PubMed Health⌕ Search

Biomedical subjects

C L Bethea

Publications and source records attributed to C L Bethea.

At least 73 records · Page 4Linked to original sources
PubMed1987

Glucocorticoid stimulation of dopamine production in PC12 cells on extracellular matrix and plastic.

PC12 cells are spherical when cultured on plastic, but flatten and spread extensively when cultured on extracellular matrix (ECM) produced by bovine corneal endothelial cells. We previously demonstrated that cells which have spread on ECM release more dopamine and contain less intracellular dopamine than cells which are rounded on plastic cultureware. Glucocorticoids increase dopamine production in PC12 cells presumably via an increase in tyrosine hydroxylase gene transcription. We questioned whether cell shape as determined by ECM would change the response of PC12 cells to glucocorticoids. Dopamine release and cell content were measured by a radioenzymatic assay in serum-free cultures of PC12 cells on ECM and plastic treated with various glucocorticoids in a dose-response fashion for 24 or 48 h. In addition, the response of cells on both substrata to one dose of dexamethasone was examined from 3-48 h. PC12 cells on ECM and plastic exhibited a dose-related increase in dopamine release and content when treated for 24 h with corticosterone or for 48 h with dexamethasone, corticosterone or cortisol. The ED50s for dexamethasone- and corticosterone-stimulated release and content were similar for cells on ECM and plastic as were the doses at which the first significant increases were detected. The average times at which the first significant increase in release and content occurred were also similar for cells on ECM and plastic. PC12 cells on ECM continue to release more dopamine and store less dopamine than cells on plastic with glucocorticoid treatment. However, glucocorticoid-treated cells on ECM showed a greater percent increase over ECM controls in the cell content of dopamine, whereas glucocorticoid-treated cells on plastic showed a greater percent increase over controls in the release of dopamine. It is hypothesized that glucocorticoids increase dopamine production to a similar extent in cells on ECM and plastic, but that storage is facilitated in cells on ECM.

Animals↗
PubMed1987

Extracellular matrix changes PC12 cell shape and processing of newly synthesized dopamine.

PC12 cells on extracellular matrix (ECM) or plastic were incubated with 3H-tyrosine (3H-TY) in the presence and absence of serum or cold tyrosine. 3H-Dopamine (3H-DA) was determined in medium and cells from 1 to 48 h later with Dowex cation exchange chromatography. In serum-free and tyrosine-free medium, PC12 cells on ECM released significantly more 3H-DA, whereas cells on plastic had a significantly higher cellular content of 3H-DA, but total 3H-DA (medium plus cells) was equal in ECM and plastic cultures. When 3H-TY was added to tyrosine-containing medium, there was a significant decrease in the levels of 3H-DA detected and the differences between ECM and plastic cultures were attenuated, but the patterns of secretion and storage were similar to those observed with tyrosine-free medium and total synthesis did not decline at 48 h. Serum decreased the efficiency of the resin to retain 3H-DA from culture medium, attenuated the difference in dopamine release between ECM and plastic cultures, and contributed to variations in 3H-TY uptake. The morphometric relationship between the cell membrane and the internal compartment in PC12 cells of different shapes was also characterized. The perimeter length and area of the midsection of cells were determined with a modular system for quantitative digital analysis. The perimeter length of cells on ECM was significantly greater than cells on plastic, whereas the internal areas were similar. The ratio of perimeter length to area (P/A) for all cells on ECM was 30% higher than the P/A ratio for cells on plastic. The ratio of P/A for a subpopulation of very flat cells on ECM was 70% higher than the ratio for round cells on plastic. Immunocytochemistry for tyrosine hydroxylase revealed a more diffuse distribution of this enzyme in cells on ECM. These data suggest that there is an increase in the ratio of cell surface area to cell volume as PC12 cells spread on ECM which could facilitate secretory vesicle fusion with the cell membrane, and hence, exocytosis. Although there is a concomitant increase in the secretion of dopamine and a decrease in the storage of dopamine, the change in cell shape does not appear to immediately alter the synthesis of dopamine.

Animals↗
PubMed1986

Effect of the anxiolytic drug buspirone on prolactin and corticosterone secretion in stressed and unstressed rats.

Buspirone is an atypical anxiolytic drug that exerts its action at a receptor site other than the GABA-benzodiazepine-chloride ionophore complex. The present study examined the effect of buspirone on plasma prolactin and corticosterone levels in both control and stressed rats. In unstressed rats, buspirone produced dose-dependent increases in plasma prolactin and corticosterone levels. The minimal doses of buspirone which led to significant elevations in plasma prolactin and corticosterone levels were 1.0 and 2.0 mg/kg (IP), respectively. The effect of buspirone on both hormones was maximal 30 minutes after injection. The plasma levels of prolactin and corticosterone were significantly elevated in rats that were stressed using a conditioned fear paradigm. Buspirone produced a dose-dependent attenuation of the stress-induced increase in prolactin secretion. The stress-induced increase in corticosterone secretion was inhibited by the 0.5 mg/kg (IP) dose but not by the 2.0 mg/kg (IP) dose of buspirone, which increased corticosterone secretion both in stressed and unstressed rats. These data suggest that the effect of buspirone on plasma prolactin and corticosterone levels may be mediated by two different mechanisms of action.

Adrenal Cortex↗
PubMed1986

The effect of estrogens and progestins on monkey prolactin synthesis.

Dispersed monkey pituitary cells were cultured on extracellular matrix and in serum-free medium for up to 1 month, with medium changes every other day. The cells were treated with ethanol vehicle or 10 nM 17 beta-estradiol (E2 beta), 17 alpha-estradiol (E2 alpha), progesterone (P4), pregnenalone (P5), 17 alpha-hydroxyprogesterone (17OH P4), and E2 beta plus P4. Immunoreactive PRL (IR-PRL) levels in 48 h medium samples were first determined with a homologous human PRL RIA and then with a heterologous monkey PRL RIA. On the last day of culture, the cells were incubated with [35S]methionine for 4 h, and 35S-labeled PRL in the medium and cells was determined and compared to 4 h IR-PRL. Differences between control and treated groups in 48 h IR-PRL were greater with the heterologous monkey RIA. E2 beta, E2 alpha, and E2 beta plus P4 significantly elevated IR-PRL in 48 h medium samples an average of 73%, as determined with the monkey RIA. P4, P5, or 17OH P4 had no effect on IR-PRL in 48 h medium samples. Secreted and intracellular [35S]PRL were consistently elevated by E2 beta and E2 beta plus P4, but less consistently elevated by E2 alpha. P4, P5, or 17OH P4 had little effect on [35S]PRL in medium or cells. IR-PRL in the 4 h medium sample and cells generally paralleled [35S]PRL, although E2 alpha caused a more consistent elevation in IR-PRL than in [35S]PRL. In summary, E2 beta and E2 alpha directly stimulate PRL synthesis by monkey pituitary cells on extracellular matrix in long term serum-free culture. Nanomolar levels of progestins have little direct effect on PRL synthesis, nor does 10 nM P4 block the stimulatory effect of E2 beta.

17-alpha-Hydroxyprogesterone↗
PubMed1986

Purification of monkey prolactin from culture medium: biochemical and immunological characterization.

Serum-free culture medium, previously incubated with dispersed monkey pituitary cells, provided a relatively uncontaminated source for extraction and purification of 15 mg of monkey prolactin. N-terminal group analysis of this preparation, M21GB, produced predominantly leucine. The amino acid composition closely resembles that of both human and sheep prolactin. M21GB monkey prolactin migrates in 10% polyacrylamide with sodium dodecyl sulfate (SDS) as a single band with a molecular weight of about 23,000. Multiple bands typical of prolactins are seen with nondenaturing polyacrylamide disc electrophoresis. M21GB contains less than 1% growth hormone, incorporates radioactive iodine with a specific activity of 15 microCi/micrograms and specifically binds to the anti-human prolactin serum-3 provided by the National Hormone and Pituitary Program (B spec/total = 23%). M21GB does not compete in a linear fashion with iodinated human prolactin-16 for the human prolactin antiserum, but M21GB does compete in a linear fashion with iodinated M21GB with the same antiserum. Monkey serum, pituitary homogenate, and culture medium containing unknown levels of monkey prolactin are not parallel with NIAMDD-HPrl-RP1 in the human prolactin assay, but are parallel when M21GB is used as the reference preparation and for iodination. Finally, antisera to M21GB were generated in rabbits which are specific for monkey and human prolactin and which can be used for radioimmunoassay or immunocytochemistry. In summary, serum-free medium from primary cultures of dispersed monkey pituitaries provided a quantitity of monkey prolactin which promoted biochemical analysis and production of a specific antiserum. This culture system may be a unique and ongoing source for extraction of significant quantities of monkey prolactin suitable for investigative use.

Amino Acids↗
PubMed1985

Pharmacological studies on stress-induced renin and prolactin secretion: effects of benzodiazepines, naloxone, propranolol and diisopropyl fluorophosphate.

Stress-induced renin and prolactin secretion was investigated using a conditioned emotional response paradigm. Three minutes after placement in a chamber the rats received an electric shock to their feet via the grid floor, then were immediately returned to their home cage. This procedure was repeated for 3 consecutive days. On the fourth day, instead of receiving an electric shock, they were removed after 3 min and sacrificed by decapitation. Control rats were treated identically with the exception that shock was not administered at any time. There was a significant increase in plasma renin activity and prolactin level in the stressed rats. The administration of the antianxiety drugs chlordiazepoxide (10 mg/kg i.p.) or midazolam (0.125-2 mg/kg i.p.) blocked the stress-induced increase in prolactin levels but not the stress-induced rise in plasma renin activity. Administration of the beta-blocker propranolol (1 mg/kg i.p.) inhibited, but did not completely block, stress-induced rise in plasma-renin activity and had no effect on stress-induced prolactin secretion. The opiate antagonist naloxone (0.1-10 mg/kg i.p.) and the acetylcholinesterase inhibitor diisopropyl fluorophosphate (0.5 mg/kg i.p.) did not block stress-induced renin or prolactin secretion. It is concluded that stress-induced prolactin secretion is regulated by a benzodiazepine-mediated mechanism and that stress-induced renin but not prolactin secretion is mediated in part via beta-receptors.

Animals↗
PubMed1985

Further characterization of substratum influence on PC12 cell shape and dopamine processing.

We recently demonstrated that PC12 cells cultured on extracellular matrix (ECM) exhibit a flattened morphology, release more dopamine and contain less intracellular dopamine than cells which have a rounded shape on plastic culture ware. To further explore the role of PC12 cell shape in dopamine processing, we characterized the interaction of ECM and various agents on cell shape and dopamine release and content. In addition, the constituents of the ECM and the corneal endothelial cells which produce the ECM were presented in soluble form to PC12 cells on plastic. The soluble polysaccharides heparin, dextran and dextran sulfate, caused a dose-related increase in rounded (refractile) cells on ECM, a dose-related decrease in dopamine release and an increase in dopamine content relative to flattened cells on ECM. Chondroitin sulfate and hyaluronic acid did not prevent cell spreading on ECM nor affect dopamine processing. These experiments demonstrate that certain polysaccharides block cell spreading on ECM and that round cells on ECM secrete and store dopamine in a fashion similar to round cells on plastic. Colchicine, cytochalasin B and cycloheximide appear to affect dopamine synthesis and thus could not distinguish the role of cell shape in transmitter release. Treatment of PC12 cells on plastic with collagens I, II, III, IV, fibronectin, fibroblastic growth factor (FGF), or solubilized ECM had little effect on dopamine release or content. Endothelial cell conditioned medium and endothelial cell lysate increased dopamine release, but also increased dopamine content which differs from the effect of ECM. In summary, these experiments suggest that extracellular matrix alters cell shape and that the physical arrangement of these cells can determine dopamine secretion and storage.

Animals↗
PubMed1985

Characterization of dopamine and alpha-adrenergic receptors in human prolactin-secreting adenomas with [3H]-dihydroergocryptine.

One tenable hypothesis for the etiology of the development of prolactin-secreting adenomas is that a decrease in inhibitory dopaminergic regulation leads to increased lactotroph proliferation. Dopamine receptors have been repeatedly characterized on prolactin-secreting adenomas using labelled antagonists as ligands; however, no data are available on characterization of the receptor with a dopaminergic agonist. An agonist was utilized as the radioligand in the present study to permit the direct comparison of the pharmacological characteristics of the binding site with the biological response, the inhibition of prolactin secretion. This comparison has never been reported in tissues from the same species. Binding of the dopamine agonist and alpha-adrenergic antagonist [3H]-dihydroergocryptine ([3H]-DHE) to particulate fractions of surgically resected human prolactin-secreting adenomas was high affinity, monophasic, and saturable. Careful characterization of the [3H]-DHE binding by competitions with a large number of dopaminergic and alpha-adrenergic agents revealed the presence of both dopaminergic and alpha-adrenergic binding sites. The presence of a saturable, high affinity alpha-adrenergic binding site was confirmed with the specific alpha-adrenergic antagonist [3H]-WB4101 as a radioligand. Although the rank order of potency for dopaminergic compounds to compete for [3H]-DHE binding was consistent with an interaction with a dopamine receptor, the inhibitory constants (Ki) calculated from the competitions were higher than expected at an anterior pituitary dopamine receptor. This appeared to be due to the lower affinity of these agents at the alpha-adrenergic sites. The observed potency of dopaminergic compounds was inversely related to the number of alpha-adrenergic sites.(ABSTRACT TRUNCATED AT 250 WORDS)

Adenoma↗
PubMed1985

Pharmacological studies on the serotoninergic and nonserotonin-mediated stimulation of prolactin and corticosterone secretion by fenfluramine. Effects of pretreatment with fluoxetine, indalpine, PCPA, and L-tryptophan.

Administration of the serotonin-releasing drug fenfluramine to male rats caused a dose-dependent increase in both plasma prolactin and corticosterone levels. The effect of fenfluramine on prolactin was maximal at 30 min after injection, whereas the effect on plasma corticosterone levels reached a maximum 2 h after injection. In order to determine if the effect of fenfluramine on both hormones was mediated via serotonin release, rats were pretreated with the serotonin uptake inhibitors fluoxetine (10 mg/kg i.p.) or indalpine (10 mg/kg i.p.) 30 min prior to administration of fenfluramine (5 mg/kg i.p.). Both fluoxetine and indalpine inhibited the effect of fenfluramine on plasma prolactin levels, but did not modify the effect of fenfluramine on plasma corticosterone levels. Pretreatment of rats with the serotonin precursor L-tryptophan (100 mg/kg i.p.) potentiated the effect of a submaximal dose of fenfluramine (2 mg/kg i.p.) on plasma prolactin levels, but did not affect the corticosterone response. Depletion of serotonin stores by pretreatment with the serotonin inhibitor p-chlorophenylalanine (300 mg/kg i.p.; 72 h) did not significantly prevent the effect of fenfluramine on either hormone. There was a 34% inhibition of the effect of fenfluramine on plasma prolactin levels, but this effect was not statistically significant. The results of the experiments suggest that the effect of fenfluramine on prolactin secretion is mediated, at least in part, by a serotoninergic mechanism, but the effect on corticosterone secretion is not mediated via serotonin release.

Animals↗
PubMed1985

Serotonergic stimulation of prolactin and corticosterone secretion is mediated by different pathways from the mediobasal hypothalamus.

In previous studies we obtained evidence that serotonin release by p-chloroamphetamine (PCA) causes an increase in corticosterone secretion but that this effect is not mediated via the raphe nuclei in the midbrain. In contrast, PCA-induced prolactin secretion was abolished by dorsal raphe lesions. In the present study, posterolateral cuts which interrupted caudal inputs to the hypothalamus attenuated the effect of PCA on plasma prolactin but did not block the PCA-induced increase in plasma corticosterone levels. Large lesions of the mediobasal hypothalamus produced a significant reduction of plasma corticosterone concentration but did not completely prevent the effect of PCA on corticosterone secretion. Hypophysectomy performed 24 h before sacrifice caused a marked decrease in plasma corticosterone levels but did not completely abolish the effect of PCA. These results suggest that PCA also stimulates corticosterone secretion via a direct action on the adrenal gland. The lesions in the mediobasal hypothalamus caused an increase in plasma prolactin concentration, and in these rats, PCA suppressed rather than stimulated prolactin secretion. This suggests that the known weak dopamine agonist activity of PCA is exposed when the effects of serotonin release in the brain are eliminated.

Amphetamines↗
PubMed1985

In vitro gonadotropin-releasing hormone release from hypothalamic tissues of ovariectomized estrogen-treated cynomolgus macaques.

The effects of in vivo 17 beta-estradiol (E2) treatment on in vitro GnRH release and serum LH levels were studied to determine the loci of E2 feedback actions and to examine the hypothalamic mechanisms by which this steroid may regulate LH secretion in monkeys. Ovariectomized cynomolgus macaques received sc Silastic capsule implants containing E2 and were killed 12, 36, 42, or 48 h later. At least one control (CTL) animal received a blank implant and was killed concurrently with each E2-treated monkey. Three untreated animals were used in validation experiments. Before death, each animal was anesthetized with ketamine (15 mg/kg, im), and blood samples were drawn for subsequent LH analysis by Leydig cell bioassay. A diencephalic tissue block was obtained at autopsy and immediately immersed in Krebs-Ringer-phosphate medium (KRP). Mediobasal hypothalamic (MBH) and anterior hypothalamic/preoptic (AH/POA) fragments were quickly dissected from the block and placed in separate superfusion chambers maintained at 37 C. Tissues were superfused at 50 microliter/min with KRP, and 10-min fractions were collected, acidified, and stored at -20 C for subsequent GnRH RIA. Basal immunoreactive GnRH (IR-GnRH) release was measurable from MBH (0.367 +/- 0.063 pg/min) and AH/POA (0.176 +/- 0.065 pg/min) fragments from CTL monkeys. In validation experiments, IR-GnRH release was increased 3- to 7-fold by superfusion with 60 mM K+-KRP only in the presence of Ca+2. Superfusate IR-GnRH coeluted with synthetic GnRH from a Sephadex G-25 chromatographic column, and superfusate and tissue extract GnRH showed appropriate LH-releasing capacities, as determined by rat pituitary cell culture assay. IR-GnRH release rates from MBH or AH/POA tissues varied as a function of in vivo estrogen treatment. GnRH release from both tissues was increased in the E2-treated group killed at 12 h when LH levels were suppressed. Thirty-six hours after E2 treatment, in vitro GnRH release was not significantly different from CTL values. GnRH release rates from MBH and AH/POA tissues obtained 42 h after E2 treatment were significantly greater than CTL release rates (P less than 0.01). This increased in vitro GnRH release at 42 h occurred during the apparent rising phase of the LH surge. Elevated GnRH release was not sustained at 48 h, when surge levels of LH were apparent.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1985

Characterization of dopamine and estrogen interaction on primate prolactin secretion with pituitary cells cultured on extracellular matrix and with pituitary stalk-transected monkeys.

To determine the direct effects of estrogen and dopamine on primate PRL secretion, cultures of dispersed monkey pituitary cells were maintained in serum-free medium on an extracellular matrix secreted by bovine corneal endothelial cells, and female monkeys with pituitary stalk-transections were prepared. Dispersed pituitary cells from male and female monkeys were cultured in a 1:1 mixture of Dulbecco's Modified Eagle's Medium H-16 and Ham's F-12 medium containing insulin, transferrin, selenium, and cadmium with or without 10.0 nM estradiol. When possible, a sister culture was established in 10% charcoal-treated fetal calf serum with or without estrogen. On days 4, 8, and 12 after plating, the incubation medium was replaced with identical medium containing increasing concentrations of dopamine with ascorbate for 6 h. Medium PRL concentrations were determined by RIA. Half-maximal inhibition (IC50) of PRL secretion occurred at about 10.0 nM dopamine with all treatments. Dopamine suppressed PRL secretion to a greater extent on day 4 when estrogen was present in the serum-free medium. There was no difference in the percent inhibition of PRL on days 8 and 12, as the serum-free cultures without estrogen appeared to increase in sensitivity. In cultures maintained in 10% charcoal-treated serum, estrogen had little effect on the dose-response inhibition of PRL on days 4 and 8, but by day 12, there was significantly less inhibition at the higher doses of dopamine. Dopamine infusion in pituitary stalk-transected (SS) monkeys caused a dose-related inhibition of PRL secretion. Serum PRL levels decreased 80% with 100 nM dopamine, and the IC50 occurred with 10 nM dopamine. In SS monkeys receiving 2 months of estrogen treatment, dopamine infusion inhibited PRL secretion to a greater extent at the lowest dose of dopamine, although the IC50 did not change. These experiments suggest that estrogen does not decrease the effectiveness of dopamine as an inhibitor of PRL secretion in SS monkeys or from primate pituitary cells cultured for 12 days in serum-free medium. Extended maintenance of cells in medium containing serum may alter this response to dopamine.

Animals↗
PubMed1984

Role of midbrain raphe in stress-induced renin and prolactin secretion.

Stress-induced changes in renin and prolactin secretion were studied using a conditioned emotional response paradigm. Three minutes after being placed in a chamber, the stressed animals received a brief electric shock (1.0 mA for 10 s through the grid floor), then were returned to their home cage. This procedure was repeated for 3 consecutive days. On the fourth day, the rats were placed in the chamber for 3 min, but instead of receiving shock, they were removed and sacrificed. Control animals were treated in the same manner, except that they never received foot shock. The sham-operated stressed rats evidenced significant elevations in plasma renin activity (270%) and prolactin level (550%). Electrolytic lesions in the dorsal raphe nucleus blocked the stress-induced increase in plasma renin activity but did not affect the stress-induced increase in prolactin secretion. Electrolytic lesions in the median raphe nucleus did not affect prolactin levels in either control or stressed animals. However, median raphe lesions led to a significant increase in plasma renin activity in non-stressed rats and potentiated the stress-induced elevation in plasma renin activity. These results suggest that neurons within the dorsal and median raphe nuclei are involved in the regulation of renin but not prolactin secretion during stress. The results also suggest that median raphe neurons play a role in basal renin secretion.

Animals↗
PubMed1984

Effect of extracellular matrix on PC 12 cell shape and dopamine processing.

Substrates of various origins can affect the morphology, growth and functional properties of many cell types. PC 12 cells (a clonal line of rat pheochromocytoma) synthesize, store and secrete dopamine as well as other transmitters. These cells are rounded and loosely attached when cultured on plastic, but flatten and spread extensively when cultured on an extracellular matrix secreted by bovine corneal endothelial cells. We determined that spontaneous dopamine release into culture medium was significantly higher from cells which were flattened on matrix, and that the cellular content of dopamine was less than in cells which were maintained on plastic. The higher levels of medium dopamine in matrix cultures were not due to an increase in cellular attachment or growth as determined by [3H]thymidine incorporation. A variant of PC 12 cells which is flat on plastic showed no change in cell shape or dopamine release when plated on matrix. These experiments suggest that extracellular matrix promotes a change in cell shape and that this change in the physical arrangement of these cells alters their release and storage of dopamine.

Adrenal Gland Neoplasms↗
PubMed1984

Stimulatory effect of estrogen on prolactin secretion from primate pituitary cells cultured on extracellular matrix and in serum-free medium.

To determine the direct effect of estrogen on primate PRL production, cultures of dispersed monkey pituitary cells were established in serum-free medium on an extracellular matrix secreted by bovine corneal endothelial cells. Medium PRL levels were monitored by RIA every fourth day after plating. PRL secretion was maintained for 24-28 days in cultures from female monkeys and for 16-20 days in cultures from male monkeys using a 1:1 mixture of Dulbecco's Modified Eagle's Medium H-16 (DME) and Ham's F-12 medium (F12) supplemented with insulin (I), transferrin (T), PTH, T4, fibroblastic growth factor, putrescine, ethanolamine, lipids (oleic, lecithin, and cholesterol), selenium (S), and cadmium (C). The mean percent changes in medium PRL of seven cultures of female pituitaries and two cultures of male pituitaries compared to the first sample (day 4) were: +26% (day 8), +17% (day 12), +11% (day 16), -4% (day 20), -13% (day 24), and -24% (day 28). The elimination of supplements except ITSC did not appear to affect PRL secretion in a culture of cells from ovariectomized female monkeys, but secretion in two cultures of male pituitary cells declined after day 12. Addition of 10(-8) M estrogen to three cultures of male pituitary cells in DME/F12 containing all supplements significantly elevated PRL over control levels and, in addition, prevented the decline observed in control wells of one culture for 28 days. In two cultures of male pituitary cells maintained in DME/F12 plus ITSC, estrogen significantly elevated medium PRL levels for the 28-day period, but did not totally prevent the decline observed in control wells after day 12. In two cultures of female pituitary cells maintained in DME/F12 plus all supplements and in three cultures of female pituitary cells maintained in DME/F12 plus ITSC, medium PRL levels were significantly higher when estrogen was present. However, estrogen addition had no effect on the pattern of PRL secretion in two cultures of female pituitary cells maintained in DME/F12 plus 10% charcoal-treated fetal calf serum. In five of seven cultures, the presence of estrogen for 28 days resulted in a significantly higher cellular content of PRL. These experiments suggest that estrogen can directly increase PRL production by primate mammotrophs and that this effect is best seen in serum-free medium. In summary, extracellular matrix and serum-free medium provide an adequate in vitro environment for studies of PRL processing by primate pituitary cells for periods up to 1 month. In this system, estrogen effectively elevated PRL secretion and cell content.

Animals↗
PubMed1984

Existence of multiple forms of follicle-stimulating hormone within the anterior pituitaries of cynomolgus monkeys.

Ovariectomized cynomolgus monkeys were treated with physiological levels of estradiol and progesterone. A reduction in serum levels of FSH was observed after steroid exposure. Anterior pituitary homogenates were prepared from monkeys after 0, 12, 24, or 36 h of exposure to estradiol and progesterone and quantitated for FSH activity by radioreceptor assay (RRA) and RIA. Pituitary FSH activity (expressed as RRA/RIA) increased with duration of exposure to steroids. Forms of FSH within these pituitaries were separated by the column isoelectric focusing technique, chromatofocusing. All pituitary homogenates tested contained FSH isohormones that eluted at similar isoelectric points. Each FSH isohormone exhibited a mol wt similar to that of a purified FSH standard, but differed in ability to displace labeled FSH from a biological receptor preparation. FSH forms with basic isoelectric points exhibited greater RRA/RIA values than forms with more acidic isoelectric points. The relative proportion of the more basic FSH forms increased within pituitary tissue with duration of exposure to steroids. All FSH forms were secreted by pituitary cells in culture. The biochemical basis for the microheterogeneity appears to be the degree of sialic acid incorporation into the FSH molecule. The results of these studies demonstrate that the cynomolgus monkey pituitary responds to the surrounding hormonal milieu by altering the relative proportions of FSH forms present within that gland.

Animals↗
PubMed1983

Inhibition of prolactin secretion delays extinction of circadian LH surges in ovariectomized rats bearing estradiol implants.

Ovariectomized rats bearing Silastic capsules containing estradiol exhibit a daily afternoon surge of luteinizing hormone (LH) which decreases with time until it is undetectable by Day 10 after implantation of estradiol. Increases in basal prolactin levels as well as afternoon surges are also observed. To determine if increased prolactin secretion contributed to the extinction of the circadian LH surges, we examined the patterns of LH and prolactin secretion in rats in which prolactin was suppressed by bromocriptine treatment. In vehicle-treated control rats, the magnitude of the LH surges decreased with time. Large LH surges were observed on Days 2 and 4. A significant decrease in the surge occurred on Day 6, and it disappeared by Day 10. Animals treated with bromocriptine also exhibited large LH surges on Days 2 and 4, and in addition, secreted a greater amount of LH than the control group on Days 6, 8, and 10. In ovariectomized rats bearing estradiol implants, large afternoon surges in prolactin were observed and by Day 6, basal prolactin levels were also elevated. Bromocriptine treatment completely suppressed prolactin secretion through Day 6, but a small afternoon rise was observed on Days 8 and 10. These findings suggest that elevated prolactin secretion may be one factor contributing to the extinction of circadian LH surges in the estrogen-treated rat.

Animals↗