Abstract

Human melanocytes, maintained on bovine corneal endothelium-derived extracellular matrix for at least 4 days in the absence of phorbol 12-myristate 13-acetate (PMA) and cholera toxin (CT), displayed increased tyrosinase activity when exposed to several pro-opiomelanocortinderived (POMC) peptides. Melanocytes from 9 of 14 donors showed significantly increased tyrosinase activity after treatment with adrenocorticotropic hormone (ACTH; mean increase 320±107 (s.e.m.)% of control, P<0·005), while melanocytes from 8 of 13 donors increased tyrosinase in the presence of diacetyl-melanocyte stimulating hormone (di-MSH; mean increase 223±31 (s.e.m.)% of control, P<0·005). Maximal increases in tyrosinase were seen after treatment with 10−10 m ACTH and with 10−6 m di-MSH. In two cell cultures which showed tyrosinase stimulation, melanin synthesis was similarly increased in the presence of added POMC peptides. PMA but not CT increased tyrosinase activity in melanocytes cultured under these conditions. In the presence of staurosporine, an inhibitor of protein kinase C (PKC), the magnitude of the increase in tyrosinase due to PMA, ACTH and di-MSH was significantly reduced. These results indicate that tyrosinase activity in melanocytes from most human donors, under appropriate conditions, is susceptible to the stimulatory effects of POMC peptides, that ACTH is considerably more potent than di-MSH in this test system and that in human cells the PKC pathway may be important in modulating melanogenesis.

Journal of Endocrinology (1995) 146, 439–447

Members of the prolactin (PRL) hormonal family have direct effects on endothelial cell proliferation, migration and tube formation. Moreover, isoforms of PRL may function as autocrine regulators of endothelial cells. Bovine brain capillary endothelial cells (BBCEC) express the PRL gene, while anti-PRL antibodies inhibit BBCEC proliferation. Here, we show the expression of the PRL gene into various PRL isoforms in endothelial cells from the human umbilical vein. Reverse transcription-polymerase chain reaction of total RNA from human umbilical vein endothelial cells (HUVEC) detected the full-length PRL mRNA as well as a 100 bp smaller PRL transcript similar to the one previously reported in BBCEC. HUVEC were positive to PRL immunocytochemistry. In addition, various PRL immunoreactive proteins were detected in HUVEC extracts and HUVEC conditioned media by metabolic labelling immunoprecipitation analysis. These PRL immunorelated proteins had apparent molecular masses of 60, 23, 21, 16 and 14 kDa. In contrast to previous findings in BBCEC, HUVEC conditioned media contained very little PRL bioactivity as determined by the selective bioassay of Nb2 cell proliferation. Moreover, some polyclonal or monoclonal antibodies directed against PRL stimulated HUVEC proliferation, in contrast to the inhibitory effect seen in BBCEC. The present findings extend the previous observations about the expression of PRL gene in endothelial cells from bovine brain capillaries to human cells of the umbilical vein, implicating that endothelium from different types of vessels and species share the expression of PRL gene but may differ in the putative autocrine role of the PRL isoforms expressed.

Micromolar concentrations of the biologically active oestrogen 17beta-oestradiol reduce agonist-induced force in vascular preparations through an unidentified mechanism. The aim of the present study was to investigate the importance of oestrogen receptor beta (ERbeta) for oestrogen-induced vascular relaxation. 17beta-oestradiol was added to aortic rings from ERbeta knock-out (-/-) and wild-type (+/+) mice precontracted with noradrenaline. 17beta-oestradiol caused a concentration-dependent (1-100 microM) relaxation of aortic rings from both -/- and +/+ animals of both sexes. Rings from male and female -/- mice were more sensitive to 17beta-oestradiol than those from +/+ mice. Medial thickness, determined by computerized image analysis, was similar in rings from -/- and +/+ animals. Endothelium, as determined by immuno-cytochemistry, was present in -/- and +/+ aorta. Maximal noradrenaline evoked force and sensitivity to noradrenaline were similar in both groups. In summary ERbeta modulates vascular relaxation to microM concentrations of oestrogen; lack of ERbeta renders the vascular wall supersensitive to 17beta-oestradiol. Lack of ERbeta caused no change in vascular wall morphology suggesting that this ER subtype is not involved in vascular structure development.

ABSTRACT

The effects of a porcine insulin-like growth factor (IGF)-binding protein on binding of IGF-I and IGF-II to porcine aortic endothelial cells (PAEC) were determined. Binding of ¹²⁵I-labelled IGF-I and -II to IGF receptors was inhibited by IGF-binding protein. IGF-binding protein inhibited binding of IGF-I and -II in a dose-dependent manner with half-maximal inhibition occurring at 5·43 and 108 μg/l respectively. A¹²⁵I-labelled IGF-I–IGF-binding protein complex, formed by incubating ¹²⁵I-labelled IGF-I with IGF-binding protein overnight at 4 °C, did not effectively bind to endothelial IGF receptors. Addition of IGF-binding protein to PAEC previously incubated with IGF-I caused a marked dissociation of bound IGF-I (47% dissociation within 12 h). These results indicate that the acid-stable IGF-binding protein which appears to be a part of the 150 kDa GH-dependent binding protein, blocks binding of IGF-I and -II by the IGF receptors and appears to exhibit a higher affinity for IGF-I than the endothelial type-I IGF receptor. The ramifications of this latter point with respect to transfer of circulating IGFs (bound to their IGF-binding proteins) across the vascular endothelium are not clear.

Journal of Endocrinology (1989) 120, 231–236

We tested the hypothesis that pregnancy might increase diabetes-associated nitric oxide (NO) production and renal hyperfiltration. Two weeks following i.v. streptozotocin (40 mg/kg), mean arterial pressure (MAP) was not modified by diabetes; glomerular filtration rate (GFR), renal plasma flow (RPF) and filtration fraction (FF) were higher in pregnant than in virgin controls and increased by diabetes to a greater extent in pregnant than in virgin rats. Urinary volume (UV), creatinine, albumin and sodium (UNaV) were significantly increased by diabetes. Diabetes led to an increase in renal, cardiac, aortic and uterine but not in placental NO synthase activities. Infusion of NG-nitro-l-arginine (l-NA) caused a dose-dependent reduction in GFR, RPF, plasma NO2-/NO3-, UV and UNaV; in general, diabetes increased these effects to a greater extent in pregnant than in virgin rats. l-NA increased MAP in all groups of rats but did not alter FF. Diabetes did not alter responses of thoracic aorta rings to vasoconstrictor effects of phenylephrine and the vasorelaxant effects of sodium nitroprusside but increased endothelium-dependent relaxant effects of acetylcholine. In general the effects of diabetes of 7 days duration were similar to those described above for diabetes of 14 days duration. These data suggest that diabetes-associated renal hyperfiltration and NO production are augmented by pregnancy.

Activin A and follistatin are normally present in relatively low amounts in the circulation. Heparin administration elicits a rapid and robust release of these proteins, although this phenomenon is poorly defined. In the present studies, the response to heparin administration was evaluated in the plasma of adult ewes in terms of whether it was dose-dependent, could be neutralized, was responsive to multiple stimulation, and the nature of the activin A and follistatin released. Activin A and follistatin were rapidly released by heparin in a dose-dependent manner (25, 100 or 250 IU/kg), with differences in the response as adjudged by peak concentration, timing of the peak and area under the curve. The heparin response could be blocked by pretreatment with protamine; conversely protamine injection alone (2 mg/kg) elicited release of follistatin but not activin A. Repeat administration of heparin at three-hourly intervals resulted in activin and follistatin responses to each injection, but each subsequent stimulation increased and extended the responses, consistent with saturation of the heparin clearance mechanism. Size exclusion chromatography of plasma samples confirmed that the majority of activin and follistatin released by heparin was a complex, whereas follistatin released by protamine was unbound. These data are consistent with a large pool of activin A and follistatin resident on extracellular matrices, with the rapid response implicating the vascular endothelium as the prime site of release following administration of these commonly used anticoagulant therapies.

Platelet-derived growth factor (PDGF) overactivity has been implicated in atherosclerosis and several fibrotic conditions including lung and kidney fibrosis, liver cirrhosis and myelofibrosis. Low oxygen tension (hypoxia) is a known stimulus for transcriptional induction of PDGF ligand and receptor genes in different tissues. We studied the expression and localization of PDGF-A, PDGF-B, and PDGF receptor (PDGFR)-alpha and -beta subunits in adult rat isolated corpus cavernosum (CC) under generalized transient hypoxia (pO(2) 10%) in comparison with normoxic conditions. Semi-quantitative RT-PCR analysis of mRNA extracted from rat penis showed higher amounts of PDGF-A, PDGF-B and PDGFR-beta mRNA transcripts in hypoxic versus normoxic animals. The immunohistochemical analysis showed that the localization of PDGF subunits and PDGFR-beta was confined to the cytoplasm of the perivascular smooth muscle cells, endothelium and trabecular fibroblasts. Our findings indicate that transient low oxygen tension induces PDGF overexpression in rat CC, which in the long term may lead to an increase of connective tissue production. We suggest that a local impairment of the PDGF/PDGFR system may contribute to CC fibrosis, which is an established cause of erectile dysfunction in man.

The presence of IGFs and their associated binding proteins (IGFBPs) in human follicular fluid is well documented. Furthermore, most of the constituents of the IGF system in follicular fluid have been found to vary, either in total amount or by proteolytic cleavage, depending on the health status of the follicle. In this study we have examined the acid-labile subunit (ALS) and found that levels in follicular fluid (mean 146 nmol/l) were almost 50% of those in the circulation. This amount of ALS was considerably greater than that found in other extracirculatory fluids (20.9 for synovial fluid and 31.4 nmol/l for skin blister fluid). As in the circulation, ALS levels were in molar excess and did not vary between atretic and dominant follicles. Although the source of ALS is probably from blood (conditioned medium from ovarian cell cultures had no measurable ALS) it would appear that this glycoprotein is not merely diffusing from the circulation as the capillary endothelium becomes more permeable in dominant follicles and this is not reflected in the level of ALS. Analysis of the distribution of IGF-I, IGF-II and IGFBP-3 in fluid from healthy and atretic follicles revealed that the majority of these growth factors (> 80% of total IGF-II) were in the 150KDa complex, indicating that the ALS present was functional, in that it formed the ternary complex with a molecule of IGFBP-3 and IGF. No free IGF-II was found in any of the follicular fluids analysed nor was there any increase in the amount of unsaturated IGFBP-3 in atretic follicles. In summary, we have shown that the majority of IGF measured in follicular fluid, whether from healthy or atretic follicles, is bound in the ternary complex.

ABSTRACT

Plasma and mammary efferent lymph concentrations of insulin-like growth factor I (IGF-I) were determined in lactating ewes before and after treatment with GH (10 mg/day) for 3 days. The lymph:plasma ratio of IGF-I increased from 0·34 to 0·47 after GH treatment when the IGF-I content of plasma increased by 19·4 nmol/l (from 32·1 nmol/l) and lymph by 13·7 nmol/l (from 10·7 nmol/l). This increase in the relative content of IGF-I in lymph was associated with increased lymph content of IGF-I in a lower molecular mass pool (nominally 50 kDa) derived by size exclusion chromatography.

GH treatment increased the total binding capacity for IGF-I in both high (150 kDa) and low (50 kDa) molecular mass pools of plasma and the 150 kDa pool in lymph but there was a proportionally greater increase in 50 kDa total binding in lymph relative to plasma. Further, GH treatment increased the 'saturation' of the 50 kDa binding proteins but decreased the 'saturation' of the 150 kDa fraction, in both plasma and lymph.

Ligand blot analysis of IGF-binding proteins (IGFBPs) in plasma and lymph showed that GH treatment of lactating sheep increased IGFBP-3 and decreased IGFBP-2 in plasma and lymph. Radioimmunoassay of IGFBP-2 showed that while GH treatment reduced the plasma content of IGFBP-2 by about half, the lymph:plasma ratio was increased from 0·68 to 0·87.

GH treatment of lactating ewes not only increased the IGF-I content of plasma but increased the apparent efficiency of transfer of IGF-I across capillary endothelium to mammary efferent lymph.

Journal of Endocrinology (1992) 132, 339–344

SUMMARY

Glycogen, and activities of amylophosphorylase, transglycosylase, uridine diphosphate glucose-glycogen glucosyl transferase (glycogen synthetase) and alkaline phosphatase were investigated by histochemical techniques in uteri of 44 spayed hamsters, untreated and injected with oestrogen (Oe) or progesterone (P) alone or in combination, and with or without relaxin (R). Chemical determinations of glycogen content were made for some uteri.

Glycogen was visualized only in myometrial and arterial muscle fibres and migrating leucocytes. Almost none was revealed by histochemical techniques in uteri of controls and after P although chemical determinations showed moderate amounts present; this is discussed. Oe and Oe + R increased glycogen in muscle fibres of the longitudinal layer and less consistently of the circular layer. Oe + P and Oe + P + R produced greater increase in the longitudinal but no increase in the circular layers. Phosphorylase activity was visualized in myometrial and arterial muscle fibres only. Controls showed greatest activity in the circular muscle fibres. Progesterone alone produced a slight increase in the longitudinal layer. All other treatments produced strong activity in the fibres of the longitudinal layer but less consistent increase in those of the circular layer. The techniques did not differentiate between the active and the inactive forms of the enzyme and this is discussed in relation to hormonal action.

The distribution of transglycosylase appeared to be similar to that of phosphorylase.

Preliminary tests of glycogen synthetase revealed activity in fibres of the longitudinal layer and (in two animals given Oe) the circular layer.

In untreated controls and after Oe and Oe + R, alkaline phosphatase activity was confined to epithelia, vascular endothelium and some macrophages. Activity also appeared in stromal cells and in fibroblasts of myometrial connective tissue after P, Oe + P and Oe + P + R. Myometrial muscle fibres showed no activity before or after any of the treatments.

With the combinations and doses used, no certain effect of relaxin was recorded.