Studies on the age-dependent nature of the response to LHRH given via different routes

The effect of synthetic LHRH on circulating levels of LH and FSH in three groups of male rats, prepubertal, pubertal and adult, was compared after intravenous, intraperitoneal and subcutaneous administration. In two further series of experiments, infusion of LHRH over 120 min or two i.v. bolus injection at an interval of 60 min were carried out. Blood was collected from individual animals at each time-point before and after LHRH administration. The results indicate that the responsiveness of LH and FSH to LHRH was dependent not only on the routes of injection but also on the maturation of the animals. The infusion of LHRH induced the greatest response of LH and FSH in all the groups of animals. The pubertal group demonstrated greater responsiveness of LH than the other two groups. The second bolus injection of LHRH after 60 min elicited a much greater response for both gonadotropins in all age groups than that following the first injection. This indicates the existence of a priming effect of LHRH on LH and FSH; this effect was observed in all groups irrespective of their maturational status.