAF)-activation and to examine the in vitro effects of PAF and platelet-derived compounds on bovine luteal progesterone (P4) production. The concentration of 5-HT in platelets, as determined by high-performance liquid chromatography, was 538.8 +/- 40.83 ng/1 x 10(8) platelets. Based on a circulating platelet concentration range of 2.3 x 10(8) 5.8 x 10(8) platelets/ml, the circulating concentration of 5-HT would be approximately 1239-3125 ng/ml of blood. Bovine platelets were found to aggregate in response to PAF (1-40 ng/0.5 ml), with maximal aggregation occurring at 20-40 ng/0.5 ml. Coincubation of luteal cells with platelets (1 x 10(7)-4 x 10(8] enhanced luteal P4 production (p less than 0.05). Addition of the 5-HT receptor antagonist mianserin blocked the platelet-induced increases in P4 (p less than 0.05). Preincubation of platelets with indomethacin did not alter the production of P4 (p greater than 0.05), nor did the addition of propranolol (p greater than 0.05). Platelet-derived growth factor at 8 and 16 ng/ml enhanced basal P4 production (p less than 0.05) but had no effect on the responsiveness of luteal cells to luteinizing hormone (LH) (p greater than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1989

Differential effects of luteinizing hormone on intracellular free Ca2+ in small and large bovine luteal cells.

The effect of LH on the intracellular free Ca2+ concentration ([Ca2+]i) was investigated in highly purified small and large bovine luteal cell populations. Luteal cells were obtained from midcycle corpora lutea dispersed with collagenase and separated by flow cytometry into large and small cells. Resting levels of Ca2+ were higher (P less than 0.05) in the large than small cells [314 +/- 25 nM (n = 5) vs. 186 +/- 13 nM (mean +/- SE; n = 13) for large and small cells, respectively]. LH rapidly increased [Ca2+]i in both small and large cells loaded with the fluorescent Ca2+ probe fura-2. In the small cells, [Ca2+]i was immediately increased 2- to 6-fold (from 176 +/- 8 to 468 +/- 8 nM; n = 5) after adding LH. The LH induced [Ca2+]i rise occurred in two phases: an initial peak due to intracellular Ca2+ mobilization and a secondary rise due to Ca2+ influx from extracellular sources. Preincubation of the small cells with EGTA reduced the initial phase and abolished the secondary rise in [Ca2+]. Both forskolin and 8-bromo-cAMP increased [Ca2+]i in the small cells. In contrast, only a single phase of [Ca2+]i rise was observed in LH-treated large cells, and the response was 1.5- to 2-fold greater than the resting Ca2+ levels [314 +/- 25 vs. 435 +/- 60 nM (n = 4), for resting vs. LH-treated values, respectively]. The addition of both LH and prostaglandin F2 alpha (PGF2 alpha) to the large cells resulted in increases in [Ca2+]i that were greater than those induced by each hormone separately (2.0-fold for LH and 2.7-fold for PGF2 alpha vs. 7- to 9-fold in the presence of both hormones). These findings demonstrate that LH induces rapid increases in intracellular [Ca2+]i that differ in magnitude and profile between the small and large bovine luteal cells. Furthermore, LH and PGF2 alpha interacted to promote increases in [Ca2+]i in the large cells, that were higher than the sum of [Ca2+]i induced by each hormone separately.

8-Bromo Cyclic Adenosine Monophosphate↗

PubMed1989

Regulation of side-chain cleavage enzyme and 3 beta-hydroxysteroid dehydrogenase by Ca2+ second messenger and protein kinase C systems in the placenta of the cow.

The steroidogenic activity of the bovine placenta is not modulated by cyclic nucleotide-mediated mechanisms. However, both translocation of intracellular Ca2+ and influx of extracellular Ca2+ activate the side-chain cleavage enzyme and 3 beta-hydroxysteroid dehydrogenase. Protein kinase C activation in concert with Ca2+ mobilization also activates the side-chain cleavage enzyme. Cholesterol availability is a rate-limiting factor. Using polyclonal antibodies against bovine adrenal cytochrome P-450scc, the presence of P-450scc was demonstrated in both placental and luteal tissues. The cytochrome P-450scc was then localized, using gold-staining electron microscopy, in the mononuclear cells but not the binuclear cells of the placentome. The results suggest that cholesterol is metabolized by the mononuclear cell to pregnenolone, where it is further metabolized to progesterone by the mononuclear and binuclear cells.

1-Methyl-3-isobutylxanthine↗

PubMed1989

Low molecular weight lipid-soluble luteotrophic factor(s) produced by conceptuses in cows.

Peripheral plasma progesterone concentrations are higher (P less than 0.05) in pregnant than in inseminated non-pregnant or cyclic heifers between Days 10 and 18 after insemination. In several experiments, it has been demonstrated that bovine conceptuses produce a low molecular weight (Mr less than 10,000), lipid-soluble, heat-labile, dextran-coated charcoal-adsorbable luteotrophic substance(s) that has the ability to stimulate progesterone synthesis in dispersed bovine luteal cells. This substance does not appear to be PAF, since addition of PAF to dispersed luteal cells at several dose levels failed to affect either basal or LH-stimulated progesterone synthesis. However, results of in-vitro and in-vivo experiments suggest that platelet-derived products are luteotrophic. In in-vitro experiments it was shown that co-incubation of dispersed bovine luteal cells with bovine platelets augments basal progesterone synthesis. Serotonin and platelet-derived growth factor appear to be the major products of platelet activation responsible for the luteotrophic activity of platelets. Products of the arachidonic acid cascade do not appear to be important, since addition of the cyclo-oxygenase blocker indomethacin did not reduce the luteotrophic activity of platelets. In in-vivo experiments, it has been possible to demonstrate a significant thrombocytopenia in pregnant heifers between Days 7 and 16 after insemination. These results are compatible with the concept that release of platelet-derived products under the influence of factors produced by the early embryo play a role in stimulating progesterone synthesis by the corpus luteum during early pregnancy.

Animals↗

PubMed1989

Identification of a luteotrophic protein in bovine allantoic fluid.

Allantoic fluids (n = 65) of Day 24-37 bovine conceptuses were collected and assayed for luteotrophic activity in vitro with dispersed bovine luteal cells. Significant luteotrophic activity was found in 41% of the samples, with the highest percentage occurring between Days 25 and 28. The activity is ammonium sulphate-precipitable, heat-labile and inactivated by trypsin and chymotrypsin. Gel filtration column chromatography identified one peak of luteotrophic activity with a molecular weight of 68,000. Concanavalin A bound the luteotrophic activity, thus allowing rapid and substantial purification from a major protein of Mr 68,000 which was concanavalin A non-reactive. The results of one- and two-dimensional SDS-PAGE of concanavalin A-reactive fractions containing activity suggest that the luteotrophic activity present in allantoic fluid is associated with a glycoprotein of Mr 68,000 present in very low concentrations. The active factor does not appear to be alpha-fetoprotein. This protein may be an important conceptus-derived luteotrophin that stimulates progesterone production by the corpus luteum of cows during pregnancy.

Allantoin↗

PubMed1988

Control of bovine placental progestin synthesis: calcium dependent steroidogenesis is modulated at the site of the cholesterol side chain cleavage enzyme.

We have previously reported that progesterone synthesis in the bovine placenta is regulated by Ca2+ dependent and cyclic nucleotide independent mechanism. In studies conducted to further define the role of Ca2+ in the synthesis of progestins in bovine placental tissue, it was found that both protein kinase C (PKC), as determined by phosphorylation, and cytochrome P-450 side chain cleavage, as determined by Western blot analysis, were detectable in the steroidogenetically active portion of the placentome. To determine the site of action of PKC, fetal cotyledon cells were incubated in media containing 25-hydroxycholesterol in the absence or or presence of 10 ng/ml 12-O-tetradecanoyl-phorbol-13-acetate (TPA). It was found that TPA significantly (P less than 0.05) increased the conversion of the exogenous cholesterol analog to progesterone. To determine if the TPA could act synergistically with calcium activators, fetal cotyledon cells were incubated with either methyl isobutyl xanthine (MIX), an activator of intracellular calcium, or the calcium ionophore, A23187, which increases extracellular calcium influx, or both of these agents, in the presence or absence of TPA. It was found that TPA synergistically increased the conversion of sterol to progestins induced by submaximal concentrations of either MIX or A23187. In the presence of both compounds, TPA induced an even more dramatic increase in progestin synthesis. In experiments in which cyanoketone, an agent that inhibits the conversion of pregnenolone to progesterone, was added, TPA addition resulted in increased pregnenolone production, indicating that side chain cleavage of cholesterol is the site of action. The data, therefore, suggest that: (a) Ca2+ affects mechanisms regulating placental steroidogenesis; (2) one locus of Ca2+ is the cholesterol side chain cleavage reaction; and (3) PKC found in this tissue has a role in the Ca activated progestin production.

1-Methyl-3-isobutylxanthine↗

PubMed1988

Control of bovine placental progesterone synthesis: roles of cholesterol availability and calcium-activated systems.

It was previously reported that dispersed bovine placentome secretes progesterone and that the steroidogenic activity of these cells is stimulated by a calcium-mediated, cyclic nucleotide independent mechanism. In the present study, the influence of substrate availability was explored and the roles of calmodulin and protein kinase C in progestin production examined. Incubation of dispersed fetal cotyledon cells with 25-hydroxycholesterol (25-OH-C), a soluble sterol which readily enters cells and is metabolized to steroid hormones, increased progesterone secretion in a dose-dependent manner. The response to 25-OH-C was dependent on the extracellular calcium concentration. Methyl isobutyl xanthine (MIX) alone also increased pregnenolone as well as progesterone secretion, and the combination of 25-OH-C and MIX stimulated progesterone secretion was inhibited by trifluoperazine. The phorbol ester, 12-O-tetradecanoyl-phorbol-13-acetate (TPA), caused no major effects on steroidogenesis but the stimulatory effects of MIX or the ionophore A23187 were enhanced in its presence. These findings suggest that (1) basal progesterone secretion by fetal cotyledon cells is limited by cholesterol availability; (2) MIX increases steroidogenesis in part by increasing the synthesis of pregnenolone, but its actions are expressed independently of cholesterol availability; (3) both calmodulin and protein kinase C may participate in the modulation of bovine placental steroidogenesis.

1-Methyl-3-isobutylxanthine↗

PubMed1988

A comparison of the effects of cyclooxygenase prostanoids on progesterone production by small and large bovine luteal cells.

Highly purified preparations of small and large bovine luteal cells were utilized to examine the effects of prostaglandins F2 alpha (PGF2 alpha), E2 (PGE2) and I2 (PGI2) analog on progesterone production. Corpora lutea were obtained from Holstein heifers between days 10 and 12 of the estrous cycle. Purified small and large cells were obtained by unit gravity sedimentation and flow cytometry. Progesterone accumulation was determined in 1 x 10(5) small and 5 x 10(3) large cells after 2 and 4 h incubations respectively. Progesterone synthesis was increased (p less than 0.05) in the small cells by the increasing levels of PGF2 alpha, PGE2, carba-PGI2 and LH. PGF2 alpha, but not PGE2 or carba-PGI2 increased (p less than 0.05) LH-stimulated progesterone production. There was no interaction of various combinations of prostaglandins on progesterone production in the small cells. In the large cells, PGF2 alpha had no effect on basal progesterone production. However, it inhibited LH-stimulated progesterone synthesis. In contrast, PGE2 and carba-PGI2 stimulated (p less than 0.05) basal progesterone production in the large cells. In the presence of LH, high levels of carba-PGI2 inhibited (p less than 0.05) progesterone synthesis. The PGE2 and PGI2-stimulated progesterone production in the large luteal cells was also inhibited in the presence of PGF2 alpha. These data suggest all of the prostaglandins used exert a luteotropic action in the small cells. In the large cells only PGE2 and carba-PGI2 are luteotropic, while PGF2 alpha exerts a luteolytic action. The effects of the prostaglandins in the small and large luteal cells suggest that their receptors are present in both cell types.

Animals↗

PubMed1988

Acute effects of prostaglandin F2 alpha on inositol phospholipid hydrolysis in the large and small cells of the bovine corpus luteum.

The present studies were conducted to determine whether the large or small bovine luteal cell was the site for the stimulatory effect of prostaglandin F2 alpha (PGF) on phospholipase C-catalyzed inositol phospholipid hydrolysis. Corpora lutea were removed from heifers during the luteal phase of the normal estrous cycle. Small luteal cells were isolated by unit-gravity sedimentation and large luteal cells were isolated by flow cytometry using a Becton Dickson FACS 440 cell sorter. PGF provoked rapid (5-30 s) and sustained (up to 30 min) increases in the levels of inositol mono-, bis-, and trisphosphates (IP, IP2, IP3, respectively) in small luteal cells. IP3 was formed more rapidly than IP2 or IP following PGF treatment. The PGF-stimulated increase in IP3 was accompanied by a transient reduction in the levels of 3H-labeled phosphatidylinositol 4,5-bisphosphate. LiCl (10 mM) enhanced inositol phosphate accumulation in response to PGF. Maximal increases in inositol phosphate accumulation were observed with 1-10 microM PGF and half-maximal increases were observed with 60 nM PGF. PGF (1-10 microM) had no effect on cAMP levels but stimulated small increases in progesterone accumulation in 30 min incubations of small luteal cells. PGF also increased the accumulation of inositol phosphates in large luteal cells. The increases were apparent within 5 min of incubation (the earliest time examined) and further increases were observed in incubations lasting 30 min. PGF had no significant effect on cAMP or progesterone in 30 min incubations of large cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1988

Early pregnancy signals in domestic animals.

Large early embryonic death losses occur in all domestic animals and these losses are temporally related to early pregnancy recognition signals. Binucleate trophoblastic cells, which migrate to the endometrial endothelium, are a potential vehicle for early (day 15-20) communication between the mother and the embryo in ruminant animals. In cattle, the first pregnancy recognition signal, which results in increased progesterone secretion by the corpus luteum as early as day 10, appears to be a small (less than 10,000 Mr) heat-labile lipid-soluble molecule that can be adsorbed by dextran-coated charcoal. Although this substance has not yet been identified, there is a possibility that it is embryo-derived platelet-activating factor (EDPAF). EDPAF appears to influence progesterone synthesis by causing the release of luteotropic factors (arachidonic acid metabolites and serotonin) from activated platelets. The second pregnancy recognition factor in cattle and sheep appears to be a trophoblastic peptide having a molecular weight of 22,000-24,000 daltons (bTP-1, cattle) or 17,000 daltons (oTP-1, sheep). These compounds do not have direct luteotropic effects, but are thought to exert their antiluteolytic effects by inhibiting the production of luteolytic eicosanoids (PGF2 alpha) by the endometrium. A third early pregnancy signal in cattle is an hCG-like protein that appears in allantoic fluid on day 25, just after the disappearance of bTP-1. There is as yet no clear evidence that steroids produced by the conceptus act as early pregnancy signals in ruminants. However, estrogens appear to provide the essential early signal for corpus luteum maintenance in the pig.

Animals↗

PubMed1988

Control of progesterone production in small and large bovine luteal cells separated by flow cytometry.

Corpora lutea were collected from Holstein heifers on Days 10 and 12 of the oestrous cycle and the cells were dispersed with collagenase. The dispersed cells were separated into preparations of highly purified (90-99%) small (less than 20 microns) and large (greater than 25 microns) luteal cells by unit gravity sedimentation and fluorescence-activated cell sorting. Net progesterone accumulation by 1 x 10(5) small cells and 1 x 10(3) large cells during 2 and 4 h incubations, respectively, were measured after additions of LH, PGF-2 alpha, and phorbol esters, alone and in combination. Progesterone synthesis was increased (P less than 0.05) by phorbol dibutyrate (PBt2) or PGF-2 alpha (P less than 0.05) in small, but not in large, luteal cells (10.1 +/- 3.0 and 18.1 +/- 5.0 ng/10(5) cells for 0 and 50 nM-PBt2, and 19.9 +/- 3.2 and 44.2 +/- 9.3 ng/10(5) cells for 0 and 1 microgram PGF-2 alpha/ml). The previously reported stimulatory effects of PKC activation and PGF-2 alpha addition to total dispersed cell preparations are therefore entirely attributable to the small, theca-derived cells. Small cells responded to low levels of LH (9.1 +/- 1.1, 69.0 +/- 5.4 and 154.7 +/- 41.4 ng/10(5) cells for 0, 1 and 5 ng LH/ml, respectively, P less than 0.05), while large cells responded only to high levels of LH (1635 +/- 318, 2662 +/- 459 and 3386 +/- 335 pg/10(3) cells for 0, 100 and 1000 ng LH/ml, respectively, P less than 0.05). PGF-2 alpha inhibited LH-, 8-Br-cAMP- and forskolin-stimulated progesterone synthesis in the large cells (3052 +/- 380, 3498 +/- 418, 3202 +/- 391 pg/10(3) cells for 1 microgram LH/ml, and 0.5 mM-8-Br-cAMP, and 1 microM-forskolin respectively and 1750 +/- 487, 2255 +/- 468, 2165 +/- 442 pg/10(3) cells for PGF-2 alpha + LH, PGF-2 alpha + 8-Br-cAMP and PGF-2 alpha + forskolin, respectively), indicating that the inhibitory effect of PGF-2 alpha on progesterone synthesis in large cells occurs at a site distal to cAMP generation. These results suggest that the large cells are the targets of the luteolytic effects of PGF-2 alpha, while the small cells are responsible for the previously reported luteotrophic effect of PGF-2 alpha in vitro.

Animals↗

PubMed1987

Control of steroidogenesis in small and large bovine luteal cells.

Evidence was cited to show that: (1) prostacyclin (PGI2) plays a luteotrophic role in the bovine corpus luteum and that products of the lipoxygenase pathway of arachidonic acid metabolism, especially 5-hydroxyeicosatetraenoic acid play luteolytic roles; (2) oxytocin of luteal cell origin plays a role in development, and possibly in regression, of the bovine corpus luteum; and (3) luteal cells arise from two sources; the characteristic small luteal cells at all stages of the oestrous cycle and pregnancy are of theca cell origin; the large cells are of granulosa cell origin early in the cycle, but a population of theca-derived large cells appears later in the cycle. Results of in vitro studies with total dispersed cells and essentially pure preparations of large and small luteal cells indicate that: (1) the recently described Ca2+-polyphosphoinositol-protein kinase C second messenger system is involved in progesterone synthesis in the bovine corpus luteum; (2) activation of protein kinase C is stimulatory to progesterone synthesis in the small luteal cells; (3) activation of protein kinase C has no effect on progesterone synthesis in the large luteal cells; and (4) protein kinase C exerts its luteotrophic effect in total cell preparations, in part at least, by stimulating the production of prostacyclin. The protein kinase C system may cause down regulation of LH receptors in the large cells.

Animals↗

PubMed1987

In-vitro synthesis of a low molecular weight lipid-soluble luteotrophic factor by conceptuses of cows at day 13-18 of pregnancy.

Two culture systems for maintenance of Day 13-18 conceptus tissue were developed. Harvested culture media were assayed for luteotrophic activity by determining their ability to stimulate progesterone synthesis by dispersed bovine luteal cells. Significant luteotrophic activity was found in 80% of the 31 tissue culture media studied. A series of experiments carried out to determine the nature of the luteotrophic activity indicate that it is a small (Mr less than 10,000), heat-labile, lipid-soluble substance that is adsorbed by dextran-coated charcoal. The nature and activity of this factor, together with its synthesis by the early bovine conceptus, suggest that it may have a significant role in stimulating progesterone synthesis by the corpus luteum during early pregnancy.

Ammonium Sulfate↗

PubMed1986

Relationships between insulin and glucose metabolism and pituitary-ovarian functions in fasted heifers.

The effects of fasting between Days 8 and 16 of the estrous cycle on plasma concentrations of luteinizing hormone (LH), progesterone, cortisol, glucose and insulin were determined in 4 fasted and 4 control heifers during an estrous cycle of fasting and in the subsequent cycle after fasting. Cortisol levels were unaffected by fasting. Concentrations of insulin and glucose, however, were decreased (p less than 0.05) by 12 and 36 h, respectively, after fasting was begun and did not return to control values until 12 h (insulin) and 4 to 7 days (glucose) after fasting ended. Concentrations of progesterone were greater (p less than 0.05) in fasted than in control heifers from Day 10 to 15 of the estrous cycle during fasting, while LH levels were lower (p less than 0.01) in fasted than in control heifers during the last 24 h of fasting. Concentrations of LH increased (p less than 0.01) abruptly in fasted heifers in the first 4 h after they were refed on Day 16 of the fasted cycle. Concentrations (means +/- SEM) of LH also were greater (p less than 0.05) in fasted (11.2 +/- 2.6 ng/ml) than in control (4.7 +/- 1.2 ng/ml) heifers during estrus of the cycle after fasting; this elevated LH was preceded by a rebound response in insulin levels in the fasted-refed heifers, with insulin increasing from 176 +/- 35 pg/ml to 1302 +/- 280 pg/ml between refeeding and estrus of the cycle after fasting. Concentrations of LH, glucose and insulin were similar in both groups after Day 2 of the postfasting cycle. Concentrations of progesterone in two fasted heifers and controls were similar during the cycle after fasting, whereas concentrations in the other fasted heifers were less than 1 ng/ml until Day 10, indicating delayed ovulation and (or) reduced luteal function. Thus, aberrant pituitary and luteal functions in fasted heifers were associated with concurrent fasting-induced changes in insulin and glucose metabolism.

Animals↗