In vitro microdialysis of the ovine corpus luteum of pregnancy: effects of insulin-like growth factor on progesterone secretion.

The effects of insulin-like growth factor-1 (IGF-1) and cAMP on progesterone (P) secretion by CL of streptozotocin-induced-diabetic pregnant ewes were compared with the effects on normal pregnant animals. Two types of CL were identified in the ovaries removed on Days 126.6 +/- 2 of pregnancy. They were either large, reddish in color, and vascular (type A) or small and pale yellow (type B). Both types were found in diabetic and normal sheep. Each CL was divided in two and perfused in parallel for 14 h in an in vitro microdialysis-perifusion system. One half was used to evaluate basal P secretion and the effect of cAMP. The effect of IGF-1 and cAMP infusion was studied in the other half. During microdialysis, fractions were collected every 15 min, and P was determined by RIA. IGF-1 stimulated secretion of P in the large type A, normal and diabetic sheep CL in discrete pulses. The smaller CL (type B) from normal sheep produced comparatively higher levels of P in discrete pulses in the presence of IGF-1. However, the small CL from diabetic sheep showed no response to IGF-1 or cAMP, and P secretion was lower. Thus, it is probable that the large CL may be the "active" CL producing P and that IGF-1 stimulates pulsatile P secretion in such CL from both normal and diabetic pregnant sheep.