Scallops possess a visual system comprising up to 200 eyes, each containing a concave mirror rather than a lens to focus light. The hierarchical organization of the multilayered mirror is controlled for image formation, from the component guanine crystals at the nanoscale to the complex three-dimensional morphology at the millimeter level. The layered structure of the mirror is tuned to reflect the wavelengths of light penetrating the scallop's habitat and is tiled with a mosaic of square guanine crystals, which reduces optical aberrations. The mirror forms images on a double-layered retina used for separately imaging the peripheral and central fields of view. The tiled, off-axis mirror of the scallop eye bears a striking resemblance to the segmented mirrors of reflecting telescopes.

Steroidal hormones produced by humans and animals are constantly excreted into the environment in their active forms. The primary steroid hormones are progesterone, estrone, estradiol, testosterone, and cortisol, all of which are lipophilic and poorly soluble in water. The steroids of major concern are estrone and estradiol-17β, since they exert their physiological effects at a lower concentration than other steroids and can be found in the environment in concentrations above their LOEL for fish and plants (10 ng/l). The steroid hormones can be readily measured in run-off, soil, and groundwater, but each steroid has its distinct pathway of transport. Since the major source of steroids in the environment appears to be cattle and chickens, the hormonal steroid input into the environment could be drastically reduced by well-established techniques such as buffer strips and composting.

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The pituitary gonadotrophins, LH and FSH, in addition to hCG, belong to the family of glycoprotein hormones consisting of two dissimilar noncovalently bound α and β subunits (Pierce and Parsons, 1981). The β subunits of hCG and LH are different from those of FSH. The β subunits of LH and hCG are similar except for an additional 30 amino acids at the carboxy terminus of the β subunit of hCG. These additional amino acids are responsible for the longer half-life of hCG in the circulation compared with that of LH.The receptors (R) for both LH and FSH belong to a common gene family, the G-protein-associated seven-transmembrane domain receptors (Catt and Dufau, 1991). There is no specific receptor for hCG, which binds to the same receptor (LH-R) as pituitary LH, with a somewhat higher affinity (Huhtaniemi and Catt, 1981).The main physiological functions of the gonadotrophins are well known. LH stimulates production of androgens by theca cells in the ovary, providing a substrate for oestrogen production by granulosa cells, which triggers ovulation and provides luteotrophic activity to maintain the production of progesterone by the corpus luteum. hCG is also a luteotrophic hormone that maintains corpus luteal function until about week 9 of pregnancy, at which time the primary site of progesterone synthesis shifts to the placenta (Csapo et al., 1972). FSH stimulates follicular maturation and oestrogen production by granulosa cells in the ovary. It has became apparent over the last decade that FSH and LH, as well as GnRH, affect organs other than their 'traditional' target sites. Receptors for the gonadotrophins have been found throughout the reproductive tract: in the oviduct, myometrium, endometrium, cervix and the uterine vessels. Receptors for GnRH have been found in the endometrium and trophoblast. Various paradigms have been proposed for the function of these receptors as their expression is dynamic and changes during the oestrous cycle.The object of the present article is to review the current knowledge of extragonadal gonadotrophin receptors in the reproductive tract and to suggest the physiological functions of these receptors. It will focus on the bovine and porcine reproductive tracts, as these have been the most extensively studied, and compare data with relevant published studies in other species. Extragonadal receptors in the reproductive tract EndometriumExpression and activity of LH receptor and GnRH receptor. In the human endometrium, LH-R and GnRH-R are expressed in both epithelial and stromal cells and both receptors are expressed maximally during the luteal phase (Reshef et al., 1990; Raga et al., 1998). Comparison of immunostaining intensities revealed that human luminal and glandular epithelial cells contain more receptors than stromal, myometrial or vascular smooth muscle cells. Binding sites for LH/hCG are found in the uterus of several species, including humans. In cattle and pigs, the LH receptor, its mRNA and LH receptor protein are present in the uterus throughout the oestrous cycle, and maxim...

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Tumor necrosis factor (TNF-a), a I7 kDa cytokine, is a product of activated macrophages which was recently shown to be produced by rat and bovine Igranulosa cells. In the present work, human granulosa cells derived from preovulatory follicles were used, It was demonstrated that human granulosa cells produce. TNF-u (510 units/300000 cells per 15 h). This production was increased by addition of follicle-stimulating hormone or by a combination of human chorionic gonadotrophin and CSF to the culture media. TNF was also found in bovine follicular fluid and the concentration was higher in the periovulatory than mid-cycle follicles. TNF-a was found to increase prostaglandin F-2a production by human granulosa cells (P< 0.001). We conclude that granulosa cells are both a source and target organ for TNF-a.

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