Growth hormone-enhanced lipolysis in the spontaneously diabetic BB rat

Responsiveness to lipolytic agents and glycerol output from rat adipocytes is altered by the diabetic process. We have confirmed reports that preincubation is required for growth hormone-induced lipolysis in isolated fat cells. Isolated fat cells were prepared from the epididymal fat pads of normal and spontaneously diabetic BB Wistar rats (weight, 250-400 gm) and their nondiabetic littermates by collagenase digestion. Lipolysis was measured by glycerol release after sequential perifusion with buffer alone, bovine growth hormone 1 microgram/ml, buffer alone, and epinephrine, 0.5 mumol/L. In each case isolated fat cells from control, nondiabetic, and spontaneously diabetic rats were perifused under two conditions, with and without preincubation with bovine growth hormone. Isolated fat cells from control and nondiabetic rats did not respond to bovine growth hormone without preincubation. When preincubation with bovine growth hormone, response in control rats increased from nonpreincubated glycerol values of 4.9 to 13.5 nmol glycerol released/10(6) cells/min. In contrast to controls, non-preincubated isolated fat cells from spontaneously diabetic rats that were stimulated with 1 microgram/ml bovine growth hormone went from 18.0 to 42.6 nmol of glycerol released/10(6) cells/min. No preincubation was necessary in spontaneously diabetic rats. In addition, in all situations in which preincubation or the diabetic state enhanced lipolysis with growth hormone, similar enhancement was seen with epinephrine. For nondiabetic rats both preincubated and nonpreincubated isolated fat cells respond minimally to bovine growth hormone. In conclusion, preincubation with bovine growth hormone is not required to elicit lipolysis in perifused isolated fat cells from spontaneously diabetic BB rats.(ABSTRACT TRUNCATED AT 250 WORDS)