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Male summer flounder (Paralichthys dentatus) were given two injections (initially and 2 weeks later) of 17beta-estradiol (E2) totaling 0.2 (2 x 0.1), 2.0 (2 x 1.0) or 20.0 (2 x 10.0) mg E2/kg body weight. Blood and tissue samples were collected 4, 6 and 8 weeks after the initial injection in the (2 x 0.1) mg/kg treatment, 4, 6, 8, and 15 weeks after the first injection in the (2 x 1.0) mg/kg treatment and at 4 weeks only in the (2 x 10.0) mg/kg treatment. Five of the 12 fish injected twice with 10.0 mg/kg were moribund before the first sampling period. Circulating levels of vitellogenin (VTG) in the blood of all E2-injected fish from all treatments were comparable with those concentrations found in the blood of wild male carp (Cyprinus carpio) and walleye (Stezostedion vitreum) previously collected near a sewage treatment plant (0.1-10.0 mg VTG/ml plasma). Excessive hyalin material accumulated in the livers, kidneys and testes of the treated fish. A portion of that material was identified as VTG by immunohistochemistry. The accumulation of VTG, and possibly other estrogen-inducible proteins, resulted in hepatocyte hypertrophy, disruption of spermatogenesis, and obstruction or rupture of renal glomeruli.

synopsis. With the exception ofthe agnathan fishes, a prolactin cell has been identified in all vertebrates in which it has been sought. This review examines the structure of the prolactin-producing pituitary cell in non-mammalian vertebrates, the manner in which it responds to natural and artificial stimuli, and its control by neural and humoral factors. Fundamental similarities and differences are described in an attempt to understand better its method of operation. Given our present state of knowledge, there is, among all the apparent diversity, a similarity in the basic structure and morphological response of this cell in teleosts, amphibi? ans, reptiles, and birds. One can identify and speak with relative certainty about a specific adenohypophysial cell called a "prolactin cell." More profound differences may be found at the level of control mechanisms, chemistry ofthe hormone(s), and the nature of receptivity and response of target tissues. It appears that although there are basic similarities in the design ofthe prolactin cell, the systems that control its activities may differ and the similar products produced by the cell may be used toward different ends. This review examines the structure of the prolactin-producing pituitary cell in nonmammalian vertebrates, the manner in which it responds to natural and artifically induced stimuli, and its relation to the

synopsis. The current state of our knowledge of the morphology and histo- and cytophysiology of the teleost pituitary gland is presented. The zonation that characterizes the adenohypophysis is based on the regional distribution of specific cell types. As a result there is also a functional zonation indicated by specific hormones emanating from clearly identifiable parts of the gland. These observations make the teleost hypophysis ideal for the study of problems that may be basic to all vertebrates. The ultrastructure of hypophysial cells is presented and related to observations at the light microscope level. The manner in which secretory granules are released from spe? cific cells is compared, and the problem of evaluating "cell activity" discussed. The application of immunohistochemical techniques to the study of the teleost pitui? tary gland is reviewed, and its use as a tool of investigation for future studies evaluated. These methods have helped to elucidate the cellular source of teleost pituitary hor? mones and have confirmed the findings of the histophysiologists.

A sex-linked gene controlling the age at which the gonadotrops of the pituitary gland differentiate has been discovered in Xiphophorus maculatus. Males homozygous for early differentiation become sexually mature between 10 and 16 weeks; those homozygous for late maturation between 22 and 40 weeks. Heterozygotes are intermediate. Since growth rate decreases when testes mature. the two classes of males differ significantly in adult size.