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SUMMARY
Keeping Xenopus laevis Daudin in sodium-rich or sodium-free media leads to hypernatraemia or hyponatraemia respectively. Approximately 3 weeks after adenohypophysectomy, sodium and chloride concentrations in plasma and tissue water were reduced; there was also a net loss of the ions from the muscle. Potassium was not significantly affected. Aminoglutethimide, a proven inhibitor of corticosteroidogenesis in mammals, produced similar though more pronounced changes. In the adenohypophysectomized animal, this drug also produced a net increase in muscle potassium. The role of the urinary bladder in reabsorbing sodium has been demonstrated in Xenopus by an in-vivo technique. While the rate of urine flow was reduced in adenohypophysectomized toads, the rate of sodium excretion was essentially unchanged.
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SUMMARY
The synthesis of steroids from [7α-3H]cholesterol, [7α-3H]pregnenolone and [7α-3H]progesterone by lizard and turtle ovarian tissues in vitro was studied. Progesterone, 17α-hydroxyprogesterone, dehydroepiandrosterone, androstenedione, testosterone, oestrone and oestradiol were identified as products. In the turtle (Pseudemys), conversion of pregnenolone to progesterone was efficient, but transformation of progesterone to other steroids was relatively slow as indicated by the accumulation of progesterone over the incubation period. In Dipsosaurus, accumulation of radioactivity was greatest in testosterone, the quantities of which continued to increase at each sampling period. The rate of utilization of pregnenolone as a substrate was similar for the two species studied and the quantities of oestrone and oestradiol formed were lower in Pseudemys. The use of progesterone as precursor by Dipsosaurus ovarian tissue revealed a similar pattern of Δ4-steroid metabolism to that obtained with pregnenolone as precursor.
The effects of addition of purified follicle-stimulating hormone (FSH) and luteinizing hormone (LH) on the metabolism of [14C]cholesterol in vitro was studied using Pseudemys follicular tissue. The pattern of cholesterol metabolism was similar to that for pregnenolone in this species. The synthesis of pregnenolone, progesterone, dehydroepiandrosterone and androstenedione in vitro was significantly enhanced in the presence of LH. Follicle-stimulating hormone had no effect on steroid synthesis except for a decrease of androstenedione formation. The stimulatory effect of LH on steroidogenesis in vitro is discussed in relation to the literature suggesting that mammalian FSH, but not LH, stimulates all phases of reptilian ovarian function when injected in vivo.
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SUMMARY
Incubation of the adrenocortical tissue of Xenopus with labelled steroidal precursors gave aldosterone, corticosterone, 11-deoxycorticosterone and 18-hydroxycorticosterone as the major products. Kinetic studies indicated that the major biosynthetic pathway in Xenopus is the same as that in the duck, cobra and frog, and follows the sequence: pregnenolone → progesterone → 11-deoxycorticosterone → corticosterone → aldosterone + 18-hydroxycorticosterone.
The effects of adenohypophysectomy and of injection of mammalian corticotrophin (ACTH) on the corticosteroidogenetic capacity of Xenopus were also studied. The production of both aldosterone and corticosterone increased after ACTH administration and decreased markedly after adenohypophysectomy. Some of the evidence suggests that ACTH was effective at biosynthetic stages following the formation of pregnenolone. The present studies on corticosteroid production were done in conjunction with parallel investigations on osmoregulation and electrolyte and water changes in Xenopus (Edwards, 1969).
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SUMMARY
Cyclical changes in the activity of adrenocortical tissue are a wellestablished phenomenon in many amphibian species but up to now they have been studied by observing changes in cytology or enzyme activity, e.g. steroid-3β-ol dehydrogenase. The present study was designed to provide a measure of corticosteroid secretion throughout the seasons using the in-vitro approach. Concomitant histological changes are also recorded and together provide evidence that the adrenal tissue of Rana rugulosa shows maximum activity in the spring spawning season and reaches a minimum in winter.
Chemical Pathology, The Chinese University of Hong Kong, Hong Kong Special Administrative Region, People’s Republic of China
Department of Biology, Xiamen University, Xiamen, People’s Republic of China
Molecular Pathology, University of Texas M D Anderson Cancer Center, 1515 Holcombe Blvd, Houston, TX 77030, USA
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Chemical Pathology, The Chinese University of Hong Kong, Hong Kong Special Administrative Region, People’s Republic of China
Department of Biology, Xiamen University, Xiamen, People’s Republic of China
Molecular Pathology, University of Texas M D Anderson Cancer Center, 1515 Holcombe Blvd, Houston, TX 77030, USA
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Chemical Pathology, The Chinese University of Hong Kong, Hong Kong Special Administrative Region, People’s Republic of China
Department of Biology, Xiamen University, Xiamen, People’s Republic of China
Molecular Pathology, University of Texas M D Anderson Cancer Center, 1515 Holcombe Blvd, Houston, TX 77030, USA
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Chemical Pathology, The Chinese University of Hong Kong, Hong Kong Special Administrative Region, People’s Republic of China
Department of Biology, Xiamen University, Xiamen, People’s Republic of China
Molecular Pathology, University of Texas M D Anderson Cancer Center, 1515 Holcombe Blvd, Houston, TX 77030, USA
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Chemical Pathology, The Chinese University of Hong Kong, Hong Kong Special Administrative Region, People’s Republic of China
Department of Biology, Xiamen University, Xiamen, People’s Republic of China
Molecular Pathology, University of Texas M D Anderson Cancer Center, 1515 Holcombe Blvd, Houston, TX 77030, USA
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Chemical Pathology, The Chinese University of Hong Kong, Hong Kong Special Administrative Region, People’s Republic of China
Department of Biology, Xiamen University, Xiamen, People’s Republic of China
Molecular Pathology, University of Texas M D Anderson Cancer Center, 1515 Holcombe Blvd, Houston, TX 77030, USA
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Chemical Pathology, The Chinese University of Hong Kong, Hong Kong Special Administrative Region, People’s Republic of China
Department of Biology, Xiamen University, Xiamen, People’s Republic of China
Molecular Pathology, University of Texas M D Anderson Cancer Center, 1515 Holcombe Blvd, Houston, TX 77030, USA
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Conversion of cholesterol to biologically active steroids is a multi-step enzymatic process. Along with some important enzymes, like cholesterol side-chain cleavage enzyme (P450scc) and 3β-hydroxysteroid dehydrogenase/isomerase (3β-HSD), several proteins play key role in steroidogenesis. The role of steroidogenic acute regulatory (StAR) protein is well established. A novel protein, BRE, found mainly in brain, adrenals and gonads, was highly expressed in hyperplastic rat adrenals with impaired steroidogenesis, suggesting its regulation by pituitary hormones. To further elucidate its role in steroidogenic tissues, mouse Leydig tumor cells (mLTC-1) were transfected with BRE antisense probes. Morphologically the BRE antisense cells exhibited large cytoplasmic lipid droplets and failed to shrink in response to human chorionic gonadotropin. Although cAMP production, along with StAR and P450scc mRNA expression, was unaffected in BRE antisense clones, progesterone and testosterone yields were significantly decreased, while pregnenolone was increased in response to human chorionic gonadotropin stimulation or in the presence of 22(R)OH-cholesterol. Furthermore, whereas exogenous progesterone was readily converted to testosterone, pregnenolone was not, suggesting impairment of pregnenolone-to-progesterone conversion, a step metabolized by 3β-HSD. That steroidogenesis was compromised at the 3β-HSD step was further confirmed by the reduced expression of 3β-HSD type I (3ß-HSDI) mRNA in BRE antisense cells compared with controls. Our results suggest that BRE influences steroidogenesis through its effects on 3β-HSD action, probably affecting its transcription.
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ABSTRACT
The distribution of 1α,25-dihydroxyvitamin D3 (1,25-(OH)2D3) receptors in isolated jejunal villous and crypt cells was investigated in normal and adrenalectomized male rats, and also in animals treated with the synthetic glucocorticoid, dexamethasone, and/or the glucocorticoid antagonist, 11-deoxycortisol. Adrenalectomy caused an increase in 1,25-(OH)2D3 receptors whilst dexamethasone treatment led to a reduction in receptor number. 11-Deoxycortisol was able to reverse the 'down-regulation' effect caused by glucocorticoids. In all cases, the changes in receptor numbers were more pronounced in crypt cells. The data suggest that, in the small intestine, glucocorticoids may control the synthesis of 1,25-(OH)2D3 receptors via the mediation of a glucocorticoid receptor, and that the adrenal hormones mainly express their effect in crypt cells. It is proposed that this phenomenon may, in part, explain the reduction in calcium absorption which occurs in man after chronic glucocorticoid treatment.
J. Endocr. (1984) 103, 295–300
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SUMMARY
A method for the bioassay of the pressor substances in extracts of the urophyses of the teleost fish, Mugil auratus and Anguilla anguilla, is described. Ultracentrifugation, chromatography on Sephadex gel and treatment with trypsin and papain showed that the pressor principles are polypeptides. One fraction was protein-bound while two other fractions seem to be small molecules. Treatment with thioglycollate showed that disulphide bonds do not form an integral part of the active molecule.
The possible function of these principles in the control of the caudal circulation is discussed.
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N-TERA-2 cl/D1 (NT2) cells, a human embryonal cell line with characteristics of central nervous system precursor cells, were utilised to study thyroid hormone action during early neuronal growth and differentiation. Undifferentiated NT2 cells expressed mRNAs encoding thyroid hormone receptors (TRs) alpha1, alpha2 and beta1, iodothyronine deiodinases types 2 (D2) and 3 (D3) (which act as the pre-receptor regulators), and the thyroid hormone-responsive genes myelin basic protein (MBP) and neuroendocrine specific protein A (NSP-A). When terminally differentiated into post-mitotic neurons (hNT), TRalpha1 and TRbeta1 mRNA expression was decreased by 74% (P=0.05) and 95% (P<0.0001) respectively, while NSP-A mRNA increased 7-fold (P<0.05). However, mRNAs encoding TRalpha2, D2, D3 and MBP did not alter significantly upon neuronal differentiation and neither did activities of D2 and D3. With increasing 3,5,3'-triiodothyronine (T(3)) concentrations, TRbeta1 mRNA expression in cultured NT2 cells increased 2-fold at 10 nM T(3) and 1.3-fold at 100 nM T(3) (P<0.05) compared with that in T(3)-free media but no change was seen with T(3) treatment of hNT cells. D3 mRNA expression in NT2 cells also increased 3-fold at 10 nM T(3) (P=0.01) and 2.4-fold at 100 nM T(3) (P<0.05) compared with control, but there was no change in D3 enzyme activity. In contrast there was a 20% reduction in D3 mRNA expression in hNT cells at 10 nM T(3) (P<0.05) compared with control, with accompanying reductions in D3 activity with increasing T(3) concentrations (P<0.05). There was no significant change in the expression of the TRalpha isoforms, D2, MBP and NSP-A with increasing T(3) concentrations in either NT2 or hNT cells. Undifferentiated NT2 and differentiated hNT cells show differing patterns of T(3)-responsiveness, suggesting that there are different regulatory factors operating within these cell types.
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Abstract
Previous studies have demonstrated the existence of several key components of the renin–angiotensin system in the pancreas. In the present study, the localization of angiotensin II receptor subtypes, type I (AT1) and type II (AT2), in the mouse and the rat pancreas was studied by immunocytochemistry using specific antipeptide antibodies against the second extracellular loops of AT1 and AT2 receptors in conjunction with confocal laser scanning microscopy. In the mouse, immunoreactivity for AT1 and AT2 was observed predominantly in the endothelia of the blood vessels and the epithelia of the pancreatic ductal system. Similar distribution of immunoreactivity for AT1 and AT2 was also observed. However, the intensity of immunoreactivity for AT1 and AT2 was stronger in the rat than that found in the mouse pancreas. Much weaker immunostaining for both AT1 and AT2, as compared with that found in ductal regions, was also found in the acini of the rodent pancreas. Together with the previous findings, the present results suggest that AT1 and/or AT2 receptors may play a role in regulating pancreatic functions in the rodent.
Journal of Endocrinology (1997) 153, 269–274
