Pituitary steroids in two teleost species: immunohistological and biochemical studies

Comparison of the effects of two fixatives for immunolocalization of testosterone in the testes of the cynomolgus monkey, mouse and rat

We compared the effect of two fixatives, Bouin's fixative and neutralized buffered 4% formaldehyde (10% formalin), for immunolocalization of testosterone in the testes of cynomolgus monkeys, mice and rats. In the samples fixed with Bouin's fixative, immunoreactive testosterone was detected as intense deposits in the cytoplasm of Leydig cells of monkeys and mice. Immunoreactive testosterone was detected not only in Leydig cells of rats but also moderately shown within tubules. Immunoreactive testosterone could not be detected in the testes of monkeys, mice or rats fixed with neutralized buffered formalin because of the poor morphology caused by the fixative. It is concluded that Bouin's fixative is a suitable fixative for immunolocalization of testosterone in the testes of cynomolgus monkeys, mice and rats.

Regulation of steady-state luteinizing hormone messenger ribonucleic acid levels, de novo synthesis, and release by sex steroids in primary pituitary cell cultures of male African catfish, Clarias gariepinus

Primary pituitary cell cultures from sexually mature adult male African catfish, Clarias gariepinus, were used to study the regulation of LH biosynthesis by sex steroids. The cell cultures were exposed to testosterone (T), estradiol (E(2)), or 5alpha-dihydrotestosterone (DHT), a nonaromatizable analogue of T, and to the likewise nonaromatizable 11-ketotestosterone (KT) and 11beta-hydroxyandrostenedione (OHA), physiologically relevant androgens in fish. Both T and E(2) elevated glycoprotein alpha (GPalpha) and LHbeta steady-state mRNA levels (quantified by RNase protection assay), de novo synthesis (metabolic incorporation of radioactive amino acids and subsequent immune precipitation of LH), and release of preferentially newly synthesized LH, while DHT had no effect. Inhibiting the aromatase activity abolished the stimulatory effects of T. The effects of E(2) on LH mRNA levels and de novo synthesis were dose dependent. Incubation with 10 ng/ml KT elevated GPalpha and LHbeta mRNA levels, while other concentrations of KT or all concentrations of OHA tested had no effect. The amount of newly synthesized LH, on the other hand, was decreased dose-dependently by OHA but not by KT. Since this OHA-induced decrease did not change the specific activity (dpm immune precipitable [(3)H]-LH/ng immune-reactive LH) of LH, we hypothesize that OHA exerted its effect by activating a crinophagic breakdown of secretory granules in catfish gonadotrophs. Electron microscopic examination of gonadotrophs after in vitro exposure to 50 ng OHA/ml revealed that breakdown organelles had increased in size significantly. We conclude that the balanced production of aromatizable (mainly stimulatory) and 11-oxygenated androgens (mainly inhibitory) may be an important factor in regulating the amounts of LH available for secretion in male African catfish.

Absence of direct regulation of prolactin cells by estradiol-17 beta in rainbow trout (Oncorhynchus mykiss)

The effects of estradiol-17 beta (E2) implants on plasma prolactin (PRL) concentrations, pituitary PRL content and pituitary PRL mRNA levels were examined in rainbow trout (Oncorhynchus mykiss). Intact immature fish treated with 1 mg estradiol-17 beta did not show significant changes in both PRL mRNA levels and pituitary PRL content after 3 days of treatment. In a similar experiment, no changes were observed in plasma PRL levels followed during 7 days. Similarly, lack of estradiol-17 beta effect on plasma PRL levels and on final PRL pituitary content was observed in ovariectomized female rainbow trout treated during 48 days with 25 mg estradiol-17 beta and in mature male fish over a 3-week treatment period. Localization of estradiol receptor (ER) mRNAs in the pituitary was carried out by Northern blot analysis using a full-length rainbow trout estrogen receptor (rtER) cDNA as a probe. The rostral pars distalis of the pituitary which contained mostly PRL cells showed the lower amount of rtER mRNA when compared to other parts of the pituitary. Moreover, two mRNAs of different size (3.5 and 1.4 kb) were detected in different parts of the pituitary. Further hybridization experiments using probes containing part of the rtER cDNA (E domain or C and D domains) indicated that the small-sized mRNA (1.4 kb) probably encodes a truncated ER protein lacking hormone binding domain or an ER-related protein. Thus, only the 3.56 kb mRNA appeared to be involved in the regulation of pituitary function by estradiol. In situ hybridization analysis allowed a more precise localization of this rtER mRNA in the pituitary.(ABSTRACT TRUNCATED AT 250 WORDS)

Galanin-like immunoreactivity is increased in the brain of estradiol- and methyltestosterone-treated eels

A galanin-like peptidergic system was demonstrated in the brain of Anguilla. A group of immunoreactive perikarya was located in the nucleus preopticus periventricularis close to the recessus preopticus. Galaninergic fibers occurred in various brain areas. Galanin identified in mammalian pituitary cells was undetectable in fish adenohypophysial cells. Estradiol increased the immunostaining of the rostral perikarya and brain fibers in both male and female European eels kept in fresh water and in female American eels in sea water. Methyltestosterone, an aromatizable androgen, increased galanin immunoreactivity in rostral perikarya and brain fibers of male European eels and female American eels. The cross-sectional area of these perikarya increased significantly after both treatments whereas cell bodies of the posteroventral hypothalamus were slightly affected. Dihydrotestosterone showed no clear effect. Fibers close to the corticotropes were sometime increased, but galanin synthesis was not induced in pituitary cells. In contrast, estradiol induced galanin synthesis in rat pituitary cells, but had a still controversed effect on hypothalamic galanin. A putative influence of galanin on the pituitary-gonadal axis is discussed as gonadal hormones diversely affect gonadotropes and gonosomatic indices in Anguilla.