No abstract

In female zebrafish ovulation could be induced by male holding water, testis homogenates, and testis fractions containing steroid glucuronides. Deglucuronidation of these fractions led to a loss of ovulation-inducing potency, indicating steroid giucuronides as ovulation inducers. The chemical substances were perceived by the recipient females by means of olfaction. Incubation experiments showed the capacity of the testes to synthesize various C,, and C,, steroids and seven different steroid glucuronides, i.e., 17ct,20P-dihydroxy-4-pregnen-3-one-, testosterone-, androsterone-, epiandrosterone-, 5u-androstane-3a,17@diol-, and 5a-androstane-3l3,17P-diol glucuronide. GC-MS analysis showed the presence of glucuronides of 5a-androstane-3a,l7@dioland cholesterol in male holding water, the latter probably originating from the liver. These compounds may be among the steroid glucuronides functioning as ovulation-inducing pheromones. 0 1987 Academic Press. Inc.

Summary. Levels of oestradiol in plasma of adult female rainbow trout Salmogairdneri were determined during the annual reproductive cycle using a radioimmunoassay. From January to June, during previtellogenesis and the period of endogenous vitellogenesis plasma levels were low (1,3 ! 0,2 ng/mi). At the beginning of the period of exogenous vitellogenesis, the cestradiol level rose and a maximum (16,9 ! 0,2 ng/ml) was reached at the end of vitellogenesis in November, some weeks before spawning. A positive correlation (r = 0,58) was established between plasma oestradiol levels and the gonadosomatic index. From enzymatic cytochemical studies it was concluded that the granulosa cells, as well as the interstitial cells in the ovary, are involved in oestradiol production.Introduction.

Aromatase activity was determined in small discrete areas of the brain of the African catfish, Clarias gariepinus, by a radiometric assay. The fore- and midbrain were divided into eighteen 500-microns transverse sections. From these sections several punches (0.3 mg of tissue) were taken and incubated with [19-3H]-androstenedione. The aromatase activity, calculated from the release of tritium label during aromatization, is expressed in pmol mg-1 tissue hour-1. The highest activity (3.7 pmol) was detected in the preoptic region. The more caudally located area tuberalis, including the nucleus lateralis tuberis and the nucleus recessus lateralis, also showed a relatively high activity (2.5 pmol). A similar activity was found in the most rostral part of the telencephalon and the dorsal parts of the mesencephalon, i.e., the tectum opticum and torus semicircularis (2.3 pmol). A moderate aromatase activity was observed in remaining parts of the brain, except the cerebellum and hindbrain, in which aromatase activity was hardly detectable (0.1-0.3 pmol). It is concluded that a high aromatase activity is present in regions known to be involved in the regulation of reproduction. Since both the torus semicircularis and the tectum opticum display a high aromatase activity, it is suggested that also these structures are involved in reproductive processes.

This is the first study to show that apoptosis as an immune regulatory mechanism is conserved in fish, demonstrating its importance in maintaining immunological homeostasis. The data further show that this mechanism is subject to control by glucocorticosteroids. Carp plasma cortisol concentrations increase from 20 to 434 ng/ml and cortisone from 5 to 50 ng/ ml within 9 min o f the onset o f handling stress. At basal steroid concentrations in vitro, cortisol, but not its conversion product cortisone, inhibits proliferation o f peripheral blood lymphocytes (PBL), as measured by [3H]thymidine incorporation. Induction of apoptosis in activated PBL is the apparent mechanism o f cortisol action. In nonstimulated PBL cultures, apoptosis is induced by neglect (a lack o f stimulating signals). Stimulation with LPS or PHA rescues lymphocytes from this type of apoptosis. Stimulated PBL populations, however, are sensitive to cortisol-induced apoptosis. Culture supematants from activated PBL protect PBL from apoptosis by neglect, probably by supplying a growth signal. These supematants, how ever, have no effect on cortisol-induced apoptosis.