Effect of Testosterone on Maturational Gonadotropin Subunit Messenger Ribonucleic Acid Levels in the Goldfish Pituitary'

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1 BIOLOGY OF REPRODUCTION 54, (1996) Effect of Testosterone on Maturational Gonadotropin Subunit Messenger Ribonucleic Acid Levels in the Goldfish Pituitary' Danielle Huggard, Zeinur Khakoo, Geetha Kassam, Soheil Seyed Mahmoud, and Hamid R. Habibi 2 Department of Biological Sciences, University of Calgary, Calgary, Alberta, Canada T2N 1N4 ABSTRACT In this study, we investigated the effects of testosterone and a nonaromatizable androgen, 11 -hydroxyandrosterone, on maturational gonadotropin (GtH-II) subunit gene expression in the goldfish pituitary. While testosterone treatment at physiological doses resulted in stimulation of GtH-II-a and - subunit mrna production, time-course and dose-response studies performed on sexually immature goldfish of mixed sex, using a wider dose range exceeding physiological levels, demonstrated a biphasic response to in vivo androgen treatment. Time-related treatment with testosterone and 110-hydroxyandrosterone (20 jg/fish) resulted in an initial inhibition of GtH-II subunit mrna production (12-24 h) followed by stimulation at h. In dose-response studies, treatment for 24 h with testosterone resulted in a significant stimulation at the low physiological doses of 0.2 and 2 g/fish. At the supraphysiological level of 20 jg/fish, testosterone treatment resulted in no stimulation or in decreased GtH-ll subunit mrna levels compared to the control values. Similarly, treatment with 11 -hydroxyandrosterone resulted in a significant stimulation of GtH-II subunit mrna levels at low physiological concentrations (0.2 g/ fish) and an inhibition, or no stimulation, at higher concentrations (2-20 jg/fish). In sexually mature goldfish of mixed sex, the biphasic effect of testosterone was not observed in vivo, and treatment with this steroid resulted in stimulation of GtH-II subunit mrna production in a dose-related manner. To investigate the direct action of testosterone, studies were carried out using isolated goldfish pituitary fragments from goldfish of mixed sex in vitro. Treatment with testosterone at various concentrations was found to stimulate GtH-II subunit mrna production in pituitary glands obtained from both sexually immature and sexually mature goldfish. Overall, the present study demonstrates a stimulatory effect of testosterone on GtH-II subunit mrna levels in goldfish. The observed stimulation of basal GtH-II subunit mrna production by testosterone occurs, in part, through a direct action at the level of the pituitary in both sexually immature and mature goldfish. INTRODUCTION Gonadotropins (GtHs) are glycoprotein hormones and include FSH and LH. In fish, GtHs are referred to as vitellogenic GtH (FSH-like; GtH-I) and maturational GtH (LHlike; GtH-II). All members of this family are heterodimers consisting of two different subunits, a and 3, which are associated for biological activity. Within a given species, the a-subunit is identical in all pituitary glycoprotein hormones (LH, FSH, and thyroid-stimulating hormone), while the 3- subunit is unique and confers the biological activity of the hormone [1]. In vertebrates, GnRH is a key regulator of GtH synthesis and release [2-5], in addition to the gonadal steroids, which are known to play an important regulatory role in this process. The observed effects of the steroids on GtH production have been found to be different depending on the experimental conditions. A number of investigators have demonstrated suppressive effects of the steroids through castration studies. It has been shown that removal of the gonads in rats increased serum LH and FSH concentrations as well as LH and FSH subunit mrna levels [6-9]. In anestrous ewes, estradiol treatment, in vivo, was shown to differentially regulate LH and FSH subunit mrna production, Accepted December 29, Received September 22, 'This study was supported by Natural Sciences and Engineering Research Council Grant U to H.R.H. 'Correspondence. FAX: (403) I. resulting in increased a-subunit mrna levels, decreased FSH-3 mrna levels, and slightly increased LH-0 mrna levels [101. In orchidectomized rats, testosterone treatment resulted in an increased FSH content and a decreased LH content as well as decreased LH-3 and -a, subunit mrna levels in the pituitary; the FSH-[ mrna levels were unchanged by these treatments [11,12]. There is also a report on the stimulatory effect of estradiol on LH-P mrna production in isolated pituitaries of ovariectomized rats with no effect on the FSH-[ and the c-subunit mrna levels [13]. It would therefore appear that steroids differentially regulate pituitary GtH secretion and synthesis in mammals. In teleosts, gonadectomy was shown to increase circulating GtH-II levels in rainbow trout [14], African catfish [15], and goldfish [16]. The observed increases in GtH-II levels were then suppressed by treatment with estradiol and/or testosterone. In sexually immature teleosts, however, sex steroids appear to exert primarily a positive feedback effect. In juvenile rainbow trout, testosterone treatment resulted in increased pituitary GtH-II content [17] and in the initiation of gonadal development [18]. In European silver eel, estradiol was found to increase pituitary GtH-II [191 and brain GnRH content [20]. In Japanese silver eel, both estradiol and testosterone stimulated pituitary GtH-II content and serum GtH-II levels [21]. In common carp and Chinese loach, testosterone treatment increased responsiveness to LHRH-A [22]. In goldfish, it was demonstrated that in vivo treatment 1184

2 REGULATION OF GONADOTROPIN SYNTHESIS 1185 with estradiol and testosterone, and in vitro treatment with testosterone, increased responsiveness to GnRH-induced GtH-II release in vitro [231. Testosterone and estradiol treatment have also been shown to stimulate GtH-II-]3 gene expression in pituitary cells from juvenile rainbow trout [24, 25] as well as GtH-II-P mrna levels in the European silver eel [26]. In juvenile teleosts, estradiol and aromatizable androgens exert stimulatory effects on GtH-II expression, although the estradiol effect was found to be restricted to juvenile female teleosts [271. Further studies in juvenile and adult rainbow trout demonstrated that both testosterone and estradiol specifically stimulate GtH-II-B3 gene expression [28]. In general, while considerable data are available on the effects of the gonadal steroids on GtH release, information regarding the mechanisms by which steroids regulate GtH subunit gene expression in teleosts and lower vertebrates is limited. In the present study, the in vitro and in vivo effect of testosterone was investigated in terms of GtH-II subunit mrna production in both sexually immature and mature goldfish. In addition, the effect of a nonaromatizable androgen, 11 p-hydroxyandrosterone, was tested to determine whether or not aromatization of androgens is essential for their action on GtH-II subunit gene expression in the goldfish pituitary. MATERIALS AND METHODS Animals Goldfish, Carassius auratus, of mixed sex (ranging from 8-10 cm in length), were purchased from a fish farm in Pennsylvania. Fish were maintained for a short period of time (7 days) in a semi-recirculating aquarium (1500 L) at 17 0 C on a 16L:8D photoperiod for acclimation before the experiments and were fed a commercial fish diet. Hormones and Chemicals Steroids (testosterone and 11 3-hydroxyandrosterone) were purchased from Sigma Chemical Company (St. Louis, MO). The carp GtH-II-13 cdna fragment (cgth-ii-03; kb in length) and GtH-II-a cdna fragment (cgth-ii-a; kb) were provided by Dr. F.L. Huang (Institute of Biological Chemistry, Academia Sinica, Taipei, Taiwan). The trout -tubulin cdna fragment (1.5 kb) was provided by Dr. G. Dixon (Department of Medical Biochemistry, University of Calgary, Calgary, AB, Canada). In Vivo Steroid Treatment Goldfish (mixed sex; -30 g each) were anesthetized lightly by immersion in 0.05% tricane methane sulfonate. Testosterone was initially dissolved in ethanol and was then diluted in physiological saline. Each fish was given an i.p. injection of 100 l of vehicle containing the appropriate concentration of the steroid. In this experiment, fish received injections of various doses of testosterone or 113- hydroxyandrosterone (5-8 goldfish per group) at different time intervals, and GtH-II subunit gene expression was investigated. At the end of the treatment period, goldfish were anesthetized by immersion in 0.05% tricane methane sulfonate and killed by means of cervical-spinal separation. Pituitaries were removed, and total RNA was extracted by the acid-guanidinium thiocyanate phenol-chloroform extraction method [29]. For time-course studies, goldfish received an injection of 20 lig/fish of testosterone or 113- hydroxyandrosterone; this was followed by removal of pituitaries and extraction of total RNA at various time intervals (12, 24, 48, 72, and 96 h). Dose-response studies were performed on sexually immature (containing immature gonads; early recrudescence) and mature (containing fully developed oocytes and sperm; late recrudescence) goldfish. Fish undergoing the transition from the immature to mature state are referred to here as mid-recrudescent. For 24 h, sexually immature goldfish were treated with 0.2, 2, or 20 l.g/fish of testosterone or 11 3-hydroxyandrosterone while sexually mature goldfish were treated with testosterone doses of 0.02, 0.2, 2, or 20 plg/fish. A 24-h treatment period was used for dose-response studies, since an inhibitory effect was observed after 24 h of treatment with 20 plg of testosterone in an earlier study (see Figs. 1-2). In Vitro Steroid Treatment Pituitary GtH-II subunit gene expression was determined in response to treatment with testosterone by means of a superfusion system as described previously [5]. Briefly, eight pituitary equivalents were equilibrated in Medium 199 for 2 h before treatment. The sexually immature pituitary fragments were then treated continuously for 15 h with testosterone concentrations of 2, 20, 200, 2000, or 5000 ng/ml, while the sexually mature pituitary fragments were treated continuously with 2, 20, or 2000 ng/ml of testosterone. The fragments were removed from the columns after treatment, and total RNA was extracted as described for the in vivo experiments. Determination of GtH-II Subunit mrna RNA extraction and Northern analysis were performed as described by Khakoo et al. [5]. Briefly, total RNA was extracted from pituitaries by the acid-guanidinium thiocyanate phenol-chloroform extraction method [291. Sample purity was determined from ratios of the sample absorbances at 260:280 nm. The ratios ranged between 1.6 and 2.1. RNA was resolved on a 1.2% agarose /formaldehyde gel and transferred onto a Hybond-N + membrane (Amersham, Arlington Heights, IL) in the presence of 20-strength salinesodium phosphate-edta (SSPE) transfer buffer through use of the capillary transfer method. Purified cdna fragments were labeled via the random primer method with [a- 32 P]- deoxycytidine 5'-triphosphate (dctp) (-3000 Ci/mmol; Amersham). The membranes were prehybridized and hy-

3 1186 HUGGARD ET AL. FIG. 1. Time-related effect of testosterone (20 g/fish) on GtH-II-a and -[ mrna levels in sexually immature goldfish (basal circulating testosterone levels = 0.5 ± 0.43 ng/ml) in vivo. Total RNA was extracted 12, 24, 48, 72, and 96 h after treatment, and 5 g was loaded per lane for Northern analysis. Data were quantified through use of a computerized densitometer. The values are percentage increase relative to control value. Quantified data represent mean of two observations. Each experimental group consisted of 5-8 animals. tosterone-treated goldfish, through use of RIA as described previously [30, 31]. For treated groups, early- to mid-recrudescent goldfish received i.p. injections of testosterone concentrations of 0, 0.02, 0.2, 2, or 20 g/fish to determine circulating levels of testosterone after injection with various concentrations of the steroid. After 6 h, fish were anesthetized and bled from the caudal vein. Blood samples were centrifuged ( X g) for 5 min and serum was isolated. For extraction of the steroids from the serum, 4 ml of ethyl ether was added to 100 [l of serum, vortexing was carried out for 10 min, and the organic phase was separated after freezing on dry ice. The remaining aqueous phase was extracted again as described above and the organic phases were pooled for steroid RIA. The ether was evaporated at room temperature, and the fractions were resuspended in 50 l of ethanol and diluted with 950 l of steroid assay buffer. The percentage recovery of testosterone in the plasma was determined to be over 90% after two extractions. All samples were analyzed in a single RIA specific for testosterone. The anti-testosterone-bsa serum (a gift from Dr. H.R. Berhman, Yale University, New Haven, CT) was characterized for its titer and cross-reactivity using [1,2,6,7-3 H]-testosterone from Amersham (TRK402). A 1: dilution of antiserum was found to be optimal, with a sensitivity of 5 pg/100 pll (ED 50 = , n = 15). This antiserum cross-reacts well with testosterone (100%), 4-androsten-173ol-3-11-dione (65%), and dihydroxytestosterone (54.9%), but reacts poorly, if at all, with estrone (0.002%), 170-estradiol (no displacement), 17a-estradiol (no displacement), estriol (no displacement), progesterone (0.069%), 17a-203-dihydroxyprogesterone (no displacement), cortisol (0.004%), and pregnelone (0.001%). bridized for 2 h through use of Amersham's Rapid Hybridization Buffer and the specific probes of interest. The membranes were subsequently washed in a series of highstringency washes up to 0.1-strength SSPE in the presence of 0.1% SDS. The membranes were initially hybridized with cgth-ii-3, stripped, and subsequently hybridized with cgth-ii-a and a-tubulin. The ac-tubulin was used as an internal standard to control for possible loading errors. In addition, the gel was stained with ethidium bromide to verify equal loading of total RNA in all lanes. The autoradiograms were scanned by means of a computerized densitometer scanner and quantified via a computerized densitometry program, Gelscan, provided by the NIH (Bethesda, MD). The quantified GtH-II-3 and GtH-II-a mrna levels were expressed with respect to a-tubulin levels of the corresponding lanes. Testosterone Determination by RIA Testosterone levels were determined in untreated fish at different stages of gonadal recrudescence, as well as in tes- RESULTS The production of mrna for both GtH-II-a and GtH-II- 3 occurred similarly under all experimental conditions and is therefore referred to collectively as GtH-II subunit mrna production in this study. Time-Related Effects of Gonadal Steroids In Vivo Sexually immature goldfish received an injection of testosterone or 11 -hydroxyandrosterone (20 ig/fish), and RNA extraction was performed at 12, 24, 48, 72, and 96 h. Treatment of sexually immature goldfish (with basal circulating testosterone levels of ng/ml) with testosterone resulted in a biphasic change in GtH-II subunit mrna levels (Fig. 1). The GtH-II-a and GtH-II-3 mrna levels were reduced initially (12-48 h); they then increased significantly after 72 and 96 h of treatment. A similar experiment was carried out on sexually immature goldfish (with basal circulating testosterone levels of ng/ ml) to study the effect of a nonaromatizable androgen, hydroxyandrosterone, on GtH-II subunit gene expression

4 REGULATION OF GONADOTROPIN SYNTHESIS 1187 FIG. 2. Time-related effect of 11-hydroxyandrosterone (20 pig/fish) on GtH-II-a and - mrna levels in sexually immature goldfish (basal circulating testosterone levels = ng/ml) in vivo. Total RNA was extracted 12, 24, 48, 72, and 96 h after treatment, and 5 g was loaded per lane for Northern analysis. Data were quantified and expressed as described for Figure 1. Quantified data represent mean of two observations. Each experimental group consisted of 5-8 animals. in vivo (Fig. 2). Treatment with 11 3-hydroxyandrosterone also resulted in an initial (12-24 h) reduction in GtH-II-a and GtH-II-]3 mrna levels, followed by a significant increase in GtH-II subunit mrna levels after h. Dose-Related Effects of Gonadal Steroids In Vivo Sexually immature goldfish were treated with 0, 0.2, 2, or 20 pg/fish of testosterone or 11 3-hydroxyandrosterone for 24 h. Treatment with testosterone resulted in a biphasic change in GtH-II subunit mrna levels (Fig. 3). At lower physiological doses (0.2 and 2 g/fish), testosterone injection significantly stimulated basal GtH-II-a and GtH-II-3 subunit mrna levels after 24 h. At a higher supraphysiological dose of 20 pg/fish, however, the stimulatory effect of testosterone on the GtH-II-[3 mrna levels was reduced almost to the control level; in the case of GtH-II-a, there was a small reduction below the control level. In a similar experiment, treatment of sexually immature goldfish with 0.2 pg/fish of 11p-hydroxyandrosterone significantly increased basal GtH-II-a and GtH-II-03 subunit FIG. 3. Dose-related effect of testosterone on GtH-II-u and -P mrna levels in vivo. Sexually immature goldfish (basal circulating testosterone levels = ng/ ml) were treated, i.p., with 0.2, 2, or 20 jig/fish of testosterone for 24 h. Total RNA was extracted and 5 pg was loaded per lane for Northern analysis. Data were quantified and expressed as described for Figure 1. Quantified data represent mean of two observations. Each experimental group consisted of 5-8 animals. mrna levels (Fig. 4). However, at the higher doses (2 and 20 pg/fish), the GtH-II-a and GtH-II-3 subunit mrna levels were estimated to be at or below the control mrna levels. It should be noted that in the sexually immature goldfish, the basal circulating testosterone levels were estimated to be between and ng/ml, as indicated. Similar dose-response experiments were carried out to study the effect of testosterone on GTH-II subunit mrna levels in sexually mature goldfish. The effect of testosterone in sexually mature goldfish was not biphasic as observed in the sexually immature goldfish. In sexually mature goldfish, injection with 0.02, 0.2, 2, or 20 plg of testosterone for 24 h resulted in a dose-related increase in GtH-II subunit mrna levels (Fig. 5). The circulating concentration of testosterone in sexually mature goldfish was estimated to be ng/ml. Effects of Gonadal Steroids In Vitro For study of the direct effect of testosterone, pituitary fragments obtained from both sexually immature and mature goldfish were treated with various doses of testosterone for 15 h. Treatment with testosterone increased GtH-II-a and GtH-II-1 mrna levels above control levels in both sexually immature (Fig. 6) and mature goldfish (Fig. 7). However, the magnitude of the testosterone stimulation of GtH-

5 1188 HUGGARD ET AL. FIG. 4. Dose-related effect of 11j-hydroxyandrosterone on GtH-II-a and - mrna levels in vivo. Sexually immature goldfish (basal circulating testosterone levels = ng/ml) were treated, i.p., with 0.2, 2, or 20 pg/fish of 111-hydroxyandrosterone for 24 h. Total RNA was extracted and 5 pg was loaded per lane for Northern analysis. Data were quantified and expressed as described for Figure 1. Quantified data represent mean of two observations. Each experimental group consisted of 5-8 animals. II-ac and GtH-II-3 mrna levels in sexually immature goldfish was found to be greater with a lower minimum effective dose than in the mature goldfish pituitary. Circulating 7istosterone Levels Basal testosterone levels were measured by RIA in the fish used in the various experiments as indicated in the appropriate sections. Furthermore, we carried out an experiment to investigate the circulating levels of testosterone after injection with the steroid. Goldfish (of mixed sex at mid-recrudescence) received i.p. injections of various concentrations of testosterone. Blood samples were obtained 6 h after injection, and the testosterone concentration was estimated by RIA. Injection with 0, 0.02, 0.2, 2, and 20 }tg/fish resulted in circulating testosterone levels of 0.86 ± 0.1, , , , and ng/ml, respectively. The testosterone concentration in goldfish was found to vary from approximately 0.5 ng/ml in fish with immature gonads to approximately 28 ng/ml in fish with fully mature gonads. FIG. 5. Dose-related effect of testosterone on GtH-ll-u and -a mrna levels in vivo. Sexually mature goldfish (basal circulating testosterone levels = ng/ml) were treated, i.p., with 0.02, 0.2, 2 or 20 lpg/fish of testosterone for 24 h. Total RNA was extracted and 5 pg was loaded per lane for Northern analysis. Data were quantified and expressed as described for Figure 1. Quantified data represent mean of two observations. Each experimental group consisted of 5-8 animals. DISCUSSION The present findings demonstrate that physiological doses of androgens stimulate GtH-II subunit gene expression in both sexually immature and mature goldfish in vivo. At higher supraphysiological concentrations, however, androgens were found to have an inhibitory effect on GtH-II subunit mrna production in sexually immature goldfish. Time-course experiments with supraphysiological concentrations of testosterone and 11 P-hydroxyandrosterone demonstrated an initial decrease in GtH-II subunit mrna production followed by an increase at longer time intervals after injection with the steroids (72 and 96 h). Dose-response studies demonstrated that the observed biphasic change in GtH-II subunit mrna levels was likely the result of differences in the concentrations of the steroids. I)uring the period in which the time-related inhibitory effect was observed (12-24 h), lower physiological doses of both testosterone and 113-hydroxyandrosterone were found to be highly stimulatory. Higher supraphysiological closes, however, were less stimulatory or inhibitory on GtH-II subunit mrna levels. A possible explanation for the observed timerelated hiphasic response in GtH-II subunit mrna levels could be the presumed higher circulating steroid concentration of the steroids during the earlier time intervals. fol-

6 REGULATION OF GONADOTROPIN SYNTHESIS 1189 FIG. 6. Dose-related effect of testosterone on GtH-ll-o and -P mrna levels in vitro. Sexually immature goldfish (basal circulating testosterone levels = ng/ ml) pituitary fragments were treated continuously with testosterone concentrations of 2, 20, 200, 2000, or 5000 ng/ml for 15 h. Total RNA was extracted and 3 lpg was loaded per lane for Northern analysis. Data were quantified and expressed as described for Figure 1. Quantified data represent mean of two observations. Each experimental group consisted of 5-8 animals. lowed by reduced levels at longer time intervals due to factors such as physiological degradation and clearance. A greater stimulation of GTH-II subunit mrna levels was observed at lower doses in sexually immature goldfish as compared to sexually mature fish. In this context, the circulating concentration of testosterone is about 10 times greater in sexually mature than in sexually immature goldfish, and high circulating levels of the steroid may have affected the regulation of GtH-II subunit gene expression by the androgens. The observed regulation of GtH-II subunit mrna production by androgenic steroids is of physiological significance, since goldfish undergo annual reproductive cycles in response to environmental cues [32]. In teleosts, concentrations of the gonadal steroids fluctuate in close correlation with circulating concentrations of GtHs throughout the year, with higher levels occurring during the reproductive season [ Previous studies in goldfish, as well as the present results, have demonstrated that the circulating concentration of testosterone reaches approximately ng/ml shortly before the ovulatory surge of GtH-II ([361; present FIG. 7. Dose-related effect of testosterone on GtH-II-a and - mrna levels in vitro. Sexually mature goldfish (basal circulating testosterone levels = ng/ml) pituitary fragments were treated continuously with testosterone concentrations of 2, 20, or 2000 ng/ml for 15 h. Total RNA was extracted and 3 pg was loaded per lane for Northern analysis. Data were quantified and expressed as described for Figure 1. Quantified data represent mean of two observations. Each experimental group consisted of 5-8 animals. results). These findings indicate that testosterone may be an important factor in controlling the circulating GtH-II surge in goldfish. The effect of rising testosterone concentration close to ovulation is likely to increase GtH-II release, which is required for stimulation of gametogenesis and steroidogenesis. The increased steroid levels, however, may also act in a negative manner to bring GtH-II levels back to basal levels through inhibition of GtH-II subunit mrna synthesis. This pattern of GtH and steroid change occurs in a number of teleosts. In sexually immature and regressing salmonids, the pituitary GtH content is low and reaches its peak during spawning [37]. In sexually mature salmonids, the sex steroid levels are high, and a negative feedback effect on the hypothalamo-hypophysial axis has been observed in response to testosterone treatment [38]. Pituitaries from sexually regressed and recrudescent goldfish demonstrated increased salmon GnRH-induced and chicken

7 1190 HUGGARD ET AL. GnRH-II-induced GtH release following treatment with testosterone and estradiol [23]. However, pituitaries from postspawning goldfish treated with testosterone demonstrated a positive effect for chicken GnRH-II-induced but not salmon GnRH-induced GtH release. Estradiol had no effect on GnRH responsiveness in these fish [23]. Studies were carried out to investigate the direct action of testosterone at the level of the pituitary. Treatment with all doses of testosterone, in vitro, resulted in increased GtH- II subunit mrna levels in both sexually immature and mature goldfish. However, the magnitude of the stimulation was greater and occurred at a lower concentration in sexually immature goldfish, indicating a differential sensitivity of the pituitary gland to testosterone depending on the maturity of the animal. A number of studies in mammals have also addressed the role of steroids, in vitro, at the level of the pituitary and have demonstrated stimulatory effects in terms of GtH release and synthesis. For example, treatment with estradiol of pituitary cells from female rats was found to stimulate basal FSH and LH secretion [39, 401. Similarly, pituitary cells from intact males and females rats treated with testosterone showed an increase in FSH-P mrna levels [411. Further studies in rats have demonstrated both a stimulation and an inhibition of LH-P subunit synthesis after in vivo treatment with steroids, whereas treatment with estradiol, in vitro, was always stimulatory [42, 43]. Studies in juvenile trout demonstrated an increase in GtH-II-[ mrna levels in response to steroid treatment in vivo [24] and in vitro [25, 28]. Pituitary cells from sexually mature (prespawning) trout, which actively synthesize GtH-II- mrna, responded positively to steroid treatments. However, steroid treatment of pituitary cells from spawning fish was without effect on GtH-II- mrna levels. In the goldfish pituitary, in vitro treatment with testosterone was shown to increase GnRHinduced GtH-II release [23]. From the present findings it appears that testosterone exerts a predominantly positive effect on GtH-II synthesis at the level of the pituitary. This may be through modulation of GnRH receptor numbers, postreceptor mechanisms, or a direct effect at the level of the gene. Recently, Sealfon et al. [44] and Wu et al. [45] demonstrated that estradiol increased GnRH receptor mrna levels in ovine pituitary cells. In addition, estrogen regulatory elements have been mapped in the rat LH-P gene [42] and salmon GtH-II-3 gene [25, 28]. These elements have been demonstrated as the site of action for the stimulatory steroid effect [28, 43]. With respect to modulation at the postreceptor level, estradiol was shown to increase LH release from rat pituitary cells via interaction with Ca 2 ' and phospholipase C-mediated secretory mechanisms but not via arachidonic acid pathways [46, 47]. Estradiol has also been shown to modulate protein kinase C activity [48]. It is possible that testosterone may also be acting in one or more of these ways. The in vivo effects of testosterone observed in the present study may be occurring at multiple sites, including the regulation of GnRH secretion. It has been demonstrated that during the breeding season in ewes, estradiol inhibits GnRH and LH pulse amplitude without affecting LH and GnRH pulse frequency [49, 50]. Steroids may also exert their effect indirectly through modulation of neuronal factors, such as gamma-aminobutyric acid and dopamine, which are known to be affected by gonadal steroids and have regulatory functions in terms of GtH-II release in goldfish [51-54]. With respect to in vivo GnRH receptor regulation, Habibi et al. [15] demonstrated seasonal variation of GnRH binding capacity in goldfish. The number of binding sites significantly increased during the time of maximal gonadal recrudescence. However, in a recent study it was demonstrated that the stimulatory effect of testosterone in goldfish GtH-II release was not mediated through changes in GnRH receptor number [23]. In summary, the present findings demonstrate that androgens, at physiological levels, directly stimulate GtH-II subunit gene expression in the goldfish pituitary. The observed changes in GTH-II subunit mrna production may be an important factor in steroidogenic regulation of goldfish reproduction through mechanisms directed at the level of both the pituitary and brain. ACKNOWLEDGMENTS We would like to thank Eila Mirhadi for her assistance with the testosterone RIA. We also thank the NIH for providing the Gelscan program used in this study. REFERENCES 1. 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8 REGULATION OF GONADOTROPIN SYNTHESIS Landefeld TD, Bagnell T, Levitan I. Effects of estradiol on gonadotropin subunit messenger ribonucleic acid amounts during induced gonadotropin surge in anestrous ewes. Mol Endocrinol 1989; 3: Kitahara S, Winters SJ, Oshima H, Troen P. Effects of gonadal steroids on follicle-stimulating and luteinizing hormone secretion by the pituitary cells from castrated and intact male rats. Biol Reprod 1991; 44: Wierman ME, Gharib SD, LaRovere JM, Badger TM, Chin WW. Selective failure of androgens to regulate follicle stimulating hormone messenger ribonucleic acid levels in the male rat. Mol Endocrinol 1988; 2: Shupnik MA, Gharib SD, Chin WW. Divergent effects of estradiol on gene transcription in pituitary fragments. Mol Endocrinol 1989; 3: Bommelaer MC, Billard R, Breton B. Changes in plasma gonadotropin after ovariectomy and estradiol supplementation at different stages at the end of the reproductive cycle in the rainbow trout (Salmo gairdnern R). 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