The posterior pituitary contains a potent prolactin-releasing factor: in vivo studies

The posterior pituitary contains a PRL-releasing factor (PRF), a small (less than 5000 mol wt) peptide which is distinct from known PRL secretagogues. The objectives of this study were to determine if posterior pituitary extracts specifically stimulate PRL release in vivo and to assess the relative contributions of oxytocin (OT), arginine vasopressin (AVP), and beta-endorphin (beta END) to the PRF activity of the extract. Rat posterior pituitaries or cerebellar tissue were extracted with 1.0 N acetic acid, boiled, and ultrafiltered through 5000 mol wt cutoff membranes. The eluates were treated with performic acid (which oxidizes disulfide bonds and methionine residues), lyophilized, and reconstituted in saline. Jugular blood was collected from conscious ovariectomized rats before and after intracarotid injection of test substances and was analyzed for PRL, LH, and GH by RIA. Injection of 0.3, 1.0, and 3.0, posterior pituitary equivalents increased plasma PRL levels by 2-, 8-, and 22-fold, respectively. PRL levels peaked within 5 min after the injection and returned to basal levels by 30 min. Plasma LH levels decreased slightly, and GH was unchanged. Cerebellar extracts did not affect plasma hormone levels. Injection of OT induced a 4-fold rise in plasma PRL levels. Oxidation of OT was well as AVP with performic acid abolished any PRL-releasing activity. Injection of beta END increased plasma PRL levels by 7-fold. Treatment of beta END with performic acid caused a 60% loss in its ability to release PRL. Pretreatment of rats with naloxone abolished the PRL-releasing effect of beta END, but did not alter the PRF activity of posterior pituitary extracts. We conclude that posterior pituitary extracts stimulate PRL release in vivo in the presence of an intact dopaminergic inhibition. This stimulation is rapid, dose dependent, and hormone specific. OT, AVP, and beta END do not contribute significantly to the PRF activity in the posterior pituitary extract.     

Evidence that thyrotropin-releasing hormone is not a major prolactin-releasing factor during suckling in the rat

The purpose of this study was to investigate whether TRH could be an important PRL-releasing factor during suckling in the rat. Plasma PRL, TSH, beta-endorphin-like immunoreactivity, and GH responses in serial blood samples from unanesthetized suckled rats were determined. The resulting hormonal profile was compared with that obtained when TRH (500 ng/kg BW, iv) was injected at the onset of suckling. Suckling evoked a rise in plasma levels of PRL, beta-endorphin-like immunoreactivity, and GH, but not in TSH. In contrast, exogenous TRH caused a 9-fold increase in plasma TSH levels during suckling without further increasing the PRL response. Since plasma PRL responses are reportedly enhanced by previous suckling, we also determined plasma PRL and TSH levels when TRH (25 ng/rat, iv) was given 30 min after a brief suckling episode. TRH caused a 2.5-fold increase in plasma TSH, but did not significantly increase plasma PRL levels. Since suckling increases plasma PRL without increasing plasma TSH, and TRH increases TSH but not PRL levels, we conclude that TRH is not a major PRL-releasing factor during suckling.     

The rat posterior pituitary contains a potent prolactin-releasing factor: studies with perifused anterior pituitary cells

We previously reported that removal of the posterior pituitary abolished the suckling-induced rise in plasma PRL. This suggested that the posterior pituitary contains a PRL-releasing factor (PRF). Using perifused anterior pituitary cells, the objectives of this study were 1) to examine whether the posterior pituitary contains PRF activity as compared to the medial basal hypothalamus (MBH), and 2) to determine to what extent substances known to be present in the posterior pituitary and/or MBH contribute to this activity. Anterior pituitary cells, attached to Cytodex beads, were perifused with medium 199. Tissues were extracted with acid, lyophilized, and reconstituted in medium 199. Tissue extracts and synthetic compounds were introduced to the cells in short pulses. Fractions were collected and analyzed for PRL, LH, and GH by RIA. Posterior pituitary extracts contained a potent substance(s) which stimulated PRL release in a concentration-dependent manner, but did not alter LH secretion. As little as 1% of the extract increased PRL release. In contrast, the MBH extract contained significantly less PRF activity but was capable of stimulating and inhibiting LH and GH release, respectively. Cerebellar extracts did not alter PRL secretion. Of more than 25 neuroactive substances tested in the perifusion system, oxytocin, TRH, and angiotensin II (A II) appeared as likely candidates for PRF. Therefore, the specific receptor antagonists d(CH2)5Tyr(Me) ornithine vasotocin (for oxytocin), chlordiazepoxide (for TRH), or saralasin (for A II) were infused together with the posterior pituitary extract. These antagonists completely abolished the PRL-releasing activities of their respective peptides but failed to reduce the PRF activity of the posterior pituitary. In contrast, PRF activity in the MBH was nearly eliminated by the TRH antagonist. Conclusions: 1) The rat posterior pituitary contains a potent PRF capable of inducing a rapid, hormone-specific, concentration-dependent stimulation of PRL release from perifused anterior pituitary cells. 2) The MBH contains significantly less PRF activity, which is largely attributable to TRH. 3) Although the chemical identity of PRF is yet unknown, the PRF activity in the posterior pituitary is not accounted for by oxytocin, TRH, or A II.     

Ovine corticotropin-releasing factor and vasopressin: antibody-quenching studies on hypothalamic extracts of normal and Brattleboro rats

Stalk median eminence (SME) extracts were preincubated with antibodies to ovine corticotropin-releasing factor (oCRF) and/or vasopressin, and the resulting CRF bioactivity tested with the isolated anterior pituitary cell column bioassay. The ACTH-releasing ability of Wistar rat SME was reduced by 60% with vasopressin antiserum, by 53% with oCRF antiserum, and by 81% after incubation with both antisera simultaneously. SME-stimulated LH release was unaffected by these antisera, which were all used at a dilution of 1:1000. The ACTH-releasing activity of SME could not be completely abolished by increasing the oCRF antibody concentration, or, in the case of ovine SME, by decreasing the tissue concentration preincubated with oCRF antibodies. With Brattleboro SME (which contains no endogenous vasopressin) ACTH-releasing activity was reduced by 37%, 51%, and 57% with anti-oCRF at dilutions of 1:5000, 1:1000, and 1:500, respectively, but could not be reduced further by more concentrated antisera. We conclude, therefore, that the CRF bioactivity of rat SME is probably not due solely to an oCRF-like peptide, but that other substances, one being vasopressin, contribute to its ACTH-releasing ability.     

Evidence that vasoactive intestinal polypeptide is a physiological prolactin-releasing factor in the bantam hen

Vasoactive intestinal polypeptide (VIP)-like material was localised immunohistochemically in the hypothalamus of the bantam hen. Abundant immunoreactive VIP terminals were seen in the external layer of the median eminence and most immunoreactive VIP cell bodies were located in the basal hypothalamus. A few immunoreactive VIP cell bodies and many fibres were found in the preoptic hypothalamus. Intravenous injections of synthetic porcine VIP over a dose range of 12.5 to 100 micrograms kg-1 body wt resulted in dose-related increase in concentration of plasma prolactin in incubating bantams deprived of their nests for 24 hr. These doses of VIP did not stimulate the release of growth hormone. Studies in vitro showed that synthetic VIP directly stimulated prolactin release from the anterior pituitary gland. The glands from incubating bantams were more responsive to the prolactin-releasing effects of VIP than were the glands from laying birds. Studies in vitro showed that the amount of prolactin released in response to an iv injection of 50 micrograms kg-1 VIP was greater in incubating birds deprived of their nests for 24 hr than in laying hens. Prolactin release was not stimulated in ovariectomized hens after an injection of 50 micrograms kg-1 VIP unless the birds were first treated with oestrogen or oestrogen and progesterone. It was concluded that a VIP-like material in the bantam hypothalamus may be a physiological prolactin-releasing factor acting at least in part at the level of the anterior pituitary gland.(ABSTRACT TRUNCATED AT 250 WORDS)     

Evidence that thyrotropin-releasing hormone and a hypothalamic prolactin-releasing factor may function in the release of prolactin in the lactating rat

We have compared the effectiveness of TRH and a rat hypothalamic PRL-releasing factor (PRF; previously incubated with rat serum to destroy TRH) in stimulating the release of PRL into the plasma of conscious lactating rats when injected before and after pituitary PRL had been depleted and transformed into releasable PRL by 10 min of suckling. TRH (1.25 microgramsss) and PRF [equivalent to 2.5 stalk median eminence (SME) fragments] each caused a small increase (38 and 30 ng, respectively) in the plasma PRL concentration within 10 min when injected into nondepleted mothers. The levels then fell quickly. Suckling, by comparison, caused a sustained 175 ng/ml increase above basal levels. Though PRL depletion occurred, as expected, as a result of suckling, there was no measurable depletion within the pituitaries of TRH- or PRF-injected rats. By contrast, the iv administration of TRH (doses ranging from 2-250 ng) and hypothalamic PRF (doses ranging from 0.2-1.0 SME equivalent) after depletion-transformation had been effected by 10 min of suckling resulted in a rapid and, in most instances, a sustained elevation in the plasma PRL concentration comparable to that seen after suckling. Dose-response relationships, though, were not clearly evident with either PRF or TRH. Neither saline, 1.25 microgram TRH previously incubated in serum, 50 mU oxytocin, 1 microgram dopamine, 25 microgram LHRH, nor an extract of cerebral cortex prepared in the same manner as hypothalamic TRH caused plasma PRL to rise after PRL depletion. We conclude that TRH and possibly a separate hypothalamic PRF have a stimulatory action upon the releasable, but not upon the depletion-transformation, phase of PRL secretion in the lactating rat.     

Evidence that serotonin stimulates a prolactin-releasing factor in the rat.

Methanol extracts of rat plasma resulted in release of prolactin (PRL) from rat hemipituitaries in vitro with a linear log-dose relationship. This prolactin-releasing factor (PRF)-like activity was not altered in plasma from rats treated with bromocryptine or chlorpromazine despite significant suppression and stimulation of plasma PRL levels, respectively. Fluoxetine, a serotonin reuptake inhibitor, plus 5-hydroxytryptophan, the immediate precursor of serotonin, markedly stimulated both plasma PRL and plasma PRF-like activity. Neither fluoxetine, 5-hydroxytryptophan, nor the combination directly stimulated PRL release from rat pituitary tissue in vitro. We conclude that serotonergic stimulation augments PRL release via a PRF.     

Oxytocin and vasopressin in rat hypophysial portal blood: experimental studies in normal and Brattleboro rats

Oxytocin (OT) and vasopressin (VP) were measured by radioimmunoassay in hypophysial portal and peripheral blood from male Wistar rats and heterozygous and homozygous Brattleboro rats anaesthetized with urethane. In Wistar rats the concentrations of OT and VP were about 50 times greater than the concentrations in peripheral blood, whether or not the pituitary gland was left in situ during collection, and also considerably greater than the reported concentrations of the peptides in the cerebrospinal fluid. The release of both peptides was increased significantly by a lesion of the supraoptico-hypophysial tract that led to diabetes insipidus, but which left intact the external layer of the median eminence (ME). Concentrations of VP were undetectable in plasma from homozygous Brattleboro rats, but the portal plasma concentrations of VP in heterozygous Brattleboro rats were not significantly lower than in Wistar rats. The concentrations of OT in portal plasma from both types of Brattleboro rat were significantly higher than in Wistar rats. The output of VP and OT into hypophysial portal blood of Wistar rats was not significantly affected by electrical stimulation of the suprachiasmatic, supraoptic or paraventricular nuclei or the ME using two types of stimuli, one of which produced an increase in peripheral plasma concentrations of VP and OT in intact rats and a significant increase in the release of LH-releasing hormone into hypophysial portal blood. The output of VP and OT into portal blood was also not significantly affected by either adrenalectomy with or without injection of dexamethasone or the injection of either the 5-hydroxytryptamine (5-HT) synthesis blocker, parachlorophenylalanine, or the 5-HT uptake blockers, alaproclate or zimelidine. These results show that large amounts of OT as well as VP are released into hypophysial portal blood from fibres of the hypothalamo-neurohypophysial system that terminate in the external layer of the ME. Although distinct from the fibres that terminate in the pars nervosa (PN), the findings in Brattleboro rats show that the VP fibres of the ME system originate in neurones with a genomic mechanism for VP synthesis similar to that of the VP neurones that project to the PN. The lack of effect of adrenalectomy and the administration of 5-HT synthesis and uptake blockers must be interpreted with caution since the results obtained with electrical stimulation suggest that when the pituitary stalk is cut the release of OT and VP into portal blood approaches a maximum and may therefore be difficult to alter by experimental manipulation.(ABSTRACT TRUNCATED AT 400 WORDS)     

Elevated serum oxytocin of the vasopressin-deficient Brattleboro rat is present throughout life and is not sensitive to treatment with vasopressin

The postnatal developmental course of the enhanced OT serum level of the vasopressin-deficient (homozygous) Brattleboro rat was investigated radioimmunochemically together with the response to treatment with Pitressin tannate. Compared with heterozygous Brattleboro (control) pups, in which serum OT appeared to have an adult value from birth onwards (about 10 pmol/l), homozygous rats had approximately 2-fold enhanced OT serum level throughout early development. Between day 55 and adulthood the levels of OT rose further to 40-50 pmol/l. A 3-day treatment with Pitressin tannate both in the period before or after the age (day 16) at which the polyuria of the homozygous Brattleboro mutant can be revealed, failed to reduce the serum OT. It was therefore concluded that the high OT serum levels in the vasopressin-deficient Brattleboro rat are not induced by osmotic imbalance, but probably originates from functional teratological aspects of the mutation.     

Serum insulinlike growth factor is not elevated in patients with multiple myeloma but is still a prognostic factor

Insulinlike growth factor 1 (IGF-1) has growth-promoting effects on myeloma cells in vitro as well as in vivo. In this study, we measured the concentration of IGF-1 and its major binding protein, IGF- binding protein 3 (IGFBP-3), in serum from 127 patients with multiple myeloma. Serum had been drawn at the time of diagnosis, before treatment with high-dose melphalan. IGFBP-3 in myeloma patients (1.6 +/- 0.73 microg/mL; mean +/- SD) was significantly decreased compared to healthy age- and sex-matched controls (2.2 +/- 0.42 microg/mL). However, IGFBP-3 had no prognostic value in this study. The mean IGF-1 level did not differ between myeloma patients (17.8 +/- 7.7 nM) and controls (17.3 +/- 5.6 nM). Nevertheless, IGF-1 was a strong indicator of prognosis. After 80 months of follow-up, myeloma patients with low levels (< 13 nM) of serum IGF-1 had not reached median survival. In the patient group with IGF-1 levels above 13 nM, median survival was 62 months (P =.006). These findings support the hypothesis of a role for IGF-1 in myeloma disease progression.     

The tissue transglutaminase gene is not a primary factor predisposing to celiac disease

OBJECTIVES: The aim of this study was to determine whether the tissue transglutaminase (tTG) gene is a causal factor in the pathogenesis of celiac disease (CD). METHODS: A total of 147 Dutch families with at least one patient with biopsy-proven CD were available for this study. In all patients, CD was diagnosed according to the revised European Society for Pediatric Gastroenterology and Nutrition criteria. A microsatellite marker in a noncoding region of the tTG gene was investigated for both linkage and association. Linkage was tested by determining the amount of allele sharing between affected brothers and sisters (affected sibling [sib] pair analysis). Association was determined by comparing transmission of certain tTG alleles from parents to CD patients to the nontransmitted alleles by the transmission/disequilibrium test. RESULTS: Linkage analysis did not show cosegregation of the tTG gene with celiac disease in our families, and there was no association between certain tTG alleles and celiac disease. Furthermore, the tTG gene could be excluded as a CD susceptibility gene. CONCLUSION: Our results indicate that the tTG gene can be excluded as a major primary genetic factor in CD pathogenesis.     

Liver tissue from lactating rats produces a factor that stimulates prolactin release and gene expression

Liver tissue from nursing rats produces a substance, termed liver lactogenic factor (LLF), that potently stimulates casein release from isolated mammary cells. Inasmuch as the production of LLF is dependent on PRL, we decided to determine whether it could influence the release of the hormone by dissociated pituitary cells in culture. This was accomplished by measuring PRL release with a reverse hemolytic plaque assay and PRL gene expression with a DNA probe complementary to PRL mRNA. Treatment of pituitary cells from day 10 lactating rats with liver slice incubates from the same type of animal caused a 35.3 +/- 4.3% increase in PRL release during a 3-h incubation. Likewise, the same dose of LLF activity markedly increased (3.5-fold) the steady state levels of PRL mRNA. The responses were reasonably specific for PRL, since neither GH plaque development nor gene expression was affected by identical treatment. Taken together these results demonstrate that LLF can act directly at the pituitary level to exert positive feedback effects on both PRL release and gene expression.     

Overweight is not a comorbidity factor during childhood asthma: the GrowthOb study

While being overweight is a risk factor for subsequent asthma in children, the importance of body mass index (BMI) as a comorbidity factor remains debated. The aim of this study was to assess the relationships between being overweight and the characteristics of childhood asthma. The BMI, BMI z-scores and International Obesity Task Force (IOTF) grades were evaluated in asthmatic children according to atopic status, symptoms during the past 3 months, exercise breathlessness, treatment and lung function in 6-15-yr-old children with confirmed asthma. 491 asthmatic children (mean ± SD age 10.8 ± 2.6 yrs; 179 females) were prospectively enrolled. There were 78 (15.5%) overweight (IOTF grade 1) and eight (1.6%) obese (grade 2) children. The children's BMI z-scores did not differ according to atopy, exacerbation, symptom-free days or treatment. The BMI z-score correlated positively with forced vital capacity and forced expiratory volume in 1 s in females, which could be related to earlier puberty in overweight females (growth spurt with increased volumes). Compared with normal weight children, overweight and obese children had reduced lung volume ratios (functional residual capacity/total lung capacity (TLC) and residual volume/TLC), no evidence of airflow limitation and similar symptoms. In conclusion, the observed functional relationships with BMI are not specific to asthma and being overweight is not associated with significant clinical impacts on asthma during childhood.     

Twenty-first century tobacco use: it is not just a risk factor anymore

Despite availability of effective treatments for nicotine addiction, smoking remains prevalent with serious health consequences. Most smokers recognize the ill effects of smoking but are unable to quit. Nicotine addiction may be viewed as any other chronic illness that results from exposure to a recognizable agent (tobacco) and manifests with a well-documented set of signs and symptoms. Much like any chronic disease, both environmental and genetic factors determine the occurrence and severity of this affliction. There has been recent focus on uncovering the genetic basis of nicotine addiction. In this article, we have attempted to briefly review the current evidence for the role of genetics in smoking as well as comment on available pharmacotherapeutic options for treating nicotine dependence.     

Interleukin-10 is a proliferation factor but not a differentiation factor for human myeloma cells

Because interleukin-10 (IL-10) is a potent differentiation factor of human B cells into mature plasma cells, we investigated its effect on human malignant plasma cells. IL-10 did not induce any differentiation and increase in Ig synthesis in four human IL-6-dependent malignant plasma cell lines. However, it stimulated the proliferation of two of four cytokine-dependent cell lines in the absence of IL-6 and IL-10- dependent myeloma cell lines have been obtained. The myeloma cell growth activity of IL-10 was unaffected by anti-IL-6 and anti-IL-6R antibodies. Similarly, IL-10 stimulated (P = .001) the proliferation of freshly-explanted myeloma cells in IL-6-deprived cultures of tumor samples from patients with active multiple myeloma (MM) and produced twice as many myeloma cells in these cultures. Again, this cytokine was unable to induce further differentiation (assessed by rate of Ig production) of fresh myeloma cells. A very sensitive enzyme-linked immunosorbent assay (ELISA; 1 pg/mL) only rarely detected IL-10 in the sera of MM patients (3 of 89). On the contrary, serum IL-10 was detected in 60% of patients with plasma cell leukemia (12 of 20). These data show that IL-10 is an IL-6-unrelated growth factor for malignant plasmablastic cells. This cytokine could be involved in the late phase of MM in vivo.     

Mild hypokalaemia is not a risk factor in treated hypertensives

The possibility that hypokalaemia might increase the mortality of treated hypertensives in the Glasgow Blood Pressure Clinic has been examined by comparison of serum potassium in decedents and survivors and by calculation of age-adjusted mortality rates for patients grouped in quartiles of serum potassium measured at the last clinic visit. In this study, 3783 patients with non-malignant hypertension were followed for an average of 6.5 years and of these 1907 had one or more measurements of serum potassium during their last year of attendance. Serum potassium fell in 414 patients given diuretics with or without other drugs except beta-blockers. This fall was similar in those who died of ischaemic heart disease (3.71 mmol/l) and in those who survived (3.72 mmol/l). Serum potassium rose in 167 patients who received beta-blockers with or without other drugs except diuretics and fell slightly among 1326 patients taking other combinations of drugs. There were no significant differences in serum potassium between decedents and survivors in either of these treatment groups. Age-adjusted mortality in deaths per 1000 patient-years in the lowest quartile of serum potassium (less than 3.7 mmol/l) was 28.1 for men and 15.0 for women. Higher serum potassium was associated with slightly, but not significantly, higher mortality in both sexes. There was no relation between serum potassium and mortality in patients with left ventricular hypertrophy, nor was there a relation when death due to ischaemic heart disease was considered separately. Failure of hypokalaemia to predict outcome was confirmed by univariate and multivariate analyses which included, in addition to potassium, assessment of cigarette smoking, initial blood urea and electrocardiographic findings.(ABSTRACT TRUNCATED AT 250 WORDS)