ISSN:0098-4108    

DOI:10.1080/15287397709529545

出版商:Taylor & Francis Group    

年代:1977

数据来源: Taylor

ISSN:0098-4108    

DOI:10.1080/15287397709529544

出版商:Taylor & Francis Group    

年代:1977

数据来源: Taylor

摘要:

Melengestrol acetate (MGA) is an orally active progestogen that is marketed for improved feed utilization, growth stimulation, and estrus suppression of feedlot heifers. The hormonal activity of MGA was investigated in humans, rhesus monkeys, cattle, dogs, rabbits, mice, and rats. The biologic activities were dose‐dependent within each species and were predictable—that is, block of ovulation and the menstrual or estrous cycle. Subtle effects were not detected for doses below the dose that blocked ovulation. The C3H An/f mouse was investigated for carcinogenic action of MGA. Data derived from the life‐span mouse studies were interpreted as indicating that MGA was not a carcinogen per se, even though massive doses (0.5 mg per mouse daily) could influence mammary tumor development in some instances; this effect was interpreted as being an influence of MGA on the general hormonal milieu. MGA was capable of increasing the serum prolactin concentration of mice fed MGA at a daily rate of about 0.2–0.8 mg. Tissue residue data demonstrated that MGA was located in the fat at concentrations less than 25 ppb in all cattle investigated and less than 10 ppb in about 90% of commercial feedlot cattle investigated. The relationship between identified MGA residues in cattle, doses that might be biologically active in the human, and human consumption leads to estimates that at least 775–1,100 pounds of meat products would have to be consumed daily to achieve a dose of 0.7 mg, which is predicted to be the minimal effective dose in humans.

ISSN:0098-4108    

DOI:10.1080/15287397709529546

出版商:Taylor & Francis Group    

年代:1977

数据来源: Taylor

摘要:

Twenty products associated with the metabolism of zearalenone by Fusarium roseum were analyzed with respect to time and culture conditions. By statistical analysis a set of six metabolites possibly related to zearalenone were selected. These products were characterized by gas chromatography‐mass spectrometry and other methods. The chemical structures of these six confirmed the statistical relationships, and evidence for the formation of these materials from zearalenone is presented. A suggested scheme of metabolism of zearalenone by F. roseum includes the formation of the two isomers of 8'‐hydroxyzearalenone, 6’,8'‐dihydroxyzearalene, 6‐(carboxypentyl)‐β‐resorcyclic acid, and phenylacetic acid derivatives.

ISSN:0098-4108    

DOI:10.1080/15287397709529547

出版商:Taylor & Francis Group    

年代:1977

数据来源: Taylor

摘要:

The ability of exogenous estrogens to alter serum levels of gonadotropins in ovariectomized rhesus monkeys was investigated in an attempt to develop a nonhuman primate model that could accurately predict both effective levels and physiologic consequences of human estrogen exposure. The ability of zearalenone (Z) and diethylstilbestrol (DES) to induce either a depression or an elevation of luteinizing hormone (LH) or follicle‐stimulating hormone (FSH) concentrations was compared to that of estradiol‐17β (E2). E2administration initially caused a reduction of gonadotropin levels (3–15 hr after injection) followed by an LH but not always an FSH surge (36–72 hr after injection). Injection of DES and Z induced similar gonadotropin patterns. The ovariectomized rhesus monkey model was used to compare the oral and parenteral potencies of Z, DES, and E2. The minimal doses of Z, DES, and E2that depressed LH levels after subcutaneous injection were 14, 0.5, and 4 μg/kg, respectively. When given orally, doses of 400, 2.5, and 5 μg/kg of Z, DES, and E2were needed to induce a significant decline in LH concentrations. FSH levels were depressed by injection of 56, 2, and 1 μg/kg of Z, DES, and E2, respectively. Additional experiments were conducted to determine whether DES or Z would interfere with either the E2‐induced gonadotropin depression or the subsequent gonadotropin peak. Since progesterone has been shown to block the estrogen‐induced LH surge but not to affect the LH depression, it was included as a positive control. As expected, progesterone blocked the induction of LH peaks by estradiol benzoate injection (40 μg/kg). Neither Z nor DES affected the LH peak or the depression.

ISSN:0098-4108    

DOI:10.1080/15287397709529548

出版商:Taylor & Francis Group    

年代:1977

数据来源: Taylor

ISSN:0098-4108    

DOI:10.1080/15287397709529549

出版商:Taylor & Francis Group    

年代:1977

数据来源: Taylor

摘要:

The long‐accepted dogma of feedback control of luteinizing hormone (LH) and follicle‐stimulating hormone (FSH) secretion by gonadal steroids is reconsidered in this article in light of recent investigations in the rat, using radioimmunoassay measurements of both the steroids and the gonadotropins.

ISSN:0098-4108    

DOI:10.1080/15287397709529550

出版商:Taylor & Francis Group    

年代:1977

数据来源: Taylor

摘要:

The concept that certain sexual differences in brain function are established by exposure of the brain to a particular hormonal environment during early perinatal development of the intrinsically female, or at least undifferentiated, brain is reviewed. Since sexual differentiation of the brain is a normal function of the neonatal testis, it had been (1) assumed that the ovary is hormonally quiescent perinatally and (2) argued that the effectiveness of exogenous estrogen in masculinizing the brain is a pharmacological oddity. However, recent studies from several laboratories indicate that endogenous estrogen levels in perinatal plasma are very high. Since a peculiar estrogen‐binding protein is present in the neonatal rat, it may be that the high plasma titers of estrogen, whatever their source, are sequestered by this protein and prevented from exerting a masculinizing action. The importance of this putative protective mechanism is emphasized by the currently popular view that estrogen is the effective molecular form of the masculinizing hormone.

ISSN:0098-4108    

DOI:10.1080/15287397709529551

出版商:Taylor & Francis Group    

年代:1977

数据来源: Taylor

摘要:

The information currently available concerning the endocrine aspects of the human menstrual cycle from puberty to menopause is briefly summarized. Features of abnormal menstrual cycles are defined and the endocrine features of the menopausal state summarized. Cautions are expressed regarding the physiologic nature of current and contemplated replacement therapy.

ISSN:0098-4108    

DOI:10.1080/15287397709529552

出版商:Taylor & Francis Group    

年代:1977

数据来源: Taylor

ISSN:0098-4108    

DOI:10.1080/15287397709529553

出版商:Taylor & Francis Group    

年代:1977

数据来源: Taylor