ABSTRACT

The receptors for TSH have been studied in human thyroid tissue to assess their density and binding characteristics in various disease states. A single set of similar independent receptors appeared to be present in both healthy and pathological thyroid tissue. Their binding affinity for bovine TSH averaged 1·1 × 10¹⁰l/mol in healthy tissue and, with the exception of papillary carcinoma which showed some reduction, was not significantly altered in the various disease states studied. No receptors with low binding affinity were found. The number of receptors was significantly greater in toxic diffuse goitre and in hyperfunctioning follicular adenoma (but these tissues came from patients given antithyroid drugs and often iodine preoperatively), and was reduced in Hashimoto's thyroiditis. In well-differentiated thyroid carcinoma, the number of receptors was similar to or greater than in normal tissue, but in undifferentiated and medullary carcinoma, and in lymphoma of the thyroid, receptors were completely absent. Tracer-binding data obtained with human TSH were uniformly lower than the corresponding data obtained with bovine TSH, but showed an analogous pattern of differences amongst the various normal and pathological tissues.

J. Endocr. (1984) 102, 369–374

Abstract

To define the hormonal influences that are directly involved in the hair follicle cycles of animals with differing patterns of fibre growth and moulting, we have investigated the possible presence of IGF-I and melatonin receptors on the dermis and hair follicles of cashmere and Angora goats, sampled in February, March and June, using quantitative in vitro autoradiography. The presence of IGF-I receptors in the dermis of both breeds of goat was determined using cryostat sections incubated with 50 pm ¹²⁵I-labelled IGF-I in the presence or absence of 50 nm IGF-I. Sections of the growing tip of deer antlers containing the cartilaginous zone, a tissue known to contain high concentrations of specific IGF-I receptors, were used as a positive control. As the production of antler velvet uniquely involves the generation of hair follicles de novo, the presence of IGF-I receptors in the velvet-producing region was also investigated. In both breeds of goat, specific ¹²⁵I-IGF-I binding was localised over the inner and outer root sheath, the matrix, the germinal matrix, the dermal papilla and the sebaceous glands and satisfied the basic kinetic criteria considered to be representative of a specific IGF-I receptor. Analysis of saturation isotherms using a one-site binding model revealed dissociation constants (K _d) in the range 0·1–0·9 nm and theoretical maximal numbers of binding sites (B _max) between 21·4 and 45·6 fmol/mg tissue. K _d and B _max values derived from cashmere and Angora goats sampled at different times of the year did not differ significantly between breeds or sampling times. Specific ¹²⁵I-IGF-I binding was also localised to the developing follicles on the deer antler dermis. The presence of melatonin receptors within the goat dermis was also investigated. Sections were incubated with 100 pm 2-[¹²⁵I]iodomelatonin with or without 0·1 μm melatonin, along with sections of sheep pars tuberalis which are known to contain high levels of high-affinity melatonin receptors. No displaceable 2-[¹²⁵I]iodomelatonin binding was found on any sections of the cashmere or Angora skin analysed. It is therefore concluded that melatonin receptors are not present on the hair follicles or associated structures. IGF-I receptors are present on the hair follicle and sebaceous gland and may be involved in the growth of both seasonally and non-seasonally produced fibre and in the development of antler velvet.

Journal of Endocrinology (1996) 151, 55–63

ABSTRACT

Plasma samples were obtained throughout pregnancy and pseudopregnancy from Sprague–Dawley (SD) rats and during pregnancy from rats of the Munich Wistar (MW) strain. The concentrations of progesterone, oestradiol, prolactin, plasma renin activity (PRA), aldosterone and corticosterone were measured by radioimmunoassay to establish hormonal profiles in the two strains of rat.

Circulating progesterone concentrations in both strains of rat were significantly higher during pregnancy than in virgin controls, except at term in the SD group. The hormonal pattern for pseudopregnancy was similar to that of the first half of pregnancy. Oestradiol concentrations were similar to, or lower than, those in virgin controls throughout pseudopregnancy and for the first 2 weeks of pregnancy in both strains of rat. Increased concentrations of steroid were seen only in the pregnant groups towards term. In SD rats, highest prolactin concentrations were apparent during the first half of pregnancy and pseudopregnancy, and at term in the pregnant group. Pregnant MW rats showed a different profile for this hormone, with low levels throughout pregnancy except at term. In all groups PRA rose to a peak at day 9 and decreased to day 16. Pregnant SD rats also showed a significant increase at term. Aldosterone concentrations were significantly increased at several stages of pregnancy in both strains of rat, particularly during the second half of gestation. Pseudopregnant animals showed a different hormone profile, with no significant changes until day 16 when lower concentrations were recorded. There was little variation in the circulating corticosterone concentration except in pregnant rats at term when levels fell.

These findings are discussed in relation to the known renal changes of pregnancy and pseudopregnancy.

J. Endocr. (1987) 113, 435–444

ABSTRACT

The effects of the mixed α/β-agonist adrenaline on insulin secretion from isolated human islets of Langerhans were studied. In static incubation experiments, adrenaline (0·1 nmol/l to 10 μmol/l) caused a concentration-dependent inhibition of glucose-induced insulin secretion from isolated human islets. However, perifusion experiments revealed that the time-course of the secretory changes induced by adrenaline was complex. When employed at a high concentration (1 μmol/l), adrenaline caused a sustained inhibition of glucose-induced insulin secretion, which could be relieved by the addition of the α₂-antagonist yohimbine (10 μmol/l). By contrast, infusion of adrenaline at a lower concentration (10 nmol/l), produced a large initial potentiation of glucose-induced insulin secretion. This response was, however, short-lived and followed by sustained inhibition of secretion, which could be relieved by yohimbine (10 μmol/l). The initial stimulation of insulin secretion provoked by 10 nmol adrenaline/l was abolished when islets were incubated in the presence of the β-antagonist, propranolol (1 μmol/l), consistent with activation of β-adrenoceptors. In support of this, treatment of human islets with the selective β₂-agonist clenbuterol, was also associated with marked stimulation of insulin secretion. By contrast, each of two selective β₃-agonists tested failed to alter insulin secretion from human islets. The results indicate that human pancreatic B-cells are equipped with both α₂-and β₂-adrenoceptors which can affect insulin secretion. Adrenaline interacts with both of these but the α₂-response is predominant and can overcome the tendency of β₂-adrenoceptors to potentiate insulin release.

Journal of Endocrinology (1993) 138, 555–563

Abstract

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

The relationship between the degree of GH deficiency and impaired bone integrity is not simple and may be influenced by related endocrine variables. To test the hypothesis that elevated adiposity and hyperleptinaemia are contributory factors, we quantified femoral trabecular organisation in two models of GH deficiency with divergent degrees of adiposity – the moderately GH-deficient/hyperleptinaemic transgenic growth retarded (Tgr) rat and the profoundly GH-deficient/hypoleptinaemic dw/dw rat. Trabecular density (bone volume/total volume) and surface were reduced by 16% in dw/dw males, with a more fragmented trabecular lattice. This impairment was more pronounced in Tgr rats, with trabecular number and density further reduced (by an additional 21%) and relative surface (bone surface/bone volume), trabecular convexity (structural modal index) and fragmentation (pattern factor) increased. To establish whether the presence of obesity/hyperleptinaemia exacerbates bone impairment in GH deficiency, trabecular structure was assessed in dw/dw rats following diet-induced obesity (DIO). DIO had minimal effect on trabecular architecture, the increased concavity of trabecular surfaces being the only observable effect. Similarly, infusion of leptin into the tibial bone marrow cavity had no effect on trabecular organisation or tibial growth in wild-type rats. However, while this procedure also failed to affect trabecular architecture or osteoclast number in dw/dw rats, distal osteoblast surface was increased by 23%, marrow adipocyte number and epiphyseal plate width being reduced (by 40 and 5% respectively), without increasing caspase-3 immunoreactivity. These findings suggest that while leptin may directly inhibit adipocyte differentiation and favour osteoblast production, hyperleptinaemia makes only a minimal contribution to the impairment of bone structure in GH deficiency.

Long-chain saturated and monounsaturated fatty acids differ in their propensity to induce β-cell death in vitro with palmitate (C16:0) being cytotoxic, whereas palmitoleate (C16:1n-7) is cytoprotective. We now show that this cytoprotective capacity extends to a poorly metabolised C16:1n-7 derivative, methyl-palmitoleate (0.25 mM palmitate alone: 92 ± 4% death after 18 h; palmitate plus 0.25 mM methyl-palmitoleate: 12 ± 2%; P < 0.001). Palmitoleate and its methylated derivative also acted as mitogens in cultured β-cells (5-bromo-2-deoxyuridine incorporation – control: 0.15 ± 0.01 units; 0.25 mM palmitoleate: 0.22 ± 0.01 units; P < 0.05). It has been proposed that alterations in neutral lipid synthesis (particularly triacylglycerol (TAG) formation) might mediate the differential responses to saturated and unsaturated fatty acids and we have examined this proposition. Palmitate and palmitoleate both promoted β-cell phospholipid remodelling and increased TAG formation (control: 0.9 ± 0.1 nmol TAG/10⁶ cells; 0.25 mM palmitate: 1.55 ± 0.07; 0.25 mM palmitoleate: 1.4 ± 0.05; palmitate plus palmitoleate: 2.3 ± 0.1). By contrast, methyl-palmitoleate failed to influence TAG levels (0.25 mM methyl-palmitoleate alone: 0.95 ± 0.06 nmol TAG/10⁶ cells; methyl-palmitoleate plus palmitate: 1.5 ± 0.05) or its fatty acid composition in β-cells exposed to palmitate. The results suggest that monounsaturated fatty acids can promote cell viability and mitogenesis by a mechanism that does not require their metabolism and is independent of alterations in TAG formation.