Steroid hormones regulate cell function via specific receptors, members of a super family of ligand activated transcription factors, expressed in their target tissues. A second oestrogen receptor (ER beta) has recently been shown by RT-PCR to have a wide tissue distribution distinct from that of oestrogen receptor alpha (ER alpha). We have raised a polyclonal antiserum using a peptide specific for ER beta in order to determine the cellular sites of expression of the receptor. In the adult rat ER beta was localised to cell nuclei in a wide range of tissues including ovary, oviduct, uterus, lung, adrenal, seminal vesicle, bladder, heart, prostate and testis. In the ovary ER beta was present in multiple cell types including granulosa cells in small, medium and large follicles, theca and corpora lutea whereas ER alpha was undetectable in these cell types. In the uterus ER beta and ER alpha were both present in epithelial cells lining the lumen and glands. In the lung ER beta was present in the cells lining the bronchioles and alveoli as well as in smooth muscle. In bladder and seminal vesicle immunostaining was intense in epithelial cells but the receptor was also expressed in nuclei of smooth muscle cells. Cell nuclei of the heart ventricle were immunopositive for ER beta as were most cells of the adult rat adrenal. In the seminiferous epithelium of the testis, nuclei of Sertoli cells were immunopositive but expression was not stage dependent. In conclusion, immunohistochemistry has proved invaluable in visualising specific sites of expression of ER beta in complex tissues including those of the reproductive tract.

Abstract

A major unresolved physiological problem is how the rate of hepatic glucose production is increased to match the increased rate of glucose utilization during exercise without a change in arterial blood glucose level. A homeostat with such capabilities is said to have infinite gain.

Daisyworld is an imaginary planet orbiting a variable star. The only life is black and white daisies. Black daisies retain heat, slightly warming the planet; white daisies cool it. When the two types of daisies grow best at slightly different temperatures, variations in solar luminosity (over a wide range) cause the ratio of white:black daisies to vary in a manner that keeps the planetary temperature constant. This model therefore achieves infinite gain by having two opposing but interdependent controllers.

Here we suggest that the pancreatic islet α- and β-cells might act as black and white daisies. For the analogy to apply, glucagon and insulin must not only have opposing effects on the blood sugar concentration, but the secretion of the one has, at some quantum level, to be at the expense of the other. Electrical coupling between heterocellular groups of α- and β-cells within the pancreatic islets suggests that this might indeed be the case. α-Cell activity must, furthermore, promote secretory activity in other α-cells; similarly with β-cells. This is probably mediated via pancreastatin and γ-amino butyric acid (GABA) which are paracrinically co-secreted with glucagon and insulin, respectively. α-Cell activity spreads (at the expense of β-cell activity) when the blood glucose level is below set point, while β-cell activity progressively replaces α-cell activity above set point. At set point changes in the ratio of α:β-cell activity are inhibited.

Journal of Endocrinology (1997) 154, 187–192

A naturally-occurring, physiological process of marrow ossification was correlated by Kyes & Potter in 1934 with the size of the ovarian follicle in female pigeons. This was perhaps the first indication that female sex hormones had what is now known to be a dynamic, physiological, and pathological effect on bone.

Body weight, as early as 1931, however, was noted by Spencer, Gustavson & D'Amour to be depressed as a result of oestrogen treatment. The fact that body growth in general was markedly depressed was later verified by innumerable investigators [Spencer, D'Amour & Gustavson, 1932; Korenchevsky & Dennison, 1934; Zondek, 1936a, 1936b; Freudenberger & Clausen, 1937a, 1937b; Silberberg & Silberberg, 1939; Day & Follis, 1941]. Zondek [1936b] offered the first explanation of this phenomenon, showing conclusively that the oestrogenic hormones depressed the function of the anterior pituitary to the extent of inhibiting the production of the

Abstract

The effects of various hormones commonly added to hepatocyte culture media upon the expression of the GH receptor (GHR) and insulin-like growth factor-I (IGF-I) genes in cultured porcine hepatocytes were investigated. Preliminary investigations indicated that there was an absolute requirement only for insulin, with high losses of cell viability upon long term exclusion of insulin from the culture medium. The decline in GHR expression with time in culture was found to be less when high levels of glucose were included in the medium. Therefore the basal culture medium used in these studies was Williams' medium E supplemented with 0·2% (w/v) BSA, 5000 mg glucose/l and 100 nmol porcine insulin/l. The addition of dexamethasone (100 nmol/l) increased the expression of both GHR and IGF-I (class 1 transcripts only) mRNA (P<0·001 and P<0·05 respectively), and resulted in an increased responsiveness of IGF-I mRNA expression to GH (1 μg/ml), when the two were added in combination (although only class 1 transcripts were shown to be statistically significant, P<0·01). The addition of either thyroid hormone (1 nmol/l T₃ or T₄) alone also increased the expression of GHR mRNA (P<0·01) in addition to the dexamethasone stimulated expression, with T₄ appearing to decrease IGF-I expression slightly (P<0·05) (either on its own or with T₃). As with dexamethasone, the thyroid hormones increased the response of IGF-I mRNA expression to GH (1 μg/ml) when added in combination with GH (P<0·001). These observations demonstrate one possible mechanism for the interactions of glucocorticoids and thyroid hormones with the GH–IGF axis.

Journal of Endocrinology (1995) 146, 239–245

ABSTRACT

The polypeptide mitogen, epidermal growth factor (EGF), was originally isolated from mouse submaxillary gland (SMG). In mice, these glands are sexually dimorphic; the SMG of male animals typically contains up to 400 pmol EGF/mg protein whereas EGF concentrations in the SMG of female mice are only 5–20 pmol/mg protein. When mice were castrated at 8 weeks of age, EGF mRNA levels in the SMG fell rapidly to the low levels observed in control female animals. Although the concentration of EGF in the SMG, measured by radioimmunoassay, also fell to very low levels (13·8 ± 0·7 (s.e.m.) pmol/mg protein) in the castrated mice, the rate of decrease was considerably slower than that of the mRNA. In contrast to the loss of EGF and EGF mRNA from mice following castration, ovariectomy led to a rise in EGF mRNA levels in SMG, with a maximal increase (approximately 100-fold) 4–6 weeks after ovariectomy. Concentrations of EGF in the SMG also rose markedly in the ovariectomized animals, from a control value of 5·4 ± 0·8 to 34·7 ± 7·9 pmol/mg protein at 6 weeks. In mice, the kidney displays the second highest level of EGF gene expression. However, in contrast to the effects on SMG, kidney EGF mRNA was not affected by either castration or ovariectomy. These results provide further evidence for the tissue-specific control of EGF gene expression in response to steroid hormones.

Journal of Endocrinology (1989) 121, 501–506

ABSTRACT

We have determined the effect of human insulin-like growth factor-binding protein-1 (hIGFBP-1) on the circulating half-life (t _½) of human insulin-like growth factor-I (hIGF-I) and on hIGF-I-stimulated 2-deoxyglucose uptake in tissues of the cannulated conscious rat. The levels of hIGF-I in rat serum were measured by radioimmunoassay. The assay was carried out in the presence of partially purified rat IGF to remove interference from any IGFBPs not removed by acid–ethanol extraction. An intravenous bolus of 12·5 μg hIGF-I, given to 12-h fasted rats, disappeared from the circulation in a double exponential fashion with an initial t _½ of 1·2±0·2 min (n = 8), which increased to 5·3 ±0·9 min when 100 μg hIGFBP-1 was co-administered (n = 5; P <0·001). The second phase of disappearance of hIGF-I indicated an apparent t _½ of 35·7±5·6 min which was not significantly altered by the co-infusion of hIGFBP-1. Circulating hIGFBP-1, measured with a primate-specific radioimmunoassay, disappeared in a single exponential fashion with a t _½ of 8·8±0·7 min. A tracer amount of 2-deoxy-[1-³H]glucose was administered intravenously at the same time as the peptide(s) and the rate of tissue uptake and phosphorylation of 2-deoxy-[1-³H]glucose determined. Compared with a control group (n = 4), hIGF-I significantly stimulated hexose uptake into heart, soleus and red quadriceps muscles and hIGFBP-1 partially reversed this effect. We propose that the insulin-like activity of unbound IGFs in the circulation may be regulated in vivo by fluctuating endogenous IGFBP-1 levels, so that the IGFs, along with IGFBP-1, may represent a dynamic glucoregulatory system.

Journal of Endocrinology (1993) 136, 253–260

Abstract

The sites of action and the physiological role of oestrogens in the male reproductive tract are poorly understood. We have undertaken a systematic study of the immunoexpression of oestrogen receptor-α (ERα) in the male rat from late fetal life through to adulthood and compared the findings with results obtained in the marmoset monkey (Callithrix jacchus) from neonatal to adult life. The testes, rete testis, efferent ducts and epididymis were examined from normal male rats (aged 4, 8, 10, 15, 20, 25, 38, 48 and 90 days) and from male rat fetuses on days 17·5 and 18·5 of gestation; comparable tissues were examined from neonatal, infantile, peripubertal and adult marmosets aged 8, 18–24, 54–62 and 92–112 weeks respectively. Immunolocalisation of ERa used antigen retrieval and a monoclonal antibody directed to the N-terminus, which had proved superior to six other antisera tested. ERa was immunoexpressed in interstitial cells, including the fetal/neonatal generation of Leydig cells, in both the rat and marmoset. In the rat, the adult generation of Leydig cells were also immunopositive for ERa whereas the comparable cells in the marmoset were only weakly immunopositive. ERa was not expressed in Sertoli cells, peritubular myoid cells, blood vessels or germ cells at any time in either species. In late fetal life in the rat, ERa was immunoexpressed in cells surrounding the mesonephric tubules, whereas postnatally it was expressed in the epithelium of the rete testis and efferent ducts at all ages from 4 to 90 days; this immunoexpression was most pronounced in the efferent ducts. In the marmoset, the efferent ducts, but not the rete testis, also showed intense immunoexpression of ERa. Apart from sporadic immunostaining for ERa in the epididymal duct of the rat in the neonatal period, the caput, corpus and cauda epididymis were negative for immunoexpression of ERa at all ages in both species. These findings suggest that the main actions of oestrogens in the male reproductive tract, mediated by ERa, are related to the development and function of the efferent ducts and the Leydig cells. In consideration of data from this and previous studies of oestrogen binding, we predict possible sites of expression of other oestrogen receptors (e.g. ERβ) in Sertoli cells and the epididymis. Interactive effects, related to the relative levels of androgens and oestrogens, could be physiologically important in the excurrent ducts of the adult testis.

Journal of Endocrinology (1997) 153, 485–495

ABSTRACT

In-vitro data from experiments on rats implicate granulosa cells as primary sites of hormone-dependent ovarian inhibin biosynthesis, but no equivalent data exist for primates. We have used the common marmoset (Callithrix jacchus) to investigate inhibin biosynthesis in primate granulosa cells in vitro and to determine its relationship to preovulatory follicular development. To relate the production of immunoactive inhibin to follicular maturity, we studied primary granulosa cell cultures from follicles at progressive stages of preovulatory development. Granulosa cells from 'large' (≥2·0 mm diameter) follicles expressed high rates of inhibin production and steroidogenesis (progesterone), and were positively regulated by human (h)LH in vitro. Less mature granulosa cells from 'medium' (1·1–1·9 mm) and 'small' (≤ 1·0 mm) follicles expressed proportionately lower rates of inhibin production and steroidogenesis, but each parameter was stimulated in a dose- and time-dependent manner by hFSH in vitro. The stimulatory action of hFSH on immunoactive inhibin was augmented by the presence of testosterone or oestradiol; testosterone (but not oestradiol) also augmented the steroidogenic response to hFSH. Marmoset luteal tissue also produced inhibin in vitro and expressed an ∼1·5 kb inhibin α-subunit mRNA, confirming the corpus luteum as a source of ovarian inhibin in primates.

These results provide direct experimental evidence that primate granulosa cells produce inhibin. They suggest that production of inhibin by immature granulosa cells is initially induced by FSH and subject to modulation by follicular steroids. During advanced preovulatory development, granulosa cell inhibin production becomes directly responsive to LH, thereby indicating a role for LH in the control of peri- and postovulatory inhibin secretion by the primate ovary.

Journal of Endocrinology (1989) 123, 65–73