Effect of plasma lipoproteins in gonadotropin stimulation of 17 beta-estradiol production in the ovarian follicle of rainbow trout (Salmo gairdneri).
The effect of trout plasma lipoproteins on the production of 17 beta-estradiol by trout ovarian follicles is investigated in vitro. 17 beta-Estradiol secretion into the medium was assayed as a function of follicular diameter in the presence of lipoproteins with and without salmonid gonadotropin (SGA-GTH). The presence of very low-density lipoproteins (VLDL) + chylomicrons (Chy), low-density lipoproteins (LDL), and high-density lipoproteins (HDL) amplified the SGA-GTH effect at the lowest concentrations tested (less than 50 micrograms protein/ml). HDL is the most effective for increasing hormone accumulation on a microgram lipoprotein sterol basis. Autoradiography of 125I-labeled LDL showed that they were preferentially bound by thecal cells. Kinetics of 17 beta-estradiol release indicated that lipoprotein amplification occurred especially after 15 hr and subsequent metabolism of 17 beta-estradiol by follicular layers also led to an equilibrium. At the end of vitellogenesis apoprotein B lipoproteins (VLDL + Chy, LDL) apparently inhibited SGA-GTH stimulation. N',O'-Dibutyryl cAMP (10 mM) considerably stimulated 17 beta-estradiol production but lipoprotein amplification did not occur. Chloroquine (30 microM) inhibition of LDL and HDL amplification indicates that this process requires lysosomal degradation. Plasma lipoproteins in trout modulate SGA-GTH stimulation of 17 beta-estradiol production during exogenous vitellogenesis. Due to the ease and frequency with which the experiments can be carried out, the ovarian follicle of salmonids is an excellent model for the study of the role of lipoproteins in the regulation of ovarian steroids biosynthesis.
D000818:Animals; D003994:Bucladesine / Q000494:pharmacology; D002738:Chloroquine / Q000494:pharmacology; D004958:Estradiol / Q000096:biosynthesis*; D005260:Female; D006062:Gonadotropins / Q000494:pharmacology; D066298:In Vitro Techniques; D008074:Lipoproteins / Q000097:blood / Q000494:pharmacology*; D006080:Ovarian Follicle / Q000187:drug effects / Q000502:physiology*; D012487:Salmonidae / Q000502:physiology*; D014337:Trout / Q000502:physiology*; D014818:Vitellogenesis
D006062:Gonadotropins; D008074:Lipoproteins; D004958:Estradiol; D003994:Bucladesine; D002738:Chloroquine