Stimulation of transport of alpha-aminoisobutyric acid into the testes of immature mice in vivo by follicle-stimulating hormone

Abstract

Groups of immature mice were injected sc with radiocarbon-labelled alpha-aminoisobutyric acid (AIB) after being given a single sc injection of hFSH or of 0.9% saline. As an index of the transport of AIB, the specific activity of isotope was measured in homogenates of testis and of liver. FSH treatment caused statistically significant increases in the specific activity of isotope in the testes and in the ratio of testicular to liver specific activity. The effect was greatest in 9-day-old mice injected with FSH 16 h before removal of the testes. Uptake of labelled AIB was not stimulated after administration of hCG or testosterone. Doses of cycloheximide sufficient to reduce the rate of protein synthesis by over 99% did not impair testicular uptake of labelled AIB or the influence of FSH on AIB uptake. These results suggest that FSH stimulates amino acid transport into cells of the immature testis and that this action is independent of the stimulatory effect of FSH on testicular protein synthesis.Follicle-stimulating hormone (FSH) has been found to increase the rates of synthesis of ribonucleic acids and of proteins in the testes of intact immature and hypophysectomised adult rats and mice (Means et al. 1980;Davies 1980). Though the effect of FSH on proteins appears to be a result of that on RNA, FSH could additionally facilitate protein synthesis by enhancing transport of amino acids into testicular cells. Two groups of workers have studied this possibility by administering FSH to rats and then measuring testicular uptake of radioactivity-labelled alpha-aminoisobutyric acid (AIB) -a non-physological compound which is transported into cells in a similar manner to physio¬ logical amino acids but which is not incorporated into proteins. Means & Hall (1967) detected no increase in in vitro uptake of AIB in teased testicu¬ lar tissue from immature rats which had been treated with FSH. On the other hand Irusta & Wassermann (1972) reported that in vitro trans¬ port of AIB into testicular tissue was stimulated when intact immature or hypophysectomized adult rats had been treated with FSH in vivo. In the experiments reported in this paper we have reinvestigated this problem, administering both FSH and radioactivity-labelled AIB to intact immature mice in vivo. This protocol was chosen because it was thought to reflect normal physiology more closely than does the uptake of AIB into testicular tissue in vitro. Materials and Methods AnimalsMice of the CFW strain (stock originally supplied by the Laboratory Animals Centre, Carshalton) were main¬ tained under constant conditions of temperature (20°C) and lighting (8 h light: 16 h dark). Groups of 10 to 15new-born male pups were fostered to pairs of lactating mothers. In each experiment foster litter mates were used to form randomized blocks for treatment. Except where specified, mice were sacrificed at 9 days of age. HormonesHuman pituitary follicle-stimulating hormone was ex¬ tracted and assayed as described by Butt 8c Lynch (1974). In an experiment in which the effects of ch...