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ABSTRACT
A corticosteroid binding globulin variant (CBGv) has been identified in a serum sample taken from an apparently healthy woman during late pregnancy. Identification was based on the observation that it exhibited approximately half the cortisol binding capacity expected when compared to its concentration measured by radioimmunoassay (RIA). Affinity purification of CBGv excluded the possibility that this anomaly was caused by assay interference, and demonstrated that immunoreactive CBGv was capable of binding cortisol. The CBGv had a molecular weight (63 800) similar to normal CBG, and no evidence of molecular aggregation was found by gel filtration. Although the electrophoretic mobility, isoelectric profile and immunochemical identity of CBGv appeared to be similar to normal CBG, it focussed as two distinct bands (pI 5·48 and pI 5·53) after desialylation with neuraminidase, unlike normal CBG which focusses only at pI 5·48. Investigation of the steroid binding characteristics of CBGv revealed a reduced association-rate constant (K a = 1·05 × 109 1/mol) and dissociation half-time (12·5 min) when compared with normal CBG (K a = 1·39 × 109l/mol and 25 min at 0 °C) but an apparently normal steroid binding specificity. Although the physiological significance of this variant is not known, the cortisol concentration in the variant serum was within the normal range of women during late pregnancy. No other CBG variants were identified among other normal controls (n = 66) or nine patients with Cushing's syndrome. It is suggested that comparisons between cortisol binding capacity and RIA will reveal other variants of CBG, and lead to greater understanding of their physiological significance.
J. Endocr. (1985) 104, 269–277
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SUMMARY
Counting of radioactivity in Japanese quail in vivo showed a rapid loss of 131I from the body 12–24 h after the i.v. injection of [131I]thyroxine (T4), followed by a period of slow decrease in counting rates to 96 h. From comparison of these [131I]T4 curves with curves for 131iodide-injected birds and from counts on serum and other tissues in vitro it was concluded that, for Japanese quail, the T4 secretion rate should be calculated using serum samples taken during the first 12 h. Using this time period, the parameters measured were: T4 distribution space, laying hens 45·7 and mature cocks 26·3 ml/100 g body weight; fractional degradation rate for T4, hens 5·73 and cocks 3·12/day; serum T4 concentration (Tetrasorb125 method), hens 1·20 ± 0.07 and cocks 1·34 ± 0.05 (s.e.m.)μg/100 ml (n= 16); T4 secretion rate, hens 3·14 and cocks 1·10 μg/100 g/day.
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Participation of lighting and the pineal gland in neuroendocrine regulation of the gonads is now recognized. The influence of the pineal on gonadal function in male rats involves action on the hypothalamo—hypophysis and on gonadotrophins (Fraschini, Mess & Martini, 1968; Debeljuk, 1969). Direct pineal—gonadal inter-relation has also been postulated since melatonin appears to inhibit steroid biotransformations in vitro (Ellis, 1969).
The effects of light restriction and melatonin administration on accessory sex gland weight and fructose content and incorporation of tritiated thymidine into testicular DNA, as indices of testis function, have been studied in two strains of rat. Effects of pinealectomy were investigated in one strain of rat.
Four groups of seven rats (24–26 days of age) were housed individually at 21 ± 1°. Control animals were exposed to a light:dark (L:D) cycle of 16:8 hr. and light-restricted animals received L:D 1:23 hr. for 24 days. A third group of animals
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Search for other papers by I. C. A. F. Robinson in
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ABSTRACT
Oxytocin (OT) and vasopressin (VP) were measured by radioimmunoassay in hypophysial portal and peripheral blood from male Wistar rats and heterozygous and homozygous Brattleboro rats anaesthetized with urethane. In Wistar rats the concentrations of OT and VP were about 50 times greater than the concentrations in peripheral blood, whether or not the pituitary gland was left in situ during collection, and also considerably greater than the reported concentrations of the peptides in the cerebrospinal fluid. The release of both peptides was increased significantly by a lesion of the supraoptico-hypophysial tract that led to diabetes insipidus, but which left intact the external layer of the median eminence (ME). Concentrations of VP were undetectable in plasma from homozygous Brattleboro rats, but the portal plasma concentrations of VP in heterozygous Brattleboro rats were not significantly lower than in Wistar rats. The concentrations of OT in portal plasma from both types of Brattleboro rat were significantly higher than in Wistar rats.
The output of VP and OT into hypophysial portal blood of Wistar rats was not significantly affected by electrical stimulation of the suprachiasmatic, supraoptic or paraventricular nuclei or the ME using two types of stimuli, one of which produced an increase in peripheral plasma concentrations of VP and OT in intact rats and a significant increase in the release of LH-releasing hormone into hypophysial portal blood. The output of VP and OT into portal blood was also not significantly affected by either adrenalectomy with or without injection of dexamethasone or the injection of either the 5-hydroxytryptamine (5-HT) synthesis blocker, parachlorophenylalanine, or the 5-HT uptake blockers, alaproclate or zimelidine.
These results show that large amounts of OT as well as VP are released into hypophysial portal blood from fibres of the hypothalamo-neurohypophysial system that terminate in the external layer of the ME. Although distinct from the fibres that terminate in the pars nervosa (PN), the findings in Brattleboro rats show that the VP fibres of the ME system originate in neurones with a genomic mechanism for VP synthesis similar to that of the VP neurones that project to the PN. The lack of effect of adrenalectomy and the administration of 5-HT synthesis and uptake blockers must be interpreted with caution since the results obtained with electrical stimulation suggest that when the pituitary stalk is cut the release of OT and VP into portal blood approaches a maximum and may therefore be difficult to alter by experimental manipulation. The concentrations of OT and VP in portal blood are sufficiently high for these peptides to play a significant role in neural control of the anterior pituitary gland.
J. Endocr. (1985) 104, 211–224
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Search for other papers by G. A. ROBINSON in
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SUMMARY
Intramuscular injection of KSCN, KClO4 or KI into laying Japanese quail resulted in the discharge of 12·6 to 34·0% of the ovarian 131I within a 1-h measurement period for birds studied 1 to 6 h after labelling. Potassium thiocyanate was as effective as an equimolar quantity of KClO4 in causing this discharge. For birds studied 18 h after labelling, no consistent effect of KClO4, KSCN or KI on ovarian 131I levels was found. Gel, thin-layer and paper chromatography of labelled oocytes determined that > 92% of the 131I was present as inorganic iodide.
Search for other papers by R. G. Clark in
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ABSTRACT
The 'Little' mouse is characterized by a body growth rate 60% of normal due to a defect in the synthesis and storage of GH in the anterior pituitary gland. We have now investigated the effects of GH releasing factor (GRF) in these mice and in normal animals. The pituitary GH content in Little mice was only 4% of that in normal C57: +/+ mice, and was not affected by twice daily i.p. injections of human (h) GRF1-29NH2 (0·2−2 μg) for 14 days. This treatment also had no effect on body growth. In anaesthetized normal mice, single i.v. injections of 0·1 or 2 μg hGRF1-29NH2 released large amounts of GH into the plasma, whereas this peptide was ineffective in Little mice, whether or not they had been pretreated with GRF. Therefore, although pituitaries of Little mice contain significant amounts of GH, this pool is not releasable by GRF. This suggests that the dwarfism in Little mice may be partly due to a pituitary defect in GRF receptors or their stimulus-secretion coupling, rather than a deficiency in hypothalamic GRF.
J. Endocr. (1985) 106, 1–5
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ABSTRACT
The GH responses to single i.v. injections of GH-releasing factor (GRF) in conscious male rats are highly variable. Although normal male rats show a pulsatile secretory pattern of GH with pulses occurring at intervals of 3–3·5 h, the peaks occur at different times in individual animals. We have compared the GH responses of young conscious male and female rats to multiple i.v. injections of 1 μg human (h) GRF1-29NH2. The peak GH responses occurred 3–5 min after hGRF1-29NH2 injection and were lower in female than in male rats. Both males and females responded uniformly to hGRF1-29NH2 injections given 180 min apart and the GH responses became entrained with no endogenous GH pulsing. Female rats produced consistent GH peaks in response to hGRF1-29NH2 injections at 90-min intervals, whereas male rats responded only to alternate injections, so that GH peaks occurred only every 180 min despite giving GRF every 90 min. When the frequency of hGRF1-29NH2 administration was increased to once every 40 min female rats again responded consistently to each injection. Male rats responded intermittently, being able to respond to two injections 40 min apart, after which they became refractory to hGRF1-29NH2. This cycle of varying sensitivity to GRF in male rats probably underlies their 3-hourly endogenous GH secretory rhythm. Female rats can respond uniformly to repeated GRF injections, consistent with their more continuous pattern of endogenous GH secretion. Introducing a pulse of 10 μg rat GH into a series of hGRF1-29NH2 injections did not induce refractoriness to hGRF1-29NH2, suggesting that GH does not itself desensitize the pituitary to GRF. Whether the different patterns of GH secretion in males and females result from different patterns of GRF and/or somatostatin secretion remains to be determined.
J. Endocr. (1985) 106, 281–289
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ABSTRACT
A monospecific antiserum against human corticosteroid binding globulin (hCBG) has been used to identify structural similarities between hCBG and CBG in the blood of other primates and representative species of different vertebrate classes. Double immunodiffusion analysis indicated that only CBG in Old World monkeys and apes cross-react with the hCBG antiserum. This was confirmed by a solid-phase radioimmunoassay for hCBG which also demonstrated that CBG in apes is immunologically identical to hCBG and that Old World monkey CBG comprises most, but not all, of the hCBG epitopes. The electrophoretic mobilities of human, gorilla and gibbon CBG were similar (R F 0·50–0·51), but differed from Old World monkey CBG (R F 0·44–0·49) and chimpanzee CBG (R F 0·47). Although serum/plasma cortisol binding capacities were similar in Old World primates, the dissociation half-times (t ½) of cortisol were higher from human and ape CBG (18–25 min) than from Old World monkey CBG (14–18 min). The steroid binding specificities of human and ape (CBG corticosterone > cortisol > progesterone ≥ testosterone) were also different from those of Old World monkey CBG (corticosterone >> cortisol ≃ progesterone > testosterone). Lemur plasma cortisol binding capacity and CBG dissociation t ½ of cortisol were similar to hCBG, but its steroid binding specificity was different (cortisol > corticosterone > progesterone ≥ testosterone) and it did not cross-react with the hCBG antiserum. We could not detect high affinity cortisol binding activity in blood samples from New World monkeys, and they did not cross-react with the hCBG antiserum. These results suggest that considerable modification in the steroid binding activity and structure of CBG has occurred since the evolutionary appearance of the primates, but that the rate of change decreased after the cladogenesis of Catarrhine primates.
J. Endocr. (1985) 104, 251–257
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ABSTRACT
A radioimmunoassay (RIA) for human corticosteroid binding globulin (CBG) has been developed using 125I-labelled CBG and a monospecific solid-phase CBG-antiserum (CBG-Ab-cellulose). In an RIA of serum CBG concentrations, pure CBG standards (1–100 ng protein) or samples (1 : 200) were incubated (16 h at 20 °C) with 125I-labelled CBG and CBG-Ab-cellulose. After addition of 2 ml 0·9% NaCl, the tubes were centrifuged, supernatants were aspirated and the 125I-labelled CBG bound to the CBG-Ab-cellulose pellet was counted. The specificity of the RIA was confirmed by parallel displacement curves for serial dilutions of male, female and pregnancy sera, as well as pure CBG standards. The mean ± s.d. recovery (99±8%) of pure CBG (1·6–25·0 ng) added to a diluted serum sample verified the accuracy of the method, and a good correlation (r = 0·97; n = 43) existed between serum CBG cortisol binding capacity (nmol/l) measurements and CBG concentrations (mg protein/l) measured by RIA. Intra- and interassay precisions (C.V.) at low to high serum CBG concentrations were <5% and <9% respectively. The mean ± s.d. serum CBG concentrations (mg protein/l) measured by the RIA were: 21·8±4·6 in boys (n = 12), 20·0±4·2 in girls (n = 9), 20·7±2·7 in men (n = 6), 20·5±2·9 in women (n = 6) and 47·1 ±10·5 in pregnant women (n = 5). The sensitivity of the standard curve used in the routine RIA of serum CBG was 1·0 ng CBG/assay tube, but this could be increased to 0·2 ng/assay tube by reducing the amount of CBG-Ab-cellulose used. The RIA is suitable for both clinical and research purposes, and will aid the identification of abnormal forms of CBG and facilitate studies of the regulation of CBG production in vitro.
J. Endocr. (1985) 104, 259–267
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SUMMARY
The endocrine activity of the thyroid glands of rabbits fed a diet containing 0·3% molybdate ion for 25 and 31 days was evaluated. Means (± s.e.m.) were plasma thyroxine (T4) concn (μg/100 ml): 15 molybdate-fed rabbits, 2·31 ± 0·34; 19 control rabbits, 4·40 ± 0·34. T4 distribution space (ml/100 g body wt): molybdate-fed rabbits, 21·5±2·1; controls, 21·4 ± 0·9. T4 secretion rate (μg/24 h/100 g): molybdate-fed rabbits, 0·320 ± 0·073; controls, 0·601 ± 0·046. Histometric measurements made on photographs of gland sections showed that the follicular epithelial cells formed 12·8% of the total area in molybdate-fed rabbits and 25·8% in controls. The histological appearance of the sections was one of increased colloidal storage and of epithelial inactivity in the molybdate-fed rabbits. Comparisons with glands from a food-restricted group of rabbits supported the view of thyroidal hypofunction in molybdenosis in rabbits, with reduced food intake as the major causal factor. Some additional degeneration of the thyroid gland was attributed directly to the molybdate ion.
