Effect of boron deprivation on reproductive parameters in Xenopus laevis

Low boron (-B), boric acid supplemented (+B), or traditional beef liver and lung (BLL) diets were administered to adult male and female Xenopus laevis for either 28 d or 120 d to evaluate reproductive status. The boron content was the only difference between the -B and +B diets. To evaluate further the potential impact of boron deprivation on adult reproduction, a detailed evaluation of ovary and testis morphology and weight, oocyte fecundity and maturation, and sperm count and dysmorphology was conducted. Adult females were depleted of boron for 120 d and subsequently superovulated to flush mature eggs from the ovaries. Following an additional 45-d oocyte maturation period in which the frogs were maintained on their respective diets, the ovaries were removed and oocytes evaluated. Adults administered the -B diet had distinctly atrophied ovaries and testes when compared to adults administered either the +B or BLL diet. Females administered the -B diet had a much greater proportion of immature oocytes in stages 1 and 2 (ca. -B = 87% vs. +B = 23% following the 120-d regimen) than females fed the +B diet, which had a greater proportion of mature oocytes in stages 5 and 6 (mature) (ca. -B = 3% vs. +B = 45% following the 120-d regimen). Co-culture of progesterone with normal stage 1 and 2 oocytes to stages 5 and 6 oocytes in vitro allowed for the successful maturation of stages 1 and 2 oocytes from the +B or BLL diet-fed females, but not from the -B females, which did not respond to hormone treatment. The adverse effects of low dietary boron in the female Xenopus were noted following both depletion periods; however, the effects were more dramatic following 120 d of boron depletion. Reductions in sperm counts and increases in sperm dysmorphology rates were noted in males fed the -B diet when compared to males fed either the BLL or the +B diet. These results on reproduction, development, and maturation further indicate the nutritional essentiality of boron in Xenopus. J. Trace Elem. Exp. Med. 12:187-204, 1999. (C) 1999 Wiley-Liss, Inc.