摘要:

The hypothalamopituitary-adrenal axis exhibits a diurnal rhythm as witnessed by the daily excursion of corticosterone in plasma. The rhythm appears to be mediated largely by the stimulation of CRH neurons in the paraventricular nucleus (PVN) of the hypothalamus. In the present study, we investigated the effects of circadian influence on CRH mRNA levels in the paraventricular hypothalamus. Animals were sacrificed through a 24-hour period to establish a detailed time course of CRH mRNA fluctuations. Levels of both type I and type II corticosterone receptor mRNAs were also measured in this area to see whether changes correlate with that of CRH mRNA. Plasma levels of ACTH were quantified as an index for CRH peptide secretion. The results indicate that changes in ACTH closely paralleled alterations in corticosterone levels with an increasing trend starting at 1 PM, suggesting that the diurnal secretory drive commences around this time. The CRH mRNA rhythm as determined by RNase protection assays appeared to change in an anticipatory fashion to these endocrine fluctuations, increasing during the light phase and reaching maximal levels just prior to dark (5-6 PM). An abrupt decrease of 30% in the CRH mRNA content was detected in the hypothalamus within 2 h after dark (8 PM) and coincided with the peak of plasma corticosterone levels. However, other periodic variations in the CRH mRNA content were not accompanied by changes in plasma corticosterone. Neither types of corticosterone receptor mRNAs showed any diurnal change suggesting that the expression of steroid receptors in the hypothalamus is not regulated by circadian influences. We conclude that CRH mRNA levels fluctuate diurnally but are inversely related to corticosterone levels only in the early evening.

ISSN:0028-3835    

DOI:10.1159/000126099

出版商:S. Karger AG    

年代:1992

数据来源: Karger

摘要:

During the neonatal period in male macaques, the testis produces adult-like levels of plasma testosterone (T), but the function of this in development is not understood. To investigate the interaction of T with the neonatal brain, 4 male and 5 female cynomolgus monkeys were gonadectomized 2-5 days after birth, and were injected subcutaneously 3 days later with 500 µCi [3H]-testosterone ([3H]-T). 60 min later, brains and other tissue samples were removed. Purified nuclear pellets were prepared by centrifugation through 2 M sucrose, extracted into ether and analyzed by high-performance liquid chromatography. The aromatized metabolite, [3H]-estradiol ([3H]-E2), was found only in the hypothalamus (HYP) and amygdala (AMG). In HYP, [3H]-E2 represented 55 ± 3% of the radioactivity in males and 53 ± 3% in females. In AMG, [3H]-E2 represented 40 ± 9% of the radioactivity in males and 47 ± 3% in females. Concentrations of unchanged [3H]-T were higher than those of [3H]-dihydrotestosterone ([3H]-DHT). Both androgens were present in nuclear pellets from all 8 brain regions studied, and concentrations were significantly higher in females than in males (p < 0.005). [3H]-T was also the main form of radioactivity in nuclear pellets from pituitary gland, adrenal gland, uterus and liver, but very high levels of [3H]-DHT were found in seminal vesicles, prostate and penis. Comparisons were made with previous results from orchidectomized fetuses at 122 days gestation and from fully adult male castrates, and the largest developmental changes occured in the AMG where concentrations of [3H]-E2 were 20-fold higher in adults than in fetuses, and most of this increase took place after the neonatal stage. Nuclear concentrations of [3H]-T also increased markedly during development in most brain regions except the cerebellar cortex where they decl

ISSN:0028-3835    

DOI:10.1159/000126100

出版商:S. Karger AG    

年代:1992

数据来源: Karger

摘要:

The topographical location of tyrosine hydroxylase (TH) neurons, a marker for dopamine neurons in the hypothalamus, that project to the median eminence was identified with immunofluorescence staining in combination with retrograde transblue, indicating that they projected to the median eminence. Only a few retrogradely labeled TH cells were observed in the periventricular nucleus and the lateral basal hypothalamus. The elution restaining procedure revealed that an average of 32% of the labeled TH cells in the ventrolateral portion of the ARC contained GRF. These findings support the hypothesis of co-expression of dopamine with GRF from the ARC.

ISSN:0028-3835    

DOI:10.1159/000126101

出版商:S. Karger AG    

年代:1992

数据来源: Karger

摘要:

Insulin-induced hypoglycemia is a metabolic stress that stimulates secretion of adrenocorticotropic hormone (ACTH) and cortisol in a number of animal species. Dexamethasone is a potent synthetic glucocorticoid that suppresses the secretion of ACTH and cortisol. Both ACTH and cortisol exhibit complex secretory patterns demonstrating ultradian and circadian rhythms. This work investigated the pattern of ACTH and cortisol response to hypoglycemia in goats and the effect of dexamethasone on this response. Five goats were pretreated with dexamethasone (0.1 mg/kg) and 5 with saline. Blood samples were taken every 2 min for 60 min before and 60 min after administration of insulin (2.5 IU/kg, i.v.). Immunoreactive ACTH and cortisol were measured in all samples and glucose in selected samples. Data sets were analyzed for significant pulses with the Cluster Analysis program. Complete data sets were compared as well as those for each 30-min interval. Plasma glucose was lower than preinsulin levels at 10 min, declined rapidly between 10 and 30 min, and remained low 30-60 min after insulin injection in both treatment groups. Controls showed a rapid rise in ACTH and cortisol beginning 30 ± 10 min postinsulin. The increase in mean plasma hormone levels during hypoglycemia was predominantly due to an increase in amplitude of secretory pulses for ACTH and cortisol compared with the 30 min before insulin. Dexamethasone significantly lowered mean ACTH and cortisol levels and prevented alteration in plasma ACTH and cortisol secretion during hypoglycemia but did not totally ablate pulsatile activity of either hormone. The amplitude of ACTH and cortisol pulses was significantly decreased by dexamethasone treatment. The frequency of cortisol but not ACTH pulses was also significantly decresed. The highest cross-correlation between plasma ACTH and cortisol occurred at a lag of 0 min in control goats. Cross-correlation was lower and no consistent lag was seen in dexamethasone-treated goats. In control goats, during the fall in plasma glucose, before the rapid rise in plasma ACTH and cortisol, secretion appeared to be relatively quiescent compared to the prior 30 min. Specifically, a slight reduction occurred in frequency, amplitude, and area of ACTH pulses, in amplitude and area of cortisol pulses, and in cortisol levels. While this unexpected observation may have been an artifact of the sampling protocol, it bears further investigation

ISSN:0028-3835    

DOI:10.1159/000126102

出版商:S. Karger AG    

年代:1992

数据来源: Karger

摘要:

Studies were undertaken to characterize angiotensin peptides in hypophysial-portal blood of conscious sheep and to determine whether the median eminence (ME) secretes angiotensin peptides into the hypophysial-portal circulation. Simultaneous measurements of angiotensin peptides in jugular and hypophysial-portal plasma were performed in 6 sheep. Cerebrospinal fluid (CSF) was collected and data for hypophysial-portal plasma were corrected for CSF contamination. Angiotensin peptides were also measured in extracts of sheep ME. In a separate group of 4 sheep, simultaneous measurements of angiotensin peptides in arterial and jugular plasma were performed. Using high performance liquid chromatography-based radioimmunoassays, 8 angiotensin peptides were measured: Ang-(1–7), Ang II, Ang-(1–9), Ang I, Ang-(2–7), Ang III, Ang-(2–9), and Ang-(2-10). Renin, angiotensinogen and prolyl endopeptidase were also measured. No differences in angiotensin peptide levels in arterial and jugular plasma were observed. Angiotensin peptide levels in hypophysial-portal plasma were similar to those in jugular plasma, except for Ang-(1–7), the levels of which were 5-fold higher in hypophysial-portal plasma, and Ang I, for which the levels in hypophysial-portal plasma were 46% of the jugular levels. Renin and angiotensinogen levels were similar in arterial, jugular, and hypophysial-portal plasma. Angiotensin peptide contents of sheep ME were < 16 fmol/ME. However, the prolyl endopeptidase content of sheep ME was 430-fold higher than plasma levels. The low levels of angiotensin peptides in sheep ME indicate that it does not secrete these peptides into the hypophysial-portal circulation. Rather, the high level of prolyl endopeptidase in ME is consistent with region-specific metabolism of Ang I delivered to the ME by arterial blood, generating increased levels of Ang-(1–7) in hypophysial portal plasma. The increased levels of Ang-(1–7) in hypophysial-portal plasma may play a role in regulation of pitui

ISSN:0028-3835    

DOI:10.1159/000126103

出版商:S. Karger AG    

年代:1992

数据来源: Karger

摘要:

Immunorective corticotropin-releasing factor (CRF) was identified and measured by radioimmunossay in rat thymic extract. Serial dilutions of thymic extract paralleled hypothalamic extract and synthetic CRF standard curves. CRF extracted from rat thymus eluted in the position of synthetic rat CRF on Sephadex G-25 column. Thymus-derived CRF was biologically active as demonstrated by stimulating adrenocorticotropic hormone secretion in dispersed rat anterior pituitary cells. These findings indicate the presence of authentic CRF in rat thymus, further supporting the concept of an integrated regulation of the neuroendocrine-immune responses to environmental stimuli.

ISSN:0028-3835    

DOI:10.1159/000126104

出版商:S. Karger AG    

年代:1992

数据来源: Karger

ISSN:0028-3835    

DOI:10.1159/000126105

出版商:S. Karger AG    

年代:1992

数据来源: Karger