摘要:

Bradykinin (10–6 and 10–5M) stimulated ACTH-IR release from rat anterior pituitary tissue in vitro concentration-dependently. The onset of this effect was delayed in comparison to that of AVP or CRF. The combined treatment of bradykinin with AVP or CRF produced additive effects of ACTH-IR release. Bradykinin may represent another candidate involved in the regulation of ACTH release. In contrast to AVP, bradykinin did not stimulate prostaglandin E2 synthesis in the pituitary tissue. Bradykinin-induced ACTH-IR release remained unchanged following cyclooxygenase inhibition by indomethacin. It can be concluded that prostaglandins are not involved in the action of bradykinin on the anterior pituitary. Bradykinin did stimulate cyclic AMP accumulation in pituitary tissue. Inhibition of phosphodiesterase by 3-isobutyl-1-methylxanthine (IBMX) potentiated the ACTH-IR release evoked by bradykinin. From the results obtained, we concluded that cyclic AMP appears to be involved as a second messenger in the bradykinin-evoked ACTH-IR rele

ISSN:0028-3835    

DOI:10.1159/000124548

出版商:S. Karger AG    

年代:1986

数据来源: Karger

摘要:

These experiments were designed to characterize the nature and extent of diabetes insipidus present in a new model of genetic vasopressin (VP) deficiency, the Roman high avoidance rat homozygous for diabetes insipidus (RHA: di/di strain). The new strain was developed from an initial cross between Long-Evans derived Brattleboro (LE: di/di) rats and normal Roman high avoidance (RHA: +/+ ) rats, and has been bred to be congenic with the parent RHA: +/+ strain. RHA: di/di rats exhibited polydipsia, excreted dilute urine, and exhibited elevated plasma osmolality. RHA: di/di rats showed a similar urinary response to dehydration as LE: di/di rats. VP was undetectable by radioimmunoassay in the serum, brain, and neurohypophysis of RHA: di/di rats. VP-neurophysin containing cells were not observed in the brains of RHA: di/di rats upon immunocytochemical analysis. Thus, the new RHA: di/di strain exhibits essentially the same profile of diabetes insipidus as the LE: di/di rat. The congenic relationship between RHA: di/di and RHA: +/+ rats makes the RHA: di/di rat a useful model under circumstances where genetic variables unrelated to VP deficiency may confound the interpretation of data.

ISSN:0028-3835    

DOI:10.1159/000124549

出版商:S. Karger AG    

年代:1986

数据来源: Karger

摘要:

In two separate experiments, cerebrospinal fluid (CSF) adrenocorticotropin immunoreactive (ACTH-IR) concentrations in the rhesus monkey followed a significant rostral-caudal gradient. In the first study, CSF was sampled from an indwelling catheter in awake animals. The mean ACTH-IR concentration in the cisternal region was 12.3 pg/ml, as compared to 8.56 pg/ml in the lumbar region. In the second study, CSF was sampled in a different group of monkeys by percutaneous puncture at the cisterna magna and at L5-L6. In this study, the mean ACTH-IR concentration in samples collected from the cistern was also greater than the concentration from L5-L6. In addition, a significant correlation within subjects was found between samples collected from the two sites (r = 0.86). These results demonstrate that the site of CSF sampling is a variable in determining CSF ACTH-IR concentrations and suggest that lumbar CSF ACTH-IR concentrations in humans may be interpreted as indexes of ACTH changes at higher levels in the central nervous system.

ISSN:0028-3835    

DOI:10.1159/000124550

出版商:S. Karger AG    

年代:1986

数据来源: Karger

摘要:

A subpopulation of norepinephrine-containing cells in the cat adrenal medulla contain neurotensin (NT) immunoreactive material. Using high performance liquid chromatography (HPLC) and radioimmunoassay with region-specific antisera we have demonstrated that electrical stimulation of the splanchnic nerve releases NT and its metabolites NT(1–8) and NT(1–12) from cat adrenal gland into the circulation. Blood samples from anesthetized cats were simultaneously collected from the adrenolumbar vein and femoral artery over a 10-min period prior to and during splanchnic nerve stimulation. Trains of stimuli (15 Hz/10V) were applied at 30-s intervals over 10 min. Plasma samples were extracted, run on HPLC and column fractions assayed with C- und N-terminal directed antisera. During splanchnic nerve stimulation there was a fivefold increase in NT levels in the adrenolumbar vein while levels in the general circulation remained unchanged. Concomitant with the increase in NT was a two- to threefold increase in the levels of NT(1–8) and NT(1–12). The chromatographic profiles of extracted adrenal glands showed a major peak of immunoreactive material with the same retention time as NT (18.6 ± 3.0 pmol/g weight wet of tissue) as well as a small peaks on NT(1–8) (0.96 ± 0.18 pmol/g) and N(1–12) (2.05 ± 0.1 pmol/g). HPLC analysis of a tryptic digest of the NT-like material gave 1.0 equivalent of NT(1–8) and NT (9–13). These results are consistent with the presence of NT in adrenal tissue and its release and metabolism during stimulation of th

ISSN:0028-3835    

DOI:10.1159/000124563

出版商:S. Karger AG    

年代:1986

数据来源: Karger

摘要:

Prolactin-secreting pituitary tumors can be induced in young rats through prolonged estrogen treatment. Recent evidence suggests that such tumors are associated with a degeneration of tuberoinfundibular dopaminergic (TI-DA) neurons, which normally inhibit prolactin secretion by the anterior pituitary’s lactrotrophs. For this study, chronic hyperprolactinemia was induced in young, ovariectomized Fischer 344 rats through Silastic capsule implants of 17β-estradiol, placed subcutaneously for 1 month prior to removal. Rats with such estrogen-induced hyperprolactinemia then received transplants of neonatal arcuate-median eminence (ME) tissue (containing TI-DA neurons) or amygdala (control) tissue, placed either within the third ventricle or bilaterally within the hypothalamus. Blood samples were obtained 1 month after transplantation and prolactin concentrations measured by radioimmunoassay. Two of 4 animals receiving ventricularly-placed arcuate-ME transplants and 4 of 7 animals receiving bilateral arcuate-ME transplants showed substantial reductions in plasma prolactin levels compared to mean values in control animals. Follow-up catecholamine (CA) histochemistry indicated a bright fluorescence intensity in the median eminence of animals bearing effective arcuate-ME transplants; this, in contrast to the weak CA fluorescence intensity within the median eminence of animals remaining hyperprolactinemic with ineffective transplants. Furthermore, in sharp contrast to the very low, nonpulsatile LH levels found during a second bleeding in recipients bearing ineffective transplants, recipients with effective arcuate-ME transplants had the high, pulsatile levels of LH characteristic of normal, ovariectomized rats. These data suggest that developing TI-DA neurons, within effective arcuate-ME transplants, became functional to reinstate or accentuate DA inhibition of prolactin secretion and, in so doing, indirectly normalized LH secretion as we

ISSN:0028-3835    

DOI:10.1159/000124551

出版商:S. Karger AG    

年代:1986

数据来源: Karger

摘要:

The intermediate lobe of the rat pituitary contains a trypsin-like protease closely related or identical to glandular kallikrein. This study examined whether glandular kallikrein in the intermediate lobe is under inhibitory control by dopaminergic systems. Male rats were treated for 4–6 days with various doses of the following drugs, alone or in combination: haloperidol (a dopamine receptor blocker), reserpine (a catecholamine depleting agent), and bromocriptine (a dopamine receptor agonist). Neurointermediate lobe () homogenates were prepared. Following activation of latent enzymes with tryspin, glandular kallikrein was measured using two chromogenic peptide substrates. Haloperidol doubled glandular kallikrein activity. Dissection of the revealed that haloperidol specifically increased glandular kallikrein in the intermediate lobe and had no effect on the small amount of activity in the neural lobe. Reserpine also doubled glandular kallikrein and haloperidol did not produce further increases. The reserpine-induced increase in glandular kallikrein was completely blocked by concurrent administration of bromocriptine: this effect was blocked by haloperidol. The results demonstrate that intermediate lobe glandular kallikrein is under inhibitory control by dopaminergic systems. This parallels the regulation of proopiomelanocortin (POMC) synthesis in the intermediate lobe and suggests that glandular kallikrein should be evaluated as a POMC-processing enzym

ISSN:0028-3835    

DOI:10.1159/000124564

出版商:S. Karger AG    

年代:1986

数据来源: Karger

摘要:

The biosynthesis of three Met-enkephalin-containing peptides was studied in the hypothalamo-hypophysial system of normal and lactating female rats by the techniques of in vivo radiolabeling and sequential high-performance liquid chromatographic purification of radiolabeled peptides. Met-enkephalin biosynthesis was stimulated in the lactating animals; however, the products derived from the post-translational processing of the enkephalin precursor appeared to remain constant between the two states, as judged by the ratio of radioactivity present in Met5-enkephalin, Met5Arg6Gly7Leu8-enkephalin and Met5Arg6Phe7-enkephalin. Additionally, 8-fold more radioactive enkephalin was harvested from the median eminence than the posterior pituitary. Measurement of preproenkephalin mRNA in the two states also revealed an increase during lactation. All of these data suggest a physiologically important role for the enkephalins in the regulation of anterior pituitary function.

ISSN:0028-3835    

DOI:10.1159/000124552

出版商:S. Karger AG    

年代:1986

数据来源: Karger

摘要:

The effects of restraint stress applied at different times of the day on levels of five stress-responsive plasma hormones (ACTH, β-endorphin, β-LPH, corticosterone and prolactin) and pituitary cyclic AMP levels were assessed. Different groups of rats were subjected to 15 min of restraint stress at 2-hour intervals over a 24-hour period. Rats were sacrificed immediately upon removal from their home cage (controls) or immediately following restraint (stressed). The time of day of stress exposure markedly affected the stress responses measured. Generally, responses to stress applied at the beginning of the dark cycle (18.00) were less than those seen following stress applied at the beginning of the light cycle (06.00). Stress at 06.00 increased levels of pituitary cyclic AMP 10-fold, while stress applied at 18.00 did not significantly increase pituitary cyclic AMP levels. In stressed rats, high correlations were seen among levels of hormones derived from the common precursor, proopiomelanocortin (ACTH, β-endorphin, β-LPH) and between these hormones and levels of pituitary cyclic AMP. These findings support the hypothesis that pituitary cyclic AMP is involved in the stress-induced release or synthesis of the pituitary hormones ACTH, β-endorphin, and

ISSN:0028-3835    

DOI:10.1159/000124553

出版商:S. Karger AG    

年代:1986

数据来源: Karger

摘要:

Theeffects of a continuous infusion of growth hormone-releasing factor (GRF) on pulsatile growth hormone (GH) secretion were studied in conscious, freely moving rats. Male Sprague-Dawley rats were prepared with 2 indwelling venous catheters and were then housed individually for 6–16 days in isolation chambers. After this period, normal saline, 1.5 µg/h GRF or 15 µg/h GRF were continuously infused for 8 or 31 h via one of the catheters. Blood samples were drawn at ≈ 20-min intervals via the other catheter during the last 6–7 h of the infusion. Plasma GH concentrations were determined by RIA. Saline-treated animals exhibited the typical pattern of spontaneous GH pulses. The frequency of GH pulses in animals infused with either dose of GRF was not different from that of the saline-infused rats. Likewise, trough GH concentrations were similar in all three treatment groups. However, peak GH concentrations in the rats receiving the 15-µg/h GRF infusion were remarkably higher than the concentrations observed in the other two groups, regardless of the duration of the infusion. This resulted in mean GH concentrations being significantly higher (p

ISSN:0028-3835    

DOI:10.1159/000124554

出版商:S. Karger AG    

年代:1986

数据来源: Karger

摘要:

An involvement of catecholamines in the preovulatory gonadotropin surge has been proposed for many years. Specifically, an α-adrenergic mechanism has been implicated in the stimulation of ovulation and LH release. On the other hand, little is known regarding the possible role of adrenergic neurotransmission once a gonadotropin surge has been initiated. In this study, drugs which affect adrenergic receptors were administered centrally to estrogen-primed ovariectomized rats and the effects on serum concentrations of LH and FSH induced by treatment with progesterone at 08.00 h were examined. As expected, the progesterone treatment caused a significant (p < 0.05) increase in blood LH and FSH levels by 14.00 and 15.00 h, respectively, when compared with those seen at 13.00 h. In control rats that received isotonic saline intraventricularly at 15.00–16.00 h, both LH and FSH levels continued to rise linearly and reached peak levels by 17.00 and 18.00 h. By contrast, intraventricular infusion of norepinephrine at 16.00 h caused a significant decrease (p<0.05) in LH levels when compared with the saline-infused control groups. Moreover, rats that received intraventricular infusion of phenylephrine (an α1-adrenergic agonist) at 15.00 h failed to show a significant increase in LH and FSH levels until 19.00 h; this inhibitory effect was mimicked by a relatively more specific α1-adrenergic agonist, methoxamine. Consistent with our previous findings, animals which received intraventricular isoproterenol (a specific β-adrenergic agonist) at 15.00 h also responded with suppressed serum LH levels at 16.00–19.00 h when compared with controls. Thus, in addition to the well-known stimulatory role of NE and α-adrenergic agonists for the onset of the LH/FSH surge, these rather unexpected data suggest that α1-adrenergic neurotransmitters may have a dual and paradoxical role and actually attenuate LH and FSH release (even in a steroid-primed environment) once a gonadotropin surge has been

ISSN:0028-3835    

DOI:10.1159/000124555

出版商:S. Karger AG    

年代:1986

数据来源: Karger