Insulin regulation of leptin expression in streptozotocin diabetic pigs

The relationship between leptin mRNA and insulin status was explored using streptozotocin diabetic pigs. Twelve male Yorkshire x Landrace crossbred sw ine (similar to 40 kg BW) were divided into three groups. Two groups were r endered diabetic with the use of streptozotocin (75 mg/kg BW). Diabetes was confirmed 24 h after streptozotocin treatment by the presence of hyperglyc emia. One group of diabetic animals received daily injections of insulin (. 5 U/(kg.d)(-1)) for 7d, whereas the other group of diabetic animals receive d saline injections. The nondiabetic group also received saline injections (controls). Tissue and blood were collected after 7 d of treatment. Leptin mRNA concentrations in dorsal s.c. adipose tissue were measured by Northern analysis and standardized against 28S rRNA expression. Diabetes reduced le ptin mRNA concentration by 67% in s.c. adipose tissue (P < .05). Serum insu lin concentrations in the diabetic animals were reduced by 69% (P < .05). I nsulin treatment of diabetic animals resulted in an increase in leptin mRNA concentration to levels in controls. Primary cell culture of porcine adipo se tissue was used to assess whether these actions were the direct or indir ect action of insulin. Acute exposure (1 to 24 h) of primary cultures of po rcine adipocytes to insulin did not result in a change in leptin expression . However, chronic (7-d) exposure to insulin elevated leptin mRNA levels by 73%. These data suggest that insulin mediates changes in porcine leptin mR NA levels in vivo or in vitro, most likely by an indirect action.