EPIDERMAL GROWTH-FACTOR RECEPTORS IN RAT OVARIAN TISSUE

Epidermal growth factor is known to have mitogenic effects in the ovar y. To determine whether this effect is receptor-mediated, and whether the receptor number changes during the estrus cycle, in this study we have evaluated the total and occupied EGF receptor (EGFr) concentratio ns and receptor binding characteristics in adult rat ovaries collected at diestrus and early estrus. These represent stages before and after the pituitary LH/FSH surges of the estrus cycle. The 100 000 g plasma membrane fractions were isolated and EGFr concentrations evaluated wi th and without 1 mM EDTA treatment at pH 4.5 in order to release recep tor-bound ligand and therefore assess the unoccupied and total recepto r concentrations. EGF receptor affinity and number were analyzed by Sc atchard analysis. No statistically significant difference between unoc cupied and total receptor concentration in the diestrus phase ovaries was found. The percentage of occupied receptors (total-unoccupied) in diestrus membranes was 7.1%. In early estrus ovaries, a significant in crease (P < 0.05) was observed in total receptor concentration when co mpared with the number of unoccupied receptors. The percentage of occu pied receptors in early estrus membranes was 35.7%. Comparison between the ovaries from the two phases indicated an almost twofold increase in total EGF receptor number in early estrus membranes when compared w ith diestrus membranes. Furthermore, the percentage of occupancy betwe en the two studied groups indicate a significant increase (P < 0.05) i n the number of occupied receptors in early estrus when compared to di estrus. Thus, we have demonstrated that not only EGF receptor concentr ations are modulated through the rat estrus cycle, but also the concen tration of EGF-like substances bound to such receptors.