TRANSCUTANEOUS ABSORPTION OF VITAMIN A 179 cations of the betrolatum containing vitamin A. Sections of abdominal skin removed from rats in Group VI were not analyzed for vitamin A they were utilized for histological studies. Both levels of vitamin A found in skins of the two rats in Group I (21 and 19 units per 100 gin.) Were at least equivalent to those reported by McCoord and Luce-Clausen (18.9 units) for rats sacrificed twenty-four hours after the administration of a dose of 1748 units of vitamin A in the form of halibut oil. Rats in groups II and III exhibited values for skin vitamin A which were sig- nificantly greater' than the results tabulated by McCoord and Clausen for rats which had received, over a period of six weeks, a total of 2622 units of vitamin A divided into weekly doses. For these rats, the authors report levels of vitamin A varying from 4.27 to 9.60 units per 100 gin. of skin. In order to obtain comparative data for vitamin A in skins of nor- mal rats, which had been maintained on a nutritionally adequate diet, seven rats in the stock breeding colony were sacrificed and sections of their abdominal skins were re- moved for determinations of con- centrations of vitamin. Results of these analyses showed variations from 10 to 25 with a mean of 16 units per 100 gm. Sections of skin were removed from both the right and left sides of the abdomens of each of three normal rats. Comparative analyses of two skin sections from one rat gave checks within a=5.7 per cent. All of the data for vitamin A in skins of rats in the groups which are reported in Tables 1 and 2 represent levels for sections of abdominal skin. For rats in the test groups, which are included in Table 2, these sec- tions included areas of skin to which the vitamin in the petrolatum base had been applied. At the time of carrying out these experiments on rats, it was not practically possible to exclude the possibility that amounts of vitamin A found in these sections may have included some of the vitamin retained in the skin from the preceding application of the petrolatum containing the concentrate of vitamin A. How- ever, several later series of experi- ments on normal rabbits demon- strated that increments in vitamin A of the skin resulting from topical applications of a concentrate of the vitamin in petrolatum disappeared within periods of four to six hours after the preceding application. Every precaution was taken to eliminate hangover, local increases in skin vitamin A attributable to either retention of the vitamin on the surface of the skin or the intra- cutaneous absorption of the vita- min. After each application, the skin was washed thoraughly with soap and water. Tests on rabbits showed this process of washing gave an average reduction of 12 per cent in the skin vitamin A. Also, an interval of twenty-four hours elapsed between the preceding ap- plication of vitamin A and the time of sacrifice of the rats.

180 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS ß However, in order to eliminate possibilities of intracutaneous ab- sorption in appraisals of influence of transcutaneous absorption upon the vitamin A of skin, sections of skin were dissected from the backs of seven rats in groups I, II, and III. TASLS 3--COMPARATIVE LsvsI. S or V•TAM• A IN SKINS or NORMAL R•ATS AND OF RATS Rac•v•so TOPreAL AVVLWAT•O•S Or V•TA- M• A Is A PaTROLATVM BASa AS THeiR SoLa SOURCE or Tins VITAMIN Units of Vitamin A per 100 Gm. of Skin Standard No. Areas of Error of Skin of Groups Rats Analyzed Mean Mean Normals 7* I, II, 7 and III (Chart II and Table 2) Ventral 16 t 1.67 Dorsal Ventral i3 ' 0'.'8'6 Dorsal 16 1.00 * Maintained on stock breeding diet--ages varied from 18 to 29 weeks with average of 24 weeks. •' Mean result of analyses of 10 sections of skin. Results of comparative analyses of ventral and dorsal sections of skins of these seven rats are reported in Table 3. The data summarized in the table indicate approximately equivalent concentrations of vita- min A in ageas of skin of both the abdomen and the backs of these animals. At the time of sacrifice of the seven rats in the three test groups, samples of blood were drawn for analyses for vitamin A in the sera. In all instances, blood levels of the vitamin were slightly lower than the corresponding values 'for skin. The range. of blood levels was from 11 to 15 with a mean of 12.6 units of vita- min A per 100 cc. of blood serum. A group of 14 rats, litter mates of the animals in groups I, II, III, and IV, received oral supplements of vitamin A daily over a period of five weeks 'after depletion of their vita- min stores. These supplements were adequate.to give total gains in weight between 12 and 60 gin. and to protect against the development of gross signs of deficiency o'f vita- min A. At the end of the test pe- riod, all animals were sacrificed and analyses were made for vitamin A in their livers and skins. Table 4 summarizes the compara- tive data for the group of 14 rats which received oral supplements of the vit/tmin and the 14-rats whose sole source of the vitamin was that applied to their skins without mas- sage. The purpose of conducting these comparative experiments was not the evaluation of the relative nutri- tional or thereapeutic merits of vita- min A administered by the oral route or through the skin. O.n the contrary, the primary objective was the utilization of the results found for rats fed vitamin A as criteria of the systemic effects of the vitamin. Data presented in Table 4 show that, during test periods, both groups of rats made approximately equivalent gains in weight. Hence, gains in weight have been adopted as common denominators in apprais- ing the significance of differences between the two groups in' respect