Binding of Prostaglandin F2α to Membranes of Shell Gland Muscle of Laying Hens: Correlations with Contractile Activity1

Specific binding of prostaglandin F2α (PGF2α) to a membrane fraction prepared from the shell gland muscle of laying hens was characterized as a concentration dependent, irreversible (at 0°C or 20°C) or partially reversible (at 37°C) interaction with a limited number of binding sites (about 1 pmol/mg protein). The 9 and 11 hydroxyl groups, the 5 (cis) double bond and the α steric position of the heptanoic acid side chain of the PGF2α molecule appear to be essential prerequisites for optimal binding. Properties of this binding reaction were compared to the characteristics of in vitro contractile responses of shell gland strips to PGF2α. The results indicate that 1) both specific binding and contractile responses can be elicited with physiological concentrations of PGF2α, 2) the binding of PGF2α and the contractile response of the shell gland muscle are both very rapid processes which attain a maximum value within 1 min, 3) both the saturation of the membranes and the maximal contractile response are achieved at 2 × 10−6 M PGF2α. However, half maximal binding can be demonstrated at 4 × 10−7 M, whereas half maximal response at 2 × 10−8 M PGF2α, 4) both the binding affinity to PGF2α binding sites and the contraction stimulating activity of PGE1 is substantially lower than those of PGF2α.