Stressor-response functions as a generalizable model for context dependence

Defining the context dependence of ecological states or processes is a fundamental goal of ecology. Stressor-response functions are the quantitative representation of context dependence, where the context (environmental contingency) is defined by location on the stressor (x) axis, and represents a unifying concept in biological science.

The reproductive outcome following a superhigh response to stimulation in gamete intrafallopian transfer program

A retrospective analysis was carried out to assess the outcome of gamete intrafallopian transfer (GIFT) in cycles when more than 10 oocytes were retrieved (superhigh responders) from October 1987 through June 1989. There were 276 (13%) cycles with more than 10 oocytes retrieved among all GIFT cycles initiated during the period. Clomiphene citrate and gonadotropin were employed for ovarian stimulation in 105 (38%) cycles, and gonadotropin releasing hormone agonist in the remaining 171 (62%) cycles, employing either the flare (104 cycles) or the pituitary down-regulation (67 cycles) protocol. A maximum number of four oocytes was transferred per GIFT (3.5 +/- 0.4). The mean number of oocytes retrieved was 14.7 +/- 4.4 (range, 11 to 35). A significantly younger age group (less than 30 years) of patients was noticed in the study (31.9), and fewer women aged 40 and over (6.2%), compared to the general population of our patients. The pregnancy rate was 33.3% (n = 92) per cycle, with a delivery rate of 23.6% (n = 64) per cycle; the pregnancy loss rate was 30.8%. The reproductive outcome was lower in women aged 40 and over (pregnancy rate was 23.5%, but delivery rate was only 5.8% per cycle). The delivery rate was lower in the clomiphene citrate- and gonadotropin-stimulated cycles (51.7% per pregnancy) in relation to gonadotropin-releasing analogue and gonadotropin cycles (76.6% per pregnancy) and significantly so compared with the pituitary down-regulation protocol (83.3% per pregnancy). We conclude that a superhigh response develops more in younger women, and in such circumstances, the use of pituitary down-regulation with gonadotropin-releasing hormone will improve the reproductive outcome.

The formation of autofluorescent granules in cultured human RPE

Although the incomplete degradation of phagocytosed outer segment discs is thought to result in the formation of lipofuscin, there has to date been no proof of this concept. We report for the first time that cultured human retinal pigment epithelial (RPE) cells fed daily doses of isolated rod outer segments for periods of up to 3 months were capable of developing intracellular autofluorescent granules whose morphology and fluorescence characteristics were similar to lipofuscin. These autofluorescent granules were observed as early as 2 weeks following daily challenge with rod outer segments and the number of granules increased with the number of challenge doses until the experiment was terminated after 3 months of daily feeding. We also studied the effects of the antioxidant vitamin E and a drug, Centrophenoxine, which has been purported to slow the formation of lipofuscin formation in vivo. Neither of these additives given either with the challenge or subsequently had any effect on the formation of the intracellular granules. In conclusion, the development of these "lipofuscin-like" inclusions in cultured RPE may provide a model with which to study ageing processes and may provide an understanding of the increased lipofuscin accumulation observed in certain retinal pathologies.

Retinal pigment epithelial cells in culture produce retinal vascular mitogens

Conditioned medium from human retinal pigment epithelial cells in culture significantly stimulated the proliferation of subcultured bovine retinal capillary endothelial cells, pericytes, and freshly isolated retinal microvessels. The vascular mitogenic activity enhanced that of retinal crude extract. No evidence emerged of an inhibitor of microvascular cellular proliferation produced by retinal pigment epithelial cells.

Retinal pigment epithelial cells produce mitogenic factors for retinal microvascular cells in culture: a preliminary report

Conditioned media from human retinal pigment epithelial cells have been shown to have mitogenic activity for retinal microvascular cells in vitro. The conditioned media stimulated the proliferation of both bovine retinal capillary endothelial cells and pericytes.