ABSTRACT

The mechanism of water conservation is impaired in ageing mammals. An age-related defect in the release of vasopressin has been implicated but, more recently, attention has moved to the renal component of the water conservation mechanism. Previous studies using renal cells prepared from mice of different ages have shown that the threshold dose of vasopressin required to elicit a significant rise in cyclic AMP (cAMP) was greater in older animals. The dose–response curve was moved to the right in 35-month-old mice, i.e. the concentration of vasopressin required to give maximum cAMP output was increased. To investigate this further we examined the binding of vasopressin to renal medullary cells maintained in short-term culture, to determine whether the decreased response of cAMP levels to vasopressin is due to changes in hormone-receptor interaction. In 6-month-old male mice the dissociation constant (K _d) was 2·38 nmol/l and the maximum binding of the hormone (B_max) was 47·6 fmol/10⁶ cells, and at 30 months of age K _d was 2·37 nmol/l and B_max was 47·0 fmol/10⁶ cells. In female mice the changes were more complicated because the data for the 6-month-old mice could be split into two groups. It is concluded that there are no age-related differences in the numbers of receptors or their affinity for vasopressin, and that the decreased cAMP response is probably associated with post-receptor mechanisms in this species.

J. Endocr. (1987) 115, 379–385

ABSTRACT

Subconfluent human thyroid cells in monolayer, isolated from thyrotoxic tissue or non-toxic goitres obtained at surgery, responded to the addition of epidermal growth factor (EGF) with an increase in cell growth as measured by increased incorporation of [³H]thymidine into trichloroacetic acid-precipitable material. The growth response to EGF was concentration-dependent and the characteristics of the responses were the same using EGF from murine or human sources. With concentrations which stimulated growth, EGF was found to inhibit human thyroid cell function as measured by the release of radioimmunoassayable tri-iodothyronine into the incubation medium. Thyrotrophin (TSH) was also found to stimulate human thyroid cell growth but at concentrations far lower than those used to stimulate thyroid cell function in this system. The effect of EGF on the differentiating action of TSH on human thyroid cells in culture was also investigated; the association of thyroid cells into two-dimensional follicular structures produced by the incubation of thyroid cells at a high cell density with TSH was found to be inhibited by the addition of EGF.

J. Endocr. (1986) 108, 393–398

ABSTRACT

A screen of a range of bacteria normally found in gut flora identified eight with the ability to bind TSH specifically. These included the previously reported Yersinia enterocolitica, Gram-positive, Gramnegative, pathogenic and commensal organisms. Eleven preparations of TSH-receptor autoantibodies strongly able to displace ¹²⁵I-labelled TSH from the mammalian TSH receptor differed in their ability to displace the tracer from binding to bacterial extracts. None could displace the tracer from E. coli 06–1, four displaced ¹²⁵I-labelled TSH from E. coli V21/1 and five displaced the tracer from Y. enterocolitica. Of those immunoglobulin preparations which did react with the bacterial protein, their apparent potency compared with that of TSH in displacing tracer from bacterial binders was an order of magnitude greater than with the mammalian receptor. This is consistent with the autoantibodies having a relatively better fit with the bacterial antigen than with the receptor when compared with TSH. The bacterial-binding activity and mammalian receptor-binding activities in each of two samples co-chromatographed on a Remazol yellow GGL–Sepharose affinity column strongly indicated that the same immunoglobulin species reacts with both antigens. These results are consistent with the proposal that a bacterial protein is the primary immunogen for the TSH-receptor antibodies in at least some patients with Graves' disease.

Journal of Endocrinology (1989) 121, 571–577

ABSTRACT

Serotoninergic control of aldosterone secretion in vivo was investigated in conscious rats with indwelling arterial cannulae. Serial blood samples were taken from the animals before and after i.p. administration of 1 ml (4 g/l) 5-hydroxytryptophan (5-HTP), the precursor of serotonin, or saline and they were analysed for 5-HTP, serotonin, 5-hydroxyindoleacetic acid, plasma renin activity (PRA), corticosterone, aldosterone, sodium and potassium concentrations. The role of the renin-angiotensin system was investigated in animals pretreated for 1 week with the angiotensin-converting enzyme inhibitor captopril (25 mg/day). 5-HTP caused a significant increase in all parameters within 45 min except for sodium and potassium. Saline administration showed no significant effect. Captopril pretreatment did not impair the increase in any parameter by 5-HTP, with the exception of the aldosterone response which was significantly attenuated, though not completely.

The results show that administration of 5-HTP, which increases serum serotonin levels, stimulates PRA, aldosterone and corticosterone secretion. Captopril pretreatment inhibits the aldosterone response, suggesting that the aldosterone stimulatory properties of 5-HTP require the presence of angiotensin II, although it is unclear whether it acts in a mediatory or permissive capacity. The failure of captopril to inhibit the aldosterone response completely suggests the involvement of other mechanisms such as the hypothalamo-pituitary adrenal axis or a direct action of serotonin on the adrenal.

Journal of Endocrinology (1991) 130, 347–355

ABSTRACT

The effect of dopamine (1 μg/kg per min) on corticosteroid response to ACTH (0·1, 1 and 10 ng/kg per min) was compared with that of a placebo in sodium-replete (150 mmol/day) and -deplete (10 mmol/day) normal man. Dopamine had no effect on aldosterone, cortisol or corticosterone responses in either dietary phase, but increased deoxycorticosterone (897·0 ± 126·4 (s.e.m.) vs 590·0 ±84·3 pmol/l, normal Na⁺; 1264·2 ±84·3 vs 764·5 ±84·3 pmol/l, low Na⁺) and deoxycortisol (6·033 ± 0·583 vs 5·048±0·680 nmol/l, normal Na⁺; 5·112 ± 0·600 vs 4·130± 0·367 nmol/l, low Na⁺) levels during ACTH administration (all P <0·01). Deoxycorticosterone and corticosterone responses to ACTH were greater during sodium depletion than repletion (both P <0·01).

Dopamine therefore increased 11-deoxycorticosteroid concentrations during ACTH-stimulated steroidogenesis. This may reflect action of dopamine to increase extra-adrenal formation of 11-deoxycorticosteroids.

J. Endocr. (1986) 109, 339–344

ABSTRACT

Material with the immunochemical properties of the β-core of human chorionic gonadotrophin (hCG) can be found in the urine of normal postmenopausal women. However, we have been unable to detect intact hCG (using an assay which is specific for the α–β heterodimer of intact hCG) in serum of such subjects. The levels of serum LH and urinary β-core were compared in matched samples from 28 women (serum LH: median 27 U/l, range 4-70 U/l, urinary β-core: median 0·27 μg/l, range < 0·05–0·645 μg/l). Urine (4 litres) from three postmenopausal women was concentrated, dialysed and subjected to gel exclusion chromatography on Sephadex G-100. Fractions were analysed by specific assays for LH, intact hCG, total β-hCG (free β-subunit and intact hCG), free α-subunit and β-core. Material eluting at the expected position of the β-core fragment of hCG was detected in all three samples by the β-core, β-hCG and LH assays, despite the fact that the LH antibody does not recognize the authentic β-core of pregnancy. Electrophoresis and Western blotting of the concentrated urines revealed that material of the same molecular size as β-core was recognized by the antibody to LH but not by a monoclonal antibody raised to free β-hCG which also recognizes the β-core molecule of hCG. We conclude that the predominant core-like material identified in postmenopausal urine is probably derived from the β-subunit of LH.

Journal of Endocrinology (1992) 133, 459–466

ABSTRACT

The effect of age on the cyclic AMP (cAMP) response to increases in the concentration of arginine vasopressin in the presence of isobutyl methylxanthine (100 μmol/l) was studied in an in-vitro renal cell suspension prepared from C57BL/Icrfa^t mice at 6, 12, 18, 24, 29 and 35 months of age. Comparison of the response of the preparation to vasopressin, calcitonin and parathyroid hormone suggested that it was enriched with renal medullary cells. Basal cAMP output was similar throughout but the threshold dose of vasopressin increased from 1 × 10⁻¹¹ mol/l (6, 12 and 18 months of age) to 1 × 10⁻¹⁰ mol/l (24, 29 and 35 months of age). The dose–response curve in 35-month-old mice was shifted to the right with the concentration of vasopressin required to give half maximal cAMP increased from 9·4 ± 0·37 × 10⁻¹¹ mol/l (6 months) to 3·5±1·6 × 10⁻¹⁰ mol/l (35 months). Maximum cAMP output at 1 × 10 ⁻⁹ mol/l was also reduced in the same animals (stimulated:basal ratio, 51·22±19·12 at 6 months; 11·50 ± 6·02 at 35 months). The results suggest that the lack of renal response to vasopressin in terms of cAMP metabolism may play a role in the well-documented age-related decline in urine-concentrating ability in experimental animals and elderly people.

J. Endocr. (1984) 103, 133–139

ABSTRACT

Infusion of dopamine is reported to reduce the response of aldosterone to infused angiotensin II in sodium-deplete but not sodium-replete man. Six normal male subjects were infused with angiotensin II in graded doses (2, 4 and 8 ng/kg per min) with or without dopamine (1·0 μg/kg per min) during both dietary sodium repletion and depletion. The responses of both aldosterone and 18-hydroxycorticosterone to infusion of angiotensin II appeared to be reduced by dopamine in sodium-deplete, but not sodium-replete, subjects. However, when the relationships between plasma concentrations of angiotensin II and corticosteroid were examined it was evident that plasma concentrations of angiotensin II were lower when dopamine was infused concurrently with the peptide (P<0·05).

In a second study, six sodium-deplete males were infused with angiotensin II at a constant rate (6 ng/kg per min) while dopamine (or placebo) was given in graded doses (0·5,1 and 5 μg/kg per min). Renal plasma flow was estimated from total body clearance of para-aminohippuric acid. Overall, angiotensin II concentrations were lower during dopamine infusion compared with those during infusion of placebo (63·2 ± 9·7 (s.e.m.) vs 92·3±6·4 pmol/l; P<0·01) and this was associated with a 40% increase in effective renal plasma flow (627 ± 68 vs 451 ± 15 ml/min; P < 0·05); there again appeared to be a reduced aldosterone response during combined angiotensin II/dopamine infusion compared with that during infusion of angiotensin II alone (1003 ± 404 vs 1225± 146 pmol/l; 0·05<P<0·1).

Dopamine appeared to increase the metabolic clearance of infused angiotensin II, possibly by altering blood flow through vascular beds, such as renal, which degrade the peptide. This may partly explain the effects of dopamine on the response of the adrenal to infusion of angiotensin II in sodium-deplete man; the physiological role of dopamine in the regulation of corticosteroidogenesis remains speculative.

J. Endocr. (1987) 113, 139–146

ABSTRACT

Non-islet-cell tumours which induce hypoglycaemia are rare. Insulin-like growth factor-II (IGF-II) produced by some tumours is thought to be responsible for the hypoglycaemia and other systemic effects, despite normal or even low serum IGF-II levels. We studied a 44-year-old woman presenting with symptomatic hypoglycaemia associated with a large intraabdominal haemangiopericytoma. The serum IGF-II level was 455 μg/l when measured after acid-ethanol extraction (normal range (NR) 450–750 μg/l) and 1063 μg/l after acid chromatography (normal human serum pool 1068 μg/l). Levels of fasting plasma insulin, C-peptide, glucose and serum IGF-I levels were low before the operation (< 2 mU/l (NR <2-14), 0·23 nmol/l (NR 0-4-1-2), 3-1 mmol/l, (NR 3-7-5-9) and 002 U/ml respectively). After tumour removal, the symptoms resolved rapidly and the patient made a full recovery. Secretion of both insulin and growth hormone was suppressed before the operation in response to a 75 g glucose meal and to an infusion of 100 μg GH-releasing hormone (GHRH) respectively in comparison with studies after the operation. Serum IGF-II levels 6 weeks and 12 weeks after the operation fell to 385 μg/1 (777 μg/1; acid chromatography) and 280 μg/1 (647 μg/1; acid chromatography) and serum IGF-I levels increased to 0-35 U/ml and 0-26 U/ml. Serum before the operation and tumour extract contained chiefly a large molecular weight precursor IGF-II (molecular weight 15 000–20 000) which disappeared from the serum after the operation. The IGF-binding proteins (IGFBP-1, IGFBP-2, IGFBP-3 and IGFBP-4) were examined. The preoperation fasting serum IGFBP-1 level was lower than expected (31 μg/l (NR 20–70 μg/l)) and similar to levels at 6 weeks after the operation (33 μg/l). This was surprising given the differences in plasma insulin levels before and after the operation (< 2 mU/l versus 13 mU/l). Using Western ligand blotting techniques, serum IGFBP-3 levels were found to be low and IGFBP-2 appeared to be the dominant IGFBP before the operation. Serum IGFBP-3 levels after the operation fell further. This further decrease appeared, in part, to be due to the presence of a cation-dependent IGFBP-3-specific protease which has previously only been described in late pregnancy.

We conclude that in this subject, despite normal serum IGF-II levels, the hypoglycaemia and systemic effects on insulin and GH secretion were due to increased bioavailability of a circulating tumour-produced precursor form of IGF-II. This increased bioavailability appears to be due to alterations in the circulating levels and perhaps affinities of the IGFBPs.

Journal of Endocrinology (1991) 131, 303–311

ABSTRACT

The insulin-like growth factors (IGF-I and IGF-II) are almost completely bound in the circulation to specific binding proteins (IGFBPs). These IGFBPs appear to play a pivotal role in maintaining circulating levels and modulating the delivery of the IGFs to the tissues. A large proportion of the circulating IGFs are bound with high affinity to one of the binding proteins, IGFBP-3. The mechanism by which these IGFs are transferred from the circulatory pool to the tissue receptors is at present unclear. Recent studies in late pregnancy have demonstrated the presence of specific proteases which may modify the IGFBPs such that their affinities for the IGFs are reduced. In this paper, we have demonstrated the presence of a heat-sensitive cation-dependent proteolytic enzyme specific for IGFBP-3 in the serum of five severely ill patients. The activity of this protease was found to vary in these patients, becoming more apparent during fasting than when studied after commencement of parenteral nutrition, indicating that one of the influencing factors in the activity of this protease is the nutritional intake of the patient. Age- and sex-matched healthy adults were also studied in a similar protocol, but no proteolytic modification of any of the IGFBPs was found in any of the samples examined. As the levels of both IGF-I and IGF-II were found to be low in the patients, the presence of a circulatory protease suggests that this may be an adaptive response to increase the bioavailability of the IGFs and possibly to improve the nitrogen retention and counter the catabolic state in severe illness.

Journal of Endocrinology (1991) 130,469–473