PubMed Health⌕ Search

Biomedical subjects

A G Amador

Publications and source records attributed to A G Amador.

At least 19 recordsLinked to original sources
PubMed1997

Modulation of the testicular steroidogenic pathway by cyclosporin A in adult rats pretreated with diethylstilbestrol.

Treatment of male Fischer-344 rats with diethylstilbestrol (DES) induces hyperprolactinemia and alterations in testicular steroidogenesis. Cyclosporin A (CsA), an immunosuppressive drug, is believed to act by opposing the effects of prolactin (PRL) and was reported to influence testicular function. We have examined the effect of CsA on gonadal function in rats pre-treated with DES. Male rats were implanted with DES-containing silastic capsules. After 19 weeks, the capsules were removed, and, starting 2.5 weeks later, rats were treated for 1 week with CsA. At sacrifice, plasma and testes were collected. Testis fragments were incubated with or without 12.5 mlU of human chorionic gonadotropin (hCG)/ml at 32 degrees C for 4 hr. As expected, plasma PRL levels were increased in DES exposed rats, while testicular, seminal vesicle, and prostate weights were reduced. Cyclosporin A treatment did not further modify these parameters. Treatment with CsA and/or DES decreased circulating levels of testosterone, while testosterone content in the testes was not modified. Although CsA did not affect in vitro release of testosterone, it reduced the stimulatory influence of DES pretreatment on testicular responses to hCG in vitro. Plasma and testicular content of progesterone (P) was increased by DES administration but was not affected by CsA. Both CsA and DES administration decreased plasma 17-OH-Progesterone (17-OH-P) levels, but only CsA decreased testicular 17-OH-P contents. Combined exposure to CsA and DES enhanced the stimulatory effect of hCG on the accumulation of 17-OH-P in the media. Media estradiol levels were not affected by treatment with either CsA or DES. The present results indicate that CsA may interfere with the enhancement of the conversion of P to testosterone in DES-treated rats. As CsA did not change plasma PRL or gonadotropin levels, a direct effect of the drug on the testicular function is suspected.

17-alpha-Hydroxyprogesterone↗
PubMed1996

Genetic determination of coat color affects testicular steroidogenesis in the Mustela vison.

Coat color genes in mammals are known to be developmental genes with wide pleiotropic effects. The present study was undertaken to study testicular steroidogenesis in American Mink (Mustela vison) of various coat color phenotypes. No differences in testicular steroid levels were observed between fertile and infertile mink with the standard phenotype and genotype (BB jj MM PP). Mink with the opaline phenotype and genotype (bb mm pp), were found to have in their testes, 20-40% higher levels of progesterone, five times higher levels of 17-hydroxyprogesterone, and eight times higher levels of testosterone, than the corresponding values in other mink. No other differences were observed among the different types of mink. Since the genotype of the opaline mink differs from the other mink studied, only in their combination at the pastel (b) and moyle (m) loci, their bb mm genotype could be assumed to be responsible for the increase in testicular steroids.

17-alpha-Hydroxyprogesterone↗
PubMed1995

Effects of somatostatin and somatotropin on the in vitro testicular steroidogenesis in hamster.

Adult hamsters were exposed to short-photoperiod, and injected with either somatotropin (GH), somatostatin (GHRIH), or saline for eight weeks. Hamster testis fragments of similar size were incubated with or without hCG. No significant differences in the basal media testosterone and estradiol levels were observed among groups. Treatment with GH potentiated the hCG-dependent increase in media testosterone. Contrary to what was expected, treatment with GHRIH did not only not reduce the hCG-related elevation in media testosterone, but even produced a numerical increase of it. Treatment with GHRIH potentiated the hCG-dependent increase in media estradiol, whereas treatment with GH produced only a numerical increase of the response. Furthermore, the combined exposure to GHRIH and hCG appeared to cause an increase in the efficiency of testicular aromatase. Since previous data indicated that the combined deficiency of lactotropic and somatotropic actions severely impairs testicular steroidogenesis, treatment with GHRIH should have caused further steroidogenic impairment in hamsters exposed to short-photoperiod. Since this does not appear to be the case, it could be postulated that GHRIH has a direct stimulatory or at least a protective effect on testicular steroidogenesis.

Animals↗
PubMed1993

Deficient testicular and adrenal steroidogenesis in mutant cream (e/e) Syrian hamsters.

Coat color genes have been shown to be developmental genes with wide pleiotropic actions. The present study was undertaken to analyze the effects of mutations at the e locus of the Syrian hamster on testicular and adrenal steroidogenesis. Although no differences in body weight were detected, cream (e/e) hamsters had larger testes and smaller adrenals than wildtype (+/+) animals. Plasma testosterone levels were lower in e/e than in +/+ hamsters. However; testicular progesterone levels were higher, and 17-OH-progesterone and testosterone levels were lower in e/e when compared to +/+ hamsters. The efficiency of testicular 17-hydroxylase appear to be reduced in e/e hamsters. Adrenal progesterone levels were higher. 17-OH-progesterone, testosterone, dehydroepiandrosterone sulphate and aldosterone levels were similar, and cortisol levels were lower in e/e when compared to +/+ hamsters. The efficiencies of adrenal 17-hydroxylase and 17-hydroxysteroid dehydrogenase appear to be reduced in e/e hamsters. The present data indicate that steroidogenic deficiencies are present in the testes and adrenals of e/e hamsters, and that the gonadal alterations are more severe than the adrenal ones. The e locus, in the hamster, could be a developmental gene, or could be coding for a component in a signaling pathway under the control of such a gene.

Adrenal Cortex↗
PubMed1992

Further observations on estrus and ovulation in woodchucks (Marmota monax) in captivity.

The woodchuck is a seasonally breeding sciurid rodent. Female woodchucks are monoestrous and, when isolated from males, remain in a prolonged period of estrus characterized by a clear predominance of cornified cells in the vaginal smear. This study was designed to characterize relationships between the degree of vaginal cornification and sexual receptivity, and to study ovulation and related phenomena of this species in captivity. Fourteen individually caged adult females, maintained under standard laboratory conditions for 9-23 mo, were used in this investigation. Females exhibiting predominantly (67-97%) cornified smears were always receptive, regardless of the time interval from the onset of estrus, and mated within 24 h of pairing. Mated females allowed to complete pregnancy gave birth to live pups 30-32 days later. Litter size ranged from 3-7 pups. Serum progesterone (P) levels increased to approximately 2 ng/ml during the first week of pregnancy and greater than 5 ng/ml during the second and third weeks of pregnancy. Serum estradiol (E2) levels were elevated during the first week of pregnancy and began to decline thereafter. Examination of ovarian serial sections revealed that ovulation took place between 20 and 32 h after copulation. Serum levels increased significantly (4-fold) after ovulation (1.2 +/- 0.3 vs. 0.3 +/- 0.01 ng/ml). However, the circulating levels of E2 remained unchanged between the periods before (53 +/- 1 pg/ml) and after ovulation (60 +/- 3 pg/ml). Ovulation was not simultaneous in all mature follicles.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1992

Differential effects of two alleles of the dy locus on the pituitary-testicular axis of mice.

Testicular function was studied in vivo and in vitro in adult male dy/dy and dy2J/dy2J dystrophic mice. The results demonstrate that testicular function in dy/dy mice is more affected. The basal levels of pituitary hormones measured were normal in dystrophic mice, except for the presence of hyperprolactinemia in dy/dy mice. In dy/dy mice testicular weight was diminished and a deficient transduction of the gonadotropic signal is present in vivo, accompanied by reduced efficiency of 17-hydroxylase and 17-hydroxysteroid dehydrogenase. In dy2J/dy2J mice the signal transduction is normal and the reduction in enzyme efficiency is limited to 17-hydroxysteroid dehydrogenase. The in vitro HCG-induced increases in production of testosterone (T) and estradiol (E2) were reduced in dy/dy/mice, and the data indicate a reduction of enzyme activity rather than in efficiency. In dy21/dy21/mice, HCG-induced T synthesis was increased, HCG-induced E2 synthesis was normal, but basal media E2 levels were reduced, with the in vitro efficiency of aromatase being suppressed under both basal and HCG-stimulated conditions, when compared to their normal littermates.

17-Hydroxysteroid Dehydrogenases↗
PubMed1992

Potentiation by epidermal growth factor of the in vitro HCG stimulation of testicular steroidogenesis in hamsters.

Epidermal Growth Factor (EGF) has been reported to stimulate or inhibit steroidogenesis in murid Leydig cells depending on the experimental conditions used. In the present study, testicular fragments from an adult cricetid rodent, the Syrian hamster, were incubated with various doses of mouse EGF (0-2.0 micrograms/ml media), in the presence or absence of HCG (0-12.5 mlU/ml media). Although EGF alone did not affect in vitro testicular steroidogenesis, it significantly potentiated the HCG-induced elevation of the accumulation of testosterone and 17-hydroxyprogesterone in the media. In contrast, the effect of HCG on media progesterone concentration was not affected by EGF. Since in the Syrian hamster intracellular calcium loading functions as a gonadotropic stimulus, the present results could be a consequence of the EGF-induced increase in cellular calcium levels.

17-alpha-Hydroxyprogesterone↗
PubMed1991

Reinitiation of spermatogenesis by exogenous gonadotropins in a seasonal breeder, the woodchuck (Marmota monax), during gonadal inactivity.

The present study was undertaken (1) to document structural and functional changes in the testes of seasonally breeding woodchuck during active and inactive states of spermatogenesis and (2) to evaluate the ability of exogenous gonadotropins to reinitiate spermatogenesis outside the breeding season. During seasonal gonadal inactivity, there were significant (P less than 0.05) reductions in volumes of several testicular features (testis, seminiferous tubules, tubular lumen, interstitial tissue, individual Leydig cells, Leydig cell nuclei, and Leydig cell cytoplasm) as compared with gonadally active animals. The diameter of the seminiferous tubules was decreased by 26%, and Leydig cell numbers also declined in the regressed testes. These changes were accompanied by a decline in testosterone (T) levels in both plasma and testis, and reduction in epithelial height of accessory reproductive organs. A hormonal regimen was developed that would reinitiate spermatogenesis in captive, sexually quiescent woodchucks. A combination of PMSG and hCG markedly stimulated testicular growth and function and restored spermatogenesis qualitatively. Quantitatively normal spermatogenesis was restored in 2 of 6 treated males. Morphometric analyses revealed substantial increases in seminiferous tubular diameter and in the volume of seminiferous tubules, tubular lumen, total Leydig cells, and individual Leydig cells in the hormone-treated animals. These increased values corresponded to 99, 75, 68, 51, and 200%, respectively, of the values measured in naturally active woodchucks. Leydig cell numbers, however, remained unchanged and approximated only 31% of the number found in naturally active testes. Hormonal stimulation also resulted in a significant rise in serum T as well as in the total content of testicular T, and a marked increase in epithelial height in various accessory reproductive glands. The most effective hormonal protocol for stimulating spermatogenesis was treatment with 12.5 IU of PMSG twice a week for 4 weeks followed by 12.5 IU of PMSG + 25 IU of hCG twice a week for 4 weeks.

Animals↗
PubMed1991

Seasonal variations in circulating levels of progesterone and estradiol in unmated adult female woodchucks (Marmota monax) in captivity.

The annual profile of serum levels of progesterone (P) and estradiol-17 beta (E2) was characterized in a seasonally breeding rodent, the woodchuck (Marmota monax). Hormonal levels were determined in serum samples taken at weekly or biweekly intervals from unmated female woodchucks maintained all year indoors under controlled conditions of photoperiod and temperature. Annual fluctuations included a rise of E2 levels during late January through February, followed by a modest increase in plasma P concentrations by late March, the latter attaining peak values during April and May. A temporal dissociation of peak values of circulating levels of P and E2 during the annual reproductive cycle was also detected. The timing of changes in serum levels of P and E2 in these captive woodchucks corresponded to reproductive events during the normal breeding season of the woodchuck in the southern part of its range.

Animals↗
PubMed1991

The estrous cycle of captive woodchucks (Marmota monax).

Changes in vaginal cytology were assessed and correlated with temporal changes in circulating concentrations of progesterone (P) and estradiol-17 beta (E2) during the breeding season (February to March) in a seasonally breeding rodent, the woodchuck (Marmota monax). Ten individually caged adult females, maintained under laboratory conditions for 3-11 mo, were studied. Vaginal smears were taken each morning for 2 consecutive months beginning 1 February 1990. Seven of 10 females exhibited readily identifiable estrus, characterized by a clear predominance (83%) of cornified cells. The earliest estrous smear was recorded on 3 February and the latest on 12 March. These animals were monoestrous and remained in a prolonged estrous period during their brief breeding season. The average duration of estrus was 18.1 +/- 2.1 days, ranging from 12-27 days. Levels of P and E2 were determined in serum samples taken before, during, and after estrus from 7 females who exhibited estrus. No changes in the circulating levels of P were apparent during the estrous cycle. However, there was a consistent pattern of estradiol secretion characterized by elevated levels of E2 before and during estrus, followed by a significant (p less than 0.05) decline in E2 levels one week after the end of estrus. Elevated levels of E2 preceded and coincided with maximal degree of vaginal cornification. Thus, the termination, but not the onset, of estrus in woodchucks reflected closely the temporal pattern of changes in serum E2 levels during the breeding season.

Animals↗
PubMed1991

Effects of in vivo and in vitro exposure to bromocriptine on testicular LH receptors and in vitro testosterone production in Syrian hamsters.

The effects of in vivo and in vitro exposure to bromocriptine (CB-154) were studied in testes of Syrian hamsters. In animals treated for two days with CB-154, a decrease in LH receptors (LH-R) was observed, with a greater decrease being measured in hamsters treated for 14 days, when compared with controls. Injection of HCG caused, in hamsters treated with CB-154 for 14 days, up-regulation of LH-R and increased testosterone synthesis in response to HCG administration in vitro. These changes were not observed in the two other groups of animals. When testis fragments were incubated with CB-154, those incubated with a large dose (10 micrograms/ml) had a normal pattern of response to HCG, and those incubated with a small dose (1 ng/ml) had a smaller maximum response. These actions are similar to those observed in men treated with CB-154. It can be therefore concluded that: a) CB-154 has a direct effect on the testes; b) it probably is through modulation of LH-R synthesis; c) Syrian hamsters probably represent the best model for the study of the effects of CB-154 on the testes; and d) the possibility of using CB-154 as an adjuvant of gonadotropin treatment in hypogonadism has to be considered.

Animals↗
PubMed1990

Studies on the thyroid in transgenic mice expressing the genes for human and bovine growth hormone.

The thyroid glands of transgenic mice (TM) expressing the genes for human (h) and bovine (b) growth hormone (GH) were studied. The percentages of larger follicles in hGH TM of either sex were significantly greater than in the corresponding normal littermates, and follicles ranging up to 350 microns in diameter were present in male hGH TM. In contrast, thyroid follicles were only slightly enlarged in male bGH TM, and were unchanged in female bGH TM. The serum concentrations of T4 were significantly decreased in male bGH TM and not altered in the other groups. Serum concentrations of T3 were slightly, but significantly increased in female hGH TM and female bGH TM, but were unaffected in male TM of either type. Since the principal difference between these foreign GHs in rodents is the additional lactogenic activity of human GH, these results may indicate that the effects of prolactin can influence the development of the thyroid.

Animals↗
PubMed1990

Hormonal regulation of testicular prolactin receptors and testosterone synthesis in golden hamsters.

A study was conducted with hypophysectomized hamsters to determine effects of administration of prolactin (PRL), luteinizing hormone (LH), and follicle-stimulating hormone (FSH)-alone or in combination-on testicular PRL receptors and in vitro testosterone production. Hormonal injections commenced the second day after hypophysectomy, and hamsters were killed on Day 5, approximately 13 h after the last hormonal injection. PRL receptor numbers were reduced by hypophysectomy, and PRL administration alone lessened the extent of this decrease. By themselves, neither LH nor FSH affected PRL receptors, but a combination of PRL + FSH + LH produced the greatest effect on these receptors. Receptor affinity was only modestly affected by any treatments. In vitro testosterone synthesis was measured after addition of 0, 2, 10, and 50 mIU of human chorionic gonadotropin (hCG) to incubations of testicular tissue. Neither PRL nor FSH by themselves in vivo affected basal or hCG-stimulated testosterone production. However, PRL + FSH increased (p less than 0.05) the magnitude of the in vitro testosterone response to hCG, as well as the sensitivity of that response (slope of the dose-response curve). LH alone increased both basal and hCG-stimulated testosterone production. PRL + LH provided no additional increase in the magnitude of the testosterone response, but increased (p less than 0.05) the sensitivity. PRL + FSH + LH in vivo provided for the greatest sensitivity of the testosterone response to hCG.(ABSTRACT TRUNCATED AT 250 WORDS)

Analysis of Variance↗
PubMed1990

Differential effects of short photoperiod on the release of progesterone and testosterone by hamster testes in vitro.

Suppression of testicular activity in hamsters and voles exposed to constant darkness or short photoperiod is associated with reduced ability of the testes to convert C21 steroid precursors to C19 androgens. In the present study, we have examined the time course of changes in testicular secretion of progesterone and testosterone in vitro in adult male golden hamsters exposed to short photoperiod. Gradual decrease in testicular weight after 1, 2, and 3 months of exposure to short photoperiod was accompanied by significant increase in the amount of progesterone released per milligram of testicular tissue in response to gonadotropin stimulation. In contrast, testosterone response to gonadotropic stimulus progressively decreased. These results suggest that photoperiod-related gonadal atrophy may be accompanied by reduced activity of the 17 alpha-hydroxylase: C17,20-lyase enzyme complex in the testes, and that seasonal transitions between the states of reproductive activity and quiescence involve changes in both the amount of steroids produced by the testes and the relative proportions of testosterone and its precursors.

Animals↗
PubMed1990

Interspecies differences in the effects of HCG on testicular function among rodents.

Adult mice, rats and hamsters were injected with 0 or 0.3 IU hCG/g BW, 24 h before sacrifice. Basal LH receptor concentration was highest in rats and lowest in hamsters (rats greater than mice greater than hamsters). Injection of hCG caused LH receptor down-regulation in rats and mice, and up-regulation in hamsters. Basal plasma progesterone was highest in hamsters and lowest in rats (hamsters greater than mice greater than rats), however, hCG increased plasma progesterone levels in mice and rats, but not in hamsters. Mice had much higher plasma and testicular testosterone levels than other species, but hCG did not induce a relatively more dramatic increase in any species. When testes fragments were incubated with 0 or 12.5 mIU hCG/ml for 4 h, hCG increased media progesterone levels in rats and control mice, but not in hamsters and hCG-injected mice. Also, hCG elevated media testosterone levels in control but not in hCG-injected animals. Furthermore, addition of hCG in vitro partially prevented the elevation of media testosterone induced by in vivo hCG. The present results indicate that the mechanisms for the transduction of the gonadotropic signal by the Leydig cells are species-defined.

Animals↗
PubMed1989

Programs for radioimmunoassays and radioreceptorassays using SPSS-X.

Two sets of programs written using SPSS-X, and designed for the analysis of data obtained by radioimmunoassay or radioreceptorassay are presented. The main advantages of the programs are that they are easily edited, their commands are simple and logical, and they can be used for any type of radioimmunoassay or radioreceptorassay, respectively. The programs for radioimmunoassay can also be used for fluorescenceimmunoassay and luminescenceimmunoassay.

Computer Systems↗
PubMed1989

Regulation of GH and TSH release from hyperplastic and ectopic pituitaries: effects of dopamine in vitro.

This study was undertaken to examine the consequences of prolonged removal of the pituitary from hypothalamic control and of estrogen-induced pituitary tumors on the susceptibility of GH and TSH release to regulatory influences of dopamine (DA). Adult male Fischer 344 rats were treated with transplants of female anterior pituitaries under the renal capsule or with Silastic capsules containing diethylstilbestrol (DES). Capsules with DES remained in place until the animals were killed (DES-IN) or were removed 7 weeks prior to sacrificing the rats (DES-OUT). Both pituitary grafts and DES caused the expected elevation in plasma prolactin and suppression of plasma GH and TSH levels. Basal GH release in vitro was not affected by exposure to DES in vivo but was reduced by transplantation of the pituitary to an ectopic site. Treatment with DA in vitro suppressed GH release from the in situ pituitaries of control, DES treated and grafted rats but increased GH release from the ectopic pituitaries. Basal release of TSH in vitro was reduced in the pituitaries of DES-IN and DES-OUT animals but was not affected by the presence of pituitary transplants. No detectable TSH was released from the ectopic pituitaries in the absence of DA. DA decreased TSH release from the pituitaries of control, DES-OUT and DES-IN rats but not from the in situ pituitaries of grafted rats. In contrast, DA produced an increase in TSH release from ectopic pituitaries. These results demonstrate that somatotrophs and thyrotrophs removed from the hypothalamic influences on subjected to direct and indirect effects of DES exhibit abnormal responses to DA. We suspect that prolonged absence of normal pituitary control leads to the development of regulatory mechanism of pituitary hormone release which are different from those operating under physiological conditions.

Animals↗