Fluid transport across retinal pigment epithelium is inhibited by cyclic AMP

Fluid transport across the retinal pigment epithelium (bullfrog) has been measured. These experiments were carried out by using a capacitance probe technique and a water-impermeable chamber that allowed the measurements to be made with an accuracy of 0.5-1.0 nl/min. With identical Ringer's solution on both sides of the epithelium, and in the absence of a hydrostatic driving force, the direction of net fluid movement is from the retina to the choroid (absorption). The net transport rate, approximately 10 nl/min (4.8 microliters/cm2 . hr), is comparable to that observed in other amphibian epithelia. It is reduced to zero by the mitochondrial uncoupler 2,4-dinitrophenol but is relatively unaffected by ouabain, which inhibits the Na+/K+-pump located on the apical membrane of this epithelium. A significant decrease in net fluid absorption was produced by dibutyryl cAMP and 3-isobutyl-1-methylxanthine (a potent phosphodiesterase inhibitor). This cAMP-dependent fluid transport may be an important mechanism for controlling the fluid volume in the subretinal space.

Age-related decrease in repair of oxidative damage to surface sulfhydryl groups on rat adipocytes

Adipocytes were isolated from the Wistar and Sprague-Dawley strains of rats of different ages. An impermeable reagent, mercury-[3H] dextran, was used to quantitate the sulfhydryl groups on the surface of these cells. The application of this reagent after the pre-reduction of cells with 2-mercaptoethanol yielded a measure of the total sulfhydryl and disulfide groups located there. Aging was found to significantly decrease the ratio of the number of exofacial sulfhydryl groups to the total number of exofacial sulfhydryl and disulfide groups.

Patient compliance with a home parenteral nutrition program

A systematic study of patient compliance to home parenteral nutrition (HPN) was done by an independent nurse who visited 10 patients and families at varying periods after HPN had been started. A compliance scale was based on assessment of aseptic technique, sequence of steps followed, safety precautions, proper use of equipment, and knowledge of complications. Compliance percentiles ranged from 73 to 97, with a median of 95. Seven of the 10 patients scored 90% or more in overall compliance. The only category that clearly showed a deficiency was patient knowledge of potential complications of HPN. Factors that correlated positively with a high compliance score were male sex, absence of children in the home, and wives who were enthusiastic about HPN and who offered the most moral support. This study shows that patients with chronic disabling diseases of the small bowel and severe malnutrition can be managed safely at home with HPN if they are properly trained and supervised.