Departments of Obstetrics-Gynecology, Anatomy, and Biochemistry

The studies in this report were designed to investigate whether the loss of pituitary luteinizing hormone (LH) responses to N’,02’-dibutyryl adenosine 3’,5’-cyclic monophosphate (DBcAMP) in aged noncycling rats was the result of age, endocrine status associated with diestrus, or noncyclic low estrogen status. Pituitary monolayer cultures were prepared from female Fischer 344 rats. Aged (18-month-old) persistent diestrous (PD) rats, young diestrous (D) rats, or noncycling neo-natally androgenized-constant estrous (AN-CE) rats were used. Enzymatically dispersed cells were maintained in the same batch of medium supplemented with dextran-coated charcoal adsorbed serums. Total LH contents were 1.75 ± 0.04, 1.15 ± 0.03, and 1.71 ± 0.02 jig LH/dish in Day 5 cultures prepared from aged PD, young D, and AN-CE rats, respectively. Incubations with 5 mM DBcAMP for 4 h significantly (P<0.05) stimulated LH release in cultures prepared from young D and AN-CE rats but inhibited LH release in cultures prepared from aged PD rats even though a 4-h incubation with 10 nM LH releasing hormone (LHRH) stimulated LH release similarly in cultures of all three types of cells. The loss of DBcAMP-induced LH release in cultures prepared from aged PD rats was reversed by 17t3-estradiol (E2). This treatment also reduced the basal LH release and increased the cellular LH content. These results indicate that the loss of DBcAMP-induced LH response in the aged rat is not an irreversible aging phenomenon but appears to be associated with the chronically low E2 status of aged PD rats but not young cycling D or noncycling AN-CE rats