The concentration of circulating plasma thyroxine (T4) appears to have little effect on the maximal binding capacity of plasma thyroxine-binding globulin (TBG). Several studies in man have shown that thyrotoxicosis results in normal or slightly lowered levels of TBG, while hypothyroidism leads to a normal or slightly increased TBG binding capacity (Oppenheimer, Squef, Surks & Hauer, 1963; Inada & Sterling, 1967; Gordon, Kleinerman, Ehrenfeld & Ehrenfeld, 1971). In contrast the binding capacities of corticosteroid-binding globulin (CBG) and sex steroid-binding globulin (SBG) have been shown to be markedly affected by the level of circulating thyroid hormone. In the rat the binding capacity of CBG was markedly depressed by thyroid-ectomy and enhanced by chronic administration of T4 (Labrie, Raynaud & Fortier, 1965). Similarly, Dray, Mowszowicz, Ledru, Crépy, Delzant & Sebaoun (1969) administered T4 to normal human subjects and observed an increase of SBG concentration. Hyperthyroidism has been shown to
R. L. SUTHERLAND and M. W. SIMPSON-MORGAN
R. L. SUTHERLAND and M. W. SIMPSON-MORGAN
A competitive binding technique is described for the estimation of the thyroxine (T4)-binding properties of serum proteins in dilute blood serum and lymph. When used in conjunction with an assay for total T4 the following parameters can be estimated: the number of functionally different T4 binding proteins, their individual association constants and binding capacities for T4, the amount of T4 which is bound to each binding species, and the concentration of unbound (free) T4.
Both human and sheep serum have three functionally different T4-binding proteins. The association constants for the three human proteins were 9·5 × 109, 1·6 × 108 and 3·1 × 105 1/mol for T4-binding globulin (TBG), T4-binding prealbumin (TBPA) and serum albumin, respectively. The corresponding sheep proteins, TBG, TBP-2 and albumin, had association constants of 8·9 × 109, 1·4 × 108 and 3·5 × 1051/mol. Human TBG had a mean binding capacity of 21·3 μg/100 ml and that of ovine TBG was 12·8 μg/100 ml. The other specific binding proteins (TBPA in man and TBP-2 in sheep) had mean binding capacities of 307 and 359 μg/100 ml respectively.
Two functionally different T4-binding proteins were identified in rat serum.
R. L. SUTHERLAND and M. W. SIMPSON-MORGAN
Electrophoretic studies employing a variety of media and buffer systems have repeatedly shown that tracer thyroxine (T4) moves with two distinct protein bands in sheep serum. These bands correspond to thyroxine-binding globulin (TBG) and serum albumin (Annison, 1960; Farer, Robbins, Blumberg & Rail, 1962; Refetoff, Robin & Fang, 1970). It has been pointed out by Gordon & Coutsoftides (1969) that such electrophoretic techniques are unlikely to depict closely T4 binding in vivo. For this reason we have developed a competitive-binding technique, using Sephadex G-25, which has enabled the measurement of the T4-binding properties of sheep serum proteins at physiological pH. This technique is similar in principle to that previously described by Pearlman & Crépy (1967).
Sephadex G-25 binds T4 in a highly predictable way. When a constant amount of G-25 is in contact with a constant volume of buffer, at equilibrium, the T4 present
MARGARET E. MORGANS, A. K. OLDHAM and W. R. TROTTER
Radio-iodine uptake has been measured by the neck/thigh ratio, before and at the end of a course of oral sodium-l-thyroxine 0·4 mg. given daily for two weeks.
Twenty normal subjects, thirteen patients with non-toxic goitres and thirteen patients who had recovered from thyrotoxicosis have been studied in this way.
In all three groups there was a significant fall in the neck/thigh ratio while the subjects were taking thyroxine.
The mean fall of the neck/thigh ratio after taking thyroxine did not differ significantly in the normal and recovered thyrotoxic groups.
These results do not support the idea that failure to respond to thyroxine is a constitutional feature of subjects who have had an attack of thyrotoxicosis.
R. L. SUTHERLAND, M. R. BRANDON and M. W. SIMPSON-MORGAN
When plasma proteins are diluted with buffer the ionic strength and ionic composition of that buffer affects the interactions between thyroxine (T4) and its plasma protein-binding sites. Increases in phosphate, chloride or barbiturate ion concentration from 50 to 200 mmol/l caused a significant decrease in the affinity of plasma proteins for T4, and a concurrent increase in the concentration of unbound T4. These results cannot be completely accounted for by changes in ionic strength since at the same ionic strength different anions caused quantitatively different effects on unbound T4 concentration. The degree of depression of T4 binding by the three anions studied was in the order barbiturate > chloride > phosphate.
The results of a systematic study on the composition of diluent buffer systems indicated that when a 50 mm-sodium phosphate–100 mm-NaCl buffer (pH 7·4) was used as a plasma diluent, there were unlikely to be gross changes in the T4-binding properties of plasma proteins with dilution.
A. Bartke, W. W. Morgan, R. N. Clayton, T. K. Banerji, A. M. Brodie, T. A. Parkening and T. J. Collins
In several species, including man and the rat, hyperprolactinaemia is associated with suppression of gonadotrophin release and male sexual behaviour. However, in the hyperprolactinaemic male mouse, plasma LH and FSH levels and copulatory behaviour are increased rather than suppressed. In an attempt to identify mechanism(s) which may be responsible for these effects of hyperprolactinaemia in the mouse, we have examined the effects of two ectopic pituitary isografts on several indices of hypothalamic and pituitary function in adult DBA/2J males. Animals with pituitary grafts had markedly increased plasma concentrations of prolactin, LH and FSH and enlarged seminal vesicles, whereas testicular and pituitary weights were not affected. Content of LHRH receptors and activity of aromatase in the pituitary, as well as dopamine-β-hydroxylase activity in the hypothalamus were nearly identical in pituitary-grafted and sham-operated males. Biosynthesis of dopamine and turnover of noradrenaline in the median eminence were significantly increased in grafted males. We suggest that the increase in the activity of hypothalamic noradrenergic neurones may mediate stimulatory action of hyperprolactinaemia on LH and FSH release in the mouse. Comparison of these results with those obtained previously in the rat suggests that species differences in the effects of prolactin on gonadotrophin release may be related to its divergent effects on noradrenaline turnover.
J. Endocr. (1987) 112, 215–220
Jennifer A Crookshank, Daniel Serrano, Gen-Sheng Wang, Christopher Patrick, Baylie S Morgan, Marie-France Paré and Fraser W Scott
It is unknown whether there is a gene signature in pancreas which is associated with type 1 diabetes (T1D). We performed partial pancreatectomies on 30-day preinsulitic, diabetes-prone BioBreeding (BBdp) rats to prospectively identify factors involved in early prediabetes. Microarrays of the biopsies revealed downregulation of endoplasmic reticulum (ER) stress, metabolism and apoptosis. Based on these results, additional investigations compared gene expression in control (BBc) and BBdp rats age ~8, 30 and 60 days using RT-qPCR. Neonates had increased ER stress gene expression in pancreas. This was associated with decreased insulin, cleaved caspase-3 and Ins1 whereas Gcg and Pcsk2 were increased. The increase in ER stress was not sustained at 30 days and decreased by 60 days. In parallel, the liver gene profile showed a similar signature in neonates but with an early decrease of the unfolded protein response (UPR) at 30 days. This suggested that changes in the liver precede those in the pancreas. Tnf and Il1b expression was increased in BBdp pancreas in association with increased caspase-1, cleaved caspase-3 and decreased proinsulin area. Glucagon area was increased in both 30-day and 60-day BBdp rats. Increased colocalization of BIP and proinsulin was observed at 60 days in the pancreas, suggesting insulin-related ER dysfunction. We propose that dysregulated metabolism leads to ER stress in neonatal rats long before insulitis, creating a microenvironment in both pancreas and liver that promotes autoimmunity.
Elizabeth K Fletcher, Monica Kanki, James Morgan, David W Ray, Lea M Delbridge, Peter J Fuller, Colin D Clyne and Morag J Young
We previously identified a critical pathogenic role for mineralocorticoid receptor (MR) activation in cardiomyocytes that included a potential interaction between the MR and the molecular circadian clock. While glucocorticoid regulation of the circadian clock is undisputed, studies on MR interactions with circadian clock signalling are limited. We hypothesised that the MR influences cardiac circadian clock signalling, and vice versa. Aldosterone or corticosterone (10 nM) regulated Cry1, Per1, Per2 and ReverbA (Nr1d1) gene expression patterns in H9c2 cells over 24 h. MR-dependent regulation of circadian gene promoters containing GREs and E-box sequences was established for CLOCK, Bmal, CRY1 and CRY2, PER1 and PER2 and transcriptional activators CLOCK and Bmal modulated MR-dependent transcription of a subset of these promoters. We also demonstrated differential regulation of MR target gene expression in hearts of mice 4 h after administration of aldosterone at 08:00 h vs 20:00 h. Our data support MR regulation of a subset of circadian genes, with endogenous circadian transcription factors CLOCK and BMAL modulating the response. This unsuspected relationship links MR in the heart to circadian rhythmicity at the molecular level and has important implications for the biology of MR signalling in response to aldosterone as well as cortisol. These data are consistent with MR signalling in the brain where, like the heart, it preferentially responds to cortisol. Given the undisputed requirement for diurnal cortisol release in the entrainment of peripheral clocks, the present study highlights the MR as an important mechanism for transducing the circadian actions of cortisol in addition to glucocorticoid receptor (GR) in the heart.
R J Lacey, S L F Chan, H C Cable, R F L James, C W Perret, J H B Scarpello and N G Morgan
Sequences from cDNA molecules encoding α2-adrenoceptor subtype genes were subcloned into prokaryotic vectors and riboprobes generated to hybridise selectively with each of the human α2C2-, α2C4- and α2C10-adrenoceptor subtype mRNA species. The riboprobes were labelled with either 32P or digoxigenin and used to study the expression of α2-adrenoceptor subtypes in sections of human pancreas, in isolated human islets of Langerhans and in clonal HIT-T15 pancreatic β-cells. Using a ribonuclease protection assay protocol, expression of mRNA species encoding both α2C2 and α2C10 was demonstrated in preparations of isolated human islets of Langerhans. mRNA encoding α2C4 was also detected in human islet RNA, using reverse transcription coupled with the polymerase chain reaction. In situ hybridisation was then employed to examine the distribution of each α2-adrenoceptor subtype in sections of human pancreas. All three subtypes of α2-adrenoceptor mRNA were identified in sections of formalin-fixed, paraffinembedded human pancreas using riboprobes labelled with digoxigenin. Although some labelling of the three α2-adrenoceptor mRNA subtypes was seen in the islets, the labelling was most intense in the exocrine tissue of the pancreas for each receptor subtype. The specificity of the digoxigenin-labelled RNA probes was confirmed in several control tissues and by in situ hybridisation studies using sense probes in the pancreas. The integrity of the pancreas sections was confirmed by in situ hybridisation with an antisense riboprobe derived from human insulin cDNA. The results demonstrate that multiple α2-adrenoceptor subtypes are expressed in human pancreas. Both the exocrine and endocrine cells express more than one receptor subtype, although the islets stain less intensely than the bulk of the tissue suggesting that the islet cells may have lower levels of expression than the acinar tissue. The presence of α2-adrenoceptor subtype mRNA species in pancreatic β-cells was confirmed by Northern blotting of RNA extracted from the clonal β-cell line, HIT-T15. Transcripts encoding each of the three cloned α2-adrenoceptor subtypes were detected in HIT-T15 cells.
Hybridisation of sections of human pancreas with oligodeoxynucleotide probes designed to hybridise with β2-adrenoceptor mRNA revealed expression of this species in islet β-cells but not in the exocrine tissue of the pancreas.
Journal of Endocrinology (1996) 148, 531–543
L. J. Leversha, D. M. Robertson, F. L. de Vos, F. J. Morgan, M. T. W. Hearn, R. E. H. Wettenhall, J. K. Findlay, H. G. Burger and D. M. de Kretser
Two forms of inhibin with molecular weights of 65 000 and 30 000 (65 and 30 kD) were isolated from ovine follicular fluid using a combination of gel permeation chromatography, reversed-phase high-performance liquid chromatography and preparative polyacrylamide gel electrophoresis. The 65 kD form was partially purified approximately 315-fold whilst the 30 kD form was isolated as two isoforms (29 and 30 kD) of similar biological activity and in >95% purity (1210-fold purification and 4·2% recoveries). On reduction the 30 kD form resolved into four components of 36, 31, 20–21 and 16 kD of which the 20–21 and 16 kD components were similar to the corresponding inhibin subunits isolated from porcine and bovine follicular fluid. The 36 kD component was established as a non-reducible inhibin-like material, based on its binding to antiserum raised against bovine 58 kD inhibin. The nature of the remaining non-reducible 31 kD component is unknown. Two NH2-terminal amino acid sequences (first 13 amino acids) identified in purified 30 kD inhibin were identical to the corresponding subunit amino acid sequences of bovine 31 kD inhibin.
J. Endocr. (1987) 113, 213–221