Epidermis mitotic activity

Mechanism of Action An antifungal that reduces scaling of the epidermis by slowing down mitotic activity Therapeutic Effect Reduces the excess scaling in patients with dandruff or seborrheic dermatitis. 

The process of keratinization is continuous in the surface epidermis, while in the hair follicle the matrix cells undergo periods of quiescence during which no mitotic activity occurs. This cyclic activity of the hair bulb allows for the seasonal change in the hair coat of domestic animals. The length of time to regrow new hairs depends... 

Phorbol esters were first detected in oil prepared from seeds of Croton tiglium, and are the most widely studied skin tumor promoters however, many other chemical compounds have been shown to possess skin tumor-promoting properties, for example, phenobarbitol, DDT, and the peroxisomal prolifera-tors. Within a few hours after application of a single effective dose of phorbol 12-myristate 13-acetate (also known as TPA and 12-O-tetradecanoyTphor-boTl3-acetate, CAS 16561-29-8) to mouse skin, localized edema and erythema characteristic of inflammation and irritation are evident, and within 24 h there is leukocytic infiltration of the dermis. Within 1 or 2 days after a single promoter treatment, stimulation of mitotic activity in the basal cell layer of the epidermis is evident and continues for several days. This results in an increased number of... 

Psoriatic epidermis with its great mitotic activity and increased thickness bears several resemblances to epidermis at the edges of a wound. 

Using the same technique in sensitized guinea pigs (see p. 11), we also observe an increase of mitotic activity in the epidermis of the nipple 33 hours after the test, but this mitotic increase is still apparent 129 hours after the test (W. Jadassohn, Bujard and Brun, 1955) (Fig. 14). 

Experiments have therefore been performed to test the action of this hormone on the mitotic activity of mouse epidermis in vitro (Bullough, 1954a,b), and typical results are summarized in Table II. With glucose as substrate the growth hormone acts as a mitotic inhibitor, although it is evident that relatively massive doses are required to produce any great effect—a point that will be discussed later. With fructose as substrate... 

The fact that the pituitary growth hormone prevents the development of a mitotic activity, at least in adult epidermis, is so surprising as to need further consideration. In recent years research on this hormone has been active, and the realization that it does in fact act as an inhibitor, particu-... 

In his review of the relations between the adrenal cortical hormones and carbohydrate metabolism, Verzdr (1952) lemarked that the present situation may be described briefly as follows the action of the adrenal cortex is related to the central process of energy production of the cell, which is the degradation or transformation of glucose. This being the case it could be expected that these hormones would also prove to have an influence on mitotic activity, at least in tissues of the type of adult mouse epidermis in which the rate of energy production is low. 

Apart from the light which this sheds on the relation of the hormone complex to growth by mitosis, confirmation is given for the theory that the process of energy production is a highly important, if not critical, factor in the mitotic activity of tissues such as epidermis. 

The results of experiments to test the actions of these three substances on the mitotic activity of mouse ear epidermis in vitro are shown in Table X (Bullough, unpublished). 

Human skin has a multifunctional role, primary among which is its role as a barrier against both the egress of endogenous substances such as water and the ingress of xenobiotic material (chemicals and drugs). This barrier function of the skin is reflected by its multilayered structure (Fig. 5.1). The top or uppermost layer of the skin known as the stratum comeum (SC) represents the end product of the differentiation process initially started in the basal layer of the epidermis with the formation of keratinocytes by mitotic division. The SC, therefore, is composed of dead cells (comeocytes) interdispersed within a lipid rich matrix. It is the brick and mortar architecture and lipophilic nature of the SC, which primarily accounts for the barrier properties of the skin [1,2]. The SC is also known to exhibit selective permeability and allows only relatively lipophilic compounds to diffuse into the lower layers. As a result of the dead nature of the SC, solute transport across this layer is primarily by passive diffusion [3] in accordance with Pick s Law [4] and no active transport processes have been identified. 

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