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SUMMARY
1. An investigation of the diurnal rhythms of keto- and ketogenic steroid excretion has been carried out in four human subjects. The subjects lived, under standardized conditions of diet, activity and lighting, in Spitsbergen where 24 hr. daylight persists during the summer.
2. A study of the adaptation of their rhythms to a reversed activity-sleep and light-darkness schedule has been made, and of the subsequent re-adaptation to normal schedules.
3. Adaptation of the ketosteroid rhythm occurred in 2 days and of the ketogenic steroid rhythm in 8 days.
4. The ketosteroid excretory rhythm may depend immediately, and the ketogenic steroid rhythm ultimately, upon habit and environment.
5. Evidence has been presented to suggest that the ketogenic steroid rhythm is dependent upon the synchronization of pituitary and adrenal responsiveness. During the reversal of rhythm, adrenocortical activity takes place initially in the early 'evening' and 'night', occurring progressively earlier each day until it synchronizes with the new time scale.
6. The significance of these findings is discussed.
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The 11beta-hydroxysteroid dehydrogenases (11beta-HSDs) convert cortisol to its inactive metabolite cortisone and vice versa. 11beta-HSD type 1 (11beta-HSD-1) functions as a reductase in vivo, regulating intracellular cortisol levels and its access to the glucocorticoid receptor. In contrast, 11beta-HSD-2 only mediates oxidation of natural glucocorticoids, and protects the mineralocorticoid receptor from high cortisol concentrations. We investigated the in vivo and in vitro effects of ACTH on the recently characterized 11beta-HSDs in guinea pig liver and kidney. Tissue slices of untreated guinea pigs were incubated with (3)H-labelled cortisol or cortisone and ACTH(1-24) (10(-10) and 10(-9) mol/l). The 11beta-HSD activities in liver and kidney slices were not influenced by in vitro incubation with ACTH(1-24). In addition, guinea pigs were treated with ACTH(1-24) or saline injections s.c. for 3 days. Liver and kidney tissue slices of these animals were incubated with (3)H-labelled cortisol or cortisone. In vivo ACTH treatment significantly increased reductase and decreased oxidase activity in liver and kidney. Furthermore, 11beta-HSD-1 activity assessed by measurement of the urinary ratio of (tetrahydrocortisol (THF)+5alphaTHF)/(tetrahydrocortisone) was significantly increased after ACTH treatment compared with the control group. Plasma levels of cortisol, cortisone, progesterone, 17-hydroxyprogesterone and androstenedione increased significantly following in vivo ACTH treatment. The enhanced reductase activity of the hepatic and renal 11beta-HSD-1 is apparently caused by cortisol or other ACTH-dependent steroids rather than by ACTH itself. This may be an important fine regulation of the glucocorticoid tonus for stress adaptation in every organ, e.g. enhanced gluconeogenesis in liver.
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The toad Xenopus laevis is able to adapt its skin color to background light intensity. In this neuroendocrine reflex, the proopiomelanocortin (POMC)-derived peptide alpha-melanophore-stimulating hormone (alphaMSH) is a key regulatory factor. In animals adapting to a black background, release of alphaMSH from the pituitary pars intermedia causes dispersal of melanin in skin melanophores. To investigate the long-term in vivo dynamics of alphaMSH production during black background adaptation, the biosynthetic rate of POMC and the contents of POMC, alphaMSH and the POMC processing enzyme precursor convertase 2 (PC2) have been studied in the pars intermedia using pulse-labeling, Western blot and radioimmunoassay. In control animals, adapted to a white background, the rate of POMC biosynthesis and the POMC content were low, while high alphaMSH and PC2 contents were found. After 1 week of adaptation to a black background, the rate of POMC biosynthesis and the POMC protein content had increased 19- and 3.7-fold respectively. These parameters attained a maximum level (28- and 5. 8-fold higher than control) after 3 weeks and remained at these elevated levels for at least 12 weeks. After 1 week, the pars intermedia content of alphaMSH was only 30% of the control level, but after 6 and 12 weeks, the alphaMSH level had increased to the control level. The PC2 content decreased to 52% of control after 1 week and stabilized after 3 weeks at a level slightly lower than the control value. The results show that during long-term background adaptation a steady-state situation is reached, with a balance between the biosynthesis, enzymatic processing and release of alphaMSH. The in vivo dynamics of the processing enzyme PC2 suggest a parallel storage and release of alphaMSH and mature PC2 in the Xenopus pituitary pars intermedia.
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ABSTRACT
β-Endorphin-and α-melanotrophin (α-MSH)-related peptides were extracted from the pars intermedia of Xenopus laevis maintained for 2, 4 or 6 weeks on a white background and for the same periods on a black background. The peptides were resolved under dissociating conditions by gel exclusion chromatography on Sephadex G-50 and they were detected by radioimmunoassay with antibodies to β-endorphin, α,N-acetyl β-endorphin and α-MSH. The β-endorphin-related peptides separated into two fractions of different molecular size. Further purification of the peptides in each fraction was by ion exchange chromatography on SP-Sephadex C-25 and by high-pressure liquid chromatography. The α-MSH-related peptides were resolved by gel exclusion and ion exchange chromatography. The purified β-endorphin- and α-MSH-immunoreactive peptides were identified by comparison of their chromatographic properties with the corresponding peptides from porcine pituitary or by comparison with synthetic peptides.
The major form of β-endorphin in the pars intermedia of the frog adapted to a white background was identified as α,N-acetyl β-endorphin (1–8); it was accompanied by a small quantity of acetylated peptides with molecular size similar to β-endorphin. In contrast, the pars intermedia of the frogs adapted to a black background contained approximately equal amounts of α,N-acetyl β-endorphin (1–8) and the larger forms of β-endorphin. The higher molecular weight forms were identified as the α,N-acetyl derivatives of β-endorphin (1–26), (1–27) and (1–31); however after 6 weeks of white adaptation the sole remaining peptide in this group was the 26-residue peptide. An additional β-endorphin immunoreactive peptide, provisionally identified as β-endorphin (10–26), was present in both black- and white-adapted animals; the amounts of this peptide increased during white adaptation. Major differences in the processing of α-MSH were also observed. In the frogs adapted to a black background des-acetyl α-MSH greatly predominated over the acetyl form whereas after 6- weeks adaptation to a white background the acetylated peptide proved to be the principal component.
The results demonstrate that the proteolytic processing of β-endorphin and the acetylation of α-MSH in Xenopus laevis are influenced by background adaptation. The formation of β-endorphin (1–8) appears to reflect the action of an endopeptidase that acts at the single arginine residue present at position 9. This cleavage does not appear to take place in mammalian β-endorphins where position 9 is occupied by lysine.
Journal of Endocrinology (1992) 135, 469–478
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Abstract
Immunocytochemical analysis revealed the presence of acetylated endorphins in both melanotropes and corticotropes of the pituitary gland of Xenopus laevis. Chemical acetylation studies to determine the steady-state level of acetylated versus non-acetylated endorphins showed that virtually all endorphins are acetylated in both melanotropes and corticotropes. Apparently Xenopus is unique among vertebrates as non-acetylated endorphins are major endproducts in the distal lobe of all other vertebrate species studied thus far. The dynamics of endorphin biosynthesis in melanotrope cells using pulse-chase analysis coupled to immunoaffinity chromatography revealed that processing of pro-opiomelanocortin to produce N-terminalacetylated endorphins is very rapid. To determine the effect of long-term background adaptation on acetylation status of endorphins and α-MSH-related peptides, Xenopus laevis were adapted for 3 or 6 weeks to either a black or a white background. In both physiological states the major intracellular form of α-MSH-related peptides in melanotropes was desacetyl α-MSH while the major endorphin-related peptide was α,N-acetyl-β-endorphin[1–8]. In the medium of superfused neurointermediate lobes of black background-adapted animals the major form of secreted melanotropins and endorphins was α-MSH and α,N-acetyl-β-endorphin[1–8] respectively. We conclude that there is a marked spatio-temporal difference in acetylation of melanotropin and endorphins, with rapid intracellular acetylation of endorphins while melanotropin is acetylated at the time of its exocytosis. In the medium of superfused neurointermediate lobes of white background-adapted animals the amount of desacetyl α-MSH was much higher than in the medium of lobes of black-adapted animals. Therefore, the secretory signals from melanotrope cells of black- and white-adapted Xenopus appear to differ with respect to the degree of acetylation of the melanotropins. This difference may underlie the strategy of Xenopus to regulate dermal melanophore activity during physiological background adaptations.
Journal of Endocrinology (1995) 146, 159–167
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Hypothyroidism was induced in adult rats by oral absorption of methimazole and its effects on brown adipose tissue (BAT) were studied. Hypothyroidism partially mimicked the effects of chronic exposure to cold: BAT weight and its DNA content were increased and the mitochondrial components (proteins, phospholipids) of the tissue were greatly enhanced when expressed per unit of fresh tissue weight. Moreover, hypothyroidism had the same effects as adaptation to cold on the fatty-acid composition of both total and mitochondrial phospholipids. Basal respiratory rate and total cytochrome C oxidase activity of the tissue were also increased. However, the increase in the concentration of the '32 000 mol. wt protein', a polypeptide which regulates the dissipation of heat by BAT, was smaller and non-selective in hypothyroid rats. The amount of this protein was increased per mg tissue, but not per mg mitochondrial proteins, as in rats adapted to cold. Furthermore, in contrast with the large mobilization of the lipid stores in BAT of euthyroid animals, the BAT lipid stores of hypothyroid rats were not mobilized during the first hours of exposure to cold. It may be concluded that (a) hypothyroidism induces several alterations in BAT which are characteristic of an active thermogenic state (this may be because of the response of the organism to the deficiency of thermogenesis induced by hypothyroidism), (b) this potential increase in thermogenic capacity in the BAT of hypothyroid rats has probably a limited physiological role, since thyroid hormones are necessary for the mobilization of the tissue lipids which are the fuel for production of heat and (c) these data provide evidence for a limited role of thyroid hormones in the trophic response of BAT during adaptation to cold.
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ABSTRACT
Radioimmunoassays for α-MSH, β-MSH, ACTH and endorphin were used to measure pituitary concentrations of these peptides in rainbow trout during adaptation to black and white backgrounds. There was no difference in the pituitary content of any of these peptides between long-term black- and white-adapted trout. Plasma levels of α-MSH immunoreactivity were significantly higher in black-adapted trout than in white-adapted trout. Time-course studies revealed that although the body colour of trout showed an initial rapid adaptation to background colour, this was not paralleled by a corresponding change in plasma α-MSH levels. These only showed significant changes after 7 or more days of background adaptation, when melanophore recruitment or degradation occurred on black or white backgrounds respectively. Intravenous administration of mammalian α-MSH, salmon β-MSH I or antibodies to these peptides did not affect short-term background adaptation. However, long-term administration of mammalian α-MSH via osmotic minipump maintained melanophore numbers in grey-adapted trout transferred to a white background, although this observation was based on only two fish. It is concluded that peptides derived from pro-opiomelanocortin do not appear to be involved in controlling physiological colour change but may be involved in regulating morphological colour change of the rainbow trout.
J. Endocr. (1984) 101, 277–284
School of Medical Science, Menzies Health Institute Queensland, Griffith University, Gold Coast Campus, Southport, Queensland, Australia
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. In turn, this increase in adrenal size at 6 months of age may have contributed to the increased production of Cort as well as aldosterone ( Cuffe et al . 2016 ). The decrease in Mc2r expression at 6 months may be a compensatory adaptation to the
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successful sustained adaptation to the increased demand of insulin. The concomitant absence of increase in the number of INGAP-positive cells and lack of a neogenetic reaction would support the idea of a stimulatory effect of this peptide upon neogenesis
Department of Pharmaceutical Sciences, University of Salerno, ‘Federico II’, Naples, Italy
Department of Pathology and Animal Health, University of Naples ‘Federico II’, Naples, Italy
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Department of Pharmaceutical Sciences, University of Salerno, ‘Federico II’, Naples, Italy
Department of Pathology and Animal Health, University of Naples ‘Federico II’, Naples, Italy
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Department of Pharmaceutical Sciences, University of Salerno, ‘Federico II’, Naples, Italy
Department of Pathology and Animal Health, University of Naples ‘Federico II’, Naples, Italy
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Department of Pharmaceutical Sciences, University of Salerno, ‘Federico II’, Naples, Italy
Department of Pathology and Animal Health, University of Naples ‘Federico II’, Naples, Italy
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Department of Pharmaceutical Sciences, University of Salerno, ‘Federico II’, Naples, Italy
Department of Pathology and Animal Health, University of Naples ‘Federico II’, Naples, Italy
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Department of Pharmaceutical Sciences, University of Salerno, ‘Federico II’, Naples, Italy
Department of Pathology and Animal Health, University of Naples ‘Federico II’, Naples, Italy
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Department of Pharmaceutical Sciences, University of Salerno, ‘Federico II’, Naples, Italy
Department of Pathology and Animal Health, University of Naples ‘Federico II’, Naples, Italy
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Department of Pharmaceutical Sciences, University of Salerno, ‘Federico II’, Naples, Italy
Department of Pathology and Animal Health, University of Naples ‘Federico II’, Naples, Italy
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). Discussion During pregnancy, physiological adaptation in the nutritional and hormonal setting is necessary for fetal growth and maternal well-being. When pathological conditions, such as obesity or hypertension, occur, further modifications are needed
