Abstract

PIP: Acidic lipids with smooth muscle-stimulating properties were extracted from rat epididymal fat pads and were shown to co-chromatograph with (PGE1) prostaglandin E1, PGE2, and PGF2alpha. Further chemical identification was not possible with the small amounts of material available. A basal efflux of PGE and PGF compounds was observed following incubation of adipose tissue in vitro. Increased efflux of PG was detected under conditions reported to enhance free fatty acid release, i.e., addition of lipolytic hormones or drugs to the incubating medium, prior fasting of the animal, or stimulation of the epididymal nerve. These results, together with a decreased release of PG-like material in the presence of insulin, suggested that the efflux may be associated with lipolysis resulting from activation of a hormone-sensitive lipase. Since the PGs are known to affect the concentration of cyclic adenosine 3', 5'-monophosphate in adipose tissue, and this nucleotide is an intermediary in hormone-stimulated lipolysis, it is possible that the PGs released may serve to maintain the homeostasis of adipose tissue by way of a physiological feedback control mechanism.