Changes in Electrophysiological Properties of Rat Skin with Age.

Abstract

Skin age is one of the biological factors affecting percutaneous absorption. 1,2) To regulate the therapeutic efficacy of transdermal drug delivery, the difference in skin permeability at various ages is a subject of considerable importance. We previously reported that the permeability through the skin decreases with aging, 3,4) and that the extent of this decrease is higher for lipophilic permeants than for hydrophilic permeants. 4) We clarified that the thickness of skin strata is an important factor for limited percutaneous absorption in aging. However, other physiological changes in the skin with age, e.g., moisture content in the skin, lipid composition, lipid content, dermis thickness, and density of skin appendages, have been also reported. [5][6][7][8] Therefore the age-related differences in the skin barrier function must be further investigated based on physiological alterations in the skin to elucidate the mechanisms of the age dependency of transdermal absorption of drugs.There have been many reports on age-related changes in the transdermal permeation of drugs, 3,4,[6][7][8][9] however, age-related changes in skin permeability have not been fully interpreted because of large interindividual variance and the limited number of model permeants. Recently, it was reported that impedance parameters can sensitively reflect the properties of skin permeation pathways. [10][11][12] The impedance technique enables us to determine rapidly changes in skin physical properties, and one measurement provides information on pathways for both hydrophilic and lipophilic permeants. Therefore skin impedance analysis may be a useful method to elucidate the skin barrier function at different ages.In the present study, we attempted to apply impedance analysis to investigate age-dependent changes in permeation pathways of rat skin. In vitro skin impedance data of rats at various ages were compared. Physiological characteristics of the skin, e.g., the water and lipid content of the stratum corneum and the thickness of the skin strata, were also evaluated. Finally, we demonstrated the age dependency of relations between these electrical and physiological properties. MATERIALS AND METHODS AnimalsMale STD: Wistar rats at the age of 5, 10, 21, 90, and 180 d (Japan SLC Inc., Hamamatsu, Japan) were used. Rats were fed commercial food pellets and tap water ad libitum. Under sodium pentobarbital anesthesia (50 mg/kg, i.p.), a round section of the abdominal skin was excised, and then the subcutaneous fat and other extraneous tissue were trimmed off carefully. The skin sample was immediately used in the following skin impedance experiments.Skin Impedance Measurement and Analysis A sideby-side, two-chamber electrochemical cell with four electrodes, two for supplying current and two for recording signals, was designed according to the procedure of Burnett and Bagniefski.11) The rat skin was mounted in an O-ring seal between the two chambers, each having 23 ml volume and 1 cm 2 exposed area. The current-supplying electrode consisted of 0....

Temporal and spatial temperature distribution in the glabrous skin of rats induced by short-pulse CO2 laser

“…20 The dermis was 800 μm thick. 19 The thermal conductivity of stratum corneum and the viable epidermis was 0.1 W∕ðm × KÞ (Refs. 24 and 25) (K is the absolute temperature).…”

“…18 This study assumed that 43°C at viable epidermis (40 to 90 μm 19,20 in depth) would activate a number of CMHs and AMHs. We calculated the onset latency, supra-threshold period, and maximal radius of 43°C at epidermis of 40 μm in depth.…”

Age Difference in Simultaneous Permeation and Metabolism of Ethyl Nicotinate in Rat Skin.

“…However, there are structural differences in the skin among ages, at least the lower epidermal thickness in young rats was observed. 25) In the younger rats, EN concentration in the skin could be expected to be higher than that of older rats after applying the same concentration of EN in the donor side. This speculation is supported by our finding of higher total flux from EN-saturated solution for younger rats (Table 1).…”

1064 nm-Nd:YAG lasers with different output modes enhancing transdermal delivery: physical and physiological mechanisms

“…The average thickness of the SC for rat skin was about 20 to 25 μm. 23 Animals were intraperitoneally anesthetized (1 ml∕100 g bodyweight) with a mixture of chloral hydrate (0.02 g∕ml) and ethylurethanm (0.1 g∕ml). Then the dorsal hair was depilated.…”