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- Author: Jennifer D Spencer x
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Institute for Pigmentary Disorders in association with EM Arndt University Greifswald, Germany and University of Bradford, Bradford BD7 1DP, UK
Biomedical Sciences, University of Bradford, Bradford BD7 1DP, UK
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Institute for Pigmentary Disorders in association with EM Arndt University Greifswald, Germany and University of Bradford, Bradford BD7 1DP, UK
Biomedical Sciences, University of Bradford, Bradford BD7 1DP, UK
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Institute for Pigmentary Disorders in association with EM Arndt University Greifswald, Germany and University of Bradford, Bradford BD7 1DP, UK
Biomedical Sciences, University of Bradford, Bradford BD7 1DP, UK
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Institute for Pigmentary Disorders in association with EM Arndt University Greifswald, Germany and University of Bradford, Bradford BD7 1DP, UK
Biomedical Sciences, University of Bradford, Bradford BD7 1DP, UK
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Institute for Pigmentary Disorders in association with EM Arndt University Greifswald, Germany and University of Bradford, Bradford BD7 1DP, UK
Biomedical Sciences, University of Bradford, Bradford BD7 1DP, UK
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Institute for Pigmentary Disorders in association with EM Arndt University Greifswald, Germany and University of Bradford, Bradford BD7 1DP, UK
Biomedical Sciences, University of Bradford, Bradford BD7 1DP, UK
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The human skin holds the full machinery for pro-opiomelanocortin processing. The α-melanocyte-stimulating hormone (α-MSH)/melanocortin-1-receptor cascade has been implicated as a major player via the cAMP signal in the control of melanogenesis. Only very recently the β-endorphin/μ-opiate receptor signal has been added to the list of regulators of melanocyte dendricity and melanin formation. In this context it was reported that (6R)-l-erythro-5,6,7,8-tetrahydrobiopterin (6BH4) can act as an allosteric inhibitor of tyrosinase, the key enzyme in melanogenesis, and this inhibition is reversible by both α- and β-MSH. It was also shown earlier that 7BH4, the isomer of 6BH4, is twice as active in this inhibition reaction. However, as yet it is not known whether 7BH4 is indeed present in loco in the melanosome. We here provide evidence that this isomer is present in this organelle in a concentration range up to 50 × 10−6 M. Determination of β-MSH in melanosomal extracts yielded 10 pg/mg protein. Moreover, we demonstrate reactivation of the 7BH4/tyrosinase inhibitor complex by β-MSH, whereas α-MSH failed to do so. Furthermore, we show intra-melanosomal l-dopa formation from dopachrome by 7BH4 in a concentration range up to 134 × 10−6 M. Based on these results, we propose a new receptor-independent mechanism in the control of tyrosinase/melanogenesis by β-MSH and the pterin 7BH4.
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The activin pathway has been postulated to be involved in regulation of multiple reproductive processes important for survival of the conceptus. These processes include luteinisation of the follicular cells and thus function of the corpus luteum, early embryo development and uterine function including implantation of the conceptus. Therefore, the aim of the current study was to determine whether the concentrations of activin A and follistatin (FST), an activin-binding protein, differed between ewes with a lifetime history of enhanced or reduced embryonic survival (ES). The mRNAs encoding FST and activin A (inhibin beta A subunit; INHBA) were present in the uterus and abundant in the uterine luminal or glandular epithelia by day 18 of gestation. A peak of activin A was observed in the systemic circulation around the time of oestrus, and activin A concentrations were elevated in animals with reduced ES during the oestrous cycle and early gestation. Concentrations of activin A in uterine fluid were approximately twofold greater on day 16 of gestation in ewes with reduced ES compared to those with enhanced ES. No consistent differences in FST were observed between these groups. Treatment of luteinising ovine granulosa cells with activin A in vitro suppressed progesterone secretion providing evidence of a potential pathway whereby increased concentrations of activin A may decrease ES.
