摘要:

AbstractThe zonal testis of the dogfish (Squalus acanthias) has proven advantageous to study biochemical changes in relation to stage of spermatogenesis, including information on steroidogenic enzymes and steroid receptors. To investigate whether sulfotransferase is part of a mechanism regulating the availability of biologically active hormone in close proximity to receptors, we measured in vitro conversion of [3H]estrone (E1) to sulfoconjugated metabolites in cytosolic subfractions of testes grossly dissected according to germ cell composition (premeiotic‐PrM, meiotic‐M, and postmeiotic‐PoM stages). Assays were carried out in the presence of adenosine 3′‐phosphate 5′‐phosphosulfate (PAPS) at 22°C and optimized for time (60 min) and protein (500 μg/ml). Michaelis‐Menten kinetics and saturation analysis gave the following reaction constants for [3H]E1: Km = 0.33 μM, Vmax = 2.5 pmol/min/mg; and for PAPS: Km = 33 μM, Vmax = 1.1 pmol/min/mg; competition studies carried out in the absence or presence of 1‐ or 5‐fold excess radioinert steroids indicated that estrogen (E2>E1) as well as androgens (T = DHEA>5α dihydrotestosterone, DHT) were effective inhibitors. Sulfotransferase activity was found to be stage‐related, being highest in PoM regions (2.31 ± 0.24 pmol/min/mg protein) When compared to M and PrM regions (1.22 ± 0.22 and 1.28 ± 0.21 pmol/min/mg protein, respectively).Sulfoconjugation and the intratesticular distribution of steroid sulfates were also measured in vivo by perfusion of the intact testis with [3H]androgen or ‐estrogen. The pathway of blood flow via the genital artery was epigonal organ → PoM → M → PrM (mature → immature). Perfused [3H]E2, T, and DHT were all extensively metabolized in a one‐pass, 1 hr perfusion, less than 10% of perfused [3H] steroid being recovered from testicular tissues as unchanged steroid. In general, recovery of polar metabolites was greater than non‐polar metabolites from all three substrates. Sequential hydrolysis with glucuronidase and glusulase indicated that sulfoconjugation is a minor component (<20%) of several “inactivating” pathways, which include glucuronide conjugation, 17‐ketosteroid synthesis, and pathways leading to unidentified polar metabolites. No consistent stage‐related distribution patterns were observed for any of the metabolite subfractions; however, total recovered radioactive steroid (polar plus non‐polar) formed a decreasing concentration gradient from point of entry of perfusate (PoM region) to point of exit (PrM region).These data support the conclusion that access to receptors by steroid ligands may be controlled by a balance between activating and inactivating pathways. Furthermore, the intratesticular blood flow pattern identified here suggests that sulfoconjugation may be one of several mechanisms for screening out hormonal signals reaching the testis via the general circulation. The parallel‐antiparallel arrangement of blood flow and the spermatogenic progression provides an anatomical basis for paracrine communication between mature → immature stages by which the orderly progression of spermatogenesis and testicular zonation is maintained. Finally, given the obvious advantages of the shark testis model it should be possible to elucidate more precisely the role of free steroids versus steroid conjugates as int

ISSN:0022-104X    

DOI:10.1002/jez.1402640202

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1992

数据来源: WILEY

摘要:

AbstractSexual size dimorphism was investigated in the African bullfrog (Pyxicephalus adspersus), a species in which adult males are about 2.5 times larger than females. Growth profile analysis revealed that males and females begin to diverge in growth rates at 4 weeks postmetamorphosis, concurrent with the appearance of differentiated gonads. At the end of 300 days, males were about 75% heavier and 20% longer than females (females remained previtellogenic). The difference was attributable primarily to an extended period of accelerated linear growth in males between days 166 and 195, and an extended period of accelerated weight gain between days 139 and 166. Surgical gonadectomy did not affect growth in males or females. Reduced plasma steroid levels, failure to show steroid response to GnRH injection, and abolishment of male agonistic behaviors confirmed the completeness of gonadectomy. In addition, there was no correlation between plasma steroid hormones and size or growth rate. The current study suggests that gonadal hormones may not play an “activational” role in establishing sexually dimorphic growth patterns. Sexual size dimorphism may be due to either “organizational” hormonal effects or genetic control of growth patterns. © 1992 Wiley

ISSN:0022-104X    

DOI:10.1002/jez.1402640203

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1992

数据来源: WILEY

摘要:

AbstractAn analysis was made of the effects of 5 neuropeptides on the isolated branchial heart ofSepia officinalis. There is evidence to suggest that these 5 neuropeptides occur in the neurosecretory system of the vena cava (NSV system) of cephalopods. YGGFMRFamide and oxytocin caused concentration‐dependent increases in pressure amplitude in the perfused preparations, with their effects on heart rate being negligible. The molluscan neuropeptide FMRFamide hardly had any effect on the branchial heart beat when applied alone, but it counteracted the positive inotropic actions of noradrenaline. FLRFamide and α‐melanotropin had no effect in our system. None of the peptides tested in bioassays on branchial hearts was as efficient as a perfusate obtained from the cephalic vein ofSepia(including the NSV area) that had been stimulated by electrical irritation of the attached visceral nerves. These findings suggest that there may be further neurohormones in the NSV system that are released into the vessel lumen. It is suggested that the branchial hearts ofSepiain vivo are influenced by humoral peptides from the NSV system and that these peptides may act directly on target myocytes or may alter (i.e., potentiate or oppose) the effects of other cardioactive compounds. © 1992 Wiley‐Li

ISSN:0022-104X    

DOI:10.1002/jez.1402640204

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1992

数据来源: WILEY

摘要:

AbstractSinus gland participation on the phase relationship between the circadian rhythms of the response to light (electroretinogram, ERG) of the visual photoreceptors in the crayfish was studied. Chronic ERG recordings were simultaneously obtained from both eyestalks in intact and sinus‐gland‐deprived animals during free‐running conditions and during the application of external periodic signals that consisted of 12 hr of light and 12 hr of darkness, or 12 hr of darkness and 12 hr of light, light regimens. It was found that the sinus glands are indispensable for preservation of the main characteristics of the circadian rhythm in the ERG and for the maintenance of a tight phase relationship between the rhythms of both eyes under free‐running conditions and during the application of the 2 kinds of light regimen. It is concluded that the sinus glands play a determining role in the processes that confer an internal temporal order on crayfish. © 1992 Wiley

ISSN:0022-104X    

DOI:10.1002/jez.1402640205

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1992

数据来源: WILEY

摘要:

AbstractMonooxygenase activity in microsomes from the LPR strain of house fly (Musca domesticaL.) was inhibited by anti‐P450lpr, an antiserum specific for house fly cytochrome P450lpr, Anti‐P450lprdid not inhibit house fly cytochrome P450 reductase or rat cytochrome P450 monooxygenase assays, consistent with specific inhibition of P450lpr. Anti‐P450lprinhibited the ability of cytochrome P450 reductase to reduce carbon monoxide treated LPR microsomal cytochrome P450, up to 49% of the total, showing that inhibition of cytochrome P450 reduction is the major mechanism of inhibition. Anti‐P450lprinhibited 98% of methoxyresorufin‐O‐demethylase activity and all the benzo(a)pyrene hydroxylase activity in LPR microsomes, but none of the pentoxyresorufin‐O‐dealkylase activity. The antiserum partially inhibited ethoxyresorufin‐O‐dealkylase and ethoxycoumarin‐O‐dealkylase activity. These results demonstrate that methoxyresorufin‐O‐demethylase activity and benzo(a)pyrene hydroxylase activity are characteristic substrates for P450lpractivity in the LPR strain of house

ISSN:0022-104X    

DOI:10.1002/jez.1402640206

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1992

数据来源: WILEY

摘要:

AbstractTo examine endogenous steroid levels during early sexual differentiation in a reptile, we measured whole‐body and plasma steroid concentrations in a turtle (Trachemys scripta) throughout embryogenesis using radioimmunoassays. Whole embryos contained testosterone, estradiol, progesterone, and corticosterone before the temperature‐sensitive period for sex determination (TSP) (stage 14). The concentration of each of these steroids increased significantly between stage 14 and the initiation of the TSP (stage 16), but no increases were evident between stage 16 and the middle of the TSP (stage 18). No sex differences in steroid content were observed prior to the TSP (stage 14). However, presumptive male embryos (26°C incubation temperature) contained significantly more testosterone and estradiol than presumptive females (31°C incubation temperature) during the TSP (stages 16 and 18), and males contained more progesterone than females at stage 18. Plasma samples collected during the TSP (beginning at stage 17+) contained testosterone, estradiol, progesterone, androstenedione, and corticosterone. Progesterone and corticosterone were present in the highest concentrations, followed by androstenedione. Testosterone and estradiol were found in plasma at lower, similar concentrations except at stage 17+, when estradiol levels were ∼3‐fold higher than testosterone levels in both sexes. The only significant sex difference found in plasma steroid levels was for estradiol at stage 19, with males having higher levels than females. Our results demonstrate the presence of a rich steroid milieu throughout early development and support our previous findings that embryonic tissues can synthesize each of these steroids in vitro. Furthermore, a role for sex steroids in the process of sexual differentiation is strongly suggested. © 1992 Wiley

ISSN:0022-104X    

DOI:10.1002/jez.1402640207

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1992

数据来源: WILEY

摘要:

AbstractThe present study was conducted to determine the role of sex steroids in the regulation of FSH receptors in pregnant rats. In the normal physiological condition, FSH bindings per unit ovarian weight (density of binding) and per 2 ovaries (total binding) increased during days 14–21 gestation. Scatchard plot analyses of the binding suggested that the increase in FSH binding was due to an increase in the number of FSH‐binding sites. The plasma FSH concentration in pregnant rats was stable during the receptor change. In contrast, the plasma estradiol‐17β concentration continuously increased from gestation day 14 to 21, and the testosterone level showed a large peak on gestation day 18. Estradiol‐17β (one silastic plate containing 13 mg crystal)‐implanted pregnant rats during 14–21 days of gestation induced significant decreases in the total FSH binding and ovarian weight on gestation day 21. Estradiol administration increased the plasma estradiol level 2.3‐fold but did not change the FSH level. Testosterone or 5 α‐dihydrotestosterone, a nonaromatizable androgen, did not influence the binding level under the same dose treatment. In contrast, continuous treatment with aminoglutethimide (2 plates containing 20 mg crystal), an inhibitor of adrenocortical steroidogenesis, for 7 days significantly increased the total FSH binding without a significant change in the ovarian weight. The plasma titers of estradiol and testosterone in pregnant rats treated with aminoglutethimide were reduced by 37% and 51%, respectively. Aminoglutethimide did not influence plasma FSH levels. These results suggest that circulating estradiol acts as a negative factor in the regulation of ovarian FSH receptors, at least during the second half of pregnancy. Other factor(s) that is (are) independent of sex steroids and FSH may contribute to FSH receptor induction. © 1

ISSN:0022-104X    

DOI:10.1002/jez.1402640208

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1992

数据来源: WILEY

摘要:

AbstractIn order to document sex differences in adrenal function and how this relates to gonadal function during the period of seasonal activity, blood samples from male and female six‐lined racerunners,Cnemidophorus sexlineatus, were taken immediately after capture in the field for determination of plasma corticosterone and gonadal steroid concentrations. Plasma testosterone and dihydrotestosterone levels for males, and 17β‐estradiol and progesterone levels for females, were measured. Trends in the concentration of plasma corticosterone differed significantly between males and females. In males the highest concentrations of corticosterone were measured in late spring and the lowest concentrations were measured in late summer. Whereas half of the variation in corticosterone levels among males could be explained as seasonal change, less than 1% of the variation among females could be explained as seasonal change. In males plasma corticosterone and androgens exhibited similar seasonal decreases. Corticosterone levels for females were not correlated with progesterone or 17β‐estradiol levels. Sex differences in seasonal variation in plasma corticosterone concentrations suggest that corticosterone may be involved in the different reproductive strategies and energy requirements of males and females during the seasonal period of activity. © 1992 Wiley

ISSN:0022-104X    

DOI:10.1002/jez.1402640209

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1992

数据来源: WILEY

摘要:

AbstractCirculating concentrations of plasma corticosterone and gonadal steroids were measured intact and gonadectomized male and female lizards (Cnemidophorus sexlineatus) following acute stress (handling) in the laboratory. There was a significant increase in plasma corticosterone after stress. Whereas intact females exhibited greater concentrations of corticosterone relative to intact males, ovariectomized females exhibited lower concentrations of corticosterone relative to castrated males. In addition to sex differences in corticosterone responses to gonadectomy, progesterone was elevated by stress in both intact and ovariectomized females but not in males. Corticosterone adjusted for castration and handling in males was negatively correlated with the plasma androgen level. The adrenal responsiveness of males to acute stress may be attenuated by androgens presumably secreted by the testis. Not only does adrenal function influence reproduction, but adrenal responses differ between males and females, and appear to be influenced by the gonadal axis. The sex differences in adrenal responses to stress likely reflect different reproductive strategies and nutritional requirements of males and females during the breeding season. © 1992 Wiley‐Liss, I

ISSN:0022-104X    

DOI:10.1002/jez.1402640210

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1992

数据来源: WILEY

摘要:

AbstractUrodele amphibians regenerate their limbs after amputation. Normally, only those parts of the limb distal to the plane of amputation are regenerated. However, retinoids are capable of inducing proximodistal (PD) duplication such that structures already present proximal to the plane of amputation are duplicated in the regenerating limb. PD duplication can be induced by retinoids even if amputation occurs some time after the retinoid treatment. Thus, the purpose of this investigation was to determine for how long after administration, retinoids were effective at inducing PD duplication, and to determine whether this persistent effectiveness was due to some change in the cells of the limb or to residual levels of retinoids in the body. Thus, forelimbs of larval axolotls,Ambystoma mexicanum, were amputated at various times in relation to retinol palmitate (RP) treatment to investigate the relationship between the induction of proximodistal duplications and the timing of the retinoid treatment. RP induced PD duplications when amputation was delayed for up to 2 weeks after cessation of the retinoid treatment. To measure the levels of retinoids actually present within the body, axolotls were treated with RP, and whole body retinoid levels were colorimetrically assayed during and after the RP treatment. Since high levels of retinoids were present for several weeks after the cessation of the treatment, we conclude that the induction of PD duplications, when amputation is delayed until after the RP treatment, is due to the persistence of retinoids in the axolotl body. © 1992 Wiley‐Liss, I

ISSN:0022-104X    

DOI:10.1002/jez.1402640211

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1992

数据来源: WILEY