SPONTANEOUS AND GNRH-INDUCED PULSATILE LH AND TESTOSTERONE RELEASE INPUBERTAL, ADULT AND AGING MALE BEAGLES

Baseline concentrations of LH and testosterone (T) in blood, their pul ses, and LH and T response to GnRH (5 mu g/kg) treatment were compared in 19 sexually sound male beagles and in 2 sexually dysfunctional dog s. The intact beagles were allocated to 4 groups according to age, whi ch ranged from pubertal 7 mo-old animals to 11-yr-old adults. Baseline concentrations of LH and T were measured every 15 min for a period of 6 h and for a further 3 h following challenge with GnRH. Both LH and T were released in a pulsatile fashion with a wide range of pulse freq uency and amplitude. The time intervals between the LH and T pulses ra nged from 30 to 60 min, with no significant difference between groups. However, LH concentrations were significantly higher (P < 0.01) and T values were markedly lower in the 7-mo-old pubertal dogs than in the other age groups. Following GnRH administration, LH peaked within 15 t o 30 min in all the animals, with a significantly higher increase occu rring in the pubertal group (P < 0.05). Peak T values occurred 15 to 1 05 min after the LH peaks, with no clear increases occurring in the pu bertal dogs. In the 2 sexually dysfunctional animals, LH levels increa sed following GnRH treatment; however, T values remained extremely low both before and after treatment, indicating loss of Leydig cell funct ion.