RELEASE AND SPECIFIC BINDING OF PROSTAGLANDINS IN BOVINE PINEAL-GLAND

Incubated bovine pineal glands released prostaglandin E- and prostaglandin F-like material (304 ± 20 and 582 ± 56 pg/mg dry tissue wt/h, respectively) and the release was increased 2.2 2.9-fold by adding 10-4-10-6M of norepinephrine to the medium. Binding assays revealed the existence of high affinity binding of 3H-prostaglandin E2 (3H-PGE2) and 3H-prostaglandin F2α (3H-PGF2α) in low speed supernatants of pineal homogenates. Binding was increased by increasing Ca++ concentration in medium up to 2 mM, was heat-labile and was depressed following incubation with trypsin. In subcellular fractionation studies maximal 3H-PG binding was found in the 27000 × g pellet. Scatchard analysis of 3H-PGE2 binding revealed the presence of a single population of binding sites with a Kd= 1.2 nM and a binding site concentration of 1-2 pmoles/g protein. A single population of binding sites for 3H-PGF2α was also detected with a Kd= 1.7 nM and a similar binding site concentration. Non-radioactive PGE1 and PGE2 were almost equally effective to compete for 3H-PGE2 binding sites (ED50= 5 and 2 nM, respectively). Unlabeled PGF2 was relatively ineffective to compete for 3H-PGE2 binding (ED50>1000 nM) but displaced effectively 3H-PGF2α binding (ED50= 1.2 nM). © 1979.