ß-1 and ß-2 adrenergic receptor polymorphism and association with cardiovascular response to orthostatic screening.

Variation in the beta-1 and beta-2 adrenergic receptor genes (ADRB1 and ADRB2, respectively) may influence cardiovascular reactivity including orthostatic stress. We tested this hypothesis in a head-up tilt (HUT) screening protocol in healthy young adults without history of syncope. Following brachial arterial catheter insertion, 120 subjects (age 18-40, 72 females, Caucasian) underwent 5min 60° HUT. Polymorphisms tested were: Ser49/Gly and Arg389/Gly in ADRB1; and Arg16/Gly, Gln27/Glu, and Thr164/Ile in ADRB2. Three statistical models (recessive, dominant, additive) were evaluated using general linear models with analysis for each physiologic variable. A recessive model demonstrated a significant association between Arg16/Gly and: absolute supine and upright HR; HUT-induced change in cardiac index (CI), stroke index (SI) and systemic vascular resistance (SVR); and supine and upright norepinephrine values. Blood pressure was not influenced by genotype. Fewer associations were present for other polymorphisms: Ser49/Gly and the change in SI (dominant model), and Arg389/Gly and supine and HUT norepinephrine (additive model). We conclude that in this population, there is a robust association between Arg16/Gly and HUT responses, such that 2 copies of Arg16 increase supine and upright HR, and greater HUT-induced decreases in CI and SI, with greater increases in SVR and norepinephrine. ADRB1 gene variation appears to impact SI and plasma NE levels but not HR. Whether ADRB2 gene variation is ultimately disease-causing or disease-modifying, this study suggests an association between Arg16/Gly and postural hemodynamics, with sympathetic noradrenergic activity affected in a similar direction. This may have implications in the development of orthostatic disorders.

In vitro hydration kinetics of recent post-mortem tissue versus pre-dried corneal stromal tissue.

Both recent post-mortem and pre-dried corneal tissue has been used for laboratory studies of stromal swelling, but it has yet to be defined whether the same hydration (H value, mg H2O/mg dry mass) is obtained after extended re-hydration. Fresh or pre-dried pieces (8x8 mm squares) of ovine stromas were immersed in 1% NaCl for 24 hr at 37 degrees C, with the wet mass assessed regularly. Pre-drying was achieved in air for 7 days (with sulphuric acid, CaSO4 or silica gel as desiccants), or in an oven for 24 hr at 60, 70 or 80 degrees C. Fresh stroma preparations (

Influence of tissue sample dimensions on the swelling of the corneal stroma.

The kinetics of imbibition of unbuffered 1% NaCl at 37 degrees C by whole ovine corneal stroma preparations were compared to those for square samples of stromas with side dimensions of 4, 6, 8, 10 and 13 mm. The rates and extent of swelling over a 24-hour period were proportionately greater for samples with smaller dimensions. After 24 h, the relative magnitude of the changes in wet mass ranged from 465% for complete stromas to 1,185% for 4 x 4-mm tissue squares. This size-dependent difference in swelling may, in part, account for differences between previous studies.

Hydration (water binding) of the mammalian corneal stroma ex vivo and vitro: sample mass and error considerations.

The corneal stroma is well-known for its capacity to absorb water from experimental solutions but there are considerable differences in how this is actually assessed and described. Measurements on rabbit, sheep, and cow samples ex vivo are presented along with examples of the progressive changes in the stroma in vitro in saline solutions. These are used as the basis for theoretically assessing the impact of systematic and unintentional errors (related to excesses of water or water vapor on the samples) on the estimates of water content, as are the effects of unintentional loss of water from wet samples. Substantial differences in data can easily arise from such errors and/or differences in sample mass. Standardization of the methods for stromal hydration and swelling is required. As a minimum, sample origin (including species), sample dimensions and mass, and the resolution of the weighing protocols are needed, along with details of dry and wet sample handling. With the likelihood of modest errors for the commonly used samples and procedures, reporting hydration data to more than one decimal place is not justified.