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.

Abstract

The pituitaries of pubertal and adult male rats release more LH in response to LHRH if the animals are pretreated with three 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 HCI (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 (tight jugular vein) of 10 ng LHRH/100 g BW or saline at time 0, 30, and 60 mm. At 90 mm an additional blood sample was obtained, and all animals received an i.v. injection of 50 ng LHRH/ 100 g BW via the left jugular. At 100 mm a final blood sample was obtained. LH concentrations in the 90 and 100 mm samples were determined by radioimmunoassay. A statistically significant (P<O.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 ALT first significantly (P<0.05) reduced on Day 42. These data suggest that the self-priming effect of LHRH develops in the male rat between Days 42 and 46 and appears to be preceded by alterations in testicular steroid concentrations.