Ganglioneuromas and renal anomalies are induced by activated RET(MEN2B) in transgenic mice.
Multiple endocrine neoplasia type 2B (MEN2B) is an autosomal dominant syndrome characterized by the development of medullary thyroid carcinoma, pheochromocytomas, musculoskeletal anomalies and mucosal ganglioneuromas. MEN2B is caused by a specific mutation (Met918-->Thr) in the RET receptor tyrosine kinase. Different mutations of RET lead to other conditions including MEN2A, familial medullary thyroid carcinoma and intestinal aganglionosis (Hirschsprung disease). Transgenic mice were created using the dopamine beta-hydroxylase promoter to direct expression of RET(MEN2B) in the developing sympathetic and enteric nervous systems and the adrenal medulla. DbetaH-RET(MEN2B) transgenic mice developed benign neuroglial tumors, histologically identical to human ganglioneuromas, in their sympathetic nervous systems and adrenal glands. The enteric nervous system was not affected. The neoplasms in DbetaH-RET(MEN2B) mice were similar to benign neuroglial tumors induced in transgenic mice by activated Ras expression under control of the same promoter. Levels of phosphorylated MAP kinase were not increased in the RET(MEN2B)-induced neurolglial proliferations, suggesting that alternative pathways may play a role in the pathogenesis of these lesions. Transgenic mice with the highest levels of DbetaH-RET(MEN2B) expression, unexpectedly developed renal malformations analogous to those reported with loss of function mutations in the Ret gene. (+info)
An alternative transcript of the rat renin gene can result in a truncated prorenin that is transported into adrenal mitochondria.
Characterization of the local renin-angiotensin system in the rat adrenal zona glomerulosa indicated a dual targeting of renin both to the secretory pathway and mitochondria. To investigate the transport of renin into mitochondria, we constructed a series of amino-terminal deletion variants of preprorenin. One of these variants, lacking the complete signal sequence for the endoplasmic reticulum and 10 amino acids of the profragment, was transported efficiently into isolated mitochondria. The transport was further shown to be dependent on mitochondrial membrane potential and ATP synthesis. Analysis of adrenal RNA revealed the existence of 2 renin transcripts. While one of the transcripts corresponds to the known full-length transcript, the other one lacks exon 1; instead, exon 2 is preceded by a domain of 80 nucleotides originating from intron 1. This domain, as well as the following region of intron 1 being excised, shows all essential sequence elements defining an additional, so-far-unknown exon. The second mRNA possibly derives from an additional transcription start in intron 1 and an alternative splicing process. Translation of this mRNA could result in a truncated prorenin representing a cytosolic form of renin, which is required for transport into mitochondria. This truncated prorenin corresponds exactly to the deletion variant being imported into mitochondria in vitro. (+info)
Cortisol in fetal fluids and the fetal adrenal at parturition in the tammar wallaby (Macropus eugenii).
Glucocorticoid hormones may play a critical role in initiating parturition in tammar wallabies. In this study, we investigated the concentration of cortisol in fetal fluids and cortisol production by fetal adrenals over the last 3 days of the 26-day pregnancy and within 24 h postpartum. The fetal adrenals almost doubled in size between Days 24 and 26 of pregnancy, and their cortisol content increased over 10-fold during this period, from 10 pg to over 100 pg per adrenal pair. After birth, neonatal adrenals continued to grow, but cortisol content fell dramatically to 20 pg. The prepartum increase in adrenal cortisol was reflected by a substantial rise in cortisol concentrations in yolk sac fluid, allantoic fluid, and fetal blood, which were below 10 ng/ml on Day 24 and rose to over 40 ng/ml by Day 26. Cortisol concentrations in neonatal blood decreased postpartum, mirroring decreased cortisol content in neonatal adrenals. Cortisol production by the fetal adrenal was stimulated in vitro by ACTH and prostaglandin E2, suggesting that the in vivo increase may be stimulated by release of ACTH from the fetal hypothalamic-pituitary axis and prostaglandin E2 from the placenta. These results indicate that increasing cortisol production by the fetal adrenal is a characteristic of late pregnancy in the tammar wallaby and support the suggestion that fetal cortisol may trigger the initiation of parturition in this marsupial species. (+info)
Identification of 17-methyl-18-norandrosta-5,13(17-dien-3beta-ol, the C19 fragment formed by adrenal side chain cleavage of a 20-aryl analog of (20S)-20-hydroxycholesterol.
Incubation of (20R)-20-phenyl-5-pregnene-3beta,20-diol, an aromatic analog of (23S)-20-hydroxycholesterol, with an adrenal mitochondrial preparation leads to the formation of four compounds: pregnenolone, phenol, a C8 ketone, acetophenone, and a nonpolar C19 compound. This latter compound has now been identified by reverse isotope dilution analysis and by gas chromatography/mass spectrometry as 17-methyl-18-norandrosta-5,13(17)-dien-3beta-ol. From these results it is evident that enzymatic fission of the C-17,20 bond of this synthetic derivative occurs. On the other hand, when (20S)-20-hydroxy[21-14C]cholesterol was used as substrate, the analogous cleavage did not take place. Thus, substitution of an aromatic group on C-20 facilitates side chain cleavage between that carbon atom and the nucleus whereas neither of the naturally occuring precursors, cholesterol or its 20-hydroxylated counterpart, are metabolized to a C8 fragment. (+info)
The treatment of insulin resistance does not improve adrenal cytochrome P450c17alpha enzyme dysregulation in polycystic ovary syndrome.
OBJECTIVE: To determine whether metformin. when given to non-diabetic women with polycystic ovary syndrome (PCOS), results in a reduction of insulin resistance and hyperinsulinemia while body weight is maintained. Also we aimed to see whether the reduction in insulin levels attenuates the activity of adrenal P450c17alpha enzyme in patients with PCOS. DESIGN: We investigated the 17-hydroxyprogesterone (17-OHP) and androstenedione responses to ACTH, insulin responses to an oral glucose tolerance test (OGTT) and glucose disposal rate in an insulin tolerance test before and after metformin therapy (500 mg, orally, twice daily, for 12 weeks). METHODS: The presence of hyperinsulinemia in 15 women with PCOS was demonstrated by an OGTT and results were compared with those of 10 healthy women. Insulin sensitivity was measured by the rate of endogenous glucose disposal after i.v. bolus injection of insulin. 17-OHP and androstenedione responses to ACTH were measured in all the women with PCOS and the normal women. RESULTS: Women with PCOS were hyperinsulinemic (102.0+/-13.0 (S.E.M.) VS 46.2+/-4.4 pmol/l) and hyperandrogenemic (free testosterone 15.3+/-1.7 vs 7.9+/-0.6 nmol/l; androstenedione 11.8+/-0.8 vs 8.2+/-0.6 nmol/l) and more hirsute (modified Ferriman-Gallwey score, 17.7+/-1.6 vs 3.0+/-0.3) than healthy women. In addition, women with PCOS had higher 17-OHP and androstenedione responses to ACTH when compared with healthy women. Metformin therapy resulted in some improvement in insulin sensitivity and reduced the basal and post-glucose load insulin levels. But 17-OHP and androstenedione responses to ACTH were unaltered in response to metformin. CONCLUSIONS: PCOS is characterized by hyperactivity of the adrenal P450c17alpha enzyme and insulin resistance. It seems that there is no direct relationship between insulin resistance and adrenal P450c17alpha enzyme dysregulation. (+info)
Glial cell line-derived neurotrophic factor rescues target-deprived sympathetic spinal cord neurons but requires transforming growth factor-beta as cofactor in vivo.
Glial cell line-derived neurotrophic factor (GDNF) is a potent neurotrophic factor for several populations of CNS and peripheral neurons. Synthesis and storage of GDNF by the neuron-like adrenal medullary cells suggest roles in adrenal functions and/or in the maintenance of spinal cord neurons that innervate the adrenal medulla. We show that unilateral adrenomedullectomy causes degeneration of all sympathetic preganglionic neurons within the intermediolateral column (IML) of spinal cord segments T7-T10 that project to the adrenal medulla. In situ hybridization revealed that IML neurons express the glycosylphosphatidylinositol-linked alpha receptor 1 and c-Ret receptors, which are essential for GDNF signaling. IML neurons also display immunoreactivity for transforming growth factor-beta (TGF-beta) receptor II. Administration of GDNF (recombinant human, 1 microg) in Gelfoam implanted into the medullectomized adrenal gland rescued all Fluoro-Gold-labeled preganglionic neurons projecting to the adrenal medulla after four weeks. Cytochrome c applied as a control protein was not effective. The protective effect of GDNF was prevented by co-administration to the Gelfoam of neutralizing antibodies recognizing all three TGF-beta isoforms but not GDNF. This suggests that the presence of endogenous TGF-beta was essential for permitting a neurotrophic effect of GDNF. Our data indicate that GDNF has a capacity to protect a population of autonomic spinal cord neurons from target-deprived cell death. Furthermore, our results demonstrate for the first time that the previously reported requirement of TGF-beta for permitting trophic actions of GDNF in vitro (Kreiglstein et al., 1998) also applies to the in vivo situation. (+info)
A possible contributory role of BK virus infection in neuroblastoma development.
The tumor suppressor protein p53 is aberrantly localized to the cytoplasm of neuroblastoma cells, compromising the suppressor function of this protein. Such tumors are experimentally induced in transgenic mice expressing the large tumor (T) antigen of polyomaviruses. The oncogenic mechanisms of T antigen include complex formation with, and inactivation of, the tumor suppressor protein p53. Samples from 18 human neuroblastomas and five normal human adrenal glands were examined. BK virus DNA was detected in all neuroblastomas and none of five normal adrenal glands by PCR. Using DNA in situ hybridization, polyomaviral DNA was found in the tumor cells of 17 of 18 neuroblastomas, but in none of five adrenal medullas. Expression of the large T antigen was detected in the tumor cells of 16 of 18 neuroblastomas, but in none of the five adrenal medullas. By double immunostaining BK virus T antigen and p53 was colocalized to the cytoplasm of the tumor cells. Immunoprecipitation revealed binding between the two proteins. The presence and expression of BK virus in neuroblastomas, but not in normal adrenal medulla, and colocalization and binding to p53, suggest that this virus may play a contributory role in the development of this neoplasm. (+info)
Lateralized effects of medial prefrontal cortex lesions on neuroendocrine and autonomic stress responses in rats.
The medial prefrontal cortex (mPFC) is highly activated by stress and modulates neuroendocrine and autonomic function. Dopaminergic inputs to mPFC facilitate coping ability and demonstrate considerable hemispheric functional lateralization. The present study investigated the potentially lateralized regulation of stress responses at the level of mPFC output neurons, using ibotenic acid lesions. Neuroendocrine function was assessed by plasma corticosterone increases in response to acute or repeated 20 min restraint stress. The primary index of autonomic activation was gastric ulcer development during a separate cold restraint stress. Restraint-induced defecation was also monitored. Plasma corticosterone levels were markedly lower in response to repeated versus acute restraint stress. In acutely restrained animals, right or bilateral, but not left mPFC lesions, decreased prestress corticosterone levels, whereas in repeatedly restrained rats, the same lesions significantly reduced the peak stress-induced corticosterone response. Stress ulcer development (after a single cold restraint stress) was greatly reduced by either right or bilateral mPFC lesions but was unaffected by left lesions. Restraint-induced defecation was elevated in animals with left mPFC lesions. Finally, a left-biased asymmetry in adrenal gland weights was observed across animals, which was unaffected by mPFC lesions. The results suggest that mPFC output neurons demonstrate an intrinsic right brain specialization in both neuroendocrine and autonomic activation. Such findings may be particularly relevant to clinical depression which is associated with both disturbances in stress regulatory systems and hemispheric imbalances in prefrontal function. (+info)