Catecholamines in the hair cycle of rats

Human pigmentation: A side effect adapted from a primitive organism's survival, acting through cell attachment with an affinity for the keratinocyte and for elastin: Part I

Pigmentation featured millions of years ago and perhaps began with an amoeba frightening off a predator with some agent such as dopamine to prevent its attachment for phagocytosis by an enemy. This paper suggests that the environmental forces of grip and stick deserve greater emphasis and that mechanical forces involved in grip and stick or release from attachment, all point to control of proteases underlying pigmentation. There is an affinity for elastin as a pathway for melanin to exit its peripheral location in the epidermis into lymphatics and play a humeral role in defense mechanisms. The hair follicle follows the epidermal-dermal pattern of behavior with an affinity for elastin, a controlling function of melanin and through the bulge, an influence of mechanical forces and control by protease inhibitors.

Bilateral adrenalectomy induces early onset of summer fur growth in mink (Mustela vison)

The purpose of this study was to determine the effects of bilateral adrenalectomy on the time at which growth of the summer pelage begins in mink. Bilateral adrenalectomy of adult female mink between 2 and 11 March 1991, supplemented with deoxycorticosterone (DOC) as a mineralocorticoid, resulted in the onset of the summer fur growth approximately 5 weeks earlier than the controls (P < 0.01). Mink with their adrenal glands intact and treated with DOC, exhibited summer fur growth 2 weeks earlier than the controls (P < 0.01). The duration of time between the first observed hair growth and attainment of maximal guard hair length, was approximately 10 days longer in mink with their adrenal glands intact and supplemented with DOC than the controls (P < 0.05). Adrenalectomized mink treated with DOC exhibited guard hair growth for approximately 13 days longer than controls (P < 0.05). Although exogenous DOC initiated hair growth, the rate of growth appeared to be reduced. These data suggest that adrenal hormones, of undetermined identity, exert a tonic inhibitory effect on the initiation of summer fur growth in mink and may be part of the mechanism through which changes in photoperiod regulate the onset of hair growth cycles.

Adenyl-cyclase activity in rat-hair-cycle

In the skin of rat, during telogen phase, a high adenyl-cyclase activity coincides with maximal catecholamines content, minimal histamine level and blocking of mitoses in epithelial cells. These events suggest that in telogen the control of mitotic activity in rat hair follicles may operate through a block of G1 cells as already suggested for epidermal cells.

Endothelial DNA synthesis in themicrovasculature of rat skin during the hair growth cycle

Earlier studies of the vascular patterns around hair follicles revealed that actively growing follicles have an extensive microvasculature relative to that around quiescent follicles. In order to determine whether the establishment of the active perifollicular vascular pattern involves replication of endothelial and perivascular cells, we studied the 3H-thymidine labeling indices of these cells in autoradiographs of rat skin from regions containing either actively growing follicles or recently inactive follicles. In skin containing inactive follicles, the endothelial labeling index was 0.22%, a figure similar to those reported for the endothelium of small blood vessels in several other non-stimulated adult tissues. However, skin containing actively growing follicles displayed an endothelial labeling index of 2.35%. The labeling indices of perivascular cells paralleled those of the endothelial cells. Thus, endothelial and perivascular cells in vessels associated with actively growing follicles undergo significantly more DNA synthesis than those in vessels associated with inactive follicles. Replication of these cells apparently contributes to the extension of the microvascular network around growing follicles.

The blood vessels of the skin

During the last 25 years, cutaneous biologists have been particularly interested in abnormal cutaneous vascular patterns, the profusion of capillary anastomoses, the leakiness of venules, clotting, fibrinolysis, and blood viscosity. As a result, the effects of hypoxia and the factors that encourage new vessel proliferation are better understood than before. Only when the biologic behavior of the two extremes of growth from hypoplasia to hyperplasia is studied and compared can the blood supply of a tissue be understood. Hyperplastic tissues are seen in wounds, psoriasis, cancer, and in selected sites of chronic stasis and hypoxia where the vessels are extremely permeable, where blood cells easily escape, and where lymphatics dilate and proliferate. The proliferation of other tissues, such as endothelium, epithelium, mast cells, and probably of locally infective organisms, is also encouraged in hyperplasia. Moreover, fibrinolysis does not occur and fibrin is deposited, the electrostatic charge on the internal vascular surface becomes more positive, and the organ is more vulnerable to subsequent injury. Atrophic or hypoplastic tissues have a reduced cellular turnover and are less hypoxic. The vessels are less permeable, blood cells do not escape, there is only a slight tendency to clot, and fibrinolysis is often increased. Lymphatics are sparse and infection is not a feature. The electrostatic charge on the internal surface of the vessel is negative.