Starting at l!J weeks of age six male rats, castrated at 16 weeks, were injected intramuscularly three times per week with 0.25 mg testosterone propionate !dissolved in sesame oil) per HlO grams body weight. Four castrated control rats received sesame oil only. Samples of dorsal skin were taken under light ether anesthesia at the time of orchidectomy and at weekly intervals during treatment. Histologic sections were cut perpendicular to the skin surface, stained with hematoxylin and eosin, and

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... nalyzed morphometrical!y for their volume content of sebaceous glands. A square grid of 42 sampling points was superimposed on each microscopic field at a magnification of 300x and an average of about 1000 points were counted over the entire thickness of the skin in each section. The average thickness of the skin was also determined for each sample. Three weeks after castration the mm' of sebaceous glands per cm 2 of skin was reduced from 1.76 to 0.96, a difference that is statistically significant at p < O.OOii. One week after starting testosterone injections. the volume of sebaceous glands was more than douhle that in the control animals: 3.0 vs 1.2 (p < 0.021. Even greater differences were found at 2 to 4 weeks of treatment. Gonadal androgens are the primary hormones involved with the development of sebaceous glands in both rat ] and man 12 ]. Administration of testosterone to the sexuallv mature rat further increases the size of sehaeeo~s glands [:3,4). Quantitative determinations of the size of rat sebaceous glands after parenteral testosterone treatments have been accomplished by cell counts [1] and hy planimetric measurements on projections of serial sections [3 .. ~ J. It has been shown that sebum production is correlated with the size of the holocrine sebaceous glands [6). Thus, the measurement of ether-extractable hair fat in the rat 171 and skin surface lipids in man [8] may he considered indirect indices of sebaceous gland size, at least whenever the rate of cell breakdown is constant. Recently a newer approach to morphometry. based on the principles of slereology 19 J, was used to measure testosterone-induced changes in rat skin [4 j. This morphometric method has the practical advantage that it can be applied to routine histologic sections both easily and with optimum efficiency. The present study is an application of this method to examine quantitatively the effects produced by orchidectomy and subsequent testosterone injections on tbe sebaceous glands of young sexually mature rats. Teo young adult male Holtzmann rats weighing 410-430 !(m were castrated at 16 weeks of age. Starting 3 weeks later. 6 of these animals were injected intramuscularly :1 times per week for 4 weeks with 0.25 mg of testosterone propionate dissolved in 0.05 ml of sesame oi I per 100 gm bodv weight. Four control rats received sesame oil onlv. All rats were maintained on routine laboratory cho;v and 3 weeks after orchidectomy had gained an average of 10 gm each. During the 4 weeks of injections, testosterone-treated rats gained an a\·erage of 17 gm in weight while control animals gained an average of 1 gm. Biopsies of dorsal skin, approximately 5 c-10 mm, were taken under light ether anesthesia at the time of orchidectomy and at weekly intervals during treatment. Histologic sections were carefully oriented perpendicular to the skin surface. stained with hematoxylin and eosin, and analyzed morpho metrically for their volume content of sebaceous glands. T'he morphometric measurements were done sur\'eying contiguous microscopic fields covering the section at a magnification of .300 x, as illustrated in Figure lA. A typical sample contained cross sections of about 20 individual sebaceous glands. A square grid of 42 samplin!" points [10 I was superimposed on each field bv means of an ocular reticle {Wild Heerbrugg lnstrume'ots. Inc. #105844), as shown in Figure lB. In each section an average of approximately 1000 points was counted over the entire thickness of the skin, including epidermis, dermis. and the thin layer of subcutaneous adipose tissue. The total number of such points, P.""' and the number of those points overlying cross sections of sebaceous gland cells, P,., were recorded and then used to calculate the volume fraction, V '"' of sebaceous glands in the skin: