Deficiencies in nerve growth factor (NGF) expression have been reported in skin and muscle [1,2] in diabetic rats and in skin biopsy specimens of patients, with an association of this deficiency with neuropathy [3]. There are also deficits in expression of neuronal genes that form targets for NGF which correlate with the NGF deficits [4] and which are reduced by NGF treatment [5]. This latter observation gives rationale to treatment of patients with NGF to prevent biochemical and functional aspects of neuropathy in those fibres, whose phenotypes are maintained by NGF [6]. Such treatment, however, is not without problems. Diabetologia (1999) AbstractAims/hypothesis. Streptozotocin-diabetic rats show impaired neurotrophic support by deficient nerve growth factor (NGF) in muscle and skin. We, therefore, examined a novel agent (CB1093; 1(S),3(R)-Dihydroxy-20(R)-(1-ethoxy-5-ethyl-5-hydroxy-2-heptyn-1-yl)-9,10-seco-pregna-5(Z),7(E),10(19)-triene), which induces expression of endogenous nerve growth factor. Methods. We gave CB1093 orally followed by measurements of mechanical nociception, nerve growth factor, neuropeptides (immunoassay) and nerve growth factor receptors (western blots).Results. In non-diabetic rats CB1093 caused dose-dependent increases in nerve growth factor production (140 % in soleus muscle and 190 % in sciatic nerve) and a mechanical hyperalgesia in the foot. There was also increased sciatic nerve expression of neuronal NGF target gene products, substance P (16 %) and calcitonin gene-related peptide (CGRP; 52 %). Depletions of nerve growth factor, substance P and CGRP in sciatic nerves of diabetic rats were prevented by CB1093, which also increased soleus nerve growth factor concentrations to 30 % over those seen in non-diabetic rats and increased its mRNA expression in skin. The CB1093 did not affect expression of nerve growth factor receptors (trkA and p75 NTR ) in dorsal root ganglia in control or diabetic rats, though the p75 NTR expression was reduced by diabetes. The mechanical hyperalgesia seen in diabetic rats treated with vehicle was not exacerbated by CB1093. Conclusion/interpretation. These findings show that in animal models of diabetes it is possible to prevent depletions of nerve growth factor and the products of its neuronal target genes by oral treatment of a highly potent inducer of NGF gene expression. Pain is a possible side-effect, though this was a function of dose and was manifest more in controls than in diabetic rats. [Diabetologia (1999)

Prolonged treatment with the beta(2)-adrenoceptor agonist clenbuterol (1-2 mg. kg body mass(-1). day (-1)) is known to induce the hypertrophy of fast-contracting fibers and the conversion of slow- to fast-contracting fibers. We investigated the effects of administering a lower dose of clenbuterol (250 microgram. kg body mass(-1). day (-1)) on skeletal muscle myosin heavy chain (MyHC) protein isoform content and adenine nucleotide (ATP, ADP, and AMP) concentrations. Male Wistar rats were administered clenbuterol (n = 8) or saline (n = 6) subcutaneously for 8 wk, after which the extensor digitorum longus (EDL) and soleus muscles were removed. We demonstrated an increase of type IIa MyHC protein content in the soleus from approximately 0.5% in controls to approximately 18% after clenbuterol treatment (P < 0.05), which was accompanied by an increase in the total adenine nucleotide pool (TAN; approximately 19%, P < 0.05) and energy charge [E-C = (ATP + 0.5 ADP)/(ATP + ADP + AMP); approximately 4%; P < 0.05]. In the EDL, a reduction in the content of the less prevalent type I MyHC protein from approximately 3% in controls to 0% after clenbuterol treatment (P < 0.05) occurred without any alterations in TAN and E-C. These findings demonstrate that the phenotypic changes previously observed in slow muscle after clenbuterol administration at 1-2 mg. kg body mass(-1). day(-1) are also observed at a substantially lower dose and are paralleled by concomitant changes in cellular energy metabolism.

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