TEMPORAL RELATIONSHIP BETWEEN THE DEVELOPMENT OF THE SELF-PRIMING EFFECT OF LHRH AND CHANGES IN SERUM CONCENTRATIONS OF TESTOSTERONE AND ANDROSTENEDIONE DURING THE SEXUAL-MATURATION OF THE MALE-RAT

The pituitaries of pubertal and adult male rats release more LH [lutropin] in response to LHRH if the animals are pretreated with 3 priming doses of LHRH than if they are pretreated with saline. Immature male rats do not exhibit a similar self-priming response. These studies were designed to determine more precisely the age of onset of this effect and to relate it to the serum levels of androstenedione (A) and testosterone (T). Beginning on day 30 (immature) and every 4 days thereafter through day 54 (pubertal), the following experiment was performed. Male rats were anesthetized with ketamine HCl (10-20 mg/kg i.p.) and a 0.7-1.0 ml blood sample was collected by heart puncture for radioimmunoassay of A and T. Next the animals received i.v. injections (right jugular vein) of 10 ng LHRH/100 g body wt or saline at time 0, 30 and 60 min. At 90 min an additional blood sample was obtained, and all animals received an i.v. injection of 50 ng LHRH/100 g body wt via the left jugular. At 100 min a final blood sample was obtained. LH concentrations in the 90 and 100 min samples were determined by radioimmunoassay. A statistically significant (P < 0.01) self-priming effect was first detected on day 46. Serum concentrations of T and A were first significantly (P < 0.05) elevated and the ratio A/T first significantly (P < 0.05) reduced on day 42. The self-priming effect on LHRH develops in the male rat between days 42-46 and appears to be preceded by alterations in testicular steroid concentrations.