Intact and castrated juvenile male rainbow trout (Salmo gairdneri) were treated with testosterone and gonadotropic hormone (GTH) to determine the maturational effects of these hormones on the GTH-cells. Electron-microscopic studies of the GTH-cells revealed that GTH and testosterone in intact animals, and testosterone in castrated fish, caused GTH-cell maturation: These cells now displayed the same appearance as GTH-cells in adult trout, including the presence of globules, a well-developed Golgi apparatus and rough endoplasmic reticulum, all of which were absent in GTH-cells of control animals. Animals with stimulated GTH-cells also had an increased GTH content of the pituitary; release of GTH could not be demonstrated. Animals treated with GTH exhibited an accelerated development of the testes, resulting in complete gametogenesis and elevated plasma testosterone levels. These results indicate that exogenous steroids as well as endogenous gonadal steroids can stimulate the full development of GTH-cells and accelerate GTH synthesis. The significance of this stimulating effect of the gonadal hormones with respect to the development of the brain-pituitary-gonadal axis and the onset of puberty is discussed.

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Ringversuch zur Bestimmung von Vitamin D-MetaboUtenZusammenfassung: In einem Ringversuch wurde die Bestimmung der 25-Hydroxy-, 24,25-Dihydroxy-und 1,25-Dihydrpxy-Metabolite von Vitamin D in 6 Laboratorien der Niederlande überprüft. Drei verschiedene Serumproben und zwei verschiedene Standardlösungeri jedes Metaboliteri wurden untersucht. Für die Bestimmung in Serumproben wurden erhebliche Unterschiede zwischen den Laboratorien festgestellt. Die mittleren Variationskoeffizienten zwischen den Laboratorien für die Bestimmung der 25-Hydroxy-, 24,25-Dihydroxy-und 1,25-Dihydroxy-Metaboliten von Vitamin D in den drei Seren betrugen 48%, 38% und 28%. Die Bestimmung in den Standardlösungen aller The term vitamin D includes both Da and 1)3 derivatives. However, vitamin D 2 metabolite concentrations are assumed to be negligible.

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