Membrane phenomenons in relation to vitamin A

The schistosome in the mammalian host: understanding the mechanisms of adaptation

In this review, we envisage the host environment, not as a hostile one, since the schistosome thrives there, but as one in which the relationship between the two organisms consists of constant communication, through signalling mechanisms involving sense organs, surface glycocalyx, surface membrane and internal organs of the parasite, with host fluids and cells. The surface and secretions of the schistosome egg have very different properties from those of other parasite stages, but adapted for the dispersal of the eggs and for the preservation of host liver function. We draw from studies of mammalian cells and other organisms to indicate how further work might be carried out on the signalling function of the surface glycocalyx, the raft structure of the surface and existence of pores in the surface membrane, the repair of the surface membrane, the role of the membrane structure in ion channel function (including recent work on the actin cytoskeleton and calcium channels) and the possible role of P-glycoproteins in the adaptation of the parasite to its environment. We are speculative in some areas, such as the suggestions that variability in surface properties of schistosomes may relate to the existence of membrane rafts and that parasite communities may exhibit quorum sensing. This speculative approach is adopted with the hope that future work on the whole organisms and their interactions will be encouraged.

High serum retinyl esters are not associated with reduced bone mineral density in the Third National Health And Nutrition Examination Survey, 1988-1994

Hypervitaminosis A is sometimes associated with abnormalities of calcium metabolism and bone mineral status. A recent study found a negative association between reported dietary vitamin A intake and bone mineral density (BMD). Some segments of the U.S. population have high fasting serum retinyl ester concentrations, a physiological marker that may reflect high and possibly excessive vitamin A intake. We examined the association between fasting serum retinyl esters and BMD in the Third National Health and Nutrition Examination Survey, 1988-1994 (NHANES III), a large, nationally representative sample of the U.S. population. BMD was measured for the femoral neck, trochanter, intertrochanter, and total hip on all nonpregnant participants aged > or = 20 years; 5,790 participants also had complete data on fasting serum retinyl esters and covariates including age, body mass index (BMI), smoking, alcohol consumption, dietary supplement use, diabetes, physical activity, and, among women, parity, menopausal status, and the use of oral contraceptives or estrogen-replacement therapy. The sample included non-Hispanic white, non-Hispanic black, and Mexican American men and women. We examined the association between fasting serum retinyl esters and BMD at each site, controlling for covariates with multiple linear regression. We examined the association with osteopenia and osteoporosis with multiple logistic regression. Although the prevalences of high fasting serum retinyl esters concentration and low BMD were both substantial in this sample, there were no significant associations between fasting serum retinyl esters and any measure of bone mineral status.

Experimental craniofacial malformations induced by retinoids and resembling branchial arch syndromes

A syndrome which showed similarities to human branchial arch syndromes could be induced in Sprague-Dawley rat embryos by exposing them to retinoids prenatally. Treatment of pregnant rats with 40 mg/kg retinoic acid or 10 mg/kg etretinate on pregnancy day 8.5-9 resulted in craniofacial defects in 100% of the embryos. A scanning electron microscopic investigation of the early stages in the development of these malformations showed abnormal skull form, disorganised surface epithelium with "cell blebbing", lateral facial clefts, facial fistulas, narrowed skull-base and reduced size of the nasal and maxillary complexes. Histological examination confirmed these findings and supported the hypothesis that a main reason for this syndrome is hindrance of migration of the cranial neural crest cells to the facial processes during early craniofacial formation.

Changes in sodium and potassium excretion and urinary volume in rats submitted to hypervitaminosis A

Hypervitaminosis A induces the following changes in rat kidney: decrease in sodium and potassium excretion and an increase of urinary volume. In order to determine the possible reversibility of these alterations, the authors allowed the hypervitaminotic animal to recover for 30 and 60 days. After a 30-day recovery period for urinary volume, a 20-day recovery period for sodium excretion, and a 10-day recovery period for potassium excretion, the alterations were reverted to normal.

Clinical manifestations of hypervitaminosis A in human gingiva. A case report

Periodontal inflammation caused by excessive doses of vitamin A was studied in a patient who had taken 200,000 international units daily for more than 6 months. Clinical manifestations of the disease disappeared when the use of vitamin A was interrupted. The role of vitamin A as a factor in periodontal inflammation is discussed.