Regulation Of Mammalian Reproduction Research Articles

Immunocytochemical localization of μ-opioid receptors in follicular cells and preimplantation mouse embryos

It has been demonstrated that opioid peptides are involved in the regulation of mammalian reproduction. In our previous studies we demonstrated direct effects of opioids on preimplantation mouse embryos, and hypothesized the existence in preimplantation embryos of receptors similar to opioid receptors in the central neuronal system of adult animals. In the present study we addressed this issue by employing immunocytochemical staining for mu-opioid receptors using antisera raised against the C-terminal portion of the cloned mu-opioid receptors (MOR1, NHQLENLEAETAPLP, 384-398) predicted from the cloned receptor. Diffuse MOR1 immunoreactivity of moderate intensity has been revealed in one-cell embryos, while in follicular cells MOR1 staining was of high intensity and appeared to be associated with plasma membrane. No MOR1 immunoreactivity has been observed in two-cell to morula stages of development. However, blastocysts displayed intense MOR1-labeling that was particularly prominent in cells within the inner cell mass. MOR1-staining was most likely specific because preincubation of MOR1 antisera with cognate peptide completely abolished the staining. Our findings suggest the presence of opioid receptors during preimplantation development, long before the formation of the nervous system. Embryonic opioid receptors may play a role in the regulation of preimplantation development and implantation.

Mammalian reproduction: an ecological perspective.

The objectives of this paper are to organize our concepts about the environmental regulation of reproduction in mammals and to delineate important gaps in our knowledge of this subject. The environmental factors of major importance for mammalian reproduction are food availability, ambient temperature, rainfall, the day/night cycle and a variety of social cues. The synthesis offered here uses as its core the bioenergetic control of reproduction. Thus, for example, annual patterns of breeding are viewed as reflecting primarily the caloric costs of the female's reproductive effort as they relate to the energetic costs and gains associated with her foraging effort. Body size of the female is an important consideration since it is correlated with both potential fat reserves and life span. Variation in nutrient availability may or may not be an important consideration. The evolutionary forces that have shaped the breeding success of males usually are fundamentally different from those acting on females and, by implication, the environmental controls governing reproduction probably also often differ either qualitatively or quantitatively in the two sexes. Mammals often live in habitats where energetic and nutrient challenges vary seasonally, even in the tropics. When seasonal breeding is required, a mammal may use a predictor such as photoperiod or a secondary plant compound to prepare metabolically for reproduction. A reasonable argument can be made, however, that opportunistic breeding, unenforced by a predictor, may be the most prevalent strategy extant among today's mammals. Social cues can have potent modulating actions. They can act either via discrete neural and endocrine pathways to alter specific processes such as ovulation, or they can induce nonspecific emotional states that secondarily affect reproduction. Many major gaps remain in our knowledge about the environmental regulation of mammalian reproduction. For one, we have a paucity of information about the annual patterns of breeding and about the mechanisms controlling these patterns in the most common mammals on the planet-the small to average-sized mammals living in the tropics. We probably have only a shallow conceptualization of the way available energy and nutrients control reproduction and, likewise, we may have only a narrow view of the potential kinds and uses of seasonal predictors. Finally, we have little appreciation of the way environmental cues interact with each other to control reproduction.

The role of rhythms in the response to melatonin.

Rhythmicity of melatonin secretion is critical to the regulation of mammalian reproduction by daylength. In the ewe, photoperiod determines ovarian function by modulating the ability of oestradiol to suppress pituitary secretion of luteinizing hormone (LH). This influence of daylength depends in turn upon the pineal gland, which mediates photic control of the frequency at which the brain stimulates the pituitary to secrete gonadotropin. Photoperiod determines the pattern of melatonin secretion, most notably setting the duration of the nightly elevation in serum concentrations. Replacement of melatonin in pinealectomized ewes drives responsiveness to oestradiol negative feedback; LH levels are determined by the duration of the nightly melatonin infusion rather than by the photoperiod to which ovariectomized, oestradiol-implanted pinealectomized ewes are exposed. Refractoriness to stimulatory and inhibitory photoperiods may reflect circannual modulation of the responsiveness of neuroendocrine mechanisms to melatonin signals of a given duration.

The Regulation of Mammalian Reproduction.

The Regulation of Mammalian Reproduction.

Regulation of Mammalian Reproduction

130 scientists met in a conference sponsored by the National Institutes of Health to review current research on the regulation of mammalian reproduction. Major topics were 1) how the pituitary function could be regulated 2) how sperm production might be regulated; 3) the process and possible points of intervention in sperm maturation and fertilization; 4) the biology of the ovum; 5) the mechanism of action by which gametes are transported in the Fallopian tubes; and 6) the effect of corpus luteum function. Among findings which appear promising are (1) data which suggests the administration of estrogens might induce ovulation at a time when the endometrium is not prepared for implantation; 2) sperm maturation in the epididymis seems to require a certain hormonal ambience which if changed could have a reversible anti-fertility effect; 3) the fallopian tubes may also require a certain hormonal environment for normal reproductive function and may be an end ocrine target for disrupting the reproductive function; 4) data from some species indicates there is a uterine luteolytic factor which could be developed for use in human fertility control.(AUTHORS MODIFIED)

Steroid biosynthetic enzymes and the regulation of mammalian reproduction

Steroid biosynthetic enzymes and the regulation of mammalian reproduction