Adhesion performance of UHMWPE after different surface modification techniques.

A novel design of an ultra-high molecular weight polyethylene (UHMWPE) glenoid component has been proposed, based on adhesion to PMMA bone cement. However, due to the non-polar nature of UHMWPE, surface modification techniques are needed to obtain good adhesion and thus for the design to be viable. The aim of the study is to investigate adhesion of UHMWPE after different surface treatments. Three gas-phase surface modification techniques were investigated, namely UV/Ozone, corona discharge and radio frequency glow discharge plasma, as well as abrasion. The surface treated samples were examined using water contact angle, surface energy and roughness measurements, as well as single lap-joint shear testing using polymethylmethacrylate (PMMA) bone cement and methylmethacrylate (MMA) adhesive. The effect of aging on bonded samples has also been investigated. Corona and glow discharge treatments were found to activate the surface as shown by an increase in surface energy of over 100% in an order of less than a minute, corresponding to an increase in ultimate shear stress from 0.12 to 0.40 MPa. In contrast, UV/Ozone required exposure times in the order of minutes to have an effect that was still incomparable to the other gas-phase treatments examined. Abrasion produced slightly better adhesion properties for single lap-joints bonded with PMMA compared to the corona treatment. The best treatment was found to be a combined treatment of surface roughening for 10 s, and subsequently a 90 s glow discharge treatment, resulting in failure of the UHMWPE sheet material.

Hemopoietin-1 activity of interleukin-1 (IL-1) on acute myeloid leukemia colony-forming cells (AML-CFU) in vitro: IL-1 induces production of tumor necrosis factor-alpha which synergizes with IL-3 or granulocyte-macrophage colony-stimulating factor.

Interleukin-1 (IL-1) has hemopoietin-1 (H-1) activity, i.e., it synergizes with macrophage-colony stimulating factor (M-CSF), granulocyte-macrophage-CSF (GM-CSF) and interleukin-3 (IL-3) in stimulating in vitro colony formation of hematopoietic progenitor cells. In this study the synergistic activity of IL-1 was investigated on IL-3 and GM-CSF induced growth of acute myeloid leukemia colony forming cells (AML-CFU) in vitro. Among 12 cases of human AML, IL-1 significantly elevated IL-3 stimulated colony numbers in eight instances and enhanced GM-CSF induced colony growth in five cases. As IL-1 is an inducer of cytokine production and since tumor necrosis factor (TNF) elevates IL-3 or GM-CSF induced proliferation of AML-CFU, we examined whether IL-1 enhanced AML-CFU growth via the induction of TNF production. Neutralizing anti-TNF-alpha antibodies significantly decreased IL-1/IL-3 or IL-1/GM-CSF stimulated colony numbers in six of seven cases studied, whereas anti-TNF-beta had no effect, indicating that endogenously produced TNF-alpha costimulated the growth of AML-CFU. Furthermore, AML blast cells stimulated by IL-1 released increased amounts of TNF-alpha (between 25 and 533 pg/ml; median 255 pg/ml) into the culture medium (TNF-alpha specific radioimmunoassay) as compared with noninduced AML cells (less than 1 to 149 pg TNF-alpha/ml; median 31 pg/ml). Thus, the effect of IL-1 on AML-CFU proliferation is not the result of direct activation of AML progenitors, but IL-1 stimulates the release of TNF-alpha by AML cells and endogenous TNF subsequently synergizes with IL-3 or GM-CSF.

Effect of interface conditions between ultrahigh molecular weight polyethylene and polymethyl methacrylate bone cement on the mechanical behaviour of total shoulder arthroplasty.

The aim of this study was to investigate the effect of the interface condition between polymethyl methacrylate (PMMA) bone cement and the ultrahigh molecular weight (UHMWPE) glenoid component on cement stresses and glenoid component tilting in a finite element (FE) model. The background of this research is that most FE models assume bonding between the PMMA bone cement and the UHMWPE component, although it is very doubtful that this bonding is present. An FE model of a cemented glenoid component was developed and a joint compression force and subluxation force of 725 and 350 N respectively were applied. The maximal principal stresses in the cement layer ranged between 21.30 and 32.18 MPa. Glenoid component tilting ranged between 0.943 degrees and 0.513 degrees. It was found that the interface condition has a large effect on the maximal principal stresses and glenoid component tilting. Whether adhesion between the UHMWPE component and PMMA bone cement occurs is unknown beforehand and, as a result, design validation using the FE technique should be carried out both by using contact elements in combination with a coefficient of friction as well as by a full bonding at this interface.

Studies on the effects of catecholestrogens on prolactin secretion by cultured normal rat anterior pituitary cells.

The catecholestrogens 2-hydroxyesterone (2-OHE1) and 2-hydroxyestradiol (2-OHE2) are shown to directly inhibit PRL release by cultured normal rat anterior pituitary cells if they have been cultured in charcoal-treated estrogen-stripped fetal calf serum. Both catecholestrogens affect PRL release in a dose-dependent bimodal way. 2-OHE1 (1 microM) maximally inhibits PRL release by 38%, but 10 microM of the substance has no effect. In contrast, 0.1 microM 2-OHE2 maximally inhibits PRL release by 37%, while the effect of 1 microM of the compound was significantly less (-26%). The effect of the catecholestrogens on PRL release by cultured pituitary cells was significant after 2 h and was still effective after 48 h. The mechanism of action of 2-OHE1 and 2-OHE2 probably does not involve dopamine receptors, as 50 nM haloperidol did not alter the PRL release inhibitory effect of these substances. Moreover, 2-OHE1 and 2-OHE2 did not affect dopamine-mediated inhibition of PRL release. The total amount of PRL (medium plus cells) present in cultures of normal pituitary cells exposed to 2-OHE1 or 2-OHE2 was identical to that in control cells. TRH (100 nM)-stimulated PRL release from cells exposed to catecholestrogens was significantly higher than that from control cells. Addition of the calcium entry-blocking agent verapamil prevented the inhibitory effect of dopamine on PRL release, but did not prevent the effects of 2-OHE1 and 2-OHE2. Preincubation of cultured normal rat pituitary cells for 30 min with 50 nM estradiol completely prevented the inhibitory effects of 2-OHE1 and 2-OHE2 on PRL release. In conclusion, the acute inhibitory effects of the catecholestrogens 2-OHE1 and 2-OHE2 on PRL release by cultured normal rat pituitary cells do not involve dopamine receptors or calcium transport over the cell membrane. These effects are only demonstrable after culture of the cells in charcoal-treated fetal calf serum and can be completely prevented by short term preincubation with estradiol. Our observations support the suggestion that the action of estradiol on lactotropic cells may be modulated by its metabolites, which have opposite effects on PRL release.

Growth hormone secretion by cultured rat anterior pituitary cells. Effects of culture conditions and dexamethasone.

Optimal conditions were sought for the study of GH secretion by cultured normal pituitary cells. Dispersed rat pituitary cells were cultured for 1 week in four different media supplemented with 10% fetal calf serum. Minimal essential medium resulted in high GH content and secretion during a 4-h incubation period, whereas GH secretion was lower (P less than 0.05) for cells cultured in medium 199, Ham's F-10, and RPMI-1640. GH secretion/24 h declined gradually with time. After 2 weeks in culture hormone secretion amounted to 30% of secretion on day 1, but after 3 weeks GH secretion was still measurable. GH recovery during the 3-weeks culture period was more than 600% of the amount initially plated. GH secretion was positively correlated with the bicarbonate concentration between 0.85 and 2.2 g/liter NaHCO3. When pituitary cells were cultured in concentrations varying from 0.5 X 10(5) to 10 X 10(5) cells per dish, GH secretion and content per cell were constant, suggesting that no direct autofeedback occurred in cultures with high cell densities and thus high medium GH. Dexamethasone stimulated GH secretion and content in a dose-dependent way (0.1 nM-10 microM). The stimulatory effect of 100 nM dexamethasone occurred within 24-48 h. After 7 days of treatment with 100 nM dexamethasone, GH secretion had increased to 190% and GH content to 230% of control. In contrast to the effects on GH, dexamethasone suppressed PRL secretion in a dose-dependent way, but this effect was seen only after 7 days of treatment and not after 4 days of treatment. Cycloheximide and actinomycin D prevented the stimulatory effect of dexamethasone on GH secretion. However, 24 h after cessation of cycloheximide treatment GH secretion was stimulated by dexamethasone. Four days of treatment with 100 nM dexamethasone did not affect the GH response to somatostatin, prostaglandin E1, and theophylline, nor the PRL response to dopamine, TRH, and theophylline. Thus, culture conditions may affect GH production, and dexamethasone can be used to culture somatotrophs for longer periods with steady GH production and normal responsiveness.

Hyperprolactinemia exerts a negative effect on the beta-endorphin content of the rat neurointermediate pituitary lobe.

Implantation of the PRL, ACTH, beta-endorphin (beta-EP), and beta-lipotropin (beta-LPH)-secreting transplantable rat pituitary tumor 7315a resulted in a suppression of the PRL and the ACTH content of the anterior pituitary gland and also of the beta-EP/beta-LPH content of the neurointermediate (NI) lobe. Treatment with bromocriptine further diminished the anterior lobe PRL content, whereas haloperidol partially inhibited this tumor-mediated diminution. The administration of these drugs did not influence the suppressed ACTH content of the anterior pituitary lobe. The diminished beta-EP/beta-LPH content of the NI lobe of tumor-bearing rats became completely normal after treatment with haloperidol, whereas bromocriptine administration further diminished the NI lobe beta-EP/beta-LPH content. There was a close correlation between the anterior pituitary lobe PRL content and the beta-EP/beta-LPH content of the NI lobe in all four groups of rats taken together (including nontumor-bearing controls, control tumor rats, and tumor rats treated with bromocriptine or haloperidol; P less than 0.01). Implantation of the pure PRL-secreting pituitary tumor 7315b resulted in hyperprolactinemia and a suppression of the PRL content of the anterior lobe and the beta-EP/beta-LPH content of the NI lobe, without affecting the ACTH content of the anterior pituitary lobe. There was a negative correlation between the level of the circulating PRL concentration and the beta-EP/beta-LPH content of the NI lobe. These results suggest a possible relationship between the synthesis of PRL by the anterior pituitary lactotroph and of the hormones of the NI lobe. The level of the circulating PRL concentration may play, directly or indirectly, a role in the regulation of both systems.

Absence of a suppressive effect of 2-hydroxyestrone on hyperprolactinemia in patients with prolactinomas before and after estradiol administration.

The effect of the infusion of 2-hydroxyestrone (125 micrograms/h for 8 h) on plasma PRL levels was investigated before and 64 h after the administration of 1 mg estradiol benzoate in five patients with PRL-secreting pituitary adenomas. There was no effect on the circulating PRL levels measured hourly for 8 h during both episodes of 2-hydroxyestrone infusion, but plasma LH and FSH levels were suppressed. Infusion of 2-hydroxyestrone in two hyperprolactinemic patients with craniopharyngeomas also did not change the circulating PRL levels. We conclude that: 1) 2-Hydroxyestrone does not suppress PRL levels in patients with prolactinomas. This is not caused by the low estrogenic state of these patients, because 2-hydroxyestrone remained ineffective after the administration of estradiol. 2-Hydroxyestrone was also not able to suppress the estradiol-induced stimulation of PRL release. 2) 2-Hydroxyestrone does not diminish PRL levels in patients with suprasellar tumors and hyperprolactinemia. Therefore, infusion of 2-hydroxyestrone cannot be used in the differential diagnosis of hypothalamic and tumoral hyperprolactinemia.

The interrelationship between the effects of somatostatin and human pancreatic growth hormone-releasing factor on growth hormone release by cultured pituitary tumor cells from patients with acromegaly.

The effects of somatostatin (SRIF) and human pancreatic tumor GRF on GH release by cultured pituitary tumor cells obtained during transsphenoidal operation from 15 acromegalic patients were investigated. In a study of the sensitivity of pathological GH release to SRIF, 1-10 nM SRIF induced maximal inhibition of hormone release in 3 consecutive tumors. In 12 of 15 tumor cell cultures, 10 nM SRIF produced statistically significant inhibition of basal GH release by 39 +/- 3% (mean +/- SEM). In 2 of the 3 other tumors, SRIF inhibited GRF-stimulated GH release, while this was not investigated in the third tumor. A dose-response study of the effect of GRF on GH release by cultured pituitary tumor cells showed that doses of 0.1, 1, 10, and 100 nM induced similar maximal (35%) stimulation of hormone secretion. In four of five consecutive tumor cell suspensions, 1 and 10 nM GRF induced statistically significant GH stimulation by 18-300%. Preincubation of the tumor cells with 5 nM dexamethasone greatly increased the sensitivity and the maximal stimulation in response to GRF and made one tumor cell suspension, which did not react to GRF initially, sensitive to GRF. In the tumors of four patients, the interrelationship between the effects of SRIF and GRF on GH release were also studied. SRIF (10 nM) inhibited the stimulatory effects of GRF on GH release virtually completely. In conclusion, GH release by in vitro cell cultures of GH-secreting pituitary adenomas was inhibited by SRIF and stimulated by GRF. The interaction of GRF and SRIF on GH release by these pituitary tumor cells was similar to that in normal rat GH cells, as SRIF virtually completely overcame the GRF-induced GH release.

Differences in the interaction between dopamine and estradiol on prolactin release by cultured normal and tumorous human pituitary cells.

We studied the interaction between dopamine and estradiol on PRL release by cultured normal and tumorous PRL-secreting cells prepared from human pituitaries. If pituitary glands were obtained within 3 h after sudden death of previously normal individuals, the viability of isolated pituitary cells prepared by dispersion with dispase was more than 75%. After 4 days of culture, dopamine (500 nM) inhibited PRL release by cells prepared from four normal pituitaries by 24 +/- 3% (+/- SEM). Pretreatment of the cells with 100 nM estradiol did not alter dopamine-mediated inhibition of PRL release. Estradiol alone increased basal PRL release and cell PRL content. Cultured PRL-secreting pituitary tumor cells, obtained by transsphenoidal operation from four patients, were similarly sensitive to dopamine. Estradiol stimulated tumor cell PRL release and content, but significantly diminished the inhibitory effect of dopamine. The estrogen receptor blocker tamoxifen did not alter PRL release, but it did reverse the estradiol-induced insensitivity of the prolactinoma cells to the dopamine agonist bromocriptine. In conclusion, these in vitro results indicate that estrogens do not antagonize the effect of dopamine on normal human PRL-secreting pituitary cells. In human pituitary tumor cells, however, estradiol decreased the sensitivity of PRL release to dopamine (agonists), and the estrogen action can be acutely reversed by tamoxifen.

The somatostatin analog SMS 201-995 induces long-acting inhibition of growth hormone secretion without rebound hypersecretion in acromegalic patients.

The acute effect of the somatostatin analog SMS 201-995 (SMS) was investigated in eight acromegalic patients. This substance is an octapeptide [DPhe-Cys-Phe-D-Trp-Lys-Thr-Cys-Thr-(ol)] that inhibits GH release in experimental animals and man. After a control day, 50 micrograms SMS were injected sc, and plasma GH and insulin and blood glucose levels were measured at multiple intervals for 24 h. GH significantly (P less than 0.001) decreased in seven of eight acromegalic patients from 30 +/- 5 (+/- SE) to an average of 10.7 +/- 4 micrograms/l from 1-10 h after drug administration. No rebound effect occurred. Postprandial blood glucose levels were significantly (P less than 0.01) higher between 2 and 4 h after SMS treatment compared with control day values, and there was a substantial reduction in insulin secretion, as estimated by the area under the curve (P less than 0.01), during the first 3 h after SMS administration. Circulating GH was not altered by SMS or the dopamine agonist mesulergine in one patient, but the combination of both substances (50 micrograms SMS, sc, and 0.5 mg mesulergine, orally) reduced GH to below 50% of basal. In vitro studies showed that 1 PM, 0.1 nM, and 10 nM SMS or natural somatostatin exerted a similar inhibitory effect (12-39% reduction; P less than 0.01 for all three strengths) on GH release by cultured human pituitary tumor cells. In conclusion, the somatostatin derivative SMS exerts a potent and prolonged inhibitory action on GH secretion and a shorter lasting suppression of insulin in acromegalic patients. Therefore, it may represent a useful tool in the chronic management of this condition.

Corticotropin-releasing factor (ovine) and vasopressin exert a synergistic effect on adrenocorticotropin release in man.

The effects of ovine CRF, lysine vasopressin (LVP), and their interrelationships, and rat hypothalamic extract (HME), on ACTH and beta-endorphin release by human pituitary tumor cells from two patients with Nelson's syndrome and one with Cushing's disease and on ACTH and cortisol secretion in vivo were studied. In cultured pituitary tumor cells, both LVP and CRF greatly stimulated ACTH and beta-endorphin release at maximally active concentrations of 0.1 microM and 10 nM, respectively. At these concentrations, the combination of the two substances had an additive or synergistic effect on hormone release. Low concentrations of HME potentiated and/or were synergistic with CRF-mediated ACTH release. In vivo, the combination of CRF (1 microgram/kg) and LVP (10 pressor units) induced greater ACTH release than the sum of the responses to CRF and LVP alone. This synergistic effect of CRF plus LVP concerned only ACTH release, while cortisol release after CRF plus LVP was equivalent to the sum of the maximal increments in this hormone after CRF and LVP alone. The peak levels of cortisol after a combination of CRF and LVP probably reflect the maximum stimulatory capacity of the adrenal cortex. These data support the concept that in man, both ovine CRF and vasopressin are corticotropin-releasing factors which act synergistically. Both substances might well regulate, at the pituitary level, the responsiveness of the pituitary-adrenal axis to stimuli reaching the hypothalamus. A test using ovine CRF and LVP together might provide a better index of total pituitary ACTH reserve than one using the two compounds separately.

Testosterone secretion by cultured arrhenoblastoma cells: suppression by a luteinizing hormone-releasing hormone agonist.

A patient with virilization was studied. The basal urinary excretion of 17-ketosteroids was at the upper limit of normal, but the plasma testosterone concentration was greatly elevated. Testosterone secretion could be stimulated by hCG, suppressed by dexamethasone, and was not affected by ACTH. At operation, an arrhenoblastoma of the left ovary was found. Isolated tumor cells in culture secreted testosterone. The addition of a LRH agonist (10 ng/ml) suppressed the secretion of testosterone by 50% (P less than 0.01). The inhibiting effect of a LRH agonist on steroidogenesis suggests that LRH receptors were present on this tumor and that treatment with LRH agonists might be beneficial in patients with metastatic steroid hormone-secreting ovarian and testicular tumors.

A met-enkephalin analog inhibits adrenocorticotropin secretion by cultured pituitary cells from a patient with Nelson's syndrome.

ACTH excretion by cultured nonenzymatically dispersed pituitary tumor cells from a patient with Nelson's syndrome was studied. Hormone release was suppressed by 74 +/- 6% by the addition of 1 microM of the met-enkephalin analog FK 33824, while naloxone (1 microM) stimulated ACTH release by 70 +/- 5%. Somatostatin, dexamethasone, bromocriptine, and cyproheptadine in a concentration of 1 microM each inhibited ACTH release by 25 +/- 2%, 35 +/- 2%, 52 +/- 2%, and 61 +/- 4%, respectively, while lysine vasopressin (0.1 microM) and dibutyryl cAMP (5 mM) stimulated ACTH release by 112 +/- 8% and 220 +/- 4%, respectively. In conclusion, it was shown that the stimuli mentioned above directly affect ACTH secretion by the pituitary tumor cells. The inhibitory action of the met-enkephalin analog and the stimulatory action of naloxone on ACTH secretion make the presence of opiate receptors on this type of tumor likely.

The effects of bromocriptine, thyrotropin-releasing hormone, and gonadotropin-releasing hormone on hormone secretion by gonadotropin-secreting pituitary adenomas in vivo and in vitro.

The characteristics and dynamics of hormone secretion in vivo and in vitro were investigated in six patients with gonadotropin-secreting pituitary adenomas. All six tumors secreted and contained FSH and different combinations of LH, beta-LH, and alpha-subunit. In addition, immunohistochemical examination of the pituitary tumor tissue showed staining with both LH and FSH in three and either LH or FSH in the other three tumors. TRH and GnRH stimulated hormone secretion in vivo and in vitro, and they also increased the hormone content of the cultured tumor cells. Bromocriptine significantly inhibited hormone release and reduced the hormone content of the tumor cells. In vivo, 2.5 mg bromocriptine significantly suppressed plasma hormone levels; the inhibiting effect on alpha-subunit concentrations was in general more marked than that on LH and FSH. We conclude that hormone release by gonadotropin-secreting pituitary adenomas can be stimulated by TRH and GnRH and inhibited by bromocriptine. Most of these tumors synthesize FSH, but there is a wide variation in the production of LH, beta-LH, and alpha-subunits. The sensitivity of hormone release to bromocriptine suggests that chronic therapy with this drug might have a beneficial effect on pituitary tumor size.

Mechanism of action and tolerance of mesulergine.

The tolerance and prolactin (PRL) release-inhibiting action of the 8 alpha-aminoergoline, mesurlergine, were investigated. In a blind crossover study in six subjects with hyperprolactinemia, 0.5 mg mesulergine induced fewer side effects than did 2.5 mg bromocriptine, while the PRL release-inhibiting effect of the two was of the same order. Six different subjects with suspected PRL-secreting pituitary adenomas who (repeatedly) had to discontinue bromocriptine because of nausea, vomiting, or symptoms of orthostatic hypotension were treated for 20 mo with mesulergine (1 to 2 mg/day). Mesulergine did not induce side effects and its actions resembled those of bromocriptine. Mesulergine induced cessation of galactorrhea and resumption of normal menstrual cycles in five subjects, while in one subject an insufficient luteal phase persisted. No abnormalities in routine blood parameter estimations were observed. In two of three subjects there was shrinkage of a pituitary tumor after 12 to 15 mo on mesulergine. Mesulergine did not directly inhibit PRL release by cultured normal rat pituitary cells and human prolactinoma cells and it antagonized the action of dopamine in a dose-dependent manner. This suggests that the dopaminergic action is carried out by a metabolite of mesulergine, while the parent drug probably prevents the well-known side effects of dopamine-agonistic drugs by its dopamine receptor blocking activity. Because of its acceptability, mesulergine might be important in the treatment of hyperprolactinemia and perhaps also of acromegaly and Parkinson's disease.

Tissue polypeptide-specific antigen: a discriminative parameter between prostate cancer and benign prostatic hypertrophy.

The serum concentration of the cell proliferation marker TPS (tissue polypeptide-specific antigen) was compared with the tumour marker PSA (prostate specific antigen). PSA was found elevated in 50% of the benign prostatic hypertrophy (BPH) patients, in 88% of the patients with active prostate cancer and in 40% of the patients who were in an inactive phase. For TPS these values were 6, 34 and 0%, respectively. The metastatic progression was biochemically mirrored by pronounced elevations of PSA and TPS. These data suggest that TPS might be a valuable adjunct in the diagnosis and follow-up of patients with prostate cancer, especially in differentiating benign from malignant deterioration of the disease.

Increases in leucocyte and platelet counts induced by the alkyl phospholipid hexadecylphosphocholine.

Hexadecylphosphocholine (HePC) is a new alkyl phospholipid that has been shown to have antitumour activity in vitro and in vivo. In vivo studies have shown absence of bone marrow toxicity at therapeutic doses. In addition, at the highest dosage group in rats, an increase in white blood cell counts (WBC) was observed. To study the presence of a similar phenomenon in man, frequent measurements of haematological parameters were performed in a series of phase II studies. 70 patients were treated with daily doses of 100-200 mg of the oral formulation of HePC. WBC and platelet counts were performed weekly. In a subgroup of 23 patients serum levels of haemopoietic growth factors were measured before and during treatment. A significant increase in WBC and platelet counts was seen in 74 and 73% of the patients, respectively. In 4 patients, bone marrow showed normal cellularity, and in 1 patient, bone marrow culture showed normal numbers and sizes of colony forming units. No abnormal levels or trends over time of cytokines were observed. We conclude that oral HePC induces an increase in WBC and platelet counts in the majority of those treated.

Human growth hormone-secreting pituitary adenoma cells in long-term culture: effects of dexamethasone and growth hormone releasing factor.

Growth hormone-secreting human pituitary adenoma cells in long-term culture show a decline in GH secretion. We investigated the effects of dexamethasone on GH production and on the responsiveness of the adenoma cells to various drugs. Twenty-four-hour GH secretion by cultures from seven acromegalics was consistently stimulated by 100 nM-dexamethasone. In four out of seven cultures the effect of dexamethasone occurred within 24 h. After 3 weeks in culture the decline in GH secretion by control cultures was over 90%, while in dexamethasone-treated cultures this was limited to less than 50%. The effect of dexamethasone was dose-dependent over a range of 1 nmol/l to 10 mumol/l. Dexamethasone stimulated not only GH secretion (fivefold), but also GH content (twofold). Cycloheximide and actinomycin D blocked the stimulatory effect of dexamethasone on GH secretion, the latter irreversibly. After 4 days of treatment with 100 nM-dexamethasone, the relative effects of somatostatin, prostaglandin E1, bromocriptine and thyrotrophin releasing hormone were the same in treated and untreated cultures. However, the response to synthetic GH releasing factor (GRF) was greatly enhanced by pretreatment of adenoma cells with dexamethasone (100 and 5 nmol/l). Cells unresponsive to small concentrations of GRF could be stimulated effectively by GRF after pretreatment with dexamethasone.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of cyproheptadine, desmethylcyproheptadine, gamma-amino-butyric acid and sodium valproate on adrenocorticotrophin secretion by cultured pituitary tumour cells from three patients with Nelson's syndrome.

The effects of cyproheptadine, desmethylcyproheptadine, serotonin, gamma-amino-butyric acid (GABA) and sodium valproate were studied on ACTH secretion by cultured nonenzymatically dispersed pituitary tumour cells from three patients with Nelson's syndrome. Cyproheptadine (1-10 mumol/l) and desmethylcyproheptadine (1-10 mumol/l) suppressed ACTH secretion significantly (P less than 0.01), while serotonin (10 mumol/l) did not have a direct effect. Serotonin was also not able to reverse the (desmethyl)cyproheptadine-mediated inhibition of ACTH release. Sodium valproate and GABA did not exert a direct effect on hormone release by these cultured pituitary tumour cells. It is suggested that cyproheptadine-mediated inhibition of ACTH release in Nelson's syndrome might be effected by a direct non-serotonin-related effect on the pituitary tumour, while sodium valproate suppresses ACTH release by a suprahypophysial action.

Basal and dopamine-inhibited prolactin secretion by rat anterior pituitary cells: effects of culture conditions.

Culture conditions for rat pituitary cells were investigated which would result in high PRL synthesis and secretion with maintenance of dopamine-mediated inhibition of PRL secretion. From five commercially available media, RPMI resulted in the highest PRL content and secretion, but no inhibition of PRL secretion by dopamine was observed. MEM with Earle's salts fulfilled best our requirements for culturing functional PRL-secreting cells. PRL secretion was not affected by variations in the concentration of fetal calf serum, but was positively correlated with increasing horse serum concentrations. TRH-induced PRL release increased with increasing serum concentrations and was positively correlated with the concentration of 17 beta-estradiol in the culture medium (P less than 0.0025). An increase in the sodium bicarbonate concentration from 0.85 to 3.0 g/l resulted in a 4-fold stimulation of PRL synthesis and in a 27-fold stimulation of PRL secretion. However, at bicarbonate concentrations above 2.6 g/l, inhibition of PRL secretion by 500 nM dopamine was lost. The addition of 20 mM Hepes to the culture medium decreased basal PRL secretion by 48 +/- 13% (P less than 0.01), while dopamine inhibition of PRL secretion was reduced from 49 +/- 10% to 24 +/- 8% (P less than 0.05). When an increasing number of pituitary cells was cultured in a constant volume, PRL secretion expressed per cell increased up to 0.3-0.4 X 10(6) cells/dish/2 ml. With higher cell concentrations of up to 1 X 10(6) cells/dish, PRL secretion per cell diminished significantly, which indicates a direct negative feedback of high medium PRL on the PRL-secreting pituitary cells. In this culture system dopamine inhibited PRL secretion over a 4 h period in a dose-dependent manner (IC50 20 nM), while no paradoxical stimulation of PRL secretion was observed with low dopamine concentrations. However, a 25% stimulation (P less than 0.05) of PRL secretion by 0.1 nM dopamine could be obtained by addition of 0.01% ascorbic acid, which by itself decreased basal PRL secretion by 49% (P less than 0.01). Thus, tissue culture conditions that result in high PRL production are not necessarily the best choice, since dopamine-mediated inhibition of PRL secretion is another important parameter for the functioning of lactotrophs in culture. The best compromise is MEM with 2.2 g/l of sodium bicarbonate, without Hepes buffer and supplemented with 10% FCS.