Physiological response to long-term peripheral and central leptin infusion in lean and obese mice

Recent data have identified leptin as an afferent signal in a negative-feedback loop regulating the mass of the adipose tissue. High leptin levels are observed in obese humans and rodents, suggesting that, in some cases, obesity is the result of leptin insensitivity. This hypothesis was tested by comparing the response to peripherally and centrally administered leptin among lean and three obese strains of mice: diet-induced obese AKR/J, New Zealand Obese (NZO), and Ay. Subcutaneous leptin infusion to lean mice resulted in a dose-dependent loss of body weight at physiologic plasma levels. Chronic infusions of leptin intracerebroventricularly (i.c.v.) at doses of 3 ng/hr or greater resulted in complete depletion of visible adipose tissue, which was maintained throughout 30 days of continuous i.c.v. infusion. Direct measurement of energy balance indicated that leptin treatment did not increase total energy expenditure but prevented the decrease that follows reduced food intake. Diet-induced obese mice lost weight in response to peripheral leptin but were less sensitive than lean mice. NZO mice were unresponsive to peripheral leptin but were responsive to i.c.v. leptin. Ay mice did not respond to subcutaneous leptin and were 1/100 as sensitive to i.c.v. leptin. The decreased response to leptin in diet-induced obese, NZO, and Ay mice suggests that obesity in these strains is the result of leptin resistance. In NZO mice, leptin resistance may be the result of decreased transport of leptin into the cerebrospinal fluid, whereas in Ay mice, leptin resistance probably results from defects downstream of the leptin receptor in the hypothalamus.

Presence of anti-hepatitis C virus serum markers in a dental school patient population

Hepatitis C virus (HCV) has joined the list of infections liver diseases of which the practicing dentist must be aware. This recently described RNA virus causes between 20% to 40% of reported cases of viral hepatitis in the United States. Patients with HCV show symptoms only one quarter of the time, but chronicity is maintained longer than with the other liver infections. The major mode of transmission is percutaneous, so dentists are potentially at risk to contact the virus. To assess the presence of exposure to HCV, a total of 500 dental school patients were screened for serum antibody to this virus (second-generation anti-HCV). In addition, participants were required to fill out a special screening questionnaire designed to indicate high-risk groups. Their serum was also analyzed for serum chemistries known to be associated with acute and chronic liver disease. Analysis of the 15 response questionnaires revealed statistical significance relating to questions inquiring about previous exposure to blood (transfusions, surgical procedures, etc) but little significance relating to lifestyle. In either case responses were not of practical predictive value. More than 5% of our sample patients were found to be positive reactors to anti-HCV, indicating previous HCV exposure. A significant number of those positive for anti-HCV also showed elevation of serum chemistries associated with hepatitis.