Temporal response of rabbits to beta-adrenergic agonist feeding: tissue weight, calpains and calpastatin activities, and nucleic acid and protein concentrations

Natural sex steroids and their xenobiotic analogs in animal production: growth, carcass quality, pharmacokinetics, metabolism, mode of action, residues, methods, and epidemiology

Natural and xenobiotic compounds having sex-related actions have long been used for growth promotion and various changes in carcass quality in meat animals. The first compounds used were synthetic estrogens; however, later on a whole battery of compounds having androgenic, and progestogenic actions have also been involved. In surveying the effects of these compounds in meat-producing animals, it became clear that these drugs increase the growth rate of the treated animals and bring about changes in the carcass that are generally characterized by lower fat content and more lean mass. Extensive studies undertaken in various countries, including the European Economic Community (EEC), have shown that if used according to good husbandry practices, the meat from treated animals does not have excessive amounts of residues compared with the endogenous amount of steroid production in the animals in question and also in human beings. The banning of these compounds in the European community brought a new phenomenon of illegal or black market cocktails. These mixtures of anabolic steroids are injected into the body of the animals rather than implanted in the ears, which is the normal practice in countries where they have not yet been banned. Several screening and confirmatory methods are now available for monitoring programs. However, these programs need excessive resources in terms of manpower, funds, and proper legislation, which in underdeveloped countries is questionable, particularly in the absence of strong scientific evidence for the exercise.

Effect of intermittent and stepwise administration of a beta-adrenergic agonist, L644,969, on rat growth performance and skeletal muscles

The effects of intermittent and stepwise administration of a beta-adrenergic agonist, L644,969 on rat growth performance and skeletal muscle growth were investigated in two studies. In experiment 1, 34 juvenile male rats were randomly assigned to two treatment groups: (1) control, 0 ppm L644,969 for 21 days; (2) BL10, 10 ppm of L644,969 for 7 days, then 0 ppm L644,969 for another 7 days, plus 10 ppm of L644,969 for the final 7 days. L644,969 increased (P < 0.05) weight gain during the 7 day initial administration period. When L644,969 was withdrawn, no difference in weight gain was observed between the two groups. Re-administration of L644,969 after the withdrawal period increased (P < 0.01) weight gain up to 3 days of re-administration, but no effect was observed thereafter. In experiment 2, 18 juvenile female rats were divided into three groups: (1) control, 0 ppm L644,969 for 22 days; (2) BL10, 10 ppm L644,969 for 22 days; (3) BL10-60, 10 ppm L644,969 for 11 days, then 60 ppm L644,969 for another 11 days. Feeding 10 ppm L644,969 increased (P < 0.05) the rate of weight gain up to 11 days, but not thereafter. Raising the dose of L644,969 from 10 to 60 ppm increased body weight gain during the initial 8 day period, but no effect was observed thereafter. Weights of skeletal muscles and heart were significantly increased by 10 ppm L644,969. Raising the dose to 60 ppm increased the mean skeletal muscle weights without statistical significance. Muscular concentration of cAMP was significantly decreased by the long-term administration of L644,969.(ABSTRACT TRUNCATED AT 250 WORDS)