Stimulation of Gonadotrophs by Pituitary Portal Vessel Infusion of Superactive LH-RH Analogues: an Ultrastructural Study

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Abstract
LH-RH [luteinizing hormone-releasing hormone] or its superactive analogs were infused into pituitary portal vessels of adult male rats for 1 min; pituitaries were then fixed for routine EM 1 min, 30 min and 3 h after infusion. A maximal increase of granule release at 2 min and a maximal increase in synthetic activity (i.e., dilated cisternae of rough endoplasmic reticulum (RER) and Golgi apparatus (GA)) at 30 min, occurred in gonadotrophs in response to both LH-RH and the superactive analogs, but not to saline infusion. Only gonadotrophs from analog infused pituitaries showed a high level of exocytosis and protein synthesis at 3 h. The superactive analogs typically stimulated formation of large vacuoles of RER at 30 min and 3 h that resembled those seen in signet ring cells following castration. Radioimmunoassay (RIA) values of serum LH [luteinizing hormone] supported these observations. Results provide morphological evidence for a prolonged action of the superactive LH-RH analogs on gonadotropin secretion and synthesis under physiological conditions.