Hen Granulosa Cells Research Articles

Effect of sodium on progesterone production in granulosa cells of rapidly growing chicken ovarian follicles

The importance of extracellular sodium ( Na o + ) in the progesterone production in hen granulosa cells from the first (F 1), second (F 2), and third (F 3) largest preovulatory follicles was investigated in short term incubations. Progesterone synthesis in the absence or presence of the gonadotropin increased with increasing Na o + concentration. Luteinizing hormone (LH) caused an additional and significant increase in steroidogenesis at every Na o + concentration tested. However, no significant difference in the ED 50 of Na o + among F 1, F 2, and F 3 cells was observed whether in the absence or the presence of the gonadotropin. Furthermore, although LH provoked steroidogenesis dose dependently in F 1, F 2, and F 3 granulosa cells, no significant change in the ED 50 of LH was observed among F 1, F 2, and F 3 cells. The Na + H + exchange inhibitor, amiloride, attenuated both basal and LH-stimulated steroidogenesis in a concentration-dependent manner in the presence of Na o + . Amiloride was ineffective in the absence of Na o + . The present studies indicate the importance of Na o + in the modulation of steroidogenesis in hen granulosa cells. Since steroidogenesis was suppressed by amiloride only in the presence of sodium, it is suggested that Na o + is important for the maintenance/regulation of intracellular pH by an exchange with intracellular H +. Our studies also suggest that the sodium modulatory mechanism may not be a determinant in the differential progesterone production observed among the three largest preovulatory follicles.

Quantitative cytochemistry of 3 beta-hydroxysteroid dehydrogenase activity in avian granulosa cells during follicular maturation.

Previous studies have shown that biosynthesis of progesterone, the major steroid product of hen granulosa cells, increases during follicular maturation. However, the contribution of individual granulosa cells to the total progesterone production of each follicle is not known. The objective of the present study was to determine the presence and relative activity of 3 beta-hydroxysteroid dehydrogenase (3 beta-HSD) in individual granulosa cells isolated from each of the five largest yolk-filled preovulatory follicles of laying hens. 3 beta-HSD cytochemistry in the presence or absence of pregnenolone substrate was performed on digitonin-permeabilized granulosa cells in suspension. The stained cells were fixed in a 70% ethanol solution until 1) the percentage of cells from each follicle that stained dark blue-indicating the presence of 3 beta-HSD activity-was determined by counting under light microscopy, and 2) the intensity of staining-indicating the relative amount of enzyme activity-was quantified using video image analysis. There were three findings. First, 100% of granulosa cells from each of the five largest preovulatory follicles stained positively for the presence of 3 beta-HSD activity. Second, the amount of 3 beta-HSD activity was normally distributed among granulosa cells in the population from each follicle. Third, as follicles matured from the fifth largest to the largest follicle, 3 beta-HSD activity increased steadily in individual cells, as indicated by increased staining intensities. The results indicate uniformity in the steroidogenic capacity of cells in the granulosa layer of hen preovulatory follicles.(ABSTRACT TRUNCATED AT 250 WORDS)

Mechanisms by which a phorbol ester and a diacylglycerol analog inhibit hen granulosa cell steroidogenesis

We have previously reported that treatment of hen granulosa cells with the tumor-promoting phorbol ester, phorbol 12-myristate 13-acetate (PMA), or the diacylglycerol analog, 1-oleoyl-2-acetylglycerol (OAG), attenuates the steroidogenic response to luteinizing hormone (LH) at sites both prior and distal to the formation of cyclic 3′,5′-adenosine monophosphate (cAMP). The present study was designed to determine the site(s) of inhibition within the steroidogenic pathway by evaluating the effects of OAG and PMA on key enzyme systems involved in hen granulosa cell steroidogenesis: adenylyl cyclase, phosphodiesterase, the cholesterol-side-chain-cleavage (CSCC) complex and 3β-hydroxysteroid dehydrogenase (3β-HSD). The adenylyl cyclase activator, forskolin (0.1 mM), stimulated a 3.3-fold increase in granulosa cell cAMP formation, and this increase was inhibited by the presence of OAG (2.5, 25 and 63 μM) in a dose-dependent manner. By contrast, a 1.8-fold increase in cAMP accumulation induced by the phosphodiesterase inhibitor, 3-isobutyl-1-methylxanthine (IBMX; 1.0 mM), was not altered by OAG at any dose (2.5, 25 and 63 μM). Inclusion of 25-hydroxycholesterol (2500 ng/tube) in the incubation medium in the presence of 1.0 μM cyanoketone resulted in a 10-fold increase in pregnenolone production. Increasing concentrations of OAG (2.5, 25 and 63 μM) caused a dose-dependent suppression of the conversion of 25-hydroxycholesterol to pregnenolone. On the other hand, granulosa cells incubated with 200 ng/tube pregnenolone increased progesterone production 100-fold, but this increase was not inhibited by either PMA (3.2, 32, 81 and 162 nM) or OAG (2.5, 25 and 63 μM). The results indicate that activation of protein kinase C can suppress the function of at least two key enzymes involved in hen granulosa cell steroidogenesis. Inhibition of adenylyl cyclase greatly reduces the steroidogenic response of granulosa cells to endocrine factors that act via increasing levels of cAMP (i.e. LH). Furthermore, a reduction in CSCC activity limits the availability of precursor required for progesterone production. These data provide additional evidence of a role for protein kinase C in modulating ovarian function in the domestic hen.

Effects of a Phorbol Ester, a Calcium Ionophore, and 3′,5′-Adenosine Monophosphate Production on Hen Granulosa Cell Plasminogen Activator Activity*

Recent studies conducted in our laboratory have demonstrated that plasminogen activator (PA) is present in granulosa cells collected from the largest preovulatory follicle in the ovary of the domestic hen, and that its activity can be modulated by a variety of hormones in vitro. The present study was conducted to evaluate the intracellular mechanisms involved in the control of hen granulosa cell PA activity through the use of physiological and pharmacological agents. Treatment of granulosa cells with increasing doses (1, 10, and 50 ng/tube) of ovine LH resulted in a significant reduction of PA activity, which was accompanied by an increase in intracellular levels of cAMP. Furthermore, the effects of LH were potentiated by cotreatment with the phosphodiesterase inhibitor 3-isobutyl-1-methylxanthine (0.1 mM). Exposure of cells to increasing concentrations of the adenylyl cyclase activator forskolin (0.005, 0.01, 0.05, and 0.1 mM) resulted in a significant reduction in PA activity at all doses given. Similarly, the presence of the cAMP analog 8-bromo-cAMP (0.005, 0.01, 0.05, 0.1, 0.5, 1.5, and 10 mM) caused a dose-dependent inhibition of PA activity from 0.005 to 1.0 mM, further suggesting the involvement of cAMP in the inhibitory regulation of hen granulosa cell PA activity. The induction of intracellular calcium mobilization through the use of the calcium ionophore A23187 (0.1, 0.5, 1, and 2 microM) resulted in a dose-dependent suppression of PA activity. By contrast, treatment of granulosa cells with the tumor-promoting phorbol ester phorbol 12-myristate 13-acetate (PMA; 0.5, 5, 10, 25, and 50 micrograms/tube), a compound that activates protein kinase-C, stimulated PA activity in a dose-dependent fashion; a non-tumor-promoting phorbol ester (phorbol 13-monoacetate; 0.5, 10, and 50 ng/tube) was without effect. Coincubation of granulosa cells with a submaximal dose of PMA (5 ng/tube) and low concentrations of A23187 (0.001, 0.005, 0.01, and 0.05 microM) could not significantly enhance the stimulatory effects of PMA on PA activity; however, higher concentrations of the ionophore (0.1, 0.5, and 1.0 microM) completely abolished PMA-stimulated PA activity. The stimulatory effects of PMA could also be eliminated by cotreatment with a protein kinase-C inhibitor (H-7; 100 microM), a mRNA transcription blocker (actinomycin-D; 5 micrograms/tube), or a protein synthesis inhibitor (cycloheximide; 50 micrograms/tube).(ABSTRACT TRUNCATED AT 400 WORDS)

Enhancement of the response of hen granulosa cells to LH with norepinephrine in vitro

1. 1. The effect of norepinephrine (NE) on progesterone production in hen granulosa cells was examined. After 4 days of the culture, the progesterone production was stimulated by chicken LH but not by NE during a 4hr incubation. 2. 2. The LH-stimulation progesterone production was not affected by the presence of NE when given together with LH, but was significantly increased when the cells were precultured with NE for 2 days. 3. 3. The effect of NE was inhibited by phentolamine, but not by propranolol. 4. 4. The results indicate that NE may enhance the responsiveness of the hen granulosa cell to LH through α-adrenergic receptors.

Influence of follicular maturation on 3-hydroxy-methylglutaryl coenzyme A reductase activity in hen granulosa cells.

The activity of 3-hydroxy-3-methylglutaryl coenzyme A reductase (HMG-CoA reductase: EC 1.1.1.34) was measured in a microsomal preparation of the granulosa of rapidly growing ovarian follicles of laying hens in the late preovulatory period (2-3 h before expected ovulation). The specific activity of the enzyme was measured in the five largest (F1-F5) preovulatory follicles, F1 being the follicle destined to ovulate first. Enzyme activity increased concomitantly with follicle size. The apparent Km of the enzyme decreased 60-80% from the smallest to the largest preovulatory follicle. There was no significant change in the Vmax during follicle development. Although our results have demonstrated the presence of HMG/CoA reductase in chicken granulosa cells and the progressive increase of its activity with follicular maturation, the quantitative significance of de-novo synthesized cholesterol as steroid hormone precursor remains to be ascertained.

Trifluoperazine inhibits progesterone and cyclic AMP production in granulosa cells of the hen ( Gallus domesticus)

Unstimulated (basal) as well as luteinizing hormone (LH)-promoted progesterone production in collagenase-dispersed hen granulosa cells was inhibited in a dose-related manner by two phenothiazines, trifluoperazine (TFP) and chlorpromazine (CP), both of which are known calmodulin antagonists. Using TFP, the more potent antagonist of the two, it was found that LH-stimulated cyclic AMP production was also suppressed. Moreover, TFP attenuated the steroidogenic effects of both 8-bromo-cyclic AMP and isobutylmethylxanthine but had no effect on the conversion of pregnenolone to progesterone. The inhibitory effects of TFP on steroidogenesis were reversible. It is concluded that phenothiazines inhibit steroidogenesis in ovarian granulosa cells by acting at multiple sites both proximal and distal to cyclic AMP generation without influencing the enzyme complex responsible for the conversion of pregnenolone to progesterone. The results are discussed in relation to calmodulin- and non-calmodulin-mediated actions of phenothiazines.

Clomiphene and tamoxifen inhibit the cholesterol side-chain cleavage enzyme activity in hen granulosa cells.

A radiochemical assay was utilized to study the inhibitory effects of clomiphene and tamoxifen on the cholesterol side-chain cleavage enzyme activity in a mitochondrial preparation of granulosa cells isolated from mature ovarian follicles of laying hens. At saturating substrate concentrations, both clomiphene and tamoxifen were able to suppress enzyme activity in a dose-related manner (IC50 1.8 X 10(-5) M). Double reciprocal plots of kinetic data show that the inhibition is mixed, exhibiting competitive kinetics at low concentrations, whereas at high concentrations, the inhibition is of a non-competitive nature. The competitive inhibition constants as determined from Dixon plots are 2 X 10(-5) M for clomiphene and 2.3 X 10(-5) M for tamoxifen. It is concluded that, in granulosa cells, clomiphene and tamoxifen directly inhibit the mitochondrial cholesterol side-chain cleavage activity. This inhibition may represent an important aspect of the mode of action of clomiphene and tamoxifen.

Influence of follicular maturation on luteinizing hormone-, cyclic 3',5'-adenosine monophosphate-, forskolin- and cholesterol-stimulated progesterone production in hen granulosa cells.

The influence of follicular maturation on progesterone production by collagenase-dispersed hen granulosa cells was measured in short-term incubations. Granulosa cells of the largest follicle (F1) produced up to ten times more progesterone than cells from smaller follicles (F3-F5), not only in response to luteinizing hormone (LH), but also when stimulated by exogenous cyclic AMP or forskolin, both of which raise intracellular cyclic AMP levels by nonreceptor-mediated mechanisms. Moreover, when granulosa cell progesterone synthesis was stimulated by incorporating 25-hydroxy-cholesterol into the incubation medium, an identical pattern was obtained. This could be attributed to a corresponding increase in the specific activity of the mitochondrial cholesterol side-chain cleavage enzyme (20,22 desmolase). An increase in the apparent Vmax was observed without a change in the apparent Km values. Pregnenolone substrate at concentrations which raised progesterone production to levels similar to those observed in response to LH stimulation was utilized equally by granulosa cells of mature and developing follicles. However, at high pregnenolone concentrations, granulosa cells of mature follicles converted significantly more of the precursor to progesterone. Assay of 3 beta-hydroxysteroid dehydrogenase (3 beta-HSD) showed that the enzyme has two Kms: a low Km present in cells of both mature and developing follicles, and a high Km found only in granulosa cells of more mature follicles. It is concluded that LH-promoted progesterone synthesis in granulosa cells of developing chicken follicles is restricted not so much by the availability of receptors and the competence of the adenylate cyclase/cyclic AMP system, but by the activity of key enzymes, principally the cholesterol-20,22 desmolase.