Influence of dietary arginine on the anabolic effects of androgens.

Feeding mice an arginine-deficient diet decreased plasma concentrations of arginine, citrulline and ornithine in the females and arginine in the males, abolishing the sexual dimorphic pattern of these amino acids found in mice fed the standard diet. In addition, the restriction of dietary arginine produced a marked decrease in body and renal weights as well as in the activity of renal ornithine decarboxylase, decreases that were gender dependent since they were observed exclusively in males. The fact that these changes were not associated with the decrease in the circulating levels of testosterone and that the dietary arginine restriction prevented the body weight gain induced by testosterone treatment of female mice fed the standard diet indicates that dietary arginine is required for the anabolic action of androgens. Moreover, under certain conditions that could compromise the renal synthesis of arginine, as in the compensatory renal hypertrophy that follows unilateral nephrectomy, the myotrophic effect of testosterone was transiently impaired. The results also revealed that arginine deficiency produced an opposite effect in the expression of IGF-I and IGF-binding protein 1 in the liver and kidney. Taken together, our results indicate that dietary arginine may be relevant to the anabolic action of testosterone, and suggest that this effect may be mediated by changes in the insulin-like growth factor system.

Gender-related differences in carnosine, anserine and lysine content of murine skeletal muscle.

The aminoacyl-imidazole dipeptides carnosine (beta-alanyl-L-histidine) and anserine (beta-alanyl-1-methyl-histidine) are present in relatively high concentrations in excitable tissues, such as muscle and nervous tissue. In the present study we describe the existence of a marked sexual dimorphism of carnosine and anserine in skeletal muscles of CD1 mice. In adult animals the concentrations of anserine were higher than those of carnosine in all skeletal muscles studied, and the content of aminoacyl-imidazole dipeptides was remarkably higher in males than in females. Postnatal ontogenic studies and hormonal manipulations indicated that carnosine synthesis was up-regulated by testosterone whereas anserine synthesis increased with age. Regional variations in the concentrations of the dipeptides were observed in both sexes, skeletal muscles from hind legs having higher amounts of carnosine and anserine than those present in fore legs or in the pectoral region. The concentration of L-lysine in skeletal muscles also showed regional variations and a sexual dimorphic pattern with females having higher levels than males in all muscles studied. The results suggest that these differences may be related with the anabolic action of androgens on skeletal muscle.

Postnatal exposure to androgens alters renal ornithine decarboxylase ontogeny and abolishes renal sexual dimorphism in mice.

The mouse kidney presents marked sexual dimorphism, manifested not only in renal size but also in the subcellular structure and enzyme activity. Ornithine decarboxylase (ODC), a key enzyme in the biosynthetic pathway of polyamines, is induced in the kidney by androgens, and its activity is higher in the kidney of male mice. The renal differences between male and female mice are not manifested during the first weeks of life and start to be expressed after weaning, simultaneously with the increase in plasma testosterone concentration. Treatment of newborn mice before postnatal day 21 with a single dose of testosterone propionate (TP, 200 microg/animal) did not increase renal ODC activity or renal size. From day 21 the same treatment elicited significant increases in renal ODC, especially in females where the basal activity of control animals was much lower than in males. The repeated injection of TP during the first 10 days of life (200 microg/animal, days 1, 4, 7 and 10) promoted an early increase in renal ODC activity but abolished the physiological rise observed in male mice at puberty and adulthood. This treatment dramatically reduced the secretion of the sexual hormones, testosterone, estradiol and progesterone, by the gonads, and diminished renal size as well as ODC and beta-glucuronidase activities in male mice. Stanozolol produced effects similar to those of TP, while the nonsteroidal antiandrogen, flutamide, did not apparently affect the normal development of the male or female kidney. The results indicate that: (a) kidney sexual dimorphism is not congenital; (b) neonatal androgens are not required to induce the sexual dimorphism of the mouse kidney; (c) the neonatal kidney is unresponsive to testosterone; (d) the premature and repeated exposure to supraphysiological levels of testosterone may accelerate the ontogeny of renal ODC but can abolish later testosterone secretion and hence alter the sexual characteristics of the male kidney, and (e) the postnatal treatment with androgens does not affect the response of the adult kidney to exogenous androgens. One can conclude that the postnatal manipulation of androgens may accelerate the development of the mechanisms of androgen responsiveness in some tissues but it may alter neural structures, probably the GnRH pulse generator, that control testosterone secretion.

Comparative tyrosine degradation in Vibrio cholerae strains. The strain ATCC 14035 as a prokaryotic melanogenic model of homogentisate-releasing cell.

The relationship between L-tyrosine catabolism and melanin formation was studied in the Vibrio cholerae strains ATCC 14035 and CECT 557. It is shown that both strains degrade L-tyrosine by the same pathway as eukaryotic cells, giving homogentisate as intermediate. ATCC 14035, an O1 strain, which is not able to grow using L-tyrosine as sole carbon and energy source, but it forms pyomelanin from homogentisate. The second strain, which is non-O1, is able to grow using L-tyrosine as sole carbon and energy source, but it does not form any pigment. Both strains contain all the enzymes involved in the L-tyrosine catabolism. The three late enzymes of the pathway, homogentisate oxygenase, maleylacetoacetate isomerase and fumarylacetoacetate hydrolase, are induced by L-tyrosine, but the degree of induction is much lower in the ATCC 14035 strain. Thus, the distal part of the pathway becomes the rate-limiting steps in the L-tyrosine catabolism, explaining homogentisate accumulation and pyomelanogenesis in this strain. It is proposed that V. cholerae might be a useful prokaryotic model to show that alkaptonuria and other diseases related to L-tyrosine metabolism could occur in animals even when no particular enzyme involved in that pathway is lacking.

Characterization of the melanogenic system in Vibrio cholerae, ATCC 14035.

The nature of the pigment formed by Vibrio cholerae and the characterization of its biosynthetic pathway is shown. This microorganism is able to synthesize melanin-like pigment when cultured in the presence of L-tyrosine. Other phenolic chemicals related to L-tyrosine do not lead to pigment production. The microorganism has no tyrosine hydroxylase activity, and the levels of dopa oxidase activity are very low, making the existence of a tyrosinase very unlikely. However, Vibrio cholerae contained transaminases that transforms L-tyrosine into p-hydroxyphenylpyruvate. Moreover, Vibrio cholerae is able to go further in the catabolic pathway, releasing a great amount of homogentisic acid. This acid can spontaneously be oxidized to its p-quinone form, which subsequently polymerizes leading to pigment formation. It is concluded that the pigment formed by Vibrio cholerae is not synthesized by the Raper-Mason pathway, but by a L-tyrosine catabolism pathway leading to homogentisic acid. Some simple properties of that melanin are compared to model eu- and pheomelanin, but no clear distinction could be stated, indicating the similarity between all these pigments.

The protein encoded by the Shewanella colwelliana melA gene is a p-hydroxyphenylpyruvate dioxygenase.

The identity of the product of the melA gene from Shewanella colwelliana with the enzyme p-hydroxyphenylpyruvic dioxygenase is shown. Cloning of the melA gene endowed Escherichia coli with the capacity to synthesize melanin-like pigments from L-tyrosine. E. coli contained transaminases that transforms L-tyrosine into p-hydroxyphenylpyruvate. This keto acid was detected in the cultures. On the other hand, E. coli containing melA was able to go further in the catabolic pathway, releasing a great amount of homogentisic acid. This acid can spontaneously polymerize giving the pigment. Furthermore, p-hydroxyphenyl-pyruvate dioxygenase activity was detected in this system. Analysis of the deduced amino acid sequence revealed a high homology with the p-hydroxyphenylpyruvate dioxygenase enzyme from different organisms.