Marylynn Barkley

Dynamics of oocyte development and related changes in serum estradiol-17β, yolk precursor, and lipid levels in the teleostean fish, Leptocottus armatus

Abstract 1. 1. The dynamics of ovarian development in Leptocottus armatus were studied. Seasonal changes of serum estradiol-17β, serum vitellogenin, serum total lipids and visceral lipid reserves were monitored. 2. 2. Two to four distinct size classes (clutches) of oocytes occurred in the ovary preceding and during the spawning period. One of these clutches contained oocytes in the vitellogenic or post-vitellogenic phase, a second clutch contained oocytes “arrested” in the cortical alveoli stage and a third clutch contained non-yolky oocytes. Only one clutch was oviposited in the annual spawning season. 3. 3. Estradiol levels increased coincident with the appearance of yolky oocytes in the ovary. Serum estrogen levels were highest during the period of ovulation and spawning. During the spawning period estradiol titers were not significantly correlated with oocyte size or gonosomatic index. 4. 4. Serum vitellogenin levels increased in parallel with oocyte size and estradiol titers. Vitellogenin levels were relatively low during the early portion of the spawning period, becoming elevated again towards the end of the spawning period. In concordance with ovarian regression, serum vitellogenin levels declined and remained low during the ovarian quiescence phase. Neither GSI nor serum estradiol titers correlated significantly with vitellogenin levels. 5. 5. With initiation of ovarian recrudescence visceral lipid reserves began to decline and continued to decline through the vitellogenic and spawning phases. Visceral lipid reserves were inversely correlated with ovarian GSI. Serum lipid levels were high during ovarian recrudescence, remaining elevated through the spawning period. During the phase of ovarian quiescence serum lipid levels were low and visceral lipid reserves were high. Visceral lipid reserves showed an inverse correlation to serum estradiol titers.

Aspects of embryo nutrition and excretion among viviparous embiotocid teleosts: Potential endocrine involvements

1. 1. Embryos of the viviparous embiotocid fishes develop free within the ovarian cavity from small eggs for approximately 6 months. The biochemical composition of ovarian fluid was determined and compared to serum constituents in three embiotocid species during the gestation phase. 2. 2. SDS-gel electrophoresis data showed that ovarian fluid collected from female Cymatogaster aggregata during late gestation was essentially devoid of serum peptides, but contained peptides absent from maternal serum. The ovarian fluid peptides are probably derived from the ovarian epithelial lining. 3. 3. Pregnant female ovarian fluid contained large quantities of urea, whereas the maternal serum was devoid of this metabolite. This suggests that embiotocid embryos, but not adults, produce urea as a nitrogenous waste: furthermore, ovarian membranes must be relatively impermeable to urea. 4. 4. Amino acids in the ovarian fluid of Cymatogaster basically correspond to those in maternal serum. but were, in most cases, at lower levels. Although absent from serum, phosphoethanolamine was present at high levels in the ovarian fluid of pregnant Cymatogaster, but not Hyslerocarpus Irciski, during late gestation. 5. 5. The principal amino compound, exclusive of urea, in the ovarian fluid of Hysterocarpus and Micrometrus minimus was taurine. Serum levels of glutamine, ethanolamine and taurine were elevated in pregnant embiotocids. 6. 6. Lipid levels were also elevated in maternal serum during late pregnancy. Precluding phospholipids, the concentration of lipids in ovarian fluids was considerably lower than in maternal serum. 7. 7. In Cymatngtisler and Hysterocarpus serum progesterone and estradiol levels were comparatively low during gestation, posing some doubt as to the significance of these steroids in maintenance of pregnancy. 8. 8. The possibility that embiotocids produce an estrogen-dependent, vitellogenin-like protein was examined. Studies with Cymatogaster and Hysterocarpus indicated that the embiotocids may be the only teleostean family yet known which do not produce a vitellogenin-like protein.

Female genotype influences the behavioral performance of mice selected for reproductive traits

The behavioral performance of mice that differ in regularity of the estrous cycle and litter size was studied after female exposure to a male of the same or a different strain. Emotional reactivity was measured using the pole, straightaway and open field tests. Factor interpretations of emotionality included motor discharge, autonomic imbalance and acrophobia. Mice characterized by regular estrous cycles and large litters (line E) were more explorative and emotionally reactive with respect to motor discharge and autonomic imbalance. In contrast, mice with less regular estrous cycles and small litter size (line CN-) were more acrophobic. These strain differences in behavioral performance were influenced by the genotype of the female rather than the cohabitating male.

Reassessment of models used to test xenobiotics for oestrogenic potency is overdue

Product safety bioassays need to include data from animals with susceptible genotypes or the potential for environmental compounds to disrupt reproductive development in hormonally sensitive populations may be greatly underestimated. The continued use of resistant animal models is likely to result in allowable releases of toxic levels of oestrogenic agents that could differentially disrupt reproductive development and function of sensitive genotypes, leading to reproductive failure and loss or extinction of susceptible individuals, populations and species. Rather than ignoring the role of genetic differences in susceptibility to oestrogenic agent‐induced carcinogenicity and endocrine disruption, government agencies should support efforts to identify the genetic mechanisms involved in these responses, and to screen for and develop strains of mice and rats which are sensitive to the induction of genotoxicity/carcinogenicity as well as the inhibition of reproductive development and function by oestrogenic agents. Such sensitive strains would be even more optimal for testing chemicals for endocrine disruptor activity.