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The tapeworm Ligula intestinalis occurs in the body cavity of its cyprinid second intermediate host, in this study the roach Rutilus rutilus, and inhibits host gonadal development. The mechanism by which infected fish are prevented from reproducing is unknown. Comparison of parameters, such as body length and weight, and condition factor and age, between infected and uninfected individuals, indicated only minor effects of parasitism on growth and condition. In contrast, seasonal gonadal development, as observed in uninfected fish, did not occur in infected fish, and gonads remained small and blocked at the primary oocyte stage in female roach. As immature ovaries and testes are still present, the parasite is presumed to act upon the brain -pituitary -gonadal axis of the fish to inhibit further development of reproductive organs. We investigated the Ligula/fish interaction at the level of the pituitary gland by determination of gonadotrophin (LH) content using a heterologous RIA for carp (Cyprinus carpio) LHb subunit. The results indicated that the pituitary glands of infected roach contained approximately 50% less LH than non-infected fish. After the cloning and sequencing of roach LHb subunit, we measured roach LHb mRNA levels by real-time RT-PCR. A corresponding 50% reduction in LHb mRNA pituitary levels was determined. These results reflect a significant and measurable effect of parasitism on the pituitary gland, and lend support to the hypothesis that excretory/secretory products released from the parasite interact with the brain -pituitary -gonadal axis of the fish host and thus inhibit gonadal development. Reproduction (2005) 130 939-945 IntroductionPrevious studies have revealed that several parasitic infections can affect host reproduction. For example, Joose & van Elk (1986) noted that Trichobilharzia ocellata induces gigantism and the cessation of egg production in its molluscan host, a snail Lymnea stagnalis, and Crews & Yoshino (1989) observed that Schistosoma mansoni similarly suppresses reproduction and gonadal growth in another snail species, Biomphalaria glabrata. Furthermore, in vertebrate hosts, Taenia taeniaeformis appears to directly affect the testis in the rat (Lin et al. 1990) and Taenia crassiceps induces feminisation in infected mice (Larralde et al. 1995).Ligula intestinalis, which is found in the body cavity of certain cyprinid fish, inhibits reproduction in both male and female fish. The gonads, however, are present but remain in an immature state, irrespective of fish age or season. Although this phenomenon has been reported several times (e.g. Arme & Owen 1968, Mahon 1976, Sweeting 1977, Bean & Winfield 1989, the mechanism of the action of this parasite remains unknown. Previous studies have indicated effects of infection at the pituitary gland level. Kerr (1948) and Arme (1968) noted that in ligulosed roach, Rutilus rutilus, the putative gonadotrophs are much reduced in number, compared with non-ligulosed individuals, are only lightly granulated, and have an irregular nucle...

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To determine the influence of nitric oxide (NO) on vascular tone during fetal development, timed pregnant rats received the NO synthase inhibitor p-nitro-L-arginine methyl ester for consecutive 4, 7, or 14 d before parturition (postorganogenesis). Offspring demonstrated limb reduction defects (incidence, 53%) involving either or both hindlimbs, whereas forelimbs were uniformly spared. Defects were dose-dependent but independent of the duration of administration occurring with equal frequency in 4-, 7-, and 14-d treatment groups. Histologic analysis revealed features characteristic of vascular disruption with hemorrhagic necrosis and loss of structure. The defects were prevented by concurrent maternal administration of L-arginine or the NO donors S-nitroso-N-acetyl-penicillamine and sodium nitroprusside. Defects were not seen after prenatal treatment with aminoguanidine. To study basal and agonist-mediated NO release, newborn femoral and brachial arteries were cannulated with a glass micropipette under constant pressure, and changes in intraluminal diameter (micrometers) were measured in response to acetylcholine and the NO synthase inhibitor Nu-nitro-L-arginine.NO is a potent vasodilator produced by vascular endothelium and smooth muscle from the amino acid L-arginine by NOS. Several isoforms of NOS have been isolated from brain (type I), macrophages (type 11), and vascular endothelium (type 111). Both the brain and endothelial isoforms are calcium1 calmodulin-dependent enzymes which are expressed under physiologic conditions (constitutive). The inducible isoform, in contrast, is calcium/calmodulin-independent and is expressed in vascular smooth muscle solely in response to various cytokines or endotoxins. The physiologic regulation of vascular tone by the constitutive isoform generally occurs through two distinct pathways: continuous or basal NO release and that which is generated in response to various agonists or physical Newborn femoral and brachial vessels demonstrated a dramatic (59%) decrease in resting diameter compared with adult vessels (16%). These findings suggest that basal NO release is upregulated during fetal development concurrent with the processes that increase maternal NO release. The data also suggest that up-regulation of NO release occurs throughout the fetal systemic circulation and is not restricted to hindlimbs. This is the first study to demonstrate inhibition of NO release in the pathogenesis of limb reduction defects. (Pediatr Res 38: 905-911, 1995) Abbreviations NO, nitric oxide NOS, nitric oxide synthase LRD, limb reduction defects L-NAME, p-nitro-L-arginine methyl ester L-NNA, N,-nitro-L-arginine SNP, sodium nitroprusside SNAP, S-nitroso-acetylpenicillamine stimuli such as shear stress (1, 2). A number of L-arginine analogs such as L-NAME and L-NNA have been identified which effectively inhibit both the constitutive and inducible isoforms. Aminoguanidine predominately inhibits the inducible NOS isoform.The mechanisms that regulate the changes in vascular tone that characterize the...