Inhibition by dexamethasone of the in vivo pituitary response to corticotropin-releasing factor (CRF)

Synthesis, F-18 radiolabeling, and microPET evaluation of 3-(2,4-dichlorophenyl)-N-alkyl-N-fluoroalkyl-2,5-dimethylpyrazolo[1,5-a]pyrimidin-7-amines as ligands of the corticotropin-releasing factor type-1 (CRF1) receptor

A series of 3-(2,4-dichlorophenyl)-N-alkyl-N-fluoroalkyl-2,5-dimethylpyrazolo[1,5-a]pyrimidin-7-amines were synthesized and evaluated as potential positron emission tomography (PET) tracers for the corticotropin-releasing factor type-1 (CRF1) receptor. Compounds 27, 28, 29, and 30 all displayed high binding affinity (⩽1.2 nM) to the CRF1 receptor when assessed by in vitro competition binding assays at 23 °C, whereas a decrease in affinity (⩾10-fold) was observed with compound 26. The logP7.4 values of [(18)F]26-[(18)F]29 were in the range of ∼2.2-2.8 and microPET evaluation of [(18)F]26-[(18)F]29 in an anesthetized male cynomolgus monkey demonstrated brain penetrance, but specific binding was not sufficient enough to differentiate regions of high CRF1 receptor density from regions of low CRF1 receptor density. Radioactivity uptake in the skull, and sphenoid bone and/or sphenoid sinus during studies with [(18)F]28, [(18)F]28-d8, and [(18)F]29 was attributed to a combination of [(18)F]fluoride generated by metabolic defluorination of the radiotracer and binding of intact radiotracer to CRF1 receptors expressed on mast cells in the bone marrow. Uptake of [(18)F]26 and [(18)F]27 in the skull and sphenoid region was rapid but then steadily washed out which suggests that this behavior was the result of binding to CRF1 receptors expressed on mast cells in the bone marrow with no contribution from [(18)F]fluoride.

Living history: F. Eugene Yates

In 2005, the American Physiological Society (APS) initiated the Living History of Physiology Archival Program to recognize senior members who have made significant contributions during their career to the advancement of the discipline and the profession of physiology. During 2008, the APS Cardiovascular Section selected Francis Eugene Yates to be profiled in Advances in Physiology Education.

Hypothalamic-pituitary-adrenal axis abnormalities in response to deletion of 11beta-HSD1 is strain-dependent

Inter-individual differences in hypothalamic-pituitary-adrenal (HPA) axis activity underlie differential vulnerability to neuropsychiatric and metabolic disorders, although the basis of this variation is poorly understood. 11beta-Hydroxysteroid dehydrogenase type 1 (11beta-HSD1) has previously been shown to influence HPA axis activity. 129/MF1 mice null for 11beta-HSD1 (129/MF1 HSD1(-/-)) have greatly increased adrenal gland size and altered HPA activity, consistent with reduced glucocorticoid negative feedback. On this background, concentrations of plasma corticosterone and adrenocorticotrophic hormone (ACTH) were elevated in unstressed mice, and showed a delayed return to baseline after stress in HSD1-null mice with reduced sensitivity to exogenous glucocorticoid feedback compared to same-background genetic controls. In the present study, we report that the genetic background can dramatically alter this pattern. By contrast to HSD1(-/-) mice on a 129/MF1 background, HSD1(-/-) mice congenic on a C57Bl/6J background have normal basal plasma corticosterone and ACTH concentrations and exhibit normal return to baseline of plasma corticosterone and ACTH concentrations after stress. Furthermore, in contrast to 129/MF1 HSD1(-/-) mice, C57Bl/6J HSD1(-/-) mice have increased glucocorticoid receptor expression in areas of the brain involved in glucocorticoid negative feedback (hippocampus and paraventricular nucleus), suggesting this may be a compensatory response to normalise feedback control of the HPA axis. In support of this hypothesis, C57Bl/6J HSD1(-/-) mice show increased sensitivity to dexamethasone-mediated suppression of peak corticosterone. Thus, although 11beta-HSD1 appears to contribute to regulation of the HPA axis, the genetic background is crucial in governing the response to (and hence the consequences of) its loss. Similar variations in plasticity may underpin inter-individual differences in vulnerability to disorders associated with HPA axis dysregulation. They also indicate that 11beta-HSD1 inhibition does not inevitably activate the HPA axis.

Alterations in carbohydrate metabolism by exogenous dexamethasone and corticosterone in post-hatched White Leghorn chicks

1. Alterations in carbohydrate metabolism in terms of tissue glycogen contents, phosphorylase (EC 2.4.1.1) activity, hepatic glucose-6-phosphatase (6-6-Pase: EC 3.1.3.9) activity and blood glucose have been evaluated in 30-d-old White Leghorn chicks under induced chronic hypocorticalism (by dexamethasone: DXM) and hypercorticalism (by corticosterone: CORT). 2. DXM treatment showed increased tissue glycogen contents and hypoglycaemia with decreased phosphorylase activity while CORT treatment produced a reverse set of changes. 3. Both steroid treatments increased hepatic G-6-Pase activity. These observations have been taken to indicate a definite role for glucocorticoids in regulating carbohydrate metabolism in neonatal chicks. 4. It is suggested that hypo- or hyper-corticalism could influence carbohydrate metabolism by affecting the secretory/activity ratio of pancreatic hormones.

Lack of glucocorticoids enhances the early activation of the medullary catecholaminergic cell groups triggered by restraint stress

We have investigated whether the stress-induced activation of the medullary catecholaminergic neurons, that was shown previously to provide the main central activation input to the hypothalamo-pituitary-adrenocortical axis during an immobilization stress, is sensitive to circulating corticosteroids. Experiments were carried out on adrenalectomized rats that were first maintained on corticosterone in the drinking water for 5 days following surgery and then switched to corticosterone-free water 15 h before stress application. Some of the latter animals were injected with dexamethasone. Activation of the brainstem Catecholaminergic neurons was estimated by assaying 3,4-dihydroxyphenylacetic acid (DOPAC), a side metabolite of the noradrenaline and adrenaline biosynthesis pathway that was established previously as a reliable index of the activity of these neurons. In the so-called A(1) C(1) and A(2) C(2) Catecholaminergic groups of the medulla, lack of corticosterone under these experimental conditions did not modify the basal level of DOPAC but led to a further enhancement (+ 35% to 40%) of the approximately 2-fold increase in DOPAC content observed 15 min after the onset of the 5-min immobilization stress. No significant further enhancement of the stress-induced DOPAC increase was observed in the locus coeruleus. In these adrenalectomized rats, dexamethasone pretreatment prevented the enhancement of the stress-induced increase in DOPAC level observed in the medullary cell groups but did not abolish the response to stress. Lack of endogenous corticosteroids led to a 10-fold enhancement of the adrenocorticotropin increase following immobilization stress. Pretreatment with dexamethasone fully abolished the stress-induced increase in adrenocorticotropin plasma level. Our results show that circulating corticosteroids reduce the stress-induced activation of the medullary A(1) and A(2) C(2) groups i.e. those that contribute mainly to the catecholaminergic innervation of the hypothalamo-pituitary-adrenocortical axis within the hypothalamic paraventricular nuclei. However, since the feedback regulation of the central catecholaminergic systems is much less efficient than the feedback actually observed on the adrenocorticotropin secretion, we suggest that it is likely to play a minor physiological role in the overall feedback regulation exerted by circulating corticosteroids on the hypothalamo-pituitary-adrenocortical axis.

Dexamethasone can prevent stress-related litter deficits in the golden hamster

This study was designed to examine the effects of social subordination during early pregnancy in the golden hamster (Mesocricetus auratus). Primiparous females were mated to proven breeders and stressed during early pregnancy. Females were housed singly throughout gestation except for Days 4, 5, and 6 when they were paired for 10-min intervals three times each day with another female matched for age, weight, and day of pregnancy. Within each of the pairs, one female was consistently dominant to the other. Controls were exposed to a novel area instead of a conspecific. At parturition, all pups were counted, sexed, and weighed. There were no significant differences between control and dominant females' litter sizes and sex ratios. Subordinate females produced significantly smaller litters than control or dominant dams and significantly lower sex ratios than control dams. Subordinates produced fewer males than control or dominant dams, but there were no differences in the number of females produced. The entire experiment was repeated exactly except that females received a small dosage of dexamethasone in their drinking water on Days 3-7 of pregnancy. In this second group, there were no significant reductions in mean litter size, sex ratio, or pup weights among litters born to subordinate dams. These results suggest that subordinate dams produce smaller litters via selective resorption of males in utero and that the typical adrenal response to stress mediates this response.

Ultrastructural localization of glucocorticoid receptor (GR) in hypothalamic paraventricular neurons synthesizing corticotropin releasing factor (CRF)

Corticotropin releasing factor (CRF) synthesizing neurons, located in the hypothalamic paraventricular nucleus (PVN), are the main central regulators of the pituitary-adrenal cortex endocrine axis. The hormone production and release of CRF-synthesizing neurons is regulated by neuronal messages and feedback action(s) of glucocorticoids secreted by the adrenal gland. In order to characterize the latter mechanism, glucocorticoid receptor (GR)-immunoreactive (IR) sites were studied in hypothalamic paraventricular neurons of intact, long-term adrenalectomized, and adrenalectomized plus glucocorticoid treated animals, by means of ultrastructural immunocytochemical labelling. In intact animals, glucocorticoid receptor immunoreactivity was found predominantly in the nuclei of parvocellular neurons. Following adrenalectomy GR-immunoreactivity was localized in the cytoplasm of the cells, and there was a concomitant disappearance of the label from the nuclei. After corticosterone administration to adrenalectomized animals, GR-IR sites were again concentrated within the cell nuclei. Immunocytochemical double labelling studies performed on adrenalectomized plus corticosterone-replaced animals demonstrated glucocorticoid receptor-IR sites in the cell nuclei of parvocellular paraventricular neurons that expressed CRF-immunoreactivity in their cytoplasm. These ultrastructural data indicate that the intracellular location of glucocorticoid receptor is dependent on the availability of glucocorticoids by the neurons. The simultaneous expression of GR- and CRF-immunoreactivity in parvocellular paraventricular neurons supports the concept of a direct feedback action of glucocorticoids upon CRF-synthesizing neurons.

Ultrastructural alterations of the paraventriculo-infundibular corticotropin releasing factor (CRF)-immunoreactive neuronal system in long term adrenalectomized rats

The corticotropin releasing factor (CRF)-immunoreactive paraventriculo-infundibular neuronal system of long-term adrenalectomized and adrenalectomized-short term dexamethasone treated rats was analyzed at the ultrastructural level using the preembedding peroxidase anti-peroxidase complex (PAP)-immunohistological method. In both groups of animals, parvocellular neurons located in the medial and dorsal subnuclei of the paraventricular nucleus (PVN) showed CRF-like immunoreactivity. The perikarya contained hypertrophied rough endoplasmic reticulum (rER) with dilated cisternae, active Golgi-complexes and numerous neurosecretory granules. The majority of the neurosecretory granules measured 80-120 nm. Dendrites of CRF-immunoreactive neurons contained labeled vesicles, secretory granules, bundles of microtubules, a well-developed smooth endoplasmic reticulum (sER) complex and free ribosomes. Unlabeled terminal boutons of axons were observed to synapse on dendrites and somata of CRF-neurons. In addition, CRF perikarya were found in direct somato-somatic apposition with both CRF-immunopositive and immunonegative parvocellular cells. Retraction of glial processes and the existence of puncta adherentia between the cell membranes characterized these appositions. Varicose CRF axons within the median eminence contained hypertrophied sER, labeled vesicles and neurosecretory granules. The preterminal portions of the CRF-axons were dilated and possessed many labeled 80-120 nm diameter granules. CRF-terminals were greatly enlarged and established direct neurohemal contacts with the external limiting basal lamina of portal vessels without the interposition of tanycytic ependymal foot-processes. These tanycytes were not CRF immunopositive. CRF positive terminals contained clusters of microvesicles, labeled small vesicles and multivesicular bodies, but fewer granular elements than were observed within the the preterminals. Many of the labeled organelles were attached to tubules of sER. Occasionally, CRF-axons were observed within the pericapillary space adjacent to portal vessels. The ultrastructural features of CRF-neurons, obtained from adrenalectomized and adrenalectomized plus short-term dexamethasone treated rats did not differ significantly from each other. The hormone content of the entire CRF-neuron was greater in the steroid treated group. Adrenocorticotrophic hormone (ACTH) synthesizing cells in the pars distalis of adrenalectomized-dexamethasone treated rats also showed increased numbers of immunopositive secretory granules (150-320 nm in diameter).(ABSTRACT TRUNCATED AT 400 WORDS)

Evidence for local corticotropin releasing factor (CRF)-immunoreactive neuronal circuits in the paraventricular nucleus of the rat hypothalamus. An electron microscopic immunohistochemical analysis

The interrelationships of corticotropin-releasing factor (CRF) immunoreactive neuronal cell bodies and processes have been examined in the paraventricular nucleus (PVN) of adrenalectomized-dexamethasone treated rats. Antisera generated against ovine CRF (oCRF) were used in the peroxidase-anti-peroxidase-complex (PAP)-immunocytochemical method at both the light and electron microscopic levels. In this experimental model, a great number of CRF-immunoreactive neurons were detected in the parvocellular subdivisions of the PVN and a few scattered labelled parvocellular neurons were also observed within the magnocellular subunits. Characteristic features of immunolabeled perikarya included hypertrophied rough endoplasmic reticulum with dilated endoplasmic cisternae, well developed Golgi complexes and increased numbers of neurosecretory granules. These features are interpreted to indicate accelerated hormone synthesis as a result of adrenalectomy. Afferent fibers communicated with dendrites and somata of CRF-immunoreactive neurons via both symmetrical and asymmetrical synapses. Some neurons exhibited somatic appendages and these structures were also observed to receive synaptic terminals. Within both the PVN and its adjacent neuropil, CRF-immunoreactive axons demonstrated varicosites which contained accumulations of densecore vesicles. CRF-containing axons were observed to branch into axon collaterals. These axons or axon collaterals established axo-somatic synapses on CRF-producing neurons in the parvocellular regions of the PVN, while in the magnocellular area of the nucleus they were found in juxtaposition with unlabeled magnocellular neuronal cell bodies or in synaptic contact with their dendrites. The presence of CRF-immunoreactive material in presynaptic structures suggests that the neurohormone may participate in mechanisms of synaptic transfer. These ultrastructural data indicate that the function of the paraventricular CRF-synthesizing neurons is adrenal steroid hormone dependent. They also provide morphological evidence for the existence of a neuronal ultrashort feed-back mechanism within the PVN for the regulation of CRF production and possibly that of other peptide hormones contained within this complex.

The corticotropin releasing factor (CRF) neurosecretory system in intact, adrenalectomized, and adrenalectomized-dexamethasone treated rats. An immunocytochemical analysis

In general, antisera generated against ovine CFR do not reveal immunopositive neuronal perikarya in the rat. If animals are adrenalectomized significant amounts of immunoreactive CFR are present in the hypothalamus. By using this model, we have visualized the CFR system of the rat. Intact, intact pretreated with dexamethasone, adrenalectomized, and adrenalectomized pretreated with dexamethasone animals were used in the present study. In adrenalectomized and adrenalectomized plus dexamethasone treated animals the CFR-immunopositive neurons were observed in the parvocellular portion of the paraventricular nucleus. Distinct pathways of CRF fibers could be seen emerging from this hypothalamic nucleus. The greatest number of these fibers exited the PVN laterally and crossed either superior to or beneath the fibers of the fornix. The fibers then turned ventrally and cascaded to form a bundle of fibers above the superio-lateral margin of the optic chiasm. They turned caudally and followed the optic tract. As these fibers reached the level of the anterior median eminence, they turned medially to run along the inferior margin of the hypothalamus and enter the median eminence. A few fibers emerged from the PVN along the periventricular margin of the third ventricle, traveled caudally in the periventricular nucleus and entered the median eminence. Adrenalectomized and adrenalectomized-dexamethasone treated rats had very dense accumulations of immunoreactive CRF in the median eminence when compared with controls. Immunoreactive neurons and fibers were also observed in the central nucleus of the amygdala in the adrenalectomized and adrenalectomized-dexamethasone treated animals.

Direct effects of thyrotropin-releasing hormone, cyproheptadine, and dopamine on adrenocorticotropin secretion from human corticotroph adenoma cells in vitro

In an attempt to delineate the mechanism and the site of action of cyproheptadine and dopaminergic agonists as well as hormones including thyrotropin-releasing hormone (TRH) and hydrocortisone, the effects of these substances on ACTH secretion from corticotroph adenoma cells in culture were examined. Dispersed cells of pituitary adenomas obtained at surgery from four patients with Nelson's syndrome and one subject with Cushing's disease formed a monolayer and actively secreted ACTH into the medium. When TRH (0.1 microM) was added to the medium, a significant increase in ACTH secretion was demonstrated by adenoma cells from two patients who responded to TRH preoperatively. Moreover, a dose-response relationship between TRH concentrations and ACTH secretion was observed. Incubation of cells with cyproheptadine (1 or 0.1 microM) resulted in a significant decrease in ACTH release, and inhibited stimulation produced by TRH in one experiment. This effect of cyproheptadine was blocked when equimolar concentrations of serotonin was coincubated, whereas serotonin by itself did not affect ACTH secretion. Dopamine (0.1 microM) lowered ACTH accumulation in the medium, which was blocked by the addition of haloperidol. When hydrocortisone was added to the culture, dose-dependent suppression of ACTH secretion was demonstrated. TRH at an equimolar concentration reversed this effect, but, failed to overcome the inhibition induced by a higher concentration of hydrocortisone in cells from one adenoma studied. Cultured normal corticotrophs obtained from a patient with metastatic breast cancer, on the other hand, did not show any response to these substances, except for hydrocortisone. We suggest that TRH, cyproheptadine, dopamine affect ACTH secretion in patients with ACTH-producing pituitary adenomas by their direct action on the adenoma.

Adrenocortical suppression in workers manufacturing synthetic glucocorticoids

A man who had worked for 16 years in the manufacture of a potent corticosteroid was found to be suffering from chronic adrenocortical insufficiency attributed to chronic absorption of the glucocorticoid. Eleven other symptom-free workers were therefore screened. Two of these workers, like the first patient, gave grossly abnormal responses to the Synacthen (tetracosactrin) test; one had been employed for only seven months. All 12 men had facial plethora, suggesting absorption of the drug in spite of their having adhered to the safety precautions. All workers manufacturing potent steroids should therfore be screened regularly by measurement of their plasma cortisol concentrations and should be moved regularly to processing other drugs.

Influence of adrenalectomy, total body x-irradiation and dexamethasone on the amount of CRF-granules and "classical" neurosecretory material in the rat neurohypophysis

In 195 female Wistar rats the influence of adrenalectomy, total body X-irradiation and dexamethasone treatment on the amount of CRF-granules in the external zone of the median eminence and "classical" neurosecretory material (NSM) in the internal zone of the median and in the posterior lobe of the hypophysis has been studied. In the normal rat only very few CRF-granules occur. 15 days after adrenalectomy increased amounts of CRF-granules but normal amounts of "classical" NSM are found. X-irradiation leads to a slight diminishment of "classical" NSM in normal rats. In adrenalectomized animals X-irradiation causes no changes in the amount of "classical" NSM but a marked decrease in the amount of CRF-granules. Application of dexamethasone from the 15th to 18th day after adrenalectomy enhances the augmentation of CRF-granules in irradiated and non-irradiated rats but does not influence the amount of "classical" NSM. The findings show that no correlation exists between the quantitative changes of CRF-granules and "classical" NSM under the experimental conditions used. Therefore it is to be assumed that the release of the two substances is regulated by different control mechanisms and that the substances have a different functional significance. The observations do not exclude the possibility that CRF-granules and "classical" NSM are biochemically identical.

Radioautographic study of the rat brain after injection of [1,2-3H]corticosterone

Cryostat sections of the central nervous system of adrenalectomized male rats injected with [3H]corticosterone were examined by radioautography. One hour after the injection, radioactivity was found to be selectively concentrated in specific neurons of the septum, the hippocampal complex (precommissural hippocampus, cornu Ammonis, gyrus dentatus, subiculum), the indusium griseum, the amygdala and in certain areas of the cortex. In the hippocampus, the pyramidal neurons in fields CA1 and CA2 of the cornu Ammonis and the granule neurons of the gyrus dentatus contained more radioactivity than did other regions of the brain. Most of the silver grains were localized in the nuclei of labeled cells. The topographic distribution of corticosterone-concentrating neurons shows that the hormonal target sites in the central nervous system are mainly extrahypothalamic.