Changes in fat cell size and in vitro lipolytic activity of abdominal and gluteal adipocytes after a one-year cross-sex hormone administration in transsexuals

We prospectively studied the effects of cross-sex hormone administration on fat cell size and in vitro lipolytic activity in subcutaneous abdominal an d gluteal fat biopsies obtained from 19 male-to-female (M-F) transsexuals a nd 17 female-to-male (F-M) transsexuals. The amount of subcutaneous fat at the abdominal and gluteal levels was quantified with the use of magnetic re sonance imaging (MRI). Before cross-sex hormone administration. M-F transse xuals had less subcutaneous fat with smaller fat cells compared with F-M tr anssexuals, with a higher baseline in vitro lipolytic activity expressed as glycerol release per milligram of triglyceride (TG) in the abdominal regio n (P < .05). Before cross-sex hormone treatment, no differences in lipolyti c activity stimulated with arterenol (ART), isoproterenol (ISO), or ISO + i nsulin (INS) were observed between groups or regions. After a 1-year treatm ent with estrogens and antiandrogens in M-F transsexuals, subcutaneous fat areas on MRI and fat cell size were increased (P < .001) and reductions wer e observed in the basal lipolytic activity of gluteal and abdominal fat bio psies (P < .05). Following administration of testosterone to F-M transsexua ls, subcutaneous fat and fat cell size at the gluteal and abdominal depots were decreased (P < .01) and basal lipolysis was increased significantly at the abdominal level (P < .05) but not at the gluteal level. In both M-F an d F-M transsexuals, no effect of sex hormone administration was observed on stimulated lipolytic activities; In conclusion, regional sex differences i n the amount of subcutaneous fat, adipocyte size, and in vitro basal lipoly tic activity were demonstrated that could be largely reversed by cross-sex hormone treatment in adult subjects, providing evidence for their dependenc e on the sex steroid milieu. Copyright (C) 1999 by W.B. Saunders Company.