摘要:

AbstractChanges in the structure and function of five neuropeptide families during evolution are considered. The families of gonadotropin‐releasing hormone (GnRH), corticotropin‐releasing factor (CRF), growth hormone‐releasing hormone (GH‐RH), somatostatin (SS), and vaso‐pressin/oxytocin (VP/Oxy) are used as models to illustrate the importance of a phylogenetic approach in understanding neuropeptide structure/activity relationships, precursors, processing, gene duplication, novel locations and functions, and gene‐associat

ISSN:0022-104X    

DOI:10.1002/jez.1402560412

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

年代:1990

数据来源: WILEY

摘要:

AbstractThe pigeon crop‐sac is an underappreciated and underutilized model that can be used to study the direct and indirect effects of hormones, growth factors, and other agents on cell proliferation and differentiative processes in vivo. It can thus allow the uncertainties that attend many in vitro methods to be avoided. In addition, the crop mucosal cells are homogeneous and the organ is structurally much less complex than most other hormone‐responsive target organs, such as the mammary gland or prostate. The organ is well suited for various other studies such as analysis of second‐messenger systems for PRL and growth factors and the effects of growth‐inhibitory sub

ISSN:0022-104X    

DOI:10.1002/jez.1402560413

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

年代:1990

数据来源: WILEY

摘要:

AbstractIn this report, we describe the use ofXenopus laevisoocytes injected with mRNA derived from cloned rat pituitary tumor (GH3) cells as a model system in which to study the mechanism of action of thyrotropin‐releasing hormone (TRH) and the regulation of the TRH recepto

ISSN:0022-104X    

DOI:10.1002/jez.1402560414

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

年代:1990

数据来源: WILEY

摘要:

AbstractThe teleostean adenohypophysis has direct innervation by neurosecretory fibers; in effect, the median eminence is located in the adenohypophysis, and neurohormones are released directly in the proximity of the endocrine cells. Immunocytochemical studies demonstrate that neurohormonal fibers and terminals are specifically localized in the pituitary in association with the target endocrine cells. Because of this special anatomical arrangement, teleosts are a unique experimental model for determining the origin(s) in the brain of peptides and monoamines involved in regulation of the endocrine cells of the pituitary. To illustrate, the terminals of a specific group of dopaminergic neurons in the preoptic region of goldfish have been shown to be associated with gonadotropes, and likely serve as the source of dopamine for inhibiting gonadotrope activity. Functional studies on the regulation of activity of the adenohypophysis and release of neurohormones can be integrated. To illustrate, norepinephrine stimulates whereas dopamine inhibits gonadotropin release by acting directly on the gonadotropes. Catecholamines also modulate the release of gonadotropin‐releasing hormone (GnRH); norepinephrine and epinephrine stimulate GnRH neurons centrally, whereas dopamine inhibits GnRH neurons centrally as well as at the level of the terminals in the pituitary. In contrast to the actions on gonadotropes, norepinephrine and epinephrine inhibit whereas dopamine stimulates growth hormone release. The overall role of catecholamines in the regulation of release of the neuropeptides involved in regulating the activity of somatotropes remains to be investigated. As demonstrated by these studies, teleosts are very useful models for neuroendocrine studie

ISSN:0022-104X    

DOI:10.1002/jez.1402560415

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

年代:1990

数据来源: WILEY

摘要:

AbstractThe hormonal control of ontogeny in fish and amphibians is reviewed. Neuroendocrine regulation and actions of metabolic and osmoregulatory hormones (thyroid, interrenal, pituitary, pancreas, and gut) during amphibian and fish metamorphosis and the parr‐smolt transformation of juvenile salmon are considered. The developmental significance of hormones in egg yolk is discussed. It is concluded that the transitions between life‐history stages provide many unique opportunities for studying basic endocrine phenom

ISSN:0022-104X    

DOI:10.1002/jez.1402560416

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

年代:1990

数据来源: WILEY

摘要:

AbstractThis review will discuss the uses of avian models, particularly the chicken, to examine nutrition‐endocrine interactions. The chicken has been employed extensively to examine nutritional effects. The effects of fasting, protein deficiency and calcium deficiency on endocrine status have been the subject of intense investigation in young chicks and adult female chickens. The ratio of circulating concentrations of triiodothyronine (T3) and thyroxine (T4) is substantially changed by fasting or protein deficiency. Similarly, protein deficiency reduces circulating concentrations of insulin‐like growth factor I (IGFI) while protein deficiency increases growth hormone (GH). Moreover, protein deficiency increases the sensitivity and responsiveness of adrenocortical cells. The chicken also has advantages for studying diabetes, endocrine pancreatic functioning due to the splenic lobe of the pancreas being predominantly endocrine in nature, and the cellular mechanism of GH on chicken adipose tissue. The adult female chicken with its high calcium requirement is a unique system for examining nutritional effects on reproduct

ISSN:0022-104X    

DOI:10.1002/jez.1402560417

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

年代:1990

数据来源: WILEY

摘要:

AbstractThe stimulation of yolk protein synthesis by estrogen is a characteristic of female non‐mammalian vertebrates; in mammals, or their reptilian ancestors, however, vitellogenesis has been suppressed as a corollary of the evolution of viviparity. It is our hypothesis that progesterone has a dual role in this phylogenetic trend: a) to inhibit myometrial contraction and thus set the stage for internal development of embryos and associated placentation and b) to inhibit yolk protein synthesis in a coordinate manner as placentation became an efficient direct supply of nutrients to the fetus. Despite the absence of vitellogenesis per se in eutherian mammals, significant sex‐differentiated hepatic protein‐lipid synthetic functions remain, which are under complex hormonal control. We have presented evidence that in the reptiles, the central vertebrate group from which the ancestors of modern mammals evolved, the control of yolk protein synthesis is also complex, involving both pituitary hormones (GH, PRL, and LH) and ovarian steroids (estradiol, testosterone, and progesterone). Adequate evidence exists to suggest that mammalian hepatic lipoprotein synthesis and its regulatory elements are phylogenetically derived from their reptilian ancestors and may be better understood in this context. This is of particular relevance to cardiovascular disease in which there is a clear sex bias yet for which no coordinated research program exists which takes into account the relevant phylogenetic history. We believe that reptilian, and possibly avian, models could be used to great advantage to probe the endocrine components of cardiovascular di

ISSN:0022-104X    

DOI:10.1002/jez.1402560418

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

年代:1990

数据来源: WILEY

摘要:

AbstractThe presence of an ovarian follicular hierarchy is a characteristic feature of reptiles and birds. The hierarchy contains follicles at all stages of maturation and therefore, varying degrees of sensitivity to the ovulation‐inducing effects of the gonadotropins. In the hen, ovulability is gained as the ability of the follicle to produce androgens and estrogens declines and the ability to produce progesterone increases. In the mature follicle, the granulosa cells are the site of progesterone production whereas the theca cells produce androgens and estrogens. Small follicles that have not yet been (and may never be) recruited into the yolk‐filled hierarchy are the major producers of androgens and estrogens within the ovary. In reptiles the ovarian follicular hierarchy includes non‐vitellogenic follicles and in some species includes follicles destined to become atretic. These two features distinguish the reptiles from the birds and provide experimental biologists with a unique model to investigate the physiological events that regulate the most common fate of ovarian follicles, at

ISSN:0022-104X    

DOI:10.1002/jez.1402560419

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

年代:1990

数据来源: WILEY

摘要:

AbstractThe channel catfish,Ictalurus punctatus, is an economically important species which is readily available, acclimates well to the laboratory setting, and is amenable to considerable experimental manipulation. Although the channel catfish is still a relatively circumscribed species in terms of comprehensive physiologic and/or endocrinologic studies, our current understanding of the basic immunobiology and immunochemistry of the channel catfish is significantly further advanced than for any other teleost species. In this respect the channel catfish is not only proving useful in the general areas of comparative immunology but it is also showing considerable promise as a model system for definitive studies on problems which bridge the fields of immunology and endocrinology, i.e., understanding the effects of environmental temperature and stress on the immune system.

ISSN:0022-104X    

DOI:10.1002/jez.1402560420

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

年代:1990

数据来源: WILEY

摘要:

AbstractThe effects of several mammalian reproductive toxins on reproductive endocrine function in female Atlantic croaker (Micropogonias undulatus) were examined. Croaker were exposed to sublethal concentrations of lead, cadmium, benzo[a]pyrene (BaP), or a polychlorinated biphenyl mixture (Aroclor 1254) for 1 month during the period of ovarian recrudescence. Reproduction was altered after exposure to all four chemicals. The plasma levels and secretion rates of reproductive hormones were augmented after exposure to cadmium resulting in precocious ovarian growth. In contrast, treatment with lead, BaP, or Aroclor 1254 caused a decline in circulating steroid hormone levels and ovarian growth. Changes in hormone secretion rates from isolated pituitary and ovarian tissues incubated in vitro were also observed after exposure to several of the reproductive toxins. It is concluded that the Atlantic croaker is a sensitive model for examining the effects of reproductive toxins on female reproductive endocrine function. Our results indicate that these chemicals may act at various sites on the hypothalamus‐pituitary‐gonadal axis to alter reproductive endocrine funct

ISSN:0022-104X    

DOI:10.1002/jez.1402560421

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

年代:1990

数据来源: WILEY