Plasma testosterone surge and luteinizing hormone beta (LH-beta) following parturition: lack of association in the male rat.

Studies examining the role of luteinizing hormone (LH) in the initiation of the postnatal surge of testosterone in the male rat have produced ambiguous results. We examined the pattern of postnatal LH secretion in the newborn male rat, coincident with plasma testosterone levels, using a specific monoclonal antibody for LH-beta. In some males, we attempted to block LH secretion and the postnatal testosterone surge by injecting males with a gonadotropin-releasing hormone (GnRH) antagonist, an LH antibody or progesterone immediately after delivery by cesarean section on day 22. Following injection, animals were immediately sacrificed (time 0) or housed in a humidified incubator maintained at 30 degrees C until sacrifice at 60, 120, 240, 360 or 480 min after delivery. Plasma from individual animals was measured subsequently for LH-beta and testosterone by radioimmunoassay. Results revealed a postnatal surge of testosterone which peaked at 2 h after delivery in males from all treatment groups. This testosterone surge was not accompanied by a postnatal rise in plasma LH-beta in any group. Administration of the GnRH antagonist or the ethanol vehicle produced a transient drop of approximately 25% in LH-beta levels at 60 min but did not decrease the postnatal testosterone surge in the same animals. Additional studies in untreated males and females born by cesarean section or natural birth also failed to reveal a postnatal rise in plasma LH-beta during the first 3 h after birth. Plasma levels in both sexes were significantly lower in animals delivered by cesarean section compared to natural birth.(ABSTRACT TRUNCATED AT 250 WORDS)