The maturational process of gonadotropin-releasing hormone neurons in the male rat: a role for the adrenal gland in the increase in secretory function.

The aim of this study was to define the maturational process of the LHRH neuron in the male rat and the role of the adrenal and testis. Maturing (7-week-old) and adult (12-week-old) male rats were adrenalectomized (ADX), castrated (TX), or ADX and TX; controls were sham operated. Two weeks later, LHRH release from explants of the median eminence area (MEA), MEA LHRH content, and serum testosterone (T) were determined. MEA were incubated for 5 min with 150 microM copper and then for 15 min with 10 microM prostaglandin E2 (Cu/PGE2). LHRH release in response to Cu/PGE2 increased 3-fold between 7 and 9 weeks of age [from 10.4 +/- 1.8 to 29.2 +/- 2.1 pg/15 min.MEA (mean +/- SE)], and there was no further increase thereafter. ADX, TX, or ADX plus TX of 7-week-old rats prevented the increase in Cu/PGE2-stimulated release. In contrast, ADX of 12-week-old rats did not alter LHRH release, whereas TX or ADX plus TX drastically reduced it (75%). The MEA content increased gradually between 7 and 14 weeks of age (from 2.0 +/- 0.2 to 3.0 +/- 0.3 ng). ADX of either 7- or 12-week-old rats did not alter LHRH content, whereas TX or ADX plus TX reduced it to 1.3 ng in both age groups. Serum T increased 6.7-fold between 7 and 9 weeks of age (from 1.06 +/- 0.42 to 6.70 +/- 0.57 ng/ml), and there was no further increase thereafter. ADX of 7-week-old rats did not alter serum T, whereas ADX of 12-week-old rats reduced serum T to 0.62 +/- 0.15 ng/ml. Serum T was undetectable in TX or ADX plus TX rats of both age groups. In summary, maturation of the male reproductive system is associated with a moderate increase in LHRH content of the median eminence and marked increases in the secretory function of the LHRH neuron and in serum T; the testis is essential for these maturational increases. In addition to the testis, the adrenal is necessary for the maturational increase in the secretory function of the LHRH neuron, but not for the increase in LHRH content or that in serum T. It is proposed that dissociable mechanisms regulate LHRH secretion and content in the maturing male, and that T and a substance of adrenal origin (steroid?) are required for the maturational increase in secretory function of the LHRH neuron.